Solar BMS a solar charge controller for LiFePO4 - Page 1
Forum section: electronics / general

author: electrodacus
author_rank: Super Contributor
timestamp: February 21, 2015, 11:37:28 pm
content: This will be the second version of the Solar BMS with a lot of improvements over the current SBMS4080.I had a successful Kickstarter last year for the SBMS4080 (Solar Battery Management System) the 4080 is from 40A charging and 80A discharging so with max configuration 8 cells of LiFePO4 that is 1000W of PV panels possible and 2000W load. I produced about 100 units of SBMS4080 and smaller version SBMS1616 for backers and I also have installed two in my offgrid house (the main reason I designed this Solar BMS).Here is a photo that I took today of my SBMS4080I made the above photo to show a record of 29.2A from 3x 240W PV panels so 720W total. The reason for this is full sun at 1:16PM snow on the ground and -22CAnd below you can see a 3D render of how the new Solar BMS will look like this will be able to handle 3000W of PV and 3000W load at the same time with a TDP of just 22WAnd here is a comparison of cost for stored energy between the best Lead Acid from Trojan and LiFePO4 from Winston.So you see why I went for LiFePO4 over the more traditional Lead Acid. There are other problems with Lead Acid especially in a cold climate like mine but the 3x difference in cost for each kWh stored is a good enough reason by his own.You can see more technical details on my webpagehttp://electrodacus.comincluding at the end of the page a nice 7 day graph with my house power production/consumption.

author: Prime73
author_rank: Regular Contributor
timestamp: February 22, 2015, 12:36:50 am
content: Seems interesting. Where can I take a look at the schematics, etc ?

author: mtdoc
author_rank: Super Contributor
timestamp: February 22, 2015, 01:07:30 am
content: Good stuff but if you want your product to be attractive to the vast majority of serious off grid and grid tie with battery backup installations you'll need to step up the specs:1) MPPT is a must - I see no mention of this on your website .2) It needs to be compatible with 48V nominal battery systems.3) It needs a max PV VOC input of at least 120V to accommodate strings of 3 in series of the commonly used and cheapest per watt PV panels which have VOCs of 35-40V. At least 3 of these in series are needed for 48V systems.Right now many are using standard programmable MPPT controllers for use with Lithium batteries in off grid and grid tie with battery back up systems. BMS if used is separate from the charge controller.As more people transition from LA to LiFePO4 batteries there is definitely a need for MPPT charge controllers with integrated BMS but you will need to step up your specs if you want to compete with the big guys (Midnite, Outback, Morningstar, Schnieder).You've got a head start on them - good luck!

author: electrodacus
author_rank: Super Contributor
timestamp: February 22, 2015, 01:18:17 am
content: Quote from: Prime73 on February 22, 2015, 12:36:50 amLinks to schematics and firmware are in the first Kickstarter project updates. Search Solar BMS on Kickstarter (only one project) and look at the latest updates.

author: electrodacus
author_rank: Super Contributor
timestamp: February 22, 2015, 01:35:03 am
content: Quote from: mtdoc on February 22, 2015, 01:07:30 amI have no intention to attract grid tie users this is a product specifically for OffGrid, RV, Boats.1) MPPT is obsolete (not going to get in to details) but if PV panels are under 5$/Watt it makes no economic sense to implement MPPT and currently at 1$/Watt or under.Look at the first photo 720W PV array generating 791W that is because I use 8x LiFePO4 with 60 cells PV an MPPT will do worse with this setup.2) I will stay with 12V and 24V compatibility no 48V variant for safety (close to 100V OC on PV with 48V battery) and a completely different strategy is better.3) Again max OC input is limited to 50V ideal for 24V setup (60 cells recommended but 72 cells can be used for long wire runs or very hot climate)BMS will not work good separate for the charging part.I do not want to compete with anyone this was designed for my on use and since there was some interest I made a small kickstarter. Now I do a new model for those that want larger PV array 3000W possible with the new Solar BMS.If you look at my Offgrid house you will see my power consumption is between 60 and 90kWh/month mostly for electric cooking and my PV array is just 720W. With the new SBMS 240 to 360kWh/month is possible depending on climate and use pattern.Many technologies are obsolete because of low cost PV panels not just MPPT but solar tracking and even solar thermal panels.I will do the heating for the house with solar PV since is by far the most cost effective option.But I will need to build a digital MPPT for that since it dose not exist from what I know.Here is a 7 day graph with my energy production consumption

author: mtdoc
author_rank: Super Contributor
timestamp: February 22, 2015, 01:52:44 am
content: Quote from: electrodacus on February 22, 2015, 01:35:03 amIf you don't understand why cheap PV does not negate the need for MPPT then you have some gaps in your knowledge.What cheap PV panels has done is make trackers (almost) obsolete and direct solar hot water less necessary as well (PV with a heat pump water heater can work very well)..Quote??QuoteThe problem with a max input of 50V for a 24 V system is that it would require a string of 2 12 V panels or a "real" 24V panel with a Vmp of 32+. The most inexpensive PV panels, due to economy of scale, are the ones produced in large quantities for the large market of "grid-tie" systems and that have VOC's of 34-40V and Vmps of less than 31V which is not high enough as a single panel string to reliably charge a nominal 24V system.. These panels are by far the most commonly used in large off grid installations now because they are more common and less expensive. Using 2 in a string for a 24V system or 3 for a 48V system is one reason why MPPT is needed. Now as LiFEPO4 battery options expand it may be that the traditional LA nominal battery bank sizes (12V,24V, 48V) are no longer the norm but that will also require some changes in available inverters. But for now, as a "plug and play" replacement for current systems that is not the case.QuoteIt works just fine - it's just that an integrated charger with BMS would be a more efficient solution.It's great that your doing this. As I said - I think charge controllers with integrated BMS for Lithium batteries is needed. If you don't plan to compete for the larger off grid systems and grid tie with battery back-up systems then that's cool.

author: electrodacus
author_rank: Super Contributor
timestamp: February 22, 2015, 02:35:34 am
content: Quote from: mtdoc on February 22, 2015, 01:52:44 amI promise I understand better than you think. An mppt needs a DC-DC converter that is large heavy and expensive (think about a 3000W DC-DC converter for my new Solar BMS able to output 120A) then take an average of 10% gain over a year for MPPT (I'm quite generous with 10% and consider using 72 cells PV panels or larger voltage for long runs) With 60 cells there is no gain at all maybe some loss if it even works.3000W at 1$/Watt is 3000$ for the array.A 10% more will cost 300% so the 3000W 120A DC-DC converter should cost less (can you provide me with a source for one less expensive than 300$) then if I ship internationally that monster MPPT charger it will cost at least 100 to 150$ do to large size and especially weight.The charger should last at least 25 years so no electrolytic allowed in the design or you will need to change that MPPT a few times over the life of the system making that even worse value. My current SBMS is about 240g and the next version will not be larger than 350g and cost about 20$ to 25$ to ship anywhere in the world.I have no electrolytic in my design so 25 years no problem all is solid state there is also no PWM or so absolutely no noise (electrical noise or interference with other devices)There is absolutely no place for MPPT in OffGrid solar system at 1$/Watt or under PV panels In grid tie is a different story since you already have the expensive DC-DC and you only need the MPPT algorithm.QuoteThe most inexpensive PV panels are the one that I use 60 cells and as you see works great with 24V LiFePO4 battery. Max power point for those vary based on cell temperature from no less than 28V to 31V there is no voltage loss on the SBMS (there is so small that it dose not count will be under 2mV/A on the new version). So yes 31V is much more than good enough for LiFePO4 and SBMS.12V and 24V will probably remain the norm for a long time do to automotive industry and there are to many things that accept this level. 4 or 8 cells LiFePO4 are a perfect replacement for this.LiFePO4 will have an almost constant voltage from 10% SOC to 90% SOC around 3.2 to 3.3V / cell and will not sag under heavy load.

author: mtdoc
author_rank: Super Contributor
timestamp: February 22, 2015, 04:32:43 am
content: Quote from: electrodacus on February 22, 2015, 02:35:34 amThe increased efficiency obtained from an MPPT controller is only part of it's advantage. Much more important in the world of system design is that it allows you to run higher string voltages. This has several advantages:1) Use of less expensive panels as I previously described.2.) The ability to have an array farther from your battery bank - higher voltage string=lower amps= less voltage drop = smaller wire gauge/less copper needed. This is a big issue since copper is expensive! Off grid systems in particular often need to locate their arrays far from their battery bank.3) Higher string voltages gives you more headroom which makes a huge difference in non - full sun conditions- i.e. partial shading and cloud cover.These are the real world system design issues that need to be addressed for a controller to have widespread appeal.QuoteNo doubt that it costs less to build a low voltage non-mppt controller. But quality high input voltage, high output MPPT controllers are being made and sold for very reasonable prices now. The market has spoken. The only place for non-mppt controllers now is small 12V systems.QuoteWell that's just nonsense for the reasons I stated and because the market has already spoken on this issue. Spend a couple of hundred dollars more on a MPPT controller or spend many hundreds or thousands more on extra PV, mounting hardware and copper wire?None of the serious charge controller manufacturers are selling non-mppt controllers for anything but very small systems. The vast majority of controllers they sell are mppt - even though PV prices have been below $1 per watt for several years now.Just because there are some small installations where your controller will make sense does not mean it will make sense for the majority of battery based PV systems. Not a problem if your plan is to fill a niche market but a big issue if you expect your controller to have a wider appeal.Oh, and I didn't even get into the advantages an MPPT controller brings to small wind or hydropower systems...

author: electrodacus
author_rank: Super Contributor
timestamp: February 22, 2015, 05:27:42 am
content: Quote from: mtdoc on February 22, 2015, 04:32:43 am1) As I mentioned before less expensive panels 60 cells work the best and is what I'm using for my system and with them MPPT will not be able to work or provide any advantage.2) You can have the allowed 3% voltage loss that will still be enough. Longer and thicker wires will cost more (not the case for RV and boats you can not have long runs there) but I just calculated the cost of wires for a long run on my future 6kW array (for heating) and the cost of cable is 500$ for a 3kWh array that will be half at 250$ and with higher voltage how much will you save from that 250$ maybe 100$ you still need cables.3) Not sure you understand how solar PV works voltage is not affected by amount of solar radiation only current is look at some PV panels datasheets.Again I'm not interested in widespread appeal this is for people like me that see the benefit of LiFePO4 and do not want to spend almost two years developing their own custom version of this Solar BMS if they are even able to do that.QuoteThe market is usually bad informed. There was a time when PV where 5$/watt even 10$/Watt and MPPT controllers where considered exotic and expensive (that was the time it made sense to invest in them since 10% with PV prices 10x higher than now made quite a bit of sense) Now after a lot of development in MPPT people seen the advantage but is to late since the advantage is gone with the much lower cost of PV panels.Another example is all those wind turbine with more than 3 blades because uniformed people thing more blades is better when the opposite is true. But there are enough small and medium wind turbine manufacturers to build this even if they make absolute no sense just because there is a request form uniformed customers.QuoteLook as I mentioned before I know MPPT makes no economic sense for OffGrid where you need the expensive DC-DC converter. Still this is open source so you can add an DC-DC converter to the design and try to commercialise that or add an external DC-DC converter that is also a possibility.As for wind and hydro MPPT "advantages" ... now I know for sure the one that dose not understand how things work is you (sorry If I seem a bit rude but I will not have time to make elaborate technical explanations about all this issues).I'm an electrical engineer. I love to know what is your qualification?

