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Forum Index : Solar : Li -ion battery
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| brucedownunder2 Guru  Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
I would like to understand the working of the rechargeable li-ion battery pack ? I understand ,by opening my flat-pack ,that the batteries are in plastic sealed packets. There must be plates of metal inside ,plus cables ,I have not touched the sealed packets. They are swelled from a previous owner ,who I do not know. Could someone out there explain to me how these packets of rare earth or whatever is a mixture of whatever in there ,how they work ,please. I have no intension of opening them , would just like to understand the mechanical working of whats in there and how does the power ,when they are charged, travel . its a fairly big unit , says 2500 watts and I've applied 48vdc ,it shows 81 watts into the unit ,don't know if this is charging(no indicators), or this 81 watts is consumed in the battery management system ?. no warm feeling on the packets, been on power for 1 hour. Thanks Bruce (change the topic heading and re-locate to another section ,if Solar is not appropriate.. thanks Bushboy |
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Hi Bruce, While I have not taken apart my new Li-ion battery pack cells I did open a shortened LYP cell (200Ah). I assume the Li-ion type is similar with different chemical inside. Basically its constructed like a very large capacitor (and I understand it works in a similar way, eg. no chemical reaction in an electrolyte). There are two different, very thin, foil type 'plates', one is aluminium and the other copper. These are coated with the special 'stuff' and are separated by a very thin plastic sheet. The plates are each connected to its terminal on the top, I think there were nearly one hundred 'plates' of each variety. There are no wires inside unless the cell has an inbuilt balancer. The 'plates' are only as big as the cell outline but the plastic separator zig zags between the alternating 'plates' and is many many meters long. There was no liquid inside the cell I opened but the plastic separator sheet felt wet and smelt funny. It also started to smoke when I bundled it into the rubbish bin, I guess it reacted with oxygen in the air. Threw it on the lawn until it had dried out. If you want a better explanation how it works just google it, there are some very good texts on this subject. My new Li-ion cells are tightly strapped into 4 cell packs with aluminium endplates to prevent bulging. The LYP cells require one to come up with one's own strapping method and, if not done very well, will swell in the middle too. |
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| nickskethisniks Guru Joined: 17/10/2017 Location: BelgiumPosts: 458 |
Good explanation, what I read/heard was that "pouch cells" should be clamped together so an evenly applied force between anode/cathode that guarantees an evenly spread current draw or charge from the plates. This way it will limit the "hot spots" in the battery cell, this is the place where gassing is created. Limiting the charge/discharge rate will reduce the stress and help with avoiding swelling. I would discourage using (heavely) swollen cells, it will get worse overtime because the plates won't make good "contact" anymore. Maybe you could take the risk with small lifepo cells, but with li(-ion)po it gets dangerous verry quickly. |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thank You , Murphy,friend,(and mine now) and Nickskethisniks (wow, what a name !). anyhow, thanks very much for the simple explanation of how they work . I think I gathered that the salient point is the "closeness" of the "plates' , so mine are badly swollen and therefore may never be recoverable. Can I buy replacements and would they be worth the gamble or expense ?. I did apply , very carefully, my 48v battery just by touching the Anderson shells together, BANG. yes, melted the POS terminal . no damage. Funny thing , 0 volts on my meter before the experiment, then after a micro-second and the BANG, I read something like 0.048 volts ,later back to 0. maybe this was the capacitor effect ???. Anyhow, the other idea was a controlled charge , like a gradual increase in charge to see if it really is a dead short or just wanting a huge input til it settles down ????. (bruce is thinking out aloud). Thanks for the discussion, luv this forum. Bruce  Bushboy |
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| pd-- Senior Member  Joined: 11/12/2020 Location: AustraliaPosts: 122 |
The " plastic sealed packets " pouch cells are best sent of to the recycle center. There are toxic chemicals in the cells so opening them is not recommended. Trying to charge them is not a good idea they are likely to continue to swell until they pop the gas and liquid inside is flammable and very toxic when burnt You can contact the manufacture and se what price they will charge for new cells or take a look on Alibaba The BANG is a concern there may be damage to the electronics |
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| nickskethisniks Guru Joined: 17/10/2017 Location: BelgiumPosts: 458 |
