Building a 12V Lipo battery from three cells. - Page 1
Forum section: electronics / beginners

author: Dave Wave
author_rank: Contributor
timestamp: November 15, 2017, 03:45:19 pm
content: I want to build a 12 volt Lipo battery from three individual cells.I am planning to have each cell have its own charge controller and then wire the cells in series to form the battery.I was planning to use ebay 5Volt one amp lipo chargers like this:https://www.ebay.com/itm/5V-1A-Micro-USB-Lithium-Battery-Charging-Module-Lipo-Charger-Board-for-Arduino/262642274750?epid=16006623848&hash=item3d26b311be:g:TugAAOSwtJZXT-vIIt specs 5.5 volts as max input.If I wire three of these in series, will any charge controller "see" more than 5 volts (assuming charge input voltage is less than 15)?Thanks!-Dave

author: ogden
author_rank: Super Contributor
timestamp: November 15, 2017, 03:54:04 pm
content: Quote from: Dave Wave on November 15, 2017, 03:45:19 pmNo. It wont' work from single 15V supply. Each controller needs it's own and separate, isolated from others, supply. If you really want to use such charge controllers, then you need to get three phone charger AC mains adapters as well.What you need is 3S balance charger, something like this (first eBay hit):https://www.ebay.com/itm/RC-B3-7-4V-11-1V-Lithium-Pro-Compact-2S-3S-Lipo-Balance-Battery-Charger/332419879036?hash=item4d65c4d07c:m:m-kQ36p-sYt_zPT_W7CMM9wYou can find those in RC model shops as well. Just to show an idea, there's one more option (don't know how good is this particular board):https://www.ebay.com/itm/3S-Li-ion-PCB-BMS-Protection-Board-Battery-Lithium-Charger-module-balance-40A/112642417236?hash=item1a3a02e254:g:G8sAAOSwGUBaDAqD

author: jcw0752
author_rank: Contributor
timestamp: November 15, 2017, 04:00:53 pm
content: If you really want 12 volts you will have to use 4 cells to get 14.8 and then use a DC to DC buck converter to drop back to 12 volts. Three cells will only get 11.1 nominal volts. As explained above the reason you can do it as described is that the input and out put of the charging boards share a common ground. As soon as you try to stack them you will short out the extra stages.John

author: ogden
author_rank: Super Contributor
timestamp: November 15, 2017, 04:10:42 pm
content: Quote from: jcw0752 on November 15, 2017, 04:00:53 pmI'm afraid that original poster planned to connect inputs of USB charger boards in series as well. Problem is that they are not designed to limit incoming voltage to 5V they will take whatever comes in. So if you connect such three in series, at first power-on weakest charger will get nearly all the voltage (15V?) applied and most likely will become damaged. If it fails short, then next charger will fail and so on while none is left but smoke.

author: Dave Wave
author_rank: Contributor
timestamp: November 15, 2017, 08:51:37 pm
content: Quote from: ogden on November 15, 2017, 04:10:42 pmThat was the plan, which wont work.So what if I take a dc-dc converter, drop the 15 to 5, then feed each cell charge controller from the same 5v source. I still need 11.1 output from the battery, so would that be wired series / parallel and be able to do both (I assume that is how most lipo hobby batteries are wired as they have individual cell taps and one big series tap).-Dave

author: Mjolinor
author_rank: Frequent Contributor
timestamp: November 15, 2017, 08:58:48 pm
content: It will not work. The first one will be OK but your 3 chargers all share a common -ve terminal so as soon as you connect the second one the first battery is shorted out.If you are planning on disconnecting all the cells to charge it then it will work but you have to disconnect both ends of each cell.

author: Nusa
author_rank: Super Contributor
timestamp: November 15, 2017, 09:26:00 pm
content: You're trying to reinvent the wheel, which is already available quite cheaply:https://www.aliexpress.com/item/New-Arrival-3S-20A-Li-ion-Lithium-Battery-18650-Charger-PCB-BMS-Protection-Board-12-6V/32799522542.htmlAnother route would be to put those three cells in parallel (3P1S), and use a boost converter to get them to the voltage you need.