author: mtdoc
author_rank: Super Contributor
timestamp: February 22, 2015, 07:22:13 am
content: Look, I was only trying to give you some constructive criticism in case you were interested in designing and/or selling a charge controller that would appeal to more than a niche market and kickstarter backers.As far as my "qualifications" - no I'm not an EE and do not claim to have the skill to design a charge controller. But designing a charge controller is very different from designing a complete PV system.What I do have is several years experience with PV systems. I have designed and installed several, including my present 4500 watt battery based system. I have helped several others design their systems. I am in regular communication with several people who design and install off grid RE systems for a living and also with some who design charge controllers. I know what people need in a charge controller for Lithium battery based systems. I know the difference between a system that barely works and one that works efficiently and is cost effective.Good luck to you with your project. In a few years when several of the big guys are selling MPPT controllers for LiFePO4 battery based systems you may think back to this discussion.

author: Seekonk
author_rank: Super Contributor
timestamp: February 22, 2015, 05:25:52 pm
content: So the story I got here was BATTERY, your on/off controller is irelevant. Everyones solar experience is different.Someone tells me 20 years life on anything and I give them a look. Nothing I had ten years ago still works. I find RE people the biggest energy wasters non the planet. I designed my system to produce hot water, it charges a battery and runs refrigeration etc on the side. No MPPT because you don't like capacitors. I share your dismay, the last MPPT controller I saw had two surface mount electrolytics on the input. Most controllers aren't much better. Sounds like a good new product, a stand alone capacitor bank with self test to place before a controller. MPPT is like your vehicle ECM. It works great till you get a faulty injector.Then it screws up everything else that is working. Some will just track down to oblivion. A controller should be smart and tell you when things have gone to crap. Don't believe in those 150A controllers. I have multiple banks and controllers for each.All are under master control. I don't have much of a battery. It is only there for startup current. Everything is real time power useage. If fridge needs to turn on, the washer turns off for a period. It is a totally different way of thinking. Seven days of power generation, what does that have to do with anything? It is those four days when the system can't even generate an amp that have to be designed for.There are a lot of solar products out there and they all meet someones need. My concept of what solar should be has changed many times over the years. I appreciate your challanging my current thoughts. There is a solar product I think will change the developed world in the next ten years, like adding extra insulation to the attic did. There are millions of electric water heaters in use. If all their lower heating elements were connected to 300-400W of solar panels through a MPPT controller, dramatic electric savings would result. Everyone has some place they could mount a couple solar panels. The cost would be farless than the $1800 many spend for a heart pump water heater. It would dramatically improve the performance of those too.

author: electrodacus
author_rank: Super Contributor
timestamp: February 22, 2015, 07:32:57 pm
content: Quote from: mtdoc on February 22, 2015, 07:22:13 amThanks for the comment. Sorry if I was looking a bit less polite in the last comment.There is not much knowledge in this field of OffGrid energy storage and many things have changed fast in the last few years.

author: electrodacus
author_rank: Super Contributor
timestamp: February 22, 2015, 07:40:29 pm
content: Quote from: 3roomlab on February 22, 2015, 10:49:45 amYou are talking about MPPT in grid tie and there it makes sense since the HW is already there is needed to push energy in to the grid.Battery bank is not infinite not even close you always have excess energy in offgrid applications.I got mine GBS 100Ah a few years a go there are better ones now I will suggest looking for Winston they have cells up to 1000Ah.I'm sure you are familiar with AGM (Absorbed glass mat) is a sealed Lead Acid battery.If you look in the comment section of that video you will see my comment about his video. I do have youtube videos about this subject.

author: electrodacus
author_rank: Super Contributor
timestamp: February 22, 2015, 07:57:30 pm
content: Quote from: Seekonk on February 22, 2015, 05:25:52 pmSony backs this type of LiFePO4 with 20 years warranty in RE condition 100% DOD every day over 7000 cycles with 100% DOD this is a totally different type of battery than what was traditionally use by small DIY offgrid people in the past (actually still present).You can make MPPT to last 25 years (no electrolytic) but it will be way more expensive and at the current price of PV it makes absolute no economic sense.Those 7 days where a tipical 7 days at the end of January beginning of February with the 3x 240W PV panels the worst day in December will still produce 0.3kWh (and that is significant part of my 0.8kWh/day in low power mode)I will actually heat my house with PV in the near future since is the most cost effective heating. But it requites a specially designed house (I designed and build my own house) that has a large thermal mass storage incorporated in to the design.I will also need to design and build a digital MPPT (this is what I call it but is totally different no DC-DC converter much more simple) this is really needed for heating to maximize power else loss is in excess of 40 to 50% but this only works for heating not battery charging.I have a video on youtube talking a bit about this digital MPPT will be open source so freely available and maybe my next Kickstarter if people understand this and need it.I will have just PV panels and resistive heat elements embedded in the concrete floor that acts as thermal storage (100kWh at 10C delta) There will be 20 to 30 resistive loops and more or less of them will be connected to keep the power from the PV array at the max power point that is a short definition of what I call a digital MPPT.

author: mtdoc
author_rank: Super Contributor
timestamp: February 22, 2015, 09:44:59 pm
content: Quote from: electrodacus on February 22, 2015, 07:32:57 pmNo worry. It's all good. I hope you succeed in building a better mousetrap.BTW - what will the price be for your new CC?

author: electrodacus
author_rank: Super Contributor
timestamp: February 22, 2015, 09:51:52 pm
content: Quote from: mtdoc on February 22, 2015, 09:44:59 pmThanks, There is a table with prices on my website see signature and there are a few variants from SBMS25 to SBMS100. There will be some discount for the early bids on Kickstarter.

author: Seekonk
author_rank: Super Contributor
timestamp: February 22, 2015, 10:30:42 pm
content: There are markets for everything. I think the real growth will be for diversion controllers that can utilize excess panel energy in a smart way and are able to be directed by a central control.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: February 22, 2015, 11:16:51 pm
content: I like what you have done electodacus and good luck with your next project. I think you have found a nice little niche.Really nice to see some backers from kick starter actually getting what was proposed.I might start using LiFePO4 in smaller remote monitoring/control type jobs. (If I ever get another)Just a few queries.I know that for you weight and space are a premium. But for me I would prefer having the common power connections coming into the controller too.Is 24 bit necessary? wouldn't 16 bit delta-sigma be more suitable? I would imagine there is a fair bit noise on your power lines.Have you decided what processor you are using? Will it have floating point capability?I think you make a reasonable argument against mppt, but when I look at your graphs it seems you get a lot of periods even in the middle of the day where you seem to get absolute zero solar energy produced. Why is this so? I thought it would produce about 10-20% even if cloudy. To me it seems that energy on cloudy days is most important of all. Possibly this would be the advantage of an mppt device.

author: electrodacus
author_rank: Super Contributor
timestamp: February 22, 2015, 11:19:19 pm
content: Quote from: Seekonk on February 22, 2015, 10:30:42 pmYes this will be my next project an addon to the new Solar BMS that will be able to heat my house it will do a sort of what I call (digital MPPT) is a new concept I thing nothing to do with DC-DC converters used in battery charging.

author: electrodacus
author_rank: Super Contributor
timestamp: February 22, 2015, 11:27:53 pm
content: Quote from: HackedFridgeMagnet on February 22, 2015, 11:16:51 pmThanks.Weight is important for the SBMS do to expensive shipping and why will I have something heavier than it needs to be?24bit is probably not necessary for larger systems but the integrated 14bit ADC (rounded to 12bit) in the ISL94203 that I used in the old version has anti alias problems and even at 100mA resolution results with small loads are not great and with noisy loads as inverter things where even worse I needed a strong SW filter since HW filter will interfere with Short-circuit and overcurrent protection.I will need to switch ranges with a 16bit and it is not less costly so I preferred the 24bit. I may use that 24bit for some other applications like a 6.5 digit multimeter.I will be using the same STM32F072 I used in the last SBMS more than capable to handle all the SBMS functions.Is an OffGrid system so when battery is full there is no place for solar to go you just have excess unused power.

author: electrodacus
author_rank: Super Contributor
timestamp: February 24, 2015, 12:04:27 am
content: The Solar BMS is now on Kickstarter here is a linkhttp://electrodacus.com/k

author: eneuro
author_rank: Super Contributor
timestamp: March 01, 2015, 08:57:19 am
content: Those connectors on top of control panel doesn't look great and its mounting high power wire just by inserting it into such connector with screw driver can lead to erosion as well as such connections are exposed to vibrations.Maybe it's easier and cheaper ship products at lower weight and size, but automotive connectors seams to be much better for high power applications if well terminated, so sometimes it is better save shipment costs and DIY something yourself which will last for years and easy to repair.There is huge advantage of using such copper wire terminators, while everybody who has a hammer skils can make it at the cost of copper pipe, cut it into small pieces, press in the vise, make hole and we have nice wire terminator capable to survive many amps

author: electrodacus
author_rank: Super Contributor
timestamp: March 01, 2015, 05:21:19 pm
content: Quote from: 3roomlab on March 01, 2015, 11:11:00 amThanks for the comment. What I want to say with that phrase is that the new SBMS has 2.5x more components on that main board and will be almost impossible to route all that on a two layer PCB as I had non the SBMS4080.If someone can find a better way to express that let me know. English is not my strong point

author: electrodacus
author_rank: Super Contributor
timestamp: March 01, 2015, 05:36:39 pm
content: Quote from: eneuro on March 01, 2015, 08:57:19 amThanks for the comment. Are you referring at the SBMS4080 or at the new SBMS100 that is now on Kickstarter. They have different connectors but both use screws to keep the wires thigh. I do not think vibrations will get those connection louse. Unless is installed on a tractor without any suspension but even then methods to secure that connection with the connectors I use exist.I do want to keep the SBMS compact and light and the connectors need to be SMD type to work with the metal core PCB. The ones on the new SBMS where the only ones that got my requirements and where able to take #2 AWG (35mm^2) copper wire.If you have a better suggestion for connectors with this restrictions I will like to see them. There is still time to improve the new SBMS if that is the case. Same for any other part of the SBMS like better power mosfets or ...It is open source and I like to take the final decision but I love to here suggestions. The dual PV input was suggested by a few of the first bakers nd since was not that hard to implement I did that. It seems that out of those 4 models (two with dual input and two without) >90% of the current bakers went for the two dual input models.