That is bad, I'm not going to encourage you to bring the others cells back to live. If you want to test the electronics you might want to assemble a small lion pack, with some 18650's, what was the voltage again? 13 or 14s for a 48V is verry commonly used. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I had one of those Lipo jumper packs. Was very good and unbelievably powerful and it got a lot of use and I did try to look after it. One day when trying to start the ute, the thing started smoking a little then obviously had a runaway. I managed to tear it off the battery and hurl it into the yard. I have NEVER seen anything so compact make so much smoke. I mean it filled the yard and you couldn't see one side to the other. Only other thing I have seen like it is videos of giant smoke bombs on Yt. There was a bit of orange fire and lots of hissing and jet like smoke emanation but the volume of smoke was astounding. Luckily it was in the morning and the breeze was gentle and took the smoke away but I guarantee the mosquito population took a month to recover. If you want a bit of entertainment, short that swollen pouch out and toss it making sure you are upwind. Don't be surprised if some rescue aircraft descends thinking it's a distress signal or you are marking an LZ for an insertion team. I would be very careful where you left the thing and myself would be putting it where it could burn and not matter like in a metal bin outside and away from anything else. From Videos I have seen these things can also go off in a spectacular fashion if shot so if you want a bit of fun with your bunny gun..... :0) |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Oh,,,,, DANGER. I GET IT I'll remove the packets ,Carefully, and take them to a recycler depot . I'm not interested in even trying to figure out IF. after reading the couple of previous warning posts, thank You. I'll keep the bus(battery management system) and battery charging module ...Some one further down the track may have a use for it or know of a way to use it again. Thank You , Bruce.  Edited 2021-03-09 11:55 by brucedownunder2 Bushboy |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
I just remember you posted about a car jumper starter pack . I have one of those ,must drag it out and take it to the recycler also ,,,,, could very well be dangerous,thank you..... There is no warm feeling on these packets . So at least that's a good sign. Looks like the connections from inside the packets ,from the plates, to the pcb outside ,is connected by some form of heat compression or maybe crimping ?. I,ll keep the flyleads and connections ,they look good for other projects. I,ll now warn my friends if they come across these type of batteries, thank you for your warning.. Bruce Bushboy |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
OK, back to the batteries-- My friend ,Aaron is progressing along the path to bring these "modules-Packets,pouches" back to life. So far ,after a few light voltage charges, medium current, he's managed to "wake" a pouch up from flat. I won't jump the gun yet, a long way to go ,but fairly good results so far . He or I will keep you informed, Bruce Bushboy |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1024 |
Before attempting to charge this pack I wrapped up the back end with some masking tape to help hold it together. I tried charging the one that has the black plastic wrap removed, I set the charger to 6v then connected it up turned the charger on and it maxed out at 40Amp for 3 seconds the dropped back. I then gradually increased the voltage as the amps dropped, after about 10 minuets I reached 12v on that pack. Turned it off and disconnected over night, checked the voltage the next morning and the battery was dead flat, Did the same cycle again the next day and the battery started to hold a little charge of about 1.5v. Did the same cycle again, this time it was holding over 6v, looks encouraging. Will do this with the other packs. These are Lifepo4 pouch cells, LFP. What We think has happened with this Flatpack is that it was left sitting flat (Discharged) for a long time. An overcharged cell that has swollen up would not flatten out with any recharge.  Now in the photo you can see the masking tape is really slack, what is most surprising is the cells (while charging and left for some time) have sucked back down flat most of the way, was expecting that.  While charging this pack I did check every cell often to make sure none of then where going over voltage, it was nice to see all cells in this group where charging and voltage was equal on each cell. Will have to peel open the cover on the end of the other 2 packs to check the while charging, see if they do the same thing, there is a small chance that they might might all charge up and work, will take some time to go through this process, but definitely worth trying. Thanks Bruce for letting Me work on this.  Can't say for certain that all this will work, too early to tell, there is also the issue of high resistance that could make the battery difficult to use, will wait and see what happens... Cheers Aaron Off The Grid |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Hi Crew. Well,Aaron has been busy getting these batteries back to some sort of decent charged state. He,s done careful voltage charging ,setting the voltage to recommended voltage,and constantly observed the rise. He,s observed only slight discharge,but more importantly, a big decrease in the physical swelling has occurred,which indicates a positive reaction to the charging cycle . So, success may be achieved after a few more cycles,well done Aaron,and thank you. I have been thinking ,that this flatpak unit may have just been neglected from new and or maybe charged incorrectly ,in the first place ?. As it was looking brand new and unused when I obtained it. Bruce Bushboy |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
