Lesser nerd requires LiFePO advice - Page 1
Forum section: electronics / general

author: IRIdiot
author_rank: Newbie
timestamp: July 29, 2022, 09:03:06 pm
content: Evenin'I require the advice of far greater nerds than I. The query is regarding undervoltage of LiFePO cells.My wife and I recently had solar and battery storage installed. We went for Givenergy batteries which use LiFePO tech. The batteries were installed yesterday and what should have been a two hour commissioning job took eight hours. Whilst I'd have loved to watch and ask questions galore, I know there's nothing worse than the homeowner looking over your shoulder whilst you're trying to work a problem. So I left them to it. They were exceptionally honest with me about the issues. The batteries have a usable capacity of 5.2kW each and we have two. They appear to be connected in series to the inverter.The batteries should have arrived ready to go with some charge in them. They arrived with no firmware installed and, on installing the firmware, the BMS immediately alarmed saying the battery was under voltage. This alarm can trigger on a per-cell basis but appears to have been on an overall battery voltage basis. The voltage at the start of them force charging the battery was 24-30V (large variation) and the undervolt alarm triggers at 45V. A decent working voltage for this pack seems to be around 55-60V. It took several hours to come up to 45V.They set the batteries to charge whereby they sucked in circa 6kWh and shut down one after the other. The breaker hasn't tripped but the batteries have totally shut down (even inactive they should register as present and have lights on). They should probably have taken close to 12kWh if they were under capacity. I suspect the BMS has detected cells outside safety limits and shut the batteries down entirely. An engineer is coming Monday. Replacement is on the table. On examining the data that I have access to, there are other very weird things happening, like the battery voltage dropping to single digits and the temperature readout going from a healthy 30C to -20C. The garage was about 14C-20C.My question, after all that prattling, is how much I should push for the batteries replacing assuming that the bugs are worked out and it's just they were at very low voltage? I know that with Li-ion cells, the under voltage could be a serious issue but I have no experience using LiFePO. Are there any specific tests I can ask to be done to look for permanent damage (like cell impedance or other indicators of lithium plating)? I'm reliant on them because I simply don't have access to per-cell data, just fairly high level stuff but, with some prep, I can at least demand some kind of proof that it's functioning entirely within spec and hasn't suffered damage if they do manage to revive the system.Any advice would be appreciated.

author: thm_w
author_rank: Super Contributor
timestamp: July 29, 2022, 10:35:00 pm
content: The ones I see here list 58.5V as charge voltage:https://www.givenergy.co.uk/pdf/Version%202.0/Giv-Bat%202.6.pdfSo that would mean 16S, 16 series cells. The fully discharged voltage would be 40V (manual says operating only goes down to 43V). 24V at 16S could mean 1.5V on some cells, which is very low, and can result in lost capacity, or if lucky no loss at all (anecdotes here).Its odd that they would self discharge that much, unless they have been sitting around for long time, or the BMS has some flaw.Surely their app has a way to determine capacity or draw? Do a full discharge and see how long it lasts. Let us know what kWh you get.Temperature readout showing -20C may be concerning if it stops you from charging the pack when it displays that.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 30, 2022, 02:41:47 pm
content: What does "force charging" mean? Bypassing the internal contactor/power switch and accessing the unprotected battery terminals?If yes, then this seems one of the simplest cases:The batteries were DOA, and should have been returned for refund or shipment of new batteries instead of trying to fix something that cannot be safely fixed.OTOH, faulty temperature reading suggests some problem with the measurement system (say, ADC).But this is something only the manufacturer can work out.If the total pack voltage was merely 24V, that means some of the cells are likely dead, and the thing is dangerous to use. Obviously, the BMS is preventing you to use it. It was broken to begin with and should not have been messed with.