author: eneuro
author_rank: Super Contributor
timestamp: March 01, 2015, 07:55:58 pm
content: Quote from: electrodacus on March 01, 2015, 05:36:39 pmIf we assume solid coper cross section than 35mm2 leads to close to 7mm diameter which is quite eaasy to fit inside copper pipe I've shown above, but it looks quite dificult to screw, but probably you have some idea how to do it, so it could be interesting to see how this wire fits into your upgraded new connectorsIn spot welder I've used 2 x 35mm2 in parallel into 15mm diameter copper pipe to help disipate welding heat at bulky transformer secondary in spot welder, so in many my projects those copper pipe based wire terminators works for me and are easy to make, but for commercial product maybe something different will be better, so its up to you to choose what better fits your requirements if you want to have happy customers.

author: electrodacus
author_rank: Super Contributor
timestamp: March 30, 2015, 01:56:27 am
content: The last 5 days on Kickstarter currently at 83% if you where thinking on supporting this project there is not much time left.

author: ScubaShan
author_rank: Contributor
timestamp: March 31, 2015, 08:24:23 pm
content: At the moment I manage my system (8kWh lithium with 1600W solar / 3000W alternator) with Bluesea ACRs, Bluesea RBS, Victron BMV, Victron MPPT controllers, SSRs, junsi cellog8s and some custom software. What would be interesting to me for the next release would be a "lite" version with the BMS functionality (cell voltage logging, cell LV/HV disconnect ) but using external COTS devices for power control. Multiple 100A SSRs ($50) could be used for PWM of charge sources, 500A relays could be used for load/charge circuit disconnection, and external shunts for current monitoring. This could make your box the centre of a very large (or small) system without you having to develop multiple SKUs.Off topic:One of the main reasons for wanting MPPT on boats and RVs is the lack of available roof space. Additional panels can be cheaper than an MPPT controller but if you don't have anywhere to put them MPPT comes to the rescue.Grid tie panels are significantly (20%) more efficient than typical RV panels which means less roof space is required however you can only use these panels with MPPT controllers due to the higher voltage.Horses for courses, PWM could make sense where you have unlimited space such as an off grid cabin but for those of us living mobile MPPT is king.

author: mtdoc
author_rank: Super Contributor
timestamp: March 31, 2015, 08:32:14 pm
content: Quote from: ScubaShan on March 31, 2015, 08:24:23 pmExcellent points and similar to ones I made earlier.Electrodacus is close to getting his funding. It's coming down to the wire and I hope he makes it. He has a interesting product that deserves funding.But IMO he should really rethink his absolutist anti-MPPT stance.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 31, 2015, 10:08:03 pm
content: I think his stance is fine, for his circumstances and for many other people too. Hope he gets his target too.His hardware wont easily support MPPT so it would be a big leap for him to change.IIRC he says he will need to use electrolytics and or larger inductors to support MPPT.This will take him out of his target market.I am sure he has definitely thought this through.He is not saying MPPT is bad it just that it wont work with this kind of on-off charger.Also by not having electrolytics he will get a lifetime matching the solar panels.One thing though,this statement isn't really fair.QuoteI am pretty sure you can easily get 10 years + out of Lead Acid if you look after them.

author: mtdoc
author_rank: Super Contributor
timestamp: March 31, 2015, 10:16:42 pm
content: Quote from: HackedFridgeMagnet on March 31, 2015, 10:08:03 pmActually, I think if you look through his postings you'll see he argues that MPPT is never needed now that PV prices are so low.Regardless, I agree that there is a market for his product as it is now, just that it is a small one.

author: electrodacus
author_rank: Super Contributor
timestamp: April 01, 2015, 12:44:10 am
content: Quote from: ScubaShan on March 31, 2015, 08:24:23 pmYou do not need (in fact is not recommended) that you use PWM for Lithium charging. The PWM part is to keep battery at constant voltage. For LiFePO4 you should only use one stage charging just the bulk part as soon as any cells get to your set limit say 3.55V the charging should be completely stop and only start recharging again if voltage drop below say 3.4V or so.Lithium cells (all of them not just LiFePO4) will degrade while keeps at high voltage the less time they spend there the better.The new SBMS will have multiple IO pins some designated for LV/HV disconnect so you can use external SSR if you want on top of that there will also be 24bit ADC inputs so you can measure the current on those external loads or chargers to be able to calculate battery SOC.Many other automations will be possible like measuring other external sensors or levels and taking actions based on they value or based on SOC values.Quote from: ScubaShan on March 31, 2015, 08:24:23 pmI see that there are more comments about MPPT here so for those that want to see in details my argument here is a link to my recent youtube video made specifically to explain this but there are some other obsolete technologies in there related to solar PV panels priceIn short additional PV panels cost less than MPPT (for 8 cell LiFePO4 the 60 cells panels will work at max power point so MPPT is completely useless)If space is a concern is usually on boats and RV where you can use LiFePO4 to save weight and use 60 cell panels to work at the max power point.Also a 2% more efficient solar PV panel will do the same as the average 15% MPPT while costing less and lasting over 25 years.But a very important reason that alone will make MPPT obsolete is that in Off Grid your energy use factor us usually well under 80% since battery is finite no matter how large.So if you have you batteries charged before noon like I do all that an MPPT will do is have them charged 20 or 30 minutes earlier and that is completely useless since all the available energy available after that remains unused.

author: electrodacus
author_rank: Super Contributor
timestamp: April 01, 2015, 12:57:31 am
content: Quote from: HackedFridgeMagnet on March 31, 2015, 10:08:03 pmMost people I talk to are replacing they battery after 5 to 6 years at most. But probably at least in theory you can get 10 years out of high quality well cared Lead Acid but that is still not the important point. You will need a realy large capacity battery so that you can only use the top 10% to 20% in order to last that long 10 years are 3500 cycles (that sort of use is also extremely inefficient since the charge efficiency of Lead Acid in top 20% is around 50% ). Also look at the fact that I mentioned "typical" as in what is valid for most installations.Then you also need a generator and charge the batteries after a few days of cloud when you where not able to fully charge them else sulfation will occur.I'm referring to offgrid energy storage not UPS type applications where you can probably get 10 years with very few cycles most of the time kept full.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 01, 2015, 02:43:04 am
content: I was referring to offgrid energy storage too.I do know of maybe 200 installations in outback northern Australia where the batteries have never been replaced. Some of these have been around for over 10 years. Batteries are Sonneschein.But yes they are only using 20% of installed capacity, and do have sophisticated charge controllers, although no generators.The other thing is they get mild winters, but they do have to be careful about temperature.

author: electrodacus
author_rank: Super Contributor
timestamp: April 01, 2015, 03:54:00 am
content: Quote from: HackedFridgeMagnet on April 01, 2015, 02:43:04 amI'm guessing they used Gel batteries.This is the spec that I foundhttp://www.sonnenschein.org/PDF%20files/GelHandbookPart1.pdfBest one here the A600 series has quoted 1600 cycles based on IEC 60896-2 standard and this document is from 2003 so probably one of this batteries was used if is 10 years old already.Here is part two of that documenthttp://www.sonnenschein.org/PDF%20files/GelHandbookPart2.pdfFrom there page 27"Discharge conditions acc. to IEC 8962: 20° C, discharge for 3 h at a current of I = 2.0 * I10This is equivalent to a depth of discharge (DOD) of 60% C10The possible numbers of cycles depends on different parameters, i.e.sufficient re-charging, depth of discharge (DOD) and temperature."It seems test are done at 20C and there is a high dependence with themperature of those particular Gel bateryes from page 35"15 years at 20° C becomes reduced to7.5 years at 30° C"High temp do affect Lithium cells also.As example storage degradation over 10 years on Sony LiFePO4 is about 3% of initial capacity at 23C and 10% at 40C if I remember correctly the numbers.Comparing even this probably quite expensive gel with 7000 cycles at 70% DOD 0.3C of a Winston LiFePO4 there is still a huge difference.Then LiFePO4 does not care about being fully charged in fact it prefers not to and as long as it is kept in the voltage limits and that is done automatically by the BMSAnd I seen tests done at 10% DOD on LiFePO4 with 20k to 80k cycles.Ideally in this times when solar PV is so inexpensive is to have larger PV array and smaller battery. That is easily possible with LiFePO4 do to higher charge discharge rates possible and better deep cycle life.And as I mentioned the Digital MPPT here that will have a function to divert more or less of the large 9kW PV array used for heating to the Solar BMS for battery charging.Ex my daily power consumption is peak 4kWh/day down to 0.8kWh / day in low power mode day (when more than a few days with clouds are expected).Monthly average is 80kWh so just under 3kWh/day average.Now the current 720W PV array can produce 3.5kWh in the best sunny day in the short day of winter in December or January and the worst case scenario extremely cloudy winter day 0.3kWh same months.With the large 9kWh array extrapolating from this I will produce about 3.6kWh/day in the worst cloudy day so I can charge my battery using that large array as if it was a full sunny day so I only need capacity storage over night (no more need for 4 to 5 days autonomy or low power mode) so infinite autonomy no matter the weather condition.All the electricity I use inside the house in any form will still end up as heat so no loss there.The Digital MPPT will have multiple PV inputs so it will divert more or less of them to the Solar BMS for battery charging based on the amount of sun so that charge rate is maintained below 0.3C.It is incredible how many things change do to low cost PV panels and the cost will probably continue to drop even is maybe not at the same rate as in the last few years.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 01, 2015, 07:50:34 am
content: I don't know if they use Gel or Sealed or Unsealed Pb. I could find out but as you say it isn't that important. I was assuming Sealed Lead Acid.I checked my email I have slightly misquoted the battery life.QuoteI Should have saidQuoteBut don't get me wrong, you have sold me on the idea of LiFePO4 and I have even suggested it to the people who installed all the Sonnensheins.