I have had some interesting experiences recently with these type of batteries; have 36 odd 40AH rectangular cells, with heavy hard PVC outer casings, removed from an ups. Charged all cells up individually and did a capacity test using a Cellpro 8 charger, then did a half charge and put them away under the bench for 6 months. Some have started to swell for no reason at all, they still have 2.6 to 3 volts odd, so they must be really old possibly. The ones that have this condition I clamped up between pieces of timber and placed on charge, repeated the capacity test; result capacity has halved from previous. Tried a few more discharges and gentle re-charge, made no difference; once they have got to this state, basically they are stuffed and its a pointless exercise to use them. And ringing around here in Wellington, I cannot find anyone who would recycle them, so off to the dump they go, I will drill a 10mm hole through them and leave them in a bucket of water for a week or so to make them inert. The remaining 30 seem to still be ok, but I wouldn't trust them, as all coming from the same batch, they could crap out any time. Their capacities are all round the 50% mark. I hope you have better success. Cheers Mike Edited 2021-04-18 20:34 by Solar Mike |
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| bob.steel Senior Member Joined: 27/02/2020 Location: AustraliaPosts: 188 |
Well I saw this a bit late so they have probably gone . Shame The below applies to LiFePo4 cells (3.65v) and probably LI (4.2v) too. What I have found works is a pulse of high voltage for only a half second to burn the dendrites out. It can stuff the cell anyway but I have successfully recovered two cells that were fully flat or nearly so ,0.06 volts I set my lab supply at 40 volts and just touch the terminals about 4 times for half a sec at a time. The interesting part is that lithium based dendrites form and its been found to be the ethylene carbonate electrolyte responsible , This seems to mostly be caused by the recharge going up near 3.65 volts . If you keep the max to 3.4 volts they are still fully charged and supposedly no dendrites form. Its also known that over charging creates copper dendrites that can be treated the same way. If you store them try to hold them at about 40 % capacity it is said but the difficulty is finding what voltage represents 40 % charge so I think that's a furphy or rabbit hole. If they have swollen it means usually too much charge or discharge has been applied and its common for people to believe LFP means big charge capability . The cells I have seen inside of can only take .5C charge and discharge or they suffer damage . The rest is sellers hype. If swollen the electrolyte has been gassed by the heat created on charging/discharging and the only thing to do is stand the cells up so the liquid electrolyte flows back in then slightly compress the cell ,drill a small hole in the top ,squeeze some more and then immediately plug the hole with glue or silicon rubber or something . Do not leave exposed to the open air as the alloy tabs connecting plates to terminal will corrode very fast. Those cells I did as above are still in use 4 years later and surprisingly the capacity is coming back up! |
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| bob.steel Senior Member Joined: 27/02/2020 Location: AustraliaPosts: 188 |
The pouch cells are the same except they don't seem to have much electrolyte in them in liquid form . I have also stood these up ,pin pricked and squeezed them and then super glued the pin prick and they seem to be saveable too. I have not tried the dendrite technique on them yet. |
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| bob.steel Senior Member Joined: 27/02/2020 Location: AustraliaPosts: 188 |