author: Faringdon
author_rank: Super Contributor
timestamp: July 31, 2022, 08:28:44 am
content: I used to work for a major Battery/Inverter/Charger company.I am surprised by what you say. Before we installed any system, we had the entire system set up in our premises. We would then conduct five consecutive full charge/discharge tests. We would note the voltage of every single cell throughout this (it was shown on a graphing software program). Ie, we would check for any cell imbalance throughout that. Any imbalanced cell was removed and replaced. We would also note the capacity of the battery was OK. We woudl also check all the efficiencies of charger and inverter, and that temperature readings were correct etc etc........ Then we would ship that exact system to customer. So the installer just had to rig up and connect the internet to it. The internet was used to continuously collect electrical data from the customer throughout the product life. The customer had their own software App which they used to get limited data, eg state of charge graphs etc. If a customer’s cell went rogue at some point , we could see this at head office, and despatch a new battery. So I would think those tests need doing for you. So presumably after install, your system will go into test mode for some time?.....and your system is connected to the internet, and the data will go back to their head office?......i think it needs to.The charge discharge test needs doing at full power, as otherwise the inverter and charger are not at their most efficient....and we need to check that efficiency.There was never any need for an installer to do analytics......they just connected unit to internet, and then we at head office coudl see everything about their system from there. We could then take charge of the system and get eg the 2 batteries to charge to the same voltage prior to connecting them etc etc.Sometimes a customer would phone up and say the system wasnt giving them the full battery capacity......so we would download their data to head office and look at it....sometimes they would have a tiny load in the house for ages......and of course, the inverter is much more inefficient at light loads, so we could see this and tell them this. Some customers would say the unit was causing spikes on their supply....then we looked from head office and we could see that they just had some malfunctioning load somewhere in there house, nothing to do with our system.There are some things about the system that customers often queried......eg, the loading needed to be at least 400W before the inverter would kick in...even then, the inverter always took at least 4 mins to come on....this was some regulatory thing that applies to all grid tied inverters.We actually had some software system which used to manage their useage.......it did it so that the battery energy was not shipped out to the grid (since customers dont get payed much for export)....have you got that software in yours?...i think its needed, otherwise your solar will be getting exported to grid and you dont get payed muich for that....so the system needs current measurement devices on the battery and on the electricity coming into the house....and these are wired up to the software in the system. There has to be software which ensures that your inverter doesnt ever take energy from your batteries and ship it out to the grid. The accuracy of these current reading devices was checked at our premises when we did all the pre-install checks.There was also a calibration thing that we could do for customers, so as to maximise the accuracy of their electric current readings.......we coudl do that from head office.....we just did a forced charge or discharge and noted the current, then we'd calibrate for them...but not everyone wanted to bother with this.Also, any unbalanced cell woudl trigger a software alarm, so we could immediately( from head office) see which customers cells had gone unbalanced..........this is needed...as otherwise, how does the company know that the batteries that are being supplied are good ones. (we had a 10 yr warrantee on batts)Some customers woudl phone up and say there energy bills werent going down as much as expected...then we would download their electrical data graphs...and we'd see that there batteries were hardly being discharged at all each day, and they were importing energy instead from the grid, so we'd help them to get their batteries to do a full charge and discharge into their load every day, then they woudl get their moneys worth....we could see this from the electrical data and give the advice over the phone....we could even set their system to our recomended settings, which maximised their payback.For some customers we could make it shutdown in the small hours, so the fans didnt make their noise in the nightHere is some quotes on battery/inverter/charger systemshttps://www.greenmatch.co.uk/blog/2018/07/solar-battery-storage-system-cost....but one company does it much much cheaper if you allow the power company to sometimes take control of your system in order to do grid balancing....AYK it obviosuly needs an internet connection for that, which they provide.it woudl be interesting to hear the cost difference with your own system, but please dont divulge if you are uncomfortableDave Jones, owner of this site, may have a battery/inverter/charger video telling just what you want to know.It wouldnt surprise me if you were to tell that you actually tried to purchase a system from the co that i worked for....but you were unable to get one, due to the massive demand that we were experiencing at the time.....i was always taking phone calls from people screaming at me about nobody having contacted them about their wish to buy our system....the demand was phenominal, and must be even more now with electricity costs.......i wonder if some undesirable competitiors have slipped in their now, in order to tap into the enormous demand levels for this kit now.

author: woodchips
author_rank: Frequent Contributor
timestamp: July 31, 2022, 03:44:42 pm
content: You are in the UK, the goods have to be of mechantable quality, they obviously aren't, so get your money back.Seem to me to be rejects from another sale, and you are expected to accept them with open arms.You need a battery tester that will give you how many Ah charge are stored, and it needs to be more than 100% of the rated number since they are, supposed to be, new.You have now paid for many kW electricity to charge them, and you want that money reimbursed.Being picky? No, bought a battery for an original Mac laptop, and it was obviously well secondhand, but they refused to swap so ended up with a not very cheap battery with less then half the life it should have.Why have lithium batteries in any case? Use lead acid batteries, much cheaper, much more robust, worth money when you need to change. The only benefit lithium gives is lighter weight, not much use in a static application.

