Alarmingly hot lithium cells! - Page 1
Forum section: electronics / projects

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 24, 2016, 07:30:52 pm
content: I have gotten into a bit of a lithium recycling hobby. I can get dead laptop batteries for free. I have been taking them apart, automatically rejecting cells under 3v (should I?) when I take the pack apart, and then I charge the rest at 650mA, spread across two cells. I currently just use some 2 cell powerbanks as chargers. They stop charging at 4.1v, oddly.Anyway, I usually leave cell pairs together (don't break the spotwelded tabs) and charge them as a pair. However, this one pack seems to be weird. I have charged two pairs overnight, and in the morning, they were still charging, according to the powerbank. And they were HOT! About 50 degrees! I charge on a flamrproof surface in case things go a bit... flamey.However, only one cell in each pair was hot, the other was just a bit warm.So I broke the tabs off and then just let them cool down. The colder cells got to room temperature pretty much instantly. The hot ones, even after 20 minutes, still feel just as hot as they were before. But the voltage has only dropped to 4.05v. Wat.Could these cells have been a different lithium chemistry in an 18650 form factor, or are they just royally dead?

author: uncle_bob
author_rank: Unknown
timestamp: June 24, 2016, 08:44:19 pm
content: HiIf the pairs of cells are in series, then the explanation is pretty easy. You don't say, but I'm guessing that your cells are set up in parallel. If so, the answer is simply that the hot cell has died.Bob

author: Gyro
author_rank: Super Contributor
timestamp: June 24, 2016, 09:00:25 pm
content: Quote from: iamdarkyoshi on June 24, 2016, 07:30:52 pmI think I'd be thinking of a bit more than a flameproof surface if charging unknown / old / suspect Lithium cells (particularly overnight!). You need protection from hot flames going outwards and upwards, not just burning the surface.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 24, 2016, 09:21:30 pm
content: Quote from: uncle_bob on June 24, 2016, 08:44:19 pmThey were in parallel. For gits and shiggles I threw the cold cell in my capacity discharge tester. Got 1.5Ah out of the cell. Not good enough for me to keep, but certainly not as bad as some of the other cells I have tested.Quote from: Gyro on June 24, 2016, 09:00:25 pmThey were out in my garage on a cast iron tablesaw with nothing else within 5 feet of it. Tablesaw was dust free as I use a 1HP dust collector.

author: Buriedcode
author_rank: Super Contributor
timestamp: June 24, 2016, 11:01:26 pm
content: Hmm yeah, don't charge lithium cells in parallel. Doing so means that the differences between cells, and differing charge state cause different currents to run through each cell. Its not only naughty and frowned upon, its downright dangerous. If you insist on charging them in groups, do it in series and monitor the voltages across the cells.They could well have a 4.1V maximum charging voltage because some nickel flavours do indeed have that as the maximum cell voltage. There are so many schematics for chargers floating about, and although some might think the 'constant current' phase is a luxury - it isn't.I know you haven't paid for these batteries but give them some love, give them a proper charging algorithm!

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 24, 2016, 11:09:48 pm
content: Quote from: Buriedcode on June 24, 2016, 11:01:26 pmI am using these cells in powerbanks. They are also what I am using to charge them, and they do have to be connected in parallel. I always try to leave them in the parallel groups they came from the laptop packs in so they are as matched as they can be.I know it is not the most ideal thing to do, but if it worked in OEM HP/Dell/Asus batteries, I think it should work fine here. The weird part about the empty powerbank cases I bought is that they do actually only put out 4.1v. Maybe china FINALLY errored on the side of caution and made it so that manufacturing tolerances never go over 4.2v. But probably not

