Laptop LI-ION 18650 Cells Help? - Page 1
Forum section: electronics / beginners

author: XMA
author_rank: Contributor
timestamp: March 20, 2018, 01:32:13 am
content: okay so i have this laptop battery that does not charge, I open it up and measure voltages, and one of the pack of 3 cells in parallel read 0v, so I take them out try charging in parallel and the charger won't even detect them, then I break them into single cells and again won't charge. before I broke the cells into singles I put the 0v pack and another pack that had a 3.5v or so voltage together and also nothing " I did that because I've read online if you put li-ion batteries in parallel they will balance themselves", it's like the battery won't even accept a charge. I bet you will say it has a protection circuit, but I checked the exact dimensions and its size is the same and won't have space to contain a protection circuit unless im wrong. I've also seen a video on youtube where a guy fixes this possible problem by briding the gas cap, but I need to know is this battery toast. cus it seems like it.also if you know more about Li-ion batteries could you tell me some facts to know if a Li-ion battery is completely toasted. because I know that Li-ion cells that are discharged to 0v or so can still be charged.

author: sleemanj
author_rank: Super Contributor
timestamp: March 20, 2018, 01:34:54 am
content: That pair of cells is dead.> I put the 0v pack and another pack that had a 3.5v or so voltageAnd if you keep playing with lithium-ion cells without knowing what you are doing, you might be too soon enough.

author: XMA
author_rank: Contributor
timestamp: March 20, 2018, 01:53:44 am
content: yeah your right, if I remember reading somewhere, it also said that if you put a pair of cells in parallel and one cell has a big voltage and one cell got a lower like under 1v or so the bigger voltage cell would put like 100a or something. correct me pls.

author: helius
author_rank: Super Contributor
timestamp: March 20, 2018, 02:25:57 am
content: Any Li-ion cell that falls below 1.5V is permanently destroyed. You cannot safely charge them at all, at any rate, under any conditions. It goes without saying that they should certainly not be used to build a battery. To prevent this and leave enough safety margin, the BMS should disconnect the cell if it drops below 2.5V (actual cutoff voltages are evidently in the 2.2 to 2.9V range). This protection is for safety and should never be bypassed casually.

author: amyk
author_rank: Super Contributor
timestamp: March 20, 2018, 02:42:17 am
content: Quote from: helius on March 20, 2018, 02:25:57 amTheresearch, and, shows otherwise. If you give them a tiny trickle of current and they rise in voltage quickly, then they're fine. If they stay near 0V and act more like a resistor, then they're dead.There is a ton of fearmongering and misinformation floating around, no doubt by the ones in a position to profit the most from it.

author: digsys
author_rank: Unknown
timestamp: March 20, 2018, 03:16:34 am
content: Here's where it gets complicated :-)First, I totally disagree with Mr Helius. I/we have taken huge EV car packs to near 0V on many many occasions, without ANY detrimental effects.I create V/I profiles that we need to keep within though, as the C discharge rate will de-rate a lot under ~3.2V.This min voltage issue is mainly targeted at Lead-acid type batteries.I often run extensive destructive tests on a new chemistry / product to check / verify their operation parameters.Unfortunately, you're going to have to decide who to follow on that point :-)For your situation - cells rarely read 0V00, so possibilities are - they have an internal fuse (sometimes thermal) and it is open-circuit.Probability is low, as you say they ALL read 0V. That also mostly discounts de-lamination / separation, when heat / currents etc force theanodes / cathodes apart. Usually though, there is some leakage still. You could try to remove a cap and check again, even apply some pressure.As far as parallel cells conditioning each other - this is quite true. In all my packs, I have up to 7+ paralleled in each block.www.pbase.com/digsys/image/164509549Some notes -equalization is greatest during large charge / discharge cycles AND at the ends of their capacity. ie ~5% at the top ~3.8V-4.2V and ~10%at the bottom ~3.2V-0.5V. When the cells are in their middle-state, capacity range of app ~80%, the voltage only varies from ~3.65-3.75VAdd tolerance variations between cells and there is only little equalization occurring when in trickle / low power modes.One good piece of news is - in the 1000s of cells we've gone through, most failures are open-circuit / high impedance (as what you MAY be seeing).In a parallel block, the O/C cell just doesn't exist - in a series block, the entire string goes O/C, so failures rarely end in fires and gassing.Usually, they look like this -www.pbase.com/digsys/image/164509551(note: we do use all types of cell types / packaging)Fires / serious failures are usually under very high currents (exceeding C ratings etc) and/or high temperatures OR physical damage.You have nothing to lose by removing the cap(s) and investigating further.

author: Daixiwen
author_rank: Frequent Contributor
timestamp: March 20, 2018, 08:01:48 am
content: Quote from: XMA on March 20, 2018, 01:53:44 amBy connecting those too cells in parallel you are short circuiting the one with the high voltage. I don't think a regular cell can deliver 100A in a short circuit, but those use for power tools can. In any case, a cell at 0V should be treated with extreme care, as said by amyk. You can try and revive it with a very low charge current, and then use a higher current when the voltage reaches 2.5V/3V. But by putting the two cells in parallel, you are trying to charge the 0V cell in a totally uncontrolled manner, and possibly with too high a current.That said, I agree with digsys that if it really reads 0.00V it could be an internal fuse that opened. In that case there is little you can do.Please be careful when playing will Li-Ion cells. If possible do it outside on concrete blocks, or if inside at least have a fire extinguisher nearby. Better safe than sorry. The electrolyte is highly flammable, and any abuse of the cell will increase it's internal pressure and temperature. That is not a good combination (and that's why some cells have an internal pressure/temperature fuse).

author: XMA
author_rank: Contributor
timestamp: March 20, 2018, 01:21:08 pm
content: so just to ask, is it okay if I go and reset the CID the pressure cap? is it safe like the next time it pops it will be the same or it will explode?