author: james_s
author_rank: Super Contributor
timestamp: July 31, 2022, 05:38:58 pm
content: Times have changed and good quality LiFePO4 batteries are significantly more robust than lead acid. I know guys that have been flying A123 cells in model airplanes for years, hundreds of cycles, left stored fully charged for months on end with no significant self discharge, over-discharged multiple times, charged regularly at 8C, they just keep going and going. Lead acid on the other hand are fragile and easily destroyed by over-discharging. Not to mention the volume, what does housing cost per square foot in your part of the world? Space consumed by the batteries is space you can't use for something else. LiFePO4 is quite a different beast from more common li-ion types.

author: bdunham7
author_rank: Super Contributor
timestamp: July 31, 2022, 06:00:22 pm
content: Don't accept those batteries no matter what and no matter who you have to get into it with. If they are 16S and the bank was down to 24V, you likely have at least some cells that were totally zero or even reverse charged. This may indicate a seriously flawed product, not just a single failed example. The only way a battery gets into that condition is a design flaw or very negligent care before delivery. LiFePO is hard to f**k up, but they seem to have managed.

author: woodchips
author_rank: Frequent Contributor
timestamp: July 31, 2022, 06:51:41 pm
content: Times have not changed, do not confuse a matchbox sized battery in an aircraft with a backup system. Given as 5.2kW, so that is four 12V 120Ah batteries, just do a search and camper wagon batteries are easy to find. If you want good ones then forklift batteries will last for decades.The size and weight of batteries in a house are irrelevant.

author: IRIdiot
author_rank: Newbie
timestamp: July 31, 2022, 08:55:44 pm
content: Thank you all. I appreciate the time.My feeling is these batteries failed QA and weren't meant to leave the factory. Hence why the firmware wasn't installed. The granular data does go back to the manufacturer but I don't have access to it. The installer was working with the manufacturer to troubleshoot. I have avoided doing any fiddling as the system hasn't been handed over to us yet and I don't want any excuses if there are issues.A "force charge" I believe just tells the inverter to charge them from the grid at full capacity. The inverter was drawing 3kW which is the most it can pull. To me, the behaviour of the batteries suggests the BMS has forced a total shutdown. This means there's no data transmitted to them as it's just dead. Whilst they're probably safe, it has made me a tad uncomfortable having a dodgy lithium based battery holding that much energy in my garage.You have confirmed my gut feeling but I wanted to be sure before I go making a stink in an area outside my expertise. My intention is now to reject the goods. I think the installer has replacement in mind and has been open with us (they didn't have to give us access to any of the data but did and said to "poke around" after telling me it had arrived undercharged).As for the question about lead acid Vs lithium - we had the choice but for us space is an issue. We're in a small terrace house and had only a couple of locations suited for installation (without going outside, which I didn't want to do). Therefore size of the units was a significant issue for us. I seriously debated making something out of lead acid but there simply wasn't the room. As it stands the location is a significant inconvenience and is kind of crammed in, but the potential savings are worthwhile.Thanks again all.

author: james_s
author_rank: Super Contributor
timestamp: August 02, 2022, 03:07:45 am
content: Quote from: woodchips on July 31, 2022, 06:51:41 pmThe size and weight of batteries in a house are only irrelevant if you have excess space, I certainly don't, it must be nice.I'm not talking about matchbox sized batteries, these are banks of 28650 A123 cells used to power large scale electric model airplanes with multi-kW motors, the same sort of batteries are used in electric cars and home energy storage. They have already displaced lead acid in medical battery backup situations and are quickly doing so elswhere too. Camper wagon and especially forklift batteries are bulky, tremendously heavy, are a lot more expensive than they used to be, and they are still more fragile than LiFe batteries. RV guys are starting to use LiFe batteries to replace the big old lead acid ones, they cost a bit more but they are far lighter, smaller, more robust, and maintenance free. Forklift batteries are huge and extremely heavy, they emit corrosive vapors and hydrogen gas. They cost a fortune too, my machinist friends have scrapped a couple of electric forklifts over the years because the cost to replace the battery significantly exceeded the value of the forklift. Things really have changed, lead acid is slowly being displaced and I expect that trend to continue as EV battery production increases and costs come down.

