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Transplanting 'safety circuit' from a dead LiPoly pack...thoughts?

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bsodmike:
Hi all,

I found a "raw" LiPo that I was able to charge using one of the Sparkfun battery charger circuits.
The LiPo that is dead has protective circuitry, so I'm thinking I can transfer this across to the raw pack?

Both packs are ~2000mAh, but can't really be sure about the raw pack.
Both 3.7vdc

thoughts?

thm_w:
Should be fine, as packs are similar in size (so protection board specs would likely be appropriate).

If possible, have the cell mostly discharged before working on it. Have some fireproof surface to work on, use non-conductive tape to cover up everything, etc.

filssavi:
The problem I see about it is that you have actually no way of knowing if the safety circuit does indeed work...

If I had to guess I would say it is probably dead. There are two ways to kill a battery completely dead (it does not even charge) either it has been overdischarged (which shouldn’t be possible if the safety circuit works, as it is one of the things it is designed. To avoid) or the pass transistors in the protection IC do not stay on. In any case that board is probably shot

The only failure mode that might leave the safety circuit intact is just old age, however I have yet to see a battery that had been used so much that it actually stops charging

NiHaoMike:

--- Quote from: filssavi on July 06, 2020, 09:03:05 pm ---The problem I see about it is that you have actually no way of knowing if the safety circuit does indeed work...

--- End quote ---
Test it with a capacitor instead of the battery and do a slow charge/discharge using a resistor and bench power supply. The time constant should be on the order of a few 10s of seconds.

bsodmike:
The old pack is very very dead.  Nothing to talk about on the output end.  |O

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