author: Dave Wave
author_rank: Contributor
timestamp: November 15, 2017, 11:30:09 pm
content: Quote from: Nusa on November 15, 2017, 09:26:00 pmI wish I had seen that when I was ordering months ago, but I am trying to get this done with what I have in the parts bin.If I put the battery in a 3P1S configuration, I do not understand why if I have three individual charge controllers fed from a common source, it would short out. The 3P1S configuration would allow the charging of the individual cells and the 11.1 volts I need.Thanks,-Dave

author: Nusa
author_rank: Super Contributor
timestamp: November 16, 2017, 12:11:42 am
content: No. 3P1S = 3 cells in parallel, 1 in series. Output voltage would be same as cell voltage, but current capability would be tripled.1P3S = 1 cells in parallel (by itself), 3 in series. Output voltage is triple cell voltage. You can't just use three chargers unless you either isolate the chargers from each other or disconnect the batteries from the circuit (same as removing and charging individual batteries). Remember the interconnections between the batteries in-circuit affect the charging circuit!There is one more option. You can simply charge the pack as a whole and not worry about balancing at the cell level. If the cells started out reasonably identical in capacity and balanced, it'll work for quite a while, but not as long as a properly balanced pack.

author: Dave Wave
author_rank: Contributor
timestamp: November 16, 2017, 01:02:26 am
content: I meant 3S1P.Anyhow, how would you isolate the chargers from each other?I do not understand why the chargers need to be isolated . I am not seeing how the charger would short out because they share a common ground.Thanks for all the help.-Dave

author: Nusa
author_rank: Super Contributor
timestamp: November 16, 2017, 01:19:33 am
content: Draw the circuit you envision with the batteries and triple chargers, including the input side from the wall plug to the chargers. Then if you haven't convinced yourself, show it to us.

author: ogden
author_rank: Super Contributor
timestamp: November 16, 2017, 02:41:15 am
content: Quote from: Dave Wave on November 16, 2017, 01:02:26 amI told you already: By powering each charger from isolated supply. All you need is 3 Phone chargers with USB cables. I agree - you shall draw circuit and doublecheck that it is ok - here.

author: beanflying
author_rank: Super Contributor
timestamp: November 16, 2017, 03:03:31 am
content: Sorry for the horrid 30 second drawingJust happened to have a 3s1P down to the tape at present for another project.Charge port as used in the model aircraft sense are wired as per the picture, these are then charged by 3 individual charge controllers with using the differential voltage on each cell. Power is drawn separately from the series of the batteries as per the left of the dodgy drawing.It is fine to charge via the main series connection but it does run the risk of getting one cell way out of balance and killing it by over discharge or letting the smoke out by overcharging itSo there is no need for isolated supplies or separating cells for charging as you use the + if you like (wrong term but for clarity) of the cell before it in the chain as the negative or ground to base the charge voltage reference from. The potential each charge circuit sees one cell so generally 5V supplies are ok for as many LiPo's as you like.

author: beanflying
author_rank: Super Contributor
timestamp: November 16, 2017, 03:33:27 am
content: By coincidence I have 10 ($3'ish) of either the same or a similar board on the wayhttps://www.ebay.com.au/itm/10Pcs-5V-Mini-USB-1A-TP4056-Lithium-Battery-Charging-Board-Power-Charger-Module/262819529692?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649.The chip claims to be this onehttps://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdfWithout knowing the complete board layoutI would suspect the ground in andground out ISwould beshared or common. So without three independent and isolated supplies (one for each board) you will be placing a short across the batteries. I will have a think and draw another bad drawing.