author: electrodacus
author_rank: Super Contributor
timestamp: April 01, 2015, 06:34:46 pm
content: Quote from: HackedFridgeMagnet on April 01, 2015, 07:50:34 amIn OffGrid most people use flooded that require quite a bit more maintenance and if that is not done correctly they will last quite a bit less than specified. Gel are probably the type that will last the most so if they have 10 years already is probably a type of Gel battery.Even between those Gel battery's there is a huge difference in cycle life and expected life and I'm sure there is also a difference in price to reflect that.Gel is also used usually with very low charge discharge rates else irreversible damage will occur.This are probably installed in some remote communication towers or something like this where load is almost constant and relatively small compared to battery capacity.I have no interest in promoting any particular type of battery but my preference is clear that is why I chose to install LifePO4 on my house.I see this almost like a capacitor or capacitor all you need to take care of is voltage limits low and high. As long as you stay in those limits they will last as specified and you will be able to estimate how much life they have left based on the amount of degradation. I'm realy curios to do this degradation test on my battery in about one months after two years of use. My prediction is 4% or less but I have if that will be the case. This GBS are not the greatest LiFePO4 available the 100Ah cells have about 1.8mohm internal DC resistance where mot others for same size batteries have about half and Winston even less at around 0.5mohm this seems to be a good indication of battery quality.I do not think I will need a new battery any time soon but if I do I will probably go with Winston this time but I will be more sure after I do the capacity test next month.

author: mtdoc
author_rank: Super Contributor
timestamp: April 01, 2015, 07:18:06 pm
content: With routine maintenance and proper charging, people routinely get 10+ years from standard flooded LA T105 deep cycle batteries from a reputable brand (e.g. Trojan). Of course if you chronically undercharge your batteries or discharge them below 50% SOC, lifespan is less. Many people undersize their solar array /battery bank size. Many try to use arrays with too low string voltages (e.g. expecting a "24 volt" grid tie panel to reliably charge a 24V battery bank). These things lead to shorter lifespan. Higher temperature exposure also shortens lifespan.For traction type flooded LA batteries (eg forklift type) 20 year lifespan is not unheard of. For example one company that markets these specifically for solar installations - theHUP Solar 1warranties their batteries for 10 years.Another advantage of traction batteries are ability to tolerate deeper discharge. Disadvantages include lower charge efficiency and higher maintenance needs.Flooded LA batteries have been used for decades in solar installations so these are well established facts.Gel batteries are a very poor choice for solar installations - so are not used very much. There are several reasons for this but a big one is that they are very easily ruined by a single mishap of overcharging - so they typically have a short lifespan in real world solar installations.AGMs can be a good choice. They generally have a longer float life, higher charge efficiency and require little maintenance so are a good choice for battery back up systems. The do not tolerate as many deep discharges/lifespan as FLAs.LiFeP04s have several advantages - but the biggest are high charge efficiency, the ability to discharge deeper and more cycles over lifespan. Intheorythey should have a longer lifespan than most FLAs IF cared for properly. But at this point they have not been proven to last more than 10 years in solar installations -they just haven't been widely available that long. We all know that real world lifespan of anything involving electricity does not always match theoretical lifespan.For proven lifespan alone - nothing beats Nickel Iron batteries. But they have several disadvantages as well.

author: electrodacus
author_rank: Super Contributor
timestamp: April 01, 2015, 08:26:42 pm
content: Quote from: mtdoc on April 01, 2015, 07:18:06 pmI agree with most of your comments.Solar OffGrid is relatively bad for any type of Lead Acid battery since is intermittent and all type of Lead Acid hate to stay discharged for long period of times (Gel are the most immune to this and in some particular applications they are a great choice and can last a long time).LiFePO4 are much more suited for Solar OffGrid since they like to stay in a partially state of charge.LiFePO4 also dose not require any maintenance and as long as is protected by a proper BMS can not be damaged by user.Thus LiFePO4 will actually survive much longer in a typical offgrid solar installation and get a much better return on investment.I know what I say has less value since it seems that I have an interest in this with the Kickstarter campaign for the Solar BMSI hope people will do their own research.Sony and Bosch have a nice LiFePO4 complete solution but they mostly ofter that for grid tie where market is much larger.Sony for example offers up to 20 years warranty on their complete solution and their battery can do 6000 cycles of 100% DOD before getting at 80% of original capacity.They also made a degradation test in storage and extrapolated the data to 10 years and in 10 years the loss in capacity was 3% at 23C and 10% at 40 or 45C.Lead Acid battery is normally quote as end of life at 60% of original capacity and from there degradation is steep nothing usable.LiFePO4 is quoted as end of life at 80% of original capacity and degradation continues to be almost linear so if you want to go to 60% it will probably last 2x or more since degradation seems to slow down similar to what you see on solar PV panels.I also find LiFePO4 much safer than any other battery and quite green no Cobalt as on the other Lithium batteries it also uses quite a bit less Lithium than those for the same capacity.

author: mtdoc
author_rank: Super Contributor
timestamp: April 01, 2015, 11:01:46 pm
content: Quote from: electrodacus on April 01, 2015, 08:26:42 pmI'm not sure where your are getting this from but it has nothing to do with real world uses IME. No one off grid would keep their batteries down to 60% unless they severely overestimated their power needs when purchasing the original pack (usually it's the opposite - people underestimate their power needs).Solar 1's 10 yr warrantyis for 80% of original capacity (prorated after 7 yrs) as is other lead acid battery warranties I have seen. Any examples of warranties on FePO4 battery packs? I'm sure there must be some - I just haven't seen any yet.

author: electrodacus
author_rank: Super Contributor
timestamp: April 02, 2015, 12:31:01 am
content: Quote from: mtdoc on April 01, 2015, 11:01:46 pmCycle tests on all Lead Acid batteries I seen are for 60% original capacity so the cycle numbers you see in their spec is for that.Lead Acid also has quite a steep drop once it starts to do so.Here is a graph but just google search images on "Lead Acid cycle life" and you will see all graph down to 60% original capacity as the end of useful lifehere is another exampleAnd I remember checking the standard tests and how they are done and I found the same thing.It makes not much difference anyway since from 80% to 60% there are very few cycles left so when you noticed that (hard to notice if you are using just 20% DOD usually) you will need to act fast in replacing them.On the other side the cycle life for LiFePO4 is almost a linear degradation so you have years to replace your battery maybe even a decade if you find a way to reduce consumption with say 10% so that you can use it down to 70% of original capacity.Here is the Sony LiFePO4 cycle life

author: mtdoc
author_rank: Super Contributor
timestamp: April 02, 2015, 02:40:09 am
content: Nice graphs but not really relevant to the question of real world lifespan as I discussed in prior post.I really hope that LiFePO4 live up to their theoretical lifespan in real world RE system use. My current 5 yr old AGM (backup) battery bank likely has 8-10 years left in it (they're rated for 15 yr float life). I'd like to be able to replace it when the time comes with a battery bank that will last 30 yrs!Still would like to see some LiFePO4 battery warranties...

author: electrodacus
author_rank: Super Contributor
timestamp: April 02, 2015, 03:00:08 am
content: Quote from: mtdoc on April 02, 2015, 02:40:09 amI'm mostly talking about OffGrid applications and not backup. In backup you barely use the battery so is more about the storage life span.Sony offers 20 years warranty but only for the complete system including the BMS.The real advantage of LiFePO4 is when is used quite hard even in the case of Sony battery.6000 cycles of 100% DOD is about 20 years of 100% DOD every day and that is why they target the Grid tie solar applications where they can use the battery to store energy when is inexpensive and sell it or use it when is expensive.Also LiFePO4 will not like to stay in float so you will probably need to keep it charged at 80% or so most of the time and only charge back to around 80% when you need to discharge it.Is just a totally different type of battery in therms of use scenario and is mostly great in OffGrid solar where you do quite a lot of cycling.If you look at my 7 day energy production consumption graph you will see that there are days where I use more than battery capacity from the battery in the way that I charge and discharge the battery a few times in the same day maybe just 20 to 30% DOD but 3 or 4 times a day.I will say for just backup type application an AGM battery is a good choice (at least that is my guess I did not think about that to much).I think is not fair to think about more than 20 years of life with LiFePO4 maybe is possible but in 20 years I expect a lot to have changed in battery technology. LiFePO4 is quite new about 2002 for the first commercial one if I remember correctly.

author: mtdoc
author_rank: Super Contributor
timestamp: April 02, 2015, 03:07:53 am
content: Quote from: electrodacus on April 02, 2015, 03:00:08 amSo was I. I only brought up my current system to point out that I am hoping LiFePO4s live up to the hype!I have experience with off grid systems and that is what I was referring to previously in my posts (go back and look).Again - off grid users who properly care for their lead acid batteries often get 10+ (or 20+ in the case of traction batteries) out of them.QuoteCool. Link?QuoteYes - that was my earlier point. It's too soon to know how long large LiFePO4 battery banks will last in the field when used in actual off grid PV systems. Time will tell.

author: electrodacus
author_rank: Super Contributor
timestamp: April 02, 2015, 03:37:15 am
content: Quote from: mtdoc on April 02, 2015, 03:07:53 amYou need a battery a few times larger in capacity so that you can only discharge the top 10 to 20% to achieve long battery life with Lead Acid that is not always possible in s solar application here winter is about 4 to 5 months and there are groups of 3 to 4 days where you can not say where the sun is and that Lead Acid battery will get quite a bit deeper discharge unless you have a separate gasoline generator to charge it back up and not keep it for days at low charge levels.It also need venting and again in this cold climate I live in that will have the battery at almost ambient temperature to to this external venting requirement.It seem to me that was just impossible to use a Lead Acid offgrid here in Canada that is why looked at other possibilities.I do not have a noisy and dirty gasoline generator as most do with Lead Acid and use that quite a bit in winter.Quote from: mtdoc on April 02, 2015, 03:07:53 amhttp://download.solarshop.net/english/uploads/FS-UK-Sony-Storage-system-data-sheet-10-08-2012.pdfWhat I consider a benchmark when selecting a battery is the cost of storing a unit of energy.This are the sort of rough calculations that I do.And I trust LiFePO4 way more since is not possible to damage by keeping it discharged because you have no sun or not doing proper maintenance in the case of flooded types.Keep in mind the L16RE-2V is the newest "smart carbon" battery available based on spec hugely superior to the previous generation not sure I buy that but I respect the spec based on the new spec for this battery it makes no difference to cycle life if you discharge the battery 20% or 100%

author: ScubaShan
author_rank: Contributor
timestamp: April 02, 2015, 03:53:24 am
content: Quote from: electrodacus on April 01, 2015, 12:44:10 amYou make a few assumptions and mistakes in this video otherwise well presented video.Your Solar BMS chart shows 27v @ 65c panel temp however at 65c the panel Vmp will be 26v which is below the battery charging voltage so you wouldn't be getting much charge into the battery.In warmer climates like Australia where temps regularly see 45c we get panel temps in excess of 80c so with that panel we'd be looking at a Vmp of just 24v, which would be pretty useless for charging a 24v battery.Boats and RVs usually operate across various climates, here in oz for example it can be 45c in one location and 0c a few hours drive away. A higher string voltage + MPPT makes more sense because of the wide range of operating environments encountered while travelling.As I said, horses for courses and I'm sure PWM or on/off charging is working fine for your cabin system but it would be foolish to write off MPPT for all users.