I mostly agree with your summation. The plastic looking separator is in fact impregnated with ethylene carbonate and the copper plate has Lithium or Lithium/Iron mix on it and the alloy plate has a pure carbon /graphite type layer usually. All of these cells are constructed the same way with the same plate chemicals be they pouch cells or prismatics or round cells in cans. The layer with Iron in it is the only difference between LFP and lithium Ion cells. I think that the LFP cells are safer due only to the lower voltage levels 3.65 v tops as opposed to 4.2 volts. In either case those cells should be charged to top voltage ONLY if they are NEW and you are sure of that. All other recharges should stop at 3.4 v and 4.0 v respectively to firstly create the SEI (Solid Electrical Interphase) then stay away from it to avoid clogging it and locking up ions that never get free. Charge/discharge rates are best kept below 0.5C if you want them to last. A lot more here if you care to join and read in Files and Pictures of the insides etc.here Edited 2021-07-01 14:32 by bob.steel |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Quite! I have seen that said in Lithium Vs Lead discussions multiple times, every single time. It's repeatedly said that they will do a C1 deemed to be if the battery is 100 AH, you can pump in 100 Amps. That seems to be a VERY common position. Goes with the other common misconception ( although I think many times Deliberate) that you can only use 20% of an LA battery's ( ANY LA) battery capacity. Showing people Manufacturers Literature for fork batteries and the like are warranted to 80% DOD isn't accepted as it undermines the position they want to push. I Do see a lot of people being conservative on the voltage though. They just seem to think you can belt the charge in to the maximum you can generate to the end voltage and all good. Similar with discharge where they virtually espouse anything less than a dead short is fine and won't bother the battery a bit. |
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| Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1024 |
The cells are sort of on the back burner for a bit While I work on other things. My intention was to try a pulse charge on these cells, as they will take charge but not hold it. The way I was thinking was to use a capacitor bank of reasonable size (what I could find), the power supply would be coupled to the capacitors with a current limiting resistor to save thrashing the power supply, the capacitors would be charged, then using a switch or something appropriate to dump it into the cell's. I have seen plenty of different cells swollen over time, overcharge or discharge, and Generally if they are still working I have let the pressure out of them sealed them and kept them in use, over a year so far. Charging one of these cells will keep gassing off over time. Also seen some cells swell over just sitting unused over a few years. The cells in the photo's above were swollen and would have expected them to keep swelling when attempting to charge them, but no, not this case, Attempting to charge these did take all the current the charger could put out, for a short time until the cells voltage had risen some amount. The pressure in these cells diminished after charging several times, not up to full voltage, when left they lost some of there voltage over night and continue until almost flat. I have left them sit for some time and now they are tight as if they are vacuum packed. Will get back on to this soon and try pulse charge, see what happens. Cheers Aaron Off The Grid |
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| bob.steel Senior Member Joined: 27/02/2020 Location: AustraliaPosts: 188 |
It is extremely informative to take a Lithium cell and a lab power supply and set it up for constant voltage /constant current supply and watch what happens . I have done so many times and have put voltage loggers on to record but most people just don't look. Discharge the cell ,any size ,down to 2.5 volta any way you like then put your charger on it and watch. Initially it will take the maximum you set in current and that is why it must be current limited. Say a 20 amp hour lithium ion cell as an example . Set te max current to 10 amps. (.5C) set the voltage push to 4.2 volts and switch on. Initially it will draw 10 amps. Not for long though ,perhaps 30 to 60 seconds. Then the current will fall under the 10 amps and continue to fall until way way along the hours line it will get down to say 200mA. Call it a day at that and call it charged . It will be at about 4.0 volts and putting more in will not add much in useable energy. Now once you have done that you will get a better appreciation of the fallacies of ,alternator burnout, massive charge rates , excessive discharge and the quite different scenario presented by the Lithium battery. A lot of people just don't have a clue really. Edited 2021-07-06 19:54 by bob.steel |
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| bob.steel Senior Member Joined: 27/02/2020 Location: AustraliaPosts: 188 |
I recommend you buy a battery resistance tester also. They are as cheap as $47 USD, $64 AUD free post and they are brilliant for fault diagnosis and matching cells. They give voltage at the same time . It is very useful and quick for testing a working battery pack while your inverter is attached and running. I meant to mention also when your charger, be it independent or in an inverter , sends charge to the battery ,you may set the max charge to say 100 Amps and fuse it all appropriately but rarely,if ever, does that sort of charge flow into your pack. Mostly on a say 6Kw syatem it will be down under 20 amps.The cells won't take it . A clamp on current meter costing $26 USD , $35 AUD is the way to go for that. Edited 2021-07-06 20:20 by bob.steel |
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