author: sleemanj
author_rank: Super Contributor
timestamp: June 24, 2016, 11:32:08 pm
content: Quote from: Buriedcode on June 24, 2016, 11:01:26 pmThere is nothing wrong with parallel charging as long as the cells are healthy, are the same voltage when paralleled, and you preferably keep an eye on temperature.This is exactly how laptop packs do it, thier cells (as shown by the op) are 1 or more parallel pairs (Ns2p) - each pair has a thermistor for monitoring.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 24, 2016, 11:37:56 pm
content: Quote from: sleemanj on June 24, 2016, 11:32:08 pmAnd the powerbanks are no different other than the lack of temp monitoring. But they are charged at such a low current that it is not much of an issue (325mA per cell)

author: CatalinaWOW
author_rank: Super Contributor
timestamp: June 25, 2016, 12:14:37 am
content: Those cells were well matched when they left the factory. That is not evidence that they are currently well matched. You have already demonstrated that some are highly mismatched. I know that it is a lot of work and time, but if you want to use these salvage batteries the best plan is to separate them, charge them separately and then do discharge curves on the cells so that you can pick matched pairs for your battery packs. I strongly believe that if you go through this procedure you will end up with very few cells going back with their original partners. I wouldn't even venture to guess if you can get a set well enough matched to use in your battery bank.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 25, 2016, 02:10:35 am
content: Quote from: CatalinaWOW on June 25, 2016, 12:14:37 amI have been testing them individually. My tester spits the voltage and current through the COM port every second, so plotting a curve wouldnt be difficult. However, every "pair" I have done (aside from these oddballs) have had amp-hour ratings within 0.05Ah of each other. Not sure of the discharge curve though. But this is certainly not an excuse to just put any two cells together.As for the "good" batteries, I recycle anything under 2Ah, so like 95% of them lolOnce the mail turtle delivers the rest of the crap I bought on ebay, I will be building a 10 cell charger that charges each cell individually at 1A. I probably should add a temp cutoff, but I won't.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 25, 2016, 05:58:32 am
content: Well, I bought some temperature protection for my upcoming 10 cell quickcharger. Some bimetalic switches should do nicely. All I could find in a quantity of 10 were 50 degree or higher ones from a US supplier. 50 degrees is higher than I would like, but it is much better than no thermal protection at all, am I right?

author: uncle_bob
author_rank: Unknown
timestamp: June 25, 2016, 12:06:47 pm
content: Quote from: iamdarkyoshi on June 25, 2016, 05:58:32 amHiSome is always better than noneIt doesn't take much time to find videos of lithium battery fires. It's rare to find one that comes with a proper analysis of what the root cause actually was. I think caution is a really good idea in this case.Bob

author: Prime
author_rank: Regular Contributor
timestamp: June 25, 2016, 03:04:03 pm
content: Quote from: sleemanj on June 24, 2016, 11:32:08 pmAnd paralleled cells should have even discharge and charge behaviour if they were well matched at the factory. They normally come in matched batches from the manufacturer. Well that's how our Boston and Panasonic cells for the solar car were supplied.However it's possible one could have been damaged through welding.Quote from: iamdarkyoshi on June 25, 2016, 05:58:32 amYou can build a simple tester and charger with a quality RC battery charger and some cell holders from Keystone. Plug the 6 or 8 cell lead from your board into the RC charger and it will ensure they all get charged relatively evenly. We used a 4 port hitec on an external power supply to do 24 cells at a time.And you should spot weld them back together after you are done pulling them apart. Solder tends to overheat them.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 25, 2016, 03:41:40 pm
content: Quote from: Prime on June 25, 2016, 03:04:03 pmI am going to use ten of those 1A USB charger boards connected to a 25A 5V PSU. I bought a bunch of cell holders. I can individually charge cells on it and have a thermal cutoff on each cell. I don't need to put any connections back on them, the powerbanks have sprint contacts. If I use cells in applications where I need wires connected, I just leave half of the tab on them and solder to it. I have a tab spotwelder, but no tabs

author: uncle_bob
author_rank: Unknown
timestamp: June 25, 2016, 03:48:47 pm
content: Quote from: iamdarkyoshi on June 25, 2016, 03:41:40 pmHiTabs should be a quick thing to get from China (for dirt cheap ...). It likely would take some quality shopping time to find the right ones.Bob