author: mtdoc
author_rank: Super Contributor
timestamp: April 02, 2015, 03:54:56 am
content: Quote from: electrodacus on April 02, 2015, 03:37:15 amThanks for the link but still no warranty info. It's fine and good to claim 20 yr life but without a warranty or a proven track record it's all just marketing hype.QuoteNot true. This is something I do have first hand experience with. i have used LiFeP04 batteries in eBikes for several years and you can if fact damage cells irreversibly by failing to keep them charged. I did it once with a $500 LiFePO4 ebike pack!Again - I am a fan of LiFePO4 and suspect they will eventually replace LA as the dominant chemistry for RE systems. I'm just trying to separate the reality from the hype.

author: mtdoc
author_rank: Super Contributor
timestamp: April 02, 2015, 04:06:02 am
content: Quote from: ScubaShan on April 02, 2015, 03:53:24 amYes - I was making the same point earlier in this thread (see post #5). You need an STC VMP of 32+V to reliably charge a 24V battery bank. Warm temps, any shading, etc prevent the standard, lowest cost "grid tie" "24V" panels from being used in single panel strings for 24V nominal systems or 2 panel strings for 48V nominal systems. I suppose with LiFePO4 you could get away with it by using non traditional bank sizing [e.g. 7s or 14s arrangement for "24V" or "48V" nominal systems)

author: electrodacus
author_rank: Super Contributor
timestamp: April 02, 2015, 05:34:10 pm
content: Quote from: ScubaShan on April 02, 2015, 03:53:24 amWrong about the way PV panels work. Yes Vmp may be lower say 26V but if your battery is 27V the current will drop a bit and you will not be anymore at the max power point but still quite close.So even if cells are at 80C and battery at 27V you will still see a charge current.Not to mention that usually when is sunny at peak in the afternoon is when you have those cells temperature and is also when you have the most excess power anyway.Here is a graph from a 250W (60 cells) but is low resolution sorry is what I found on a quick google searchIf you look closely even at 30V and 65C you still get around 4A LiFePO4 is basically charged at 27V and probably with no load as soon as you connect a significant load the voltage will drop and you get the max power point current. I'm offgrid with this sort of set-up and even if here is just below 40C panels still get relatively hot in some summer days. From what I remember 38C is about the record hot days here.Quote from: mtdocYou probably had that improper BMS used on eBikes that uses that 5 pin IC designed for LiCoO2 and not LiFePO4 with 2V and 3.9V limits well outside the LiFePO4 limits of 2.8V and 3.6VIf you live a LiFePO4 for months at 20% SOC there will be absolutely no degradation. My SBMS limits are set at 3V and 3.55V so say I'm not home for months the panes from so reason fail and the battery discharge slowly to 3V when the SBMS will disconnect the load there is enough charge in the battery 10% at least at this point to keep the battery above the critical limits for quite some time.With my 100Ah cells 10% represent 10Ah with your smaller bike cells it will have been much less. There is a self discharge of around 2% probably per months so I cold not live them there from more than 4 to 5 months in theory then there is the SBMS as a load even if is just 3mA for SBMS4080 it will still add 2.16Ah/month or about the same as self discharge so that will cut the possible survival to about 2 months from 3V or around 10% SOC .So is very easy to see how your smaller ebike battery failed. As long as you keep the battery always above 2.8V (2.5V is acceptable under high load) and below 3.6V they will last as specified.

author: mtdoc
author_rank: Super Contributor
timestamp: April 02, 2015, 05:44:15 pm
content: Quote from: electrodacus on April 02, 2015, 05:34:10 pmNope, he's not wrong.QuoteIt's not just about the power. PV panels act as current sources. But batteries have minimum voltages that they require to charge correctly.QuoteNope. That wasn't it.QuoteYep, that's the issue. If you don't have your battery connected to a charging source and voltage drops too low (due to slow spontaneous discharge) a BMS can't prevent that. So LiFePO4, just like LAcanbe ruined if not kept sufficiently charged - which was my point.

author: electrodacus
author_rank: Super Contributor
timestamp: April 02, 2015, 07:23:34 pm
content: Quote from: mtdoc on April 02, 2015, 05:44:15 pmLook at the IV curve especially the 65C one even if your battery is 30V you still get 4A. Do not forget that 60 cells PV panels is exactly what I use and even if my location does not get as warm as other places is still warm enough to be relevant.The max power point voltage is all that it is an optimum point on a curve. If that is 26V at 65C you still get current at 27V a bit less and not optimum but you do.Quote from: mtdoc on April 02, 2015, 05:44:15 pmWhat does slow spontaneous discharge means ?A BMS protected battery (of course proper BMS) will have no problem as explained in the earlier example. You need to consider the battery self discharge rate and the BMS power consumption the you can know exactly how long will it last before it needs recharge after charger is lost and load is disconnected. The two months for my system seems more than reasonable since I will never be away from the system for more than two months. And the chance of PV array to fail is extremely low.

author: mtdoc
author_rank: Super Contributor
timestamp: April 02, 2015, 08:08:34 pm
content: Quote from: electrodacus on April 02, 2015, 07:23:34 pmThose voltages are not adequate to fully charge a nominal 24V lead acid or LiFePO4 (8s) battery bank.QuoteThe discharge that occurs in any battery when it just sits, unconnected to any load or charging source.QuoteNo argument there.I was only pointing out that your prior statement that for LiFePO4 it "is not possible to damage by keeping it discharged because you have no sun or not doing proper maintenance" is incorrect - which it is.

author: electrodacus
author_rank: Super Contributor
timestamp: April 02, 2015, 08:44:42 pm
content: Quote from: mtdoc on April 02, 2015, 08:08:34 pmThey are more than adequate at 3.4V under 0.3C charge rate a battery is around 90% SOCAnd looking at that IV graph again you can see about 32V open circuit voltage with cell temperature at 65CSo even at 28V battery voltage you still get a decent charge current with cell temperature at 65 even 75CAs I also mentioned few times before if you have any load connected voltage will drop quite a bit more and current from the panel will go to load thus PV panel even in those high temperature work close to max power point.If you do not have any load and temp of the panels are so high and your battery is at 27V or above it means is in the middle of the day sunny and your battery is above 90% SOC and for LiFePO4 it will be a good thing to slow down charging at this point they hate to be fully charged.But you are probably a half hour from full charged if your panels is 65 or 75C and battery voltage is 27V.Quote from: mtdoc on April 02, 2015, 08:08:34 pmThat self discharge on any good LifePO4 is below 2% capacity per month so as long as you stop at about 10% SOC (3V very low discharge rate OffGrid or 2.8V high discharge rate eBike) you have enough time to recharge as I mentioned before.

author: mtdoc
author_rank: Super Contributor
timestamp: April 02, 2015, 10:35:23 pm
content: Quote from: electrodacus on April 02, 2015, 08:44:42 pmYou will not fully charge a LiFePO4 cell with 3.4V or below.There's a reason LiFePO4 chargers use a voltage of 3.6-3.65 per cell for the constant voltage portion of the charge cycle.What voltage does your charger use?QuoteSure, but that has nothing with the point I was making about your incorrect statement that you can't damage LiFePO4 batteries by failing to charge them or maintain them.Look - I'm a big fan of LiFePO4. If I was designing an off grid solar system today I would seriously consider using them instead of LA batteries. But this is an EE forum and hyperbolic, incorrect statements such as "MPPT is uneccessary due to cheap PV prices" and " you can't damage LiFePO4 like you can LA by not charging or properly maintaining them" are not going to go unchallenged

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 02, 2015, 10:45:02 pm
content: QuoteAny specs on this?So if you left some LiFePO4 at 10% SOC. would it be 8% next month, 6% after 2 months, 0% after 5 months?Roughly at what point do they start getting damaged? Or what SOC should they never go below?

author: electrodacus
author_rank: Super Contributor
timestamp: April 02, 2015, 11:37:48 pm
content: Quote from: mtdoc on April 02, 2015, 10:35:23 pmA LiFePO4 can be charged full 100% SOC with just 3.4V you just need to wait more and charge at lower charge rate.This not what I wanted to say. I wanted to say that at 3.4V normal 0.2C or 0.25C charge rate the SOC is around 90% so is just a half hour from a full charge when it gets to 3.55VMy charger uses constant current charging only and will stop the charging as soon as the highest cell gets to 3.55Vconstant voltage portion of the charge only adds at most 5% more capacity while reducing the life of the battery substantially. This is valid for LiCoO2 also.A LiCoO2 is you mobile phone or laptop is usually charged in two stages first bulk or constant current up to 4.2V then the constant voltage part until the current drops to 10 or 5% or the initial charge current.If you only do the fist part of the charge on a LiCoO2 you only get about 85% SOC but the life of the battery will be almost double same thing if you reduce the charge voltage for every 100mV you double the battery life wile reducing a bit the max available capacity.In military applications 3.95V was used with LiCoO2 so that battery life cycle was about 8x higher. Lithium degradation is related to the amount of time the battery spends at the higher end voltage.In Phones or other mobile devices the energy density is way more important than cycle life since those are usually upgraded by customers before the battery will die but that 15% extra capacity is more valuable.Quote from: mtdoc on April 02, 2015, 10:35:23 pmI was referring to a battery protected by a BMS where the discharge is terminated by the BMS at proper voltage level based on battery and application requirement. If that low cut of voltage is properly set for that particular application so that at least 10% capacity is still available then that 10% is enough for that battery and protection circuit to survive a few weeks or months without a charge.In an OffGrid application you will notice immediately if the load is disconnected and that should never happen in a properly dimensioned installation.So yes all you need to do to protect a LifePO4 is to keep it between 2.8V and 3.6V and not charge when battery temp below 0C seems way simpler than all the conditions that affect Lead Acid life and can be done by BMS.