author: ogden
author_rank: Super Contributor
timestamp: November 16, 2017, 04:08:50 am
content: Quote from: beanflying on November 16, 2017, 03:03:31 amWell. we did expect to see in details how you connect charger boards - with power inputs, outputs. Everything. Batteries are in series - this is already known

author: beanflying
author_rank: Super Contributor
timestamp: November 16, 2017, 06:05:12 am
content: Quote from: ogden on November 16, 2017, 04:08:50 amSorry for not instantly solving your problem while I was roasting coffee this afternoonThe OP seemed to be having issues with visualising what you and others were talking about and telling them you had already given them an answer they didn't understand isn't useful. So I dropped a rough sketch to help.Also in having a quick look online between roasts the data sheet (first thing you should have tried to find) in particular shows that the IC used on the cheap boards doesn't isolate the grounds. Some of the other LiPo IC options out there do isolate the grounds and can be then run off a single supply but the $ goes up and you would likely have to build from scratch.Depending on the charge rate required (not mentioned above) I quite like these cheapy supplies. They are rated to 600mA @ 5V and I have load tested them and dropped them on a CRO and the ripple is very low at under 5mV. Ground to mains earth with no connection is well under 2Vac. I have used a bunch of them on Arduino projects. A few others I have tested are HORRID. If you need or want a higher current then just check the supply when it arrives some of them have very high floating AC outputs!https://www.ebay.com.au/itm/AC-DC-220-to-5V-12V-5V-600mA-Isolated-Switching-Power-Supply-Module-Power-Supply/400914188250?hash=item5d585907da:g:AYkAAOSwv0tVRd-RSo using one of these and one of the boards above, the data sheet to drop the current to 600mA you have 1S independent chargers for under $4 per cell.

author: beanflying
author_rank: Super Contributor
timestamp: November 16, 2017, 06:25:24 am
content: The other option is splurge and buy several of these

author: soubitos
author_rank: Frequent Contributor
timestamp: November 16, 2017, 06:27:03 am
content: You might find these modules interestinghttps://easyeda.com/catech75/TP4056FLEX_ADV-58d7e425439444be8c66cc66a3923362https://easyeda.com/catech75/TP5100FLEX_ADV-cf5fb967f9774e009362a2e0f0cc8656I am expecting boards and parts from easyeda and parts from other sources to build my first batch....I used to buy TP4056 modules with or without protection from Aliexpress but besides you never know their quality, their USB ports fail very easy damaging the pcbs and you also need to replace the current resistors in many cases. Then in a myriad of cases you need higher voltage in the output, so you need more modules to boost the voltage from the battery so i added a boost converter in both modules.I welcome all and any comments that could help me improve my frankensteins!https://easyeda.com/catech75/

author: soubitos
author_rank: Frequent Contributor
timestamp: November 16, 2017, 06:33:25 am
content: Quote from: jcw0752 on November 15, 2017, 04:00:53 pmThree fully charged cells will swing from as low as 9 and up to 12,6V when properly charged.Unless you need 12v sharp, 3cells will do the job in 90% of the cases without any need to add another stage with its relevant power loss....

author: sleemanj
author_rank: Super Contributor
timestamp: November 16, 2017, 06:33:42 am
content: Quote from: Nusa on November 15, 2017, 09:26:00 pmPlease note that this is a protection board, it is not a charge controller.Specifically, it should protect each cell against over/under voltage, and protect the entire pack against over discharge current (including short circuit), but it won't likely protect against over charge current, nor will it balance the series cells if they are not closely matched.

author: soubitos
author_rank: Frequent Contributor
timestamp: November 16, 2017, 06:39:27 am
content: Quote from: beanflying on November 16, 2017, 06:05:12 amIf you must calculate the build cost, the best solution to charge a 2-3-4-x cell Lithium battery pack is to incorporate a BMS module with OC-OD protection and charge the battery pack with a CC-CV module.... for 2S you can then use a common 12v PSU which could come from say a router or even an old computer ATX PSU... for 3-4S a laptop PSU could save the day....

author: beanflying
author_rank: Super Contributor
timestamp: November 16, 2017, 06:54:24 am
content: Quote from: soubitos on November 16, 2017, 06:39:27 amWithout knowing the full details of the intended use or application you can't necessarily recommend or suggest protection boards. Also the OP needs help with some of the basics.Most of my toys would turn any BMS board into ash BTW 20+V and 100+ampsAnd yes I do run low voltage cutout on my speed controllers but they are designed for the job and application and programmed accordingly.