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 25, 2016, 06:00:42 pm
content: Quote from: uncle_bob on June 25, 2016, 03:48:47 pmYeah, I will buy some eventually. Not entirely sure why I made a spotwelder but didn't buy any tabs

author: ez24
author_rank: Super Contributor
timestamp: June 26, 2016, 04:39:36 am
content: Quote from: iamdarkyoshi on June 25, 2016, 03:41:40 pm"sprint contacts" do you mean spring contacts ? I cannot find anything on sprint contactsCan you link to your 1A USB boardsthanks

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 26, 2016, 05:41:59 am
content: Quote from: ez24 on June 26, 2016, 04:39:36 amYeah, spring contacts. As for the charger boards, they are just the dirt cheap TP4056 boards.http://www.ebay.com/itm/252335209689?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITYeah I am going to charge these things in a flameproof environment

author: ez24
author_rank: Super Contributor
timestamp: June 26, 2016, 06:54:46 am
content: Keep us updated. I have several used batteries so I think I will try the same thing.

author: uncle_bob
author_rank: Unknown
timestamp: June 26, 2016, 01:22:42 pm
content: Quote from: iamdarkyoshi on June 25, 2016, 06:00:42 pmHiThe tabs really are not anything special at all. It should be a "pay a dollar and get a bunch in the mail (including free gift)" sort of thing. The ones you get may not last for a hundred years in a salt spray environment. I doubt that is a big risk with used batteries.Bob

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 26, 2016, 07:33:32 pm
content: Looked up a datasheet for the hot cells. They were Sanyo cells, rated at 3.6v instead of 3.7, but still said to charge up to 4.2v. I got sixteen laptop batteries yesterday and tore them apart.I have been rejecting cells under 3v out of the packs, is this a good plan or should I keep lower voltage ones as well?Also, should I bother keeping cells that are between 1 and 1.9 Ah? I have been recycling ones under 2Ah. Would anybody be interested in lower capacity cells due to being used?

author: uncle_bob
author_rank: Unknown
timestamp: June 26, 2016, 10:00:53 pm
content: Quote from: iamdarkyoshi on June 26, 2016, 07:33:32 pmHiI would not reject anything until you try a test charge at a constant current. If it's below 3V after maybe an hour at 1A then reject it. If you have the time, I'd save the good lower capacity cells. You never know whey them might make a good trade for something you are looking for.Bob

author: juanfermed
author_rank: Regular Contributor
timestamp: June 28, 2016, 01:48:19 am
content: I think those cells getting hot could be well explained by an internal short circuit. The short circuit produces heat generation inside the cell. The cells are probably in a point in which the short circuit is still small enough to not make the cell enter in thermal runaway, and the the heat generation rate is still lower than the heat dissipation rate. You are still able to charge and discharge the battery because the short circuit might not consume all energy. Does it makes sense with your experiments?