author: electrodacus
author_rank: Super Contributor
timestamp: April 03, 2015, 12:14:47 am
content: Quote from: HackedFridgeMagnet on April 02, 2015, 10:45:02 pmThe open circuit voltage should not go below 2.8V you get all this in any proper LiFePO4 battery spec 2% self discharge is an average some are better some are worst.here for example is quoted as less than 3% per month for Winston 100Ah cellshttp://en.winston-battery.com/index.php/products/power-battery/item/wb-lyp100aha?category_id=176This self discharge rate is also quite dependent on storage temperature the higher the temperature the higher the self discharge rate.The GBS that I have is also stated as less than 3% per months sorry this is the 200Ah version but I'm sure the 100Ah has the same spechttp://liionbms.com/pdf/gbs/LFP-GBS200AH.pdfNot all manufacturers put this in the spec not sure why.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 03, 2015, 03:37:10 am
content: Just noticed, you got funded. Congrats.

author: electrodacus
author_rank: Super Contributor
timestamp: April 03, 2015, 03:38:55 am
content: Quote from: HackedFridgeMagnet on April 03, 2015, 03:37:10 amYes a few hours ago. Thanks.

author: mtdoc
author_rank: Super Contributor
timestamp: April 03, 2015, 08:03:04 pm
content: Yes, congrats on getting your funding!.Quote from: HackedFridgeMagnet on April 02, 2015, 10:45:02 pmA LiFePO4 cell at 2.0V or below is generally considered permanently dead.Quote from: electrodacus on April 02, 2015, 11:37:48 pmAny references on that? I have seen that stated for other Lithium battery chemistries but not for LiFePO4.It seems you're claiming something different than all the other LiFePO4 charger manufacturers I've seen. All the ones I've researched have a constant current stage followed by a constant voltage stage at 3.6-3.65V. This is true for the charges used by home build EVs with LiFePO4 banks and Ebike users. Also, the people who I know of using large LiFePO4 banks for off grid homes are using one of the currently available programmable MPPT controllers with CC and CV stages.QuoteOk thanks for clarifying but that's entirely different than your previous statement and in fact no different than Lead Acid batteries in that as long as you properly maintain them they do no suffer premature damage.

author: electrodacus
author_rank: Super Contributor
timestamp: April 03, 2015, 09:55:21 pm
content: Quote from: mtdoc on April 03, 2015, 08:03:04 pmThanks.Quote from: mtdoc on April 03, 2015, 08:03:04 pmLiFePO4 is no different in this regard from any other Lithium-ion battery. The less time it spends above 3.4V the better.There is actually even less advantage for LiFePO4 to be fully charged (using CV) since you only get about 5% extra vs LiCoO2 where is more significant at 15% extra.If you charge LiCoO2 with about 0.3C up to 4.2V CC and then terminate charging immediately the capacity is at 85% SOCIf you charge LiFePO4 with about 0.3C up to 3.6V CC and then terminate charging the capacity is 95% SOCThe degradation on both is based on the time spend charging at that higher voltage and temperature.In portable applications those 15% extra make sense as I mentioned.The manufacturers of LiFePO4 of course want to specify a larger capacity so by using CC and CV charging in their spec they can quote a 5% larger capacity.They usually do cycle life test at high charge discharge rates around 1C so time spent at 3.6V is extremely small not enough to make a significant impact in cycle life.In a solar setup using normal MPPT Lead Acid charger with CC and CV charging you will keep the battery for many hour every day forced at that higher than 3.4V level.LiFePO4 at rest is below that 3.4V so keeping it above that creates stress and encourages dendrite growth.The dendrite formation on LiFePO4 is less problematic than LiCo variants but will still exist and affect the life of the battery even if is harder to see in real life do to superior cycle life of the LiFePO4.Quote from: mtdoc on April 03, 2015, 08:03:04 pmIs different from Lead Acid in the sense that if lead acid is kept at a partial state of charge for long periods the life of the battery is affected and in OffGrid solar that is where the battery spends most of is life and not fully charged. As soon as the sun is set the battery will be at a partial state of charge and there can be many days in a row in this partial state of charge.In this conditions LiFePO4 feel the most comfortable is where they love to be, where Lead Acid will sulfate and battery capacity will be affected.Lead Acid has also a much higher self discharge rate but normally not a problem in OffGrid applications same as lower energy density is also normally not a problem in stationary off grid applications.

author: mtdoc
author_rank: Super Contributor
timestamp: April 03, 2015, 10:19:25 pm
content: Quote from: electrodacus on April 03, 2015, 09:55:21 pmNo - not many hours. Usually just until you meet your specified end amps.QuoteOk - sounds reasonable enough but it seems that you're making a pretty remarkable claim - that is that you know something the other LiFePO4 charger manufacturers don't - some actual references to support your theory would be nice. I mean there are many battery chemists, physicists, and engineers who have spent a lot of time developing LiFePO4 technology. How is it that you know something they don't - or if they do - where have they published it?

author: electrodacus
author_rank: Super Contributor
timestamp: April 03, 2015, 11:50:02 pm
content: Quote from: mtdoc on April 03, 2015, 10:19:25 pmWhat other LiFePO4 chargers ?I do not know how Sony and Bosch implemented their chargers for their complete solution but I can guess they only use CC as I do to get the most out of their battery.Also all car manufacturers have implemented 80% fast charging so that the battery can last much longer with the option of full charge in case you realy need that extra range to the detriment of battery life. This is with LiCo variants.With LiFePO4 and stationary storage is just 5% that you gain by doing CV charging and no advantage (like the extra range on cars).There are very few experts in Lithium battery charging and most chargers you probably refer to as those Lead Acid chargers where they added support for LiFePO by just adding a new limit are far from experts and do not care if your battery life is affected it will still be long enough that no one will notice or realise.And most of those BMS designed for DIY EV cars are as or even worse designed.With those usually cell voltage is allowed to even exceed 3.6V accelerating even more battery degradation. Inefficient cell balancing done on individual cell not taking in to account the other cell voltages so no being able to do an effective cell balancing.All this and more are the reason I decided to invest the time and do my own version.Most laptops for example will charge the battery with CC and CV to 4.2V with no option to set that lower to prolong the battery life except for some expensive IBM / Lenovo models that have that functionality in BIOS. I mostly used laptops plugged in and kept the battery there as an UPS sort of protection but that damaged the battery quite fast I will have liked to have such a function so that battery will only be charged to 80% and last a lot longer.It dose not mean that other laptop manufacturers did not know about this benefit is just that they did not care the battery lasted enough anyway and they preferred that they clients where happy with the run time did not care they will need to buy another laptop or battery soon after the warranty was goneSame with my current phone with non removable battery that is almost dead because the phone is always connected to charger since the phone is used for internet acnes all day.You probably know this graph from battery university about the cycle life versus just small cell over voltage on LiCoO2 the LiFePO4 has better tolerance to over voltage but the life cycle will still be affected in a similar way.

author: mtdoc
author_rank: Super Contributor
timestamp: April 04, 2015, 12:05:19 am
content: Quote from: electrodacus on April 03, 2015, 11:50:02 pmMany. Here's two companies to start:Manzanita MicroPowerstreamFrom Powerstream (the second link):QuoteQuoteNice graph but not relevant to the question.BTW - I'm not disputing that you can charge LiFePO4 cells at 3.4V - it's just that I've never seen any data supporting what you say about a CC stage followed by a CV stage at 3.6V shortens battery life.LiFePO4 do have the advantage over LA in that the don't sulphate or otherwise degrade by chronic mild undercharging. But with LiFePO4 batteries relatively expensive - I don't think anyone will want to pay for more capacity than necessary/

author: electrodacus
author_rank: Super Contributor
timestamp: April 04, 2015, 01:21:27 am
content: Quote from: mtdoc on April 04, 2015, 12:05:19 amThey have absolutely no idea of what they talking about.How will a LiFePO4 with CC charging to 3.65V be just 60% SOC it will be around 95% and even their own graph shows that. I do not what to insert that graph here since it shows LiFePO4 charging to 4.2V that no LiFePO4 battery manufacturer will approve.If you look at their graph it shows around 90% (not 60%) charge level after CC up to 3.6V and that is at 0.5C rate a bit high most battery manufacturers recommend 0.2 to 0.3C for long life not fast charging.Then they talk about LiFePO4 self balance (again absolute garbage) I hate to see that website as reference to anything. There is no loss reaction like hydrogen production in Lead Acid to allow for self balancing by wasting energy on the overcharged cell.The say all this garbage so they can sell 12V LiFePO battery without any real protection. All and I mean all 12V LiFePO4 sold as replacement for Lead Acid are useless at best for many reasons. Cells will become unbalanced since proper balancing and charging can not be stopped on cell over-voltage unless it gets critical and second they do no make a good starter battery replacement since they will get damaged if charged below freezing (by an effect called lithium plating that is irreversible and leads to capacity loss).Sorry about language I got a bit annoyed by that Powerstream pageQuoteLike I mentioned before Battery manufacturers give spec based on dual stage CC and CV up to 3.6V most mention that 3.65V is acceptable in a sting of series connected cells for the highest cell.The Solar BMS does not charge the battery at 3.4V but at 3.55V (highest cell not average pack voltage) then as soon as it gets there it stops charging so that battery is as much as possible above 3.4V and charging. With this do to the nature of the solar PV panels I can achieve 100% SOC wile only using constant current charging and not exceeding 3.55V on any cell.Cells are also balanced within 10mV because the balancing is done at any voltage level by comparing each individual cell voltage and not using fixed voltage threshold where balancing is performed independent of the other cell voltages as other less complex balancers do.I say price of LiFePO4 can be the same as quality Lead Acid because you can do the same thing with half capacity do to higher charge-discharge efficiency and higher DOD accepted.I use a 2.5kWh battery with an average monthly power consumption of 80kWh. For that you will need probably around 3x capacity with Lead Acid even if is just about the 0.1C charging recommendation on Lead Acid. My panels put up to 30A in cold whether that is acceptable for 100Ah LiFePO4 but will require a 300Ah Lead Acid.I actuals have even better ideas for the future with the integration of the Solar BMS and Digital MPPT and large PV array where with this same battery I can increase power consumption to 150 even 200kWh/month with infinite autonomy in any sort of whether conditions.