author: miceuz
author_rank: Frequent Contributor
timestamp: November 16, 2017, 07:06:16 am
content: I was breaking my teeth on this a month ago. Was trying to come up with a proper solution to replace 12V lead acid with LiPo batteries. I don't get it - why is there no ready made proper battery pack solution available with all the charging and balancing circuitry integrated?You can't use aliexpress boards in a commercial product design and you have to implement all the same circuitry others have implemented numerous times -- and this is no trivial task if you want to go any substantial charge/discharge current (~3A).I have ended up using an off the shelf 12V LiFePo4 battery pack.

author: soubitos
author_rank: Frequent Contributor
timestamp: November 16, 2017, 07:16:34 am
content: Quote from: beanflying on November 16, 2017, 06:54:24 amYou do understand you are swinging this from charging thishttps://cdn3.bigcommerce.com/s-1ihdrfh4qi/images/stencil/1280x1280/products/260/808/vtc5__93889.1490847004.jpg?c=2with thishttps://i.ebayimg.com/images/g/AYkAAOSwv0tVRd-R/s-l300.jpgto charging thishttps://www.lithiumion-batteries.com/uploads/shopping_cart/4881/large_12v-100ah-lithium-ion-battery.jpgwith God knows what with LOL...Based on original post, it is logical only to assume we are talking 3S 1-2P maybe?And if you are going to put money, time and effort into putting a 3S1P or 2-3P battery pack together, most likely with recycled cells, the most cost effective solution is a brick psu you already have, a cc-cv step-down module and the battery pack escorted with a BMS OC-OD module... 1-2-3 and you are done .... at this level you have spent 3-4$ total and the job is done....

author: soubitos
author_rank: Frequent Contributor
timestamp: November 16, 2017, 07:24:46 am
content: Quote from: miceuz on November 16, 2017, 07:06:16 amThere are direct replacement Lithium batteries for Lead-Acid batteries... they are EXPENSIVENot to mention if you want to replace say a UPS sealed Lead battery, you have to deal with the UPS charging circuitry in the first place which is not suitable for Lithium batteries....If you are building a new product from scratch though, there are plenty of solutions for most needs.Frankly, I find it more difficult and expensive to find a 100-150W power supply (ATX PSUs excluded) to power a CC-CV board which in turn charges a 3S8P pack for example

author: beanflying
author_rank: Super Contributor
timestamp: November 16, 2017, 07:25:40 am
content: Part of the issue is market segment and use of the different technologies not to mention the different electrical needs etc.Since the early 8-10C LiPo's started appearing we R/C fliers dumped our Nickel batteries as fast as we could. Low weight and energy density is king. Balanced 12V input based chargers and simple low voltage cutouts are all we needed. Currents and discharge currents available have seen Methanol and Petrol engines losing market share too.Low power LiPo use in phones, tablet etc is also well established but dedicated built in device specific solutions are normal.For a lot of terrestrial applications Lead or Nickel chemistry and the low fuss fairly abuse tolerant nature of them has kept them the defacto standard until the last few years. Weight doesn't matter for a lot of applications but service life and reliability do.So I would suggest there has not been a lot of development in systems to replace the old technologies until recently.As for the other Lithium chemistry and LiPo's lots of work to be done.I would agree as above Evilbay block solutions are not always the best but for a simple solution and in particular for beginners in the hobby buy them play with them and learn

author: paulca
author_rank: Super Contributor
timestamp: November 16, 2017, 07:59:36 am
content: Another (ex) RC Flyer here.I don't understand in this use case why something like an Accucell-6 wouldn't do. It will be cheaper, better and safer than trying to Frankenstein something up.https://hobbyking.com/en_us/turnigy-accucell-6-50w-6a-balancer-charger-lihv-capable.html?___store=en_usor even one of these:https://hobbyking.com/en_us/turnigy-12v-2-3s-basic-balance-charger.htmlFor what it's worth, you can passively balance cells between each other:https://hobbyking.com/en_us/turnigy-dlux-lipo-battery-cell-display-and-balancer-2s-6s.htmlIf you must Frankenstein something up, I recommends some of these:https://hobbyking.com/en_us/lithium-polymer-charge-pack-25x33cm-jumbo-sack.htmlOr an old metal army ammo case to put the batteries in while you torture them.