author: sleemanj
author_rank: Super Contributor
timestamp: June 28, 2016, 04:45:52 am
content: Quote from: iamdarkyoshi on June 26, 2016, 07:33:32 pmUnder 2.7v I would discard.Under 3.2v I would charge at a very low rate at least the first time.QuoteSure, if you have a use for them, it's 3-6 Watt Hours, it's probably better than most of the "new" Ultrafire, Trustfire etc ones that come from China.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 28, 2016, 06:09:10 am
content: If you discard at 3.0V, you are discarding cells that are potentially just fine.For voltages between about 2.5V and 3.2V, run a conditioning cycle - charge at C/100 until you get to about 3.3V, then let the cell rest for a few hours to measure the voltage again. If the cell is taking more than a few hours to reach 3.3V (or is not reaching it at all), or if the voltage drops back below 3.2V after this slow charge, discard the cell.Cells slightly below 2Ah might be just fine, they may have been lowish capacity (think about 2.2Ah!) to begin with, in which case they may be in very good shape.Old, recycled laptop cells, especially when paralleled, should be rated at low currents, something like C/2 absolute maximum, C/5 preferred. Build high-energy, low-power packs from these cells.If you rate a 2Ah cell at 1A, you can't exactly rate two paralleled 2Ah cells at 2A because they don't share the load perfectly, but something like 1.5A instead.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 28, 2016, 05:11:04 pm
content: Interesting. I shall keep the lower capacity cells around as well as try some of the other ones (like the ones that come out of the packs at lower voltages, though they are usually 3 and higher or 2 and lower)Maybe I will add some low current cell holders on my battery charger.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 28, 2016, 06:13:55 pm
content: The TP4056 is the chip I will be using to charge the cells.It has a pin for a temp sensor, so I can use that instead of the friggin bimetalic switches I bought. For frig's sake

author: ez24
author_rank: Super Contributor
timestamp: June 28, 2016, 08:01:10 pm
content: Quote from: iamdarkyoshi on June 26, 2016, 07:33:32 pmJust curious Did you get 16 batteries or 16 battery packs? If packs that is a lot of batteries. How do you take them apart? My Dells are hard to take apart, a lot of effort is needed (and band-aids)

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 28, 2016, 09:10:10 pm
content: Quote from: ez24 on June 28, 2016, 08:01:10 pmBattery packs. I get them from a PC repair store.I have gotten lucky lately with their glue, but I do the following:Take off any labels, often there is just a skeleton of the shell underneath.Get your onehunglow sidecuttersStart at the corner and try to just nip into the top half of the case, if you are lucky and the glue is loose, you can peel most of the case apart like an old sardines can. If not, just keep nipping away at the plastic edges.Once inside, carefully cut any wires going to the BMS in two places (so they don't have a chance of meeting each other again) If you can't get to it, then carefully remove the pack from the shell and place it on your electrically INSULATED desk. AvE's copper desktop would be a bad idea here.Once the BMS is gone, snip off any wires sticking off. After this, fold the cells away from each other.Cut the tabs, seperating it into each parallel pack. Then I usually cut the tabs that join each cell on the NEGATIVE side. The whole shell is negative, so trying to cut through the tabbing material can short them out to the shell if you nick the heatshrink.You should now have two, three, or four cells joined on the positive end, unless you took apart a weird battery.Grab two cells and pull until the tabbing wire breaks at the welds. Pull off any tabbing material left with a pliars, and then cut the sharp spotweld peaks down so they arent pokey. Or tap it on your workbench.Repeat on the negative side if there is tabbing matetial left.And you should be left with a bunch of batteries.If you can find thinkpad g40 batteries anywhere, they are usually 12 cell packs using sanyo cells...

author: ez24
author_rank: Super Contributor
timestamp: June 29, 2016, 04:07:54 am
content: Thanks that is about what I do with my Dells (from my old computers) I once saw a YT video of someone doing this and making power packs for an electric bicycle.I think this is what I would do if I had a good source.Did you say what you are doing with them?What heat sensor are you going to use?thanks

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: June 29, 2016, 04:26:03 am
content: Quote from: ez24 on June 29, 2016, 04:07:54 amI am using mine in powerbanks or portable bluetooth speakers. As for the temp sensor, the TP4056 supports an NTC and resistor based temp sensor.

author: ez24
author_rank: Super Contributor
timestamp: June 29, 2016, 04:52:03 am
content: Quote from: iamdarkyoshi on June 29, 2016, 04:26:03 amI was going to use mine for a powerbank but I do not have a big need and Makita came out with a 18v to USB adapter. And I have several 18v Makita batteries, so I just use them now. I do like the idea of a blue tooth speaker.