author: mtdoc
author_rank: Super Contributor
timestamp: April 04, 2015, 01:57:22 am
content: Quote from: electrodacus on April 04, 2015, 01:21:27 amI think you're misreading what they wrote. I read it to mean it is the second, CV stage with a charging voltage of 3.65 that completes the charging. The 60% is what they cite for the 1st, CC stage.But regardless, I don't hold them to be "the experts". You asked for links to charger manufacturers that use CC - CV staged charging and I just linked them as one. I am not familiar with them or their products beyond what their web site says.I am familiar with Manzita Micro who make very high quality chargers used for EVs and who also do CC - CV staged charging.QuoteYou realize that a charge voltage of 3.65 during the CV stage does not mean you actually charge the cell to that voltage, right? As soon as it is disconnected from the charger the voltage will drop - just as it at the end of the absorption stage in traditional LA 3 stage charging algorithms.So, I'd still like to see some references to support your idea that using lower charge voltages and only a CC stage improves the lifespan of LiFePO4. This is not an academic question. If it's true I'd really like to see the evidence so that I can consider it in the care of my eBike LiFePO4s and probable future LiFePO4 battery bank for off grid use.Any actual references to support your idea?

author: electrodacus
author_rank: Super Contributor
timestamp: April 04, 2015, 02:56:26 am
content: Quote from: mtdoc on April 04, 2015, 01:57:22 amYes I read correctly no misunderstanding with the first CC charge to 3.65V you get well over 90% even at 0.5C charge rate and not 60%.QuoteYou can only say you do CV charging when the voltage is at that level you specify as CV charging voltage before that is CC charging.If you apply a CC-CV charger (can even be a lab power supply)You set the Voltage at 3.65V and constant current limiting say at 5A for a 10Ah cellSay cell is fully discharged when you connect.Cell will be in CC mode for about 110 minutes probably and then get to 3.65V and constant voltage will start and current will slowly drop at this point cell is well over 90% charged probably 95% and during constant voltage part of the charge where battery voltage will stay for around 20 minutes or so at 3.65V and current will drop you will gain the rest of that 5% or so SOC to 100% but this part of the charge is the one having the most stress on battery for almost no gain (that extra 5% is useless but the battery degradation is relatively high)Not sure anyone has done long therm testing on this but I expect about 20% lower life for batteries charged with the second stage CV so you gain 5% additional capacity that you have no use for anyway and lose 20% of your battery life.Anyway this is fine but charging LiFePO4 to 4.2V fast charging as they suggest on the page will drop the battery life by at least a factor of 5 and instead of 10 to 20 years you get at most 2 to 4 years out of your battery.Yes LiFePO4 will not catch on fire at 4.2V but will suffer the same way as if you charge a LiCoO2 at 4.35V instead of 4.2V as you seen in that graph a few post earlier.There are quite a few variation of LiFePO4 my GBS for example is LiFeMnPO4 the Winston is LiFeYPO4 some do not specify any additional elements and are more plain LiFePO4 but still have some unlisted additives that make they battery spacial. Each of this will react a bit different to overcharging but they will all get affected.Is quite easy to see what the optimum working voltage is for any Lithium battery by just looking at a charge discharge curve.In a car people want a charger that gets 100% SOC so CC-CV because they want as much capacity as they can get even if arguably this is useless for LiFePO4 where you only gain 5% by that CV stage.Most EV car manufacturers use LiCo because it has 2x the energy density of LiFePO4 and can get 2x the range. There they gain 15% extra by using CV so is more significant and they implement that but they also have a recommended 80% charge if you do not need the extra so that you can have a longer battery life.You can go and check the spec and recommendation of any care manufacturer.So they care about battery life but at the same time are interested in higher range in the detriment of battery life.Stationary energy storage normally dose not care about using the entire battery capacity especially since this comes to the detriment to battery life.All DIY solar installations use a car BMS in combination with a Lead Acid charger in combination with LiFePO4 and that is because there is no real alternative and because there is not enough eduction about Lithium in stationary energy storage.If you did not see this you should watch is a relatively good video about Lithium-ion batteries in general

author: mtdoc
author_rank: Super Contributor
timestamp: April 04, 2015, 03:32:26 am
content: Quote from: electrodacus on April 04, 2015, 02:56:26 amThat depends entirely on how long the CC stage is. Also the goal of a CC stage is not to "charge to 3.65V". Surely you understand how multistage charging works ?I do agree that CC-CV charge algorithms generally do not bring the battery to only 60% SOC by the end of the CC stage - I suspect it was a typo and meant to be 90%But what you said is:QuoteWhich I don't understand how that came from what they wrote (right or wrong) - but that's besides the point.QuoteNo. There are BMS designed specifically for RE installations. Though I agree there needs to be more.In any case, based on your (non) answers - I guess your charging algorithm is based on your own ideas. Nothing wrong with that. It will be interesting to see the evolution of LiFePO4 charging as they become more widely used in home RE systems.Good luck with your Kickstarter product.

author: electrodacus
author_rank: Super Contributor
timestamp: April 04, 2015, 03:50:01 am
content: Quote from: mtdoc on April 04, 2015, 03:32:26 amThe advantage of my Solar BMS is that is fully programmable by user over 30 parameters can be programmed that affect how the charging is done.There are present parameters that I recommend but if you think something else is better you can do that very easy.99% of Off-Grid people still use Lead Acid so there is a long way to go for Lithium batteries.Education about lithium batteries is extremely important for their adoption.I see Lead Acid vs LiFePO4 as Incandescent vs LED was a few years ago.

author: mtdoc
author_rank: Super Contributor
timestamp: April 04, 2015, 04:10:13 am
content: I agree. It's early in the LiFePO4 adoption phase. Lots of room for experimentation.LiFePO4 prices still need to come down a bit and BMS systems to be more robust.One thing LA still has on LiFePO4. One bad mistake will generally not kill a LA battery as it will a LiFePO4 cell.

author: electrodacus
author_rank: Super Contributor
timestamp: April 04, 2015, 04:21:18 am
content: Quote from: mtdoc on April 04, 2015, 04:10:13 amI will say LiFePO4 is already cheap enough especially when considering the alternative. My choice of LiFePO4 was based on price mostly.As I mentioned using a good BMS should not allow for any mistakes.Price calculation should be done something like this. Here is the best Lead Acid (the new so called smart carbon) vs the best China based LiFePO4 (Sonny or A123 will be way better but they are harder to get)This are idealized prices based on spec real life cost of energy storage will be higher so prices are for comparison and no one should take this as the real life price and go OffGrid (grid is still better than OffGrid)

author: mtdoc
author_rank: Super Contributor
timestamp: April 04, 2015, 05:03:42 am
content: Sorry, but you lose some credibility with a table like that which is very skewed in its numbers and assumptions.TheTrojan L16RE-2V batteriesare a top of the line LA battery with a 7 year warranty and can be expected to routinely last 10 yrs or more from a company with a long history of real world experience and your comparing them to a no name Chinese brand with no warranty and no proven track record with an optimistic guess of 20-25 yr lifespan.The L16RE-2V have a (20hr) Ah rating of 1110 not 1021.Charging efficiency of these is typically going to be much better than 75% - more like 85%,Again - I'm a big fan of LiFePO4 based on their real merits. No reason to overhype them. It just makes knowledgable consumers skeptical of what you're selling.Also, where are you finding that price for the WB- LYP400AHA? the best price i can find online is about $1000 more than your number.

author: electrodacus
author_rank: Super Contributor
timestamp: April 04, 2015, 05:39:58 am
content: Quote from: mtdoc on April 04, 2015, 05:03:42 amThis comparison is purely based on manufacturer data-sheet.Is not reasonable to use capacity at 20h since most of the energy consumption will be at much higher discharge rate.Charge efficiency of a Lead Acid in the top 20% of SOC where most Lead Acid are use are way worse close to 50% so my 75% average efficiency was relatively optimistic.85% is close to the best case if you do not include the top SOC charge.But even if you want to ad this more optimistic values price will improve just slightly to $0.233/kWh so still as bad compared to LiFePO4And LiFePO4 will have more chances to met the spec since it will probably not be discharged daily at 70% and the number of charge cycles rise almost exponentially and not in a direct linear way as on the new Lead Acid battery where there is zero advantage to cycle the battery at 20% vs 50% DOD at least based on spec it was not the case with older Lead Acid where using the battery closer to the top SOC provided a somehow better cycle life so more energy over life.I'm a bit sceptical on their claim but I take the spec as it is.Winston is a large battery manufacturer and independent tests done by universities and private laboratories show their spec is correct or extremely close.I will know more in a month when I have two years of full offgrid on my LiFeMnPO4 battery from GBS I expect 4% capacity loss if my expectations are met then this battery will be the one I recommend (based on spec is one of the worse compared to other LiFePO4)And again if that 4% loss is right my cost per kWh including all equipment (SBMS + inverter + PV panels) + battery amortisation cost per kWh is 16 centSo that will make even grid look bad in many countries. But that is just equipment dose not include installation cost so the price will be valid just for DIY that enjoy installing this and do not count their time as money.I have a youtube video with the way I made capacity measurement on my GBS battery 3 years ago (one year battery was mostly in storage) and I have all the equipment so I can replicate exactly and precision will be good enough to be able to see a few % difference.

author: mtdoc
author_rank: Super Contributor
timestamp: April 04, 2015, 06:13:07 am
content: The 20AH rate is the standard number used in the RE industry since it most closely approximates a 24 hr day. It's impotant to use that number when discussing AH ratings with RE system designers.I can find nothing on where the 400 AH rating comes fom on the WB-LY400AHA datasheet. Is it 10h, 20h, 100h?You really need to compare apples to apples.Charging efficiency does drop off at higher SOC but it's not as simple as you state.When discussing charge efficiency, you need to be sure you understand the difference between energy efficiency and AH efficiency. As you know when batteries (LA or LiFePO4) are close to full they do not accept charge as easily. But PV panels as current sources simply decrease current. Potential electricity production from the PV is wasted but that does not mean that the AH in/AH out - which is what most people mean when they discuss charge efficiency - is dropping off that quickly as well.Real world experience from off grid users who cycle their batteries daily and closely track SOC, AH in and out via shunt based battery monitors and SG readings shows average efficiencies > 80% IME - and depending on the type of LA battery can be >90% (e.g. with AGMs).When people quote 95% charge efficiency for LiFePO4 they are talking about AH efficiency not energy efficiency.Again - you need to compare apples to apples for a fair comparison.Anyways, my point is really that you shouldn't pick best case numbers for LiFePO4 and worse case for LA when doing a comparison. LiFePO4 stands up on its own merits and skewed comparisons damage credibility.

author: Mike_del_Caribe
author_rank: Newbie
timestamp: November 27, 2015, 01:45:37 am
content: Have you retested the capacity of your system now that it has passed the two year mark?Is there any need to balance or equalize LiFePO4 cells? If so, how is this done? Would periodic CV charging do this?