author: jonpaul
author_rank: Super Contributor
timestamp: August 03, 2022, 02:49:12 pm
content: Lithium = firebomb, waiting to explode.Poor quality, old age, high temp, damaged case, overcharging.....I would question the battery manufacturer and the expertise of the installer.Advanced lead acid battery..no fires..A backup generator with natural gas and propane fuel?just my thoughtsj

author: james_s
author_rank: Super Contributor
timestamp: August 03, 2022, 06:23:20 pm
content: LiFe batteries are not the fire risk that other Li based batteries are, I've seen tests where a nail was driven through a fully charged cell and it did not catch fire. Lead acid is generally safe but they can have issues too. I have seen the results of hydrogen explosions that blasted the battery to bits. I have also seen electrical fires from the huge current they can supply, something that Lithium batteries also share. There is no way around the fact that stored energy can be dangerous.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 03, 2022, 07:12:26 pm
content: Quote from: james_s on August 03, 2022, 06:23:20 pmDon't trust that. Specifically low-quality Chinese LFP cells in those large plastic cases (yellow for Winston Chung's crap, etc.) are well known to thermally run away and catch fire.LFP is indeed much safer cathode chemistry than LCO, NCA or NCM, requiring way higher temperature to start thermal runaway, but it can still happen, so ignoring other cell-level passive safety mechanism during design and manufacture, like low-end LFP manufacturers do, is a risk.Low quality LCO/NCA is of course the biggest risk of all.And indeed, overcharging lead acid carries a real risk of hydrogen explosion and subsequent fire.

author: bdunham7
author_rank: Super Contributor
timestamp: August 03, 2022, 08:11:07 pm
content: Quote from: Siwastaja on August 03, 2022, 07:12:26 pmThe yttrium batteries aren't good? I was almost going to use them at one point, but the project never materialized. Did I dodge a bullet?

author: Siwastaja
author_rank: Super Contributor
timestamp: August 04, 2022, 06:28:03 am
content: Quote from: bdunham7 on August 03, 2022, 08:11:07 pmWinston Chung sells what he happens to find or manages to produce. I bet the yttrium is an inside joke like some analysis coming back as exceeding allowed limits for some trace contamination containing yttrium, and mr. Chung chuckling: hey marketing department, I got this great idea... Or more seriously, just a made-up differentiation because of the legal disputes over the ThunderSky products, so they had to make a "significant" change.And I'm not saying these Chinese LFP bricks are absolute disasters. No, they mostly do not catch fire randomly; the inherent "safety" of LFP forgives a lot. It is just that people assume (and lie on the internets) they are provencompletelysafe and cannot catch fire. This is obviously not true.I suggest looking at some studies about the thermal runaway onset temperatures and released energy for different li-ion cathode chemistries. From the top of my head, LFP is like 300-350degC compared to 160degC of NCA, and released energy is maybe one quarter. That is still far from being "safe". The upside of the "more dangerous" li-ion chemistries is, you can buy good brand products (like Panasonic, Samsung, LG...) which have a lot of safety engineering like shutdown separators instead of cheapest plastic film you can find, overpressure breakers (CID), polyfuses integrated etc.Demonstrations of mr. Chung's LFP bricks being penetrated with a nail are misleading for three reasons:1) they only demonstrate this one unit did not catch fire. No one knows what happens if you penetrate 1000 LFP bricks.2) they demonstrate one cell in isolation in open air. Build a pack of 20 cells inside a casing and try again. Thermals will be different.3) typical FUD element: they don't demonstrate penetrating a proper quality LCO/NCA cell with a nail for comparison. Theyassumepeople have seen videos about crap quality pouch cells being penetrated and catching fire, assuming all behave the same way, and only LFP being the savior.

author: james_s
author_rank: Super Contributor
timestamp: August 04, 2022, 05:18:19 pm
content: Quote from: Siwastaja on August 04, 2022, 06:28:03 amI did not intend to imply that they are completely safe, only that they are not nearly the same fire risk as many other lithium based cells. Stored energy is dangerous! Also there is good stuff and there is crap, my experience is mostly with A123 cells which are top quality, I have very little experience with random no-name Chinese specials.