author: soubitos
author_rank: Frequent Contributor
timestamp: November 16, 2017, 08:04:18 am
content: Quote from: paulca on November 16, 2017, 07:59:36 amIf we are talking about a plug-in battery pack sure it will do (yet its more expensive than other solutions)... if we are talking about a solution for a built-in battery-pack + charger/protection circuit i am not so sure.... not about its functionality or results but about its practicality...

author: paulca
author_rank: Super Contributor
timestamp: November 16, 2017, 11:24:16 am
content: Quote from: soubitos on November 16, 2017, 08:04:18 amThe OP wants to build a 3S LiPo. He appears to want to build a charger for it using 3x single cell chargers.He could charge the cells individually. They would need to be wired correctly/unorthodox-ly However you cannot use the balance charge input (if one was wired) to charge the cells individually. They are wired in part-series.Cell 1: 4.2V (Cell 1 only)Cell 2: 8.4V (Cells 1 and 2)Cell 3: 12.6V (Cells 1, 2 and 3)A balance charger is able to derive the individual cell voltages by basic subtraction and modify each charge voltage/current accordingly. But you can see you can't use a 4.2V charger circuit to charge individual cells (except cell 1) using a normally wired balance charge lead.The question would be.. if the balance lead was connected directly to each cell, so for 3S you would have 6 wires. How would the cells being wired in series for the output effect the results.If the aim is to be able to create a 3S Lipo capable of being charged from a USB plug, as part of a product, then that's different.As to lead acid versus LiPo charging the only difference that I am aware of if that LiPos use a peak voltage, min current cut out, where as Lead Acid chargers usually carry on with a trickle charge mode.

author: paulca
author_rank: Super Contributor
timestamp: November 16, 2017, 11:35:11 am
content: Quote from: soubitos on November 16, 2017, 07:16:34 amThat's not that big a battery.You'll want something like this:https://www.lindinger.at/en/drones-und-fpv/chargers-und-power-supplies/chargers-12v/hyperion-eos-0840i-1000w-max.-40a-charger-11-30v-input-for-1-8s-lipos

author: soubitos
author_rank: Frequent Contributor
timestamp: November 16, 2017, 11:42:08 am
content: Quote from: paulca on November 16, 2017, 11:35:11 amhow about we talk about a few 18650's which are most probably what the original post is talking about and leave the elephants for another day? LOLFun aside, i am not familiar at all with Li-Ion batteries other than 18650's and a few more rare but small cells... I am building bigger packs for some applications but to put a size indicator I'd say i stay under 5A charging current and under 100W total powerAlso, besides a DC UPS for a mini-ITX based PC +router and monitor, i prefer to use boost converters after say 1S4P pack to power a 9V or 12V device.... for low or lower power applications i find them easier to handle and much easier to charge and properly maintain.... well, each one chooses his own poison!

author: paulca
author_rank: Super Contributor
timestamp: November 16, 2017, 11:52:44 am
content: Speaking of Elephants:http://www.globalsources.com/gsol/I/Electronic-speed/p/sm/1154660446.htm#1154660446Though, above about 800A they stop being for RC motors and for electric planes.... real planes. There is a 22S 1200A paraglider electric motor from China. I paraglide and I am NOT strapping the kind of LiPo that needs to my back! No sir.Some serious kit. I've seen 60kW rated ESCs for RC boats! Running on 28S LiPos. Obviously the higher the series, the higher the voltage and you stop needing railway tracks to run the current.

author: Mjolinor
author_rank: Frequent Contributor
timestamp: November 16, 2017, 11:54:31 am
content: Here is a charger that is exactly what you are outlining. I use this to charge 2 cell batteries.The small USB chargers only regulate the +ve side, the -ve side is connected directly to the cable as shown with the green line.In order to connect the four wires of the charger to the three wires of a two series battery you have to connect as shown with the red line.If you try to connect these to the same USB device or five volt source then you effectively add the blue line.You can now see that you are shorting out the battery connected to the lower USB device.The way round this is to use two isolated wall warts, one for each.