author: electrodacus
author_rank: Super Contributor
timestamp: November 27, 2015, 08:26:27 am
content: Quote from: Mike_del_Caribe on November 27, 2015, 01:45:37 amI was extremely busy and did not had time to test the capacity I will do that probably in the spring when there are 3 years of full offgrid use 4 years since I purchased the battery.Is a bit hard to test since this is my main source of energy.I'm also curious is for sure less than 10% since if it will have been more I will have noticed.Yes a small cell balancing current is required to maintain the cells in balance. The charge discharge rate is very small in offgrid energy storage around 0.3C for charging and 0.5 to 0.6C for discharging.In this conditions my cells (100Ah GBS) without any cell balancing will get about 1 to 2% imbalance after 3 to 4 months of use.But now there is no imbalance since I use the SBMS4080 for the last year and that keeps the cells in balance with small cell balancing current.I'm working now on the next version SBMS100 so I'm really busy with this but in spring I will take one day to test the capacity loss on this GBS cells.

author: donovanpl123
author_rank: Newbie
timestamp: April 09, 2016, 12:40:21 am
content: Quote from: electrodacus on February 22, 2015, 02:35:34 am

author: electrodacus
author_rank: Super Contributor
timestamp: April 09, 2016, 02:16:40 am
content: Quote from: donovanpl123 on April 09, 2016, 12:40:21 amLithium cells require only cc and cv charging that is if you want to take advantage of the battery entire capacity and do not care as much about the cycle life.For long cycle life you can only use one stage the cc ( bulk ) charge.The most common Lithium cells used in most portable electronic devices and recently electric cars will only charge up to 85% if you are using just one stage cc charging (you stop the charging as soon as the voltage gets to in this case 4.2V).If you do that you almost double the battery life cycle while you are losing about 15% of the stated capacity. Since in mobile electronics energy density is important that 15% is way more important then cycle life that is anyway good enough for this type of applications.I recommend and use LiFePO4 batteries for stationary solar energy storage systems and those will charge to at least 95% with just a single stage charging cc and have a much better life cycle than the more common Lithium-ion mentioned above so cost amortization over the life of the battery is way better.Typical LiCoO2 cells (usually found as small 18650 cylindrical cells) will last 500 cycles at 100% DOD and if charged with just cc up to 4.2 they can do 700 to 1000 cycles while just around 85% of capacity is available cost in volume is at around $220/kWhSo for a 1kWh battery 500 cycles x 100% x 1kWh = 500kWh over the usable life of the battery $220/500kWh = 44 cent/kWh stored (this is the theoretical amortization cost of this battery charged with cc to 4.2V and cv until current drops to 0.02C)If the same 1kWh battery is charged with cc only 800 cycles x 85% x 1kWh = 680kWh better than first case $220/680kWh = 32cent/kWhLiFePO4 costs more at around $400/kWh but you can find large cells hundred of Ah capacity and can last 3000cycles at 100% DOD (even 6000cycles for quality Sony cells) and around 7000cycles at 70% DOD for Winston cells that I usually recommend for solar storageSo same 1kWh capacity will be 2x as heavy as a LiCoO2 so not good if energy density is important but 7000 x 70% x 1kWh = 4900kWh so $400/4900kWh = 8 cent/kWh and the life of the cell is probably 20+ years in typical solar application.In real life you will not be able to use 70% of the battery capacity every day so over 20 years (about 7000 days with one cycle every day) with an average of 30 to 40% DOD per day you can not realy get to use 4900kWh but still it will be close and probably real life cost of storage will be around 20 to 30 cent/kWh still will be way better than LiCoO2Sorry for the long explanation the idea is that in stationary offgrid storage cost of storing each kWh over the life of the battery is important and for that you need to only use cc charging so stop the charging as soon as the cell gets to the set level 3.55V for LiFePO4 or 4.1V or even 4V for long life using LiCoO2 the PWM or other methods of constant voltage charging will be detrimental to battery life.Since last time I wrote here the new SBMS model was done. Here is a video I just uploaded about the last version if you are curios

author: scttnlsn
author_rank: Newbie
timestamp: August 06, 2017, 07:25:48 pm
content: Quote from: electrodacus on April 01, 2015, 12:44:10 amI've tried this approach with my own LiFePO4 setup and noticed that it tends to toggle the charging on and off. Once the max cell voltage hits 3.55V then the charging is cutoff and the cell voltages relax. Often, only a few minutes later all the voltages dip below 3.4V and the cycle repeats. Is this bad for the cells? I assume it would eventually stop but wasn't sure if this is too much stress for the cells. Curious how you chose 3.4V? Should I be picking a value specific to my cells? Something just above where they tend to fall?

author: electrodacus
author_rank: Super Contributor
timestamp: August 06, 2017, 08:22:29 pm
content: Quote from: scttnlsn on August 06, 2017, 07:25:48 pmYes you should select this values based on your configuration and battery characteristics for best results.Of course if you have a Load connected then battery will discharge below the set point and charging will start again. If there was no load and charging started again only a few minutes later then maybe you are charging the battery at very high current more than typical 0.25C or you have a battery with high internal resistance.My new battery made of A123 cells (8s10p) about 185Ah usable capacity has a very small internal resistance and the limits for this where set at 3.5V charging cutoff and 3.35V charge recovery voltage.See below a screenshot from the system.Notice the battery charge current graph with green the 1h graph (one minute interval) there was a charge current of about 44A for about 4minutes (that is about 2.9Ah put in to battery) then at current load of about 2.835A average (blue graph 1h) it will take just over 1h before the charging will start again for another 4 minutes or so.Of course if Load will increase there will be more frequent charge cyclesThat 2.9Ah charge discharge cycle is about 1.5% DOD and since that repeats about once an hour it means there will probably be 5 or 6 of this cycles per day so not a big deal since at such low DOD the battery can perform few hundred thousand of this cycles so absolutely no problem.With this quality LiFePO4 batteries used in offgrid energy storage the most significant degradation is with aging and not cycling.

author: scttnlsn
author_rank: Newbie
timestamp: August 06, 2017, 11:03:05 pm
content: Thanks, that's very helpful info. I'm using 4 of these cellshttp://www.batteryspace.com/lifepo4-prismatic-module-3-2v-20-ah-10c-rate-64-wh-6-0---un38-3-passed-dgr.aspxin series and charging with up to 10A from a PV panel. The cells are fairly new so I would have expected a fairly low internal resistance (though I have not measured...probably something I should check). Even at 5A (0.25C) I see rather quick charge toggling so I'll play around with the voltage thresholds a bit.

author: asimlink
author_rank: Newbie
timestamp: August 22, 2017, 04:48:37 pm
content: Hi, I have seen SBMS100 schematic mentioned in SBMS100 manual pdf. while looking at the Balancing MOSFET i find that Qb6 MOSFET node after the series 12+12 resistors seems to have repeatedBAT5label. Shouldnt it be BAT6? All of the next Balancing MOSFETS have shifted net lable issue. For example GCB7 MOSFET QB7 has BAT6 and so on.Please have a look at the attached snapshot of the SBMS100 scheme:Can someone suggest if it is a mistake or am i unable to understand the scheme the way it is implemented?

author: electrodacus
author_rank: Super Contributor
timestamp: August 22, 2017, 07:01:51 pm
content: Quote from: asimlink on August 22, 2017, 04:48:37 pmThere is no mistake in the schematic. You can notice that last 3 mosfets are also p-channel and this has to do with how the ISL94203 is build internally.

author: asimlink
author_rank: Newbie
timestamp: August 23, 2017, 08:14:56 am
content: You have done a wonderful job by making this open source SBMS100. Thank you for the explanation and pointing out that the last 3 mosfets are P type.Kind Regards

author: asimlink
author_rank: Newbie
timestamp: August 25, 2017, 07:03:36 am
content: Can you please suggest what are part numbers for following components?I dont find any part number in sch, pcb, bom or in pdf files for these components:Page 42 or SBMS100 manual:D17, D4 schotky diodesD9-D12 schotky diodesQb1-Qb8Page 43 or SBMS100 manual:TVS1-TVS2 zener diodesAnd can you explain where do you have connected CSI1/PWR_FLAG in the schematic i dont find any connection of CSI1/PWR_FLAG to BAT+?Thank you

author: electrodacus
author_rank: Super Contributor
timestamp: August 25, 2017, 08:15:33 am
content: Quote from: asimlink on August 25, 2017, 07:03:36 amAll diodes are 60V 1A except for D15 and D16 that need to be 100V rated.Q1 to Q5 are n-channel Q6 to Q8 are p-channel and the rating will depend on what sort of current you want to use for cell balancing. if you use the same 24Ohm then they should be rated at least 300mATVS1 and TVS2 as seen in schematic are 36V and the pulse power ration will depend on what sort of current you expect to be using on the PV input in my case I used 1500W TVSCSI1 is connected to Battery+ trough a short 2m max 16mm2 cable (Is the P3 high power connector on SBMS labeled Batt+) not the same with BAT+ in the schematic that is just connected to Battery+ (cell8 positive terminal) trough a thin cell balancing cable.I hope you will not try to build an SBMS since that will be extremely expensive. I usually spend well over $1000 when I build a prototype with big part of that for all the PCB's needed but also the components since they are in low volume.Maybe you are just building a different device based in ISL94203.

author: asimlink
author_rank: Newbie
timestamp: August 25, 2017, 05:20:32 pm
content: Thanks for the explanation.No I am not rebuilding SBMS100. I am working on a charger which will use single 300W panel and will have Li-ION batteries. I was studying ICL94203 chip and its reference design (AN1952.PDF) and i came across SBMS100. SBMS100 looks great reference design to me. I also liked the use of Aluminium PCB for heat dissipation.

author: electrodacus
author_rank: Super Contributor
timestamp: August 25, 2017, 05:29:57 pm
content: Quote from: asimlink on August 25, 2017, 05:20:32 pmISL94203 is great except for the very small TQFN package with just 0.4mm pin pitch. Good luck with the charger.

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 27, 2017, 08:00:47 pm
content: Excuse me if this is slightly off topic but how is this open source hardware if you are charging people money to obtain the details of it ?

author: electrodacus
author_rank: Super Contributor
timestamp: August 27, 2017, 08:08:35 pm
content: Quote from: fourtytwo42 on August 27, 2017, 08:00:47 pmI do not charge any money this are fully open source for anyone. I do sell the SBMS since is less expensive than you building just one or two SBMS for your own use because of the low volume (and that is not including the work and equipment needed just the parts).