|Aug 18, 2012, 02:31 PM|
Bringing LiPos Back From The Dead
So I fly FPV, and about a month and a half ago, landed one of my planes in a very nice tree about 100 feet up. It just came down today, and, to cut to the chase, my LiPos were at about 0 volts (0-1 volts on two 3 cells).
Anyway, I have this pretty rough method I use to bring LiPos back, which is charging them as a NiCAD at 1 amp until they accept a charge from the LiPo charge mode. I use a Dynam Supermate DC6 for this. I know this is dangerous, they are kept in LiPo bunkers the rest of their life, and I sit by them as they are revived.
However, I was wondering if this process really revives them, or if it just seems like it does. I can get them to accept a full charge and discharge, but even still, it was pretty bad in this case. Usually the LiPos I do this to were at 5-6 volts, but these were at 0 to 1 volt.
I have two LiPos, a 1000 3s, which wasn't puffed at all, but was at about .5v, and a 5000 3s, which was severely puffed, same voltage. They both have retaken a charge, and have been balanced, but I am curious as to whether they can ever fly again in a plane I don't care much about (the plane that crashed and is now frankenstein with more glue). Do they still have the same, or close to the same discharge rate? Should I worry about the puffed one? I believe the reason the other didn't puff is because it was held tightly with tape, so there was no room for puffing. They were both Turnigy LiPos from HK.
Anyway, I am going to keep a close eye on these, will report back with further results. I made this thread so the battery experts can yell at me for this and help me to answer some of my questions.
If it matters, my restoration process is:
1 - Charge at 1a as NiCAD
2 - Charge to full (~12.5v) as LiPo when they accept charge
3 - Discharge with charger
4 - Balance charge to full
5 - Discharge with charger
6 - Balance charge
7 - Repeat discharge/balance until battery is balanced to an acceptable limit
EDIT: Also, just realized I could use these to power my FPV ground station.
|Aug 18, 2012, 03:55 PM|
In the end the Lipoly may recover but it has suffered real permanate damage if the cells spent hours below 3.5 per cell so do not expect much from it.
|Aug 18, 2012, 06:32 PM|
I'm expecting nothing actually. Just because this battery is so far gone already (the 5000) I vented the cells by poking holes in them. No more swelling, but now the cells are down to around 3 volts total, so 1v each, before venting and after sitting in freezer I measured 3v per cell. I may have ruined the cells, didn't poke too far in, just the outer layer of sheathing. I used a black sealant and wrapped the cells super tight in electrical tape. I put a few more layers around the holes that I made.
I may have let oxygen get in and destroy them, we shall see. Charging as NiMH now, it seems to work better than charging as a NiCAD.
|Aug 18, 2012, 08:40 PM|
You are very lucky.
Others doing what you have done with charged cells ended up with a blowtorch in their hand.
Here's what can happen with charged cells.
The question is how far poking in is too far. No matter, once the seal is ruptured and O2 gets into the pack, it is reported to be shot.
|Aug 19, 2012, 12:47 AM|
Yep, after hours trying to force a charge into the 5000 after piercing the seals to un-puff it it vented. Lots of smoke, some flames. My other battery is taking a full charge 987MAH put into it, it's a 1000MAH, so not gonna experiment with that. The 5000 only took 2300MAH before my experiments started so I would of probably just threw it out anyway.
Ahh well, it was fun!
EDIT: Also, gotta use a toothpick in the future, used a razor blade and I believe it caused an internal short.
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