author: thm_w
author_rank: Super Contributor
timestamp: August 04, 2022, 09:27:31 pm
content: Quote from: Siwastaja on August 04, 2022, 06:28:03 amFrom the discussion here:https://diysolarforum.com/threads/can-lifepo4-batteries-combust-in-thermal-runaway-event.999/They will not catch fire unless physically punctured.Assuming anything is completely safe is dumb of course, as there are many things that could occur even with a completely safe chemistry: wires shorting, electronics failing, etc. that could result in heat.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 05, 2022, 07:53:08 am
content: Quote from: james_s on August 04, 2022, 05:18:19 pmOh, by adding enough weasel words we can get out of this, sure,manyothers are even more dangerous, I can totally agree with that.But if we just assume random LFP cell is safer than random LCO/NCA cell, this assumption is possibly false, too, because it not only depends on chemistry, but other safety mechanisms and manufacturing quality. I can't say because I don't have enough statistical data. In any case, I remember looking at a paper which compared COTS 18650 LCO and 25650 LFP cells in overcharge situations and LFP cells did thermally run away while LCO cells did not. But I don't remember the authors or title right now.Crappy LCO is definitely more dangerous than crappy LFP, but it is more fruitful to compare actually available options, which basically are: crappy LFP, good LFP, crappy LCO/NCA/NMC, gooc LCO/NCA/NMC. Most important is to avoid crappy LCO/NCA/NMC, second most important to avoid crappy anything. But here's the catch: people usuallyknowto avoid crappy LCO cells, but while good LFP may be available, it is not obviously so, so peopletendto turn to products like Winston & similar, because they aremarketedas being safe "because of safe chemistry". But this assumption is false sense of security!It is like having a well engineered car with crumple zones, air bags but which can go 200km/h (Panasonic/Samsung NCA), vs. some plastic scooter which can only go 50km/h (Winston tier LFP). Latter will be less risky by having more reaction time thanks to lower speed, plus any accident is much less energetic, but that does not make it any safer, could be the opposite, because of the lack of passive and active safety layers, and quality in general (it might just break in half in a bump).It is also kinda wrong-ish to say the problem is inherent with storing a lot of energy. The problem with li-ion (also LFP, even if to lesser degree!) is the risk of uncontrolledreleaseof that energy due to manufacturing error or relatively small abuse. As the increasingly better safety when going from LCO->NCA->NMC->LFP->LTO->NiMH/NiCd/lead acid demonstrates, such failure mechanisms are not inherent to storing a lot of energy. There is a correlation to energy density, but that is not dictated by any fundamental physical law either, and it is well possible to come up with dangerous low energy density storage, and respectively, finding/engineering a safe high energy density battery is a real possibility everybody is eager to see in the future.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 05, 2022, 07:58:45 am
content: Quote from: thm_w on August 04, 2022, 09:27:31 pmThis is just wrong. I have seen countless of pictures of conversion EVs where these have caused total loss of vehicle (no physical accident, justpossibleelectric abuse if even that), and also am aware of at least two cases where they caused massive damages in warehouses, in one case multi-million loss.LFP cells are totallyableto thermally run away and spew the same flammable electrolyte (ethylene carbonate or similar) as any of the "more dangerous" li-ion chemistry.Spreading disinformation about this is actually dangerous.

author: Faringdon
author_rank: Super Contributor
timestamp: August 05, 2022, 09:08:27 am
content: Interesting...if you want to know about total abuse of lithiums...go to Formula E and get yourself in the paddock.......when theres a pitstop, they overcharge the lithiums to heck and back.......and they (lith batts) often start smoking.....as far as i know, they havent yet had explosions,.......but maybe they just keep it under wraps who knows.BTW, a lot of "lithium fires" are co's wanting to destroy their premises and claim insurance.

author: james_s
author_rank: Super Contributor
timestamp: August 05, 2022, 05:55:58 pm
content: Quote from: Siwastaja on August 05, 2022, 07:53:08 amI'm not adding weasel words, I'm clarifying what I *thought* was a totally obvious statement, that LiFe cells are not the fire danger that other lithium based rechargeable batteries are, ie they are considerably safer. Some seemed to interpret that statement as meaning they are totally safe, which is not the case and not what I claimed at all. I'm sorry if this was not clear in the first place.It should be obvious that NO form of stored energy is completely safe, even lead acid batteries can cause fires or even explosions.

author: thm_w
author_rank: Super Contributor
timestamp: August 05, 2022, 09:18:17 pm
content: Quote from: Siwastaja on August 05, 2022, 07:58:45 amAny link to these photos?It looks like pouch cells are worse, but still in both cases here there was no propagation:Quotehttps://www.fire.tc.faa.gov/pdf/TC-16-17.pdf

author: Siwastaja
author_rank: Super Contributor
timestamp: August 06, 2022, 06:03:28 am
content: Quote from: thm_w on August 05, 2022, 09:18:17 pmI don't collect links to everything just because someone might question me on the internets, sorry. The links would be dead anyway, as I did look at this thoroughly around 2012-2014 or so.I have no need to prove my claims, it's up to you to decide who to listen.