Electronics > Beginners
LiPo Questions
jerryk:
I have a Micro-Start XP-1 jump pack that was given to me after a pilot had it swell up when he was trying to jump start his airplane. The photos below are the three LiPo cells that went through the stress event. The cell on the right shows signs of swelling and there is a small amount of slack in the foil. The other two cells are tight and look good to me. The cell in the center has a little rounding in bottom of the cell but otherwise looks in perfect condition.
In a perfect world I would like to replace the swollen cell and save this jump pack. The photos show all the identification marks on these cells but I cannot find anything on the net that leads me to a possible replacement. Is there anything in these numbers that generically describe these cells?
Currently all cells have a charge and are balanced at close to 3.75V. Is a visual inspection of LiPo cells a valid way to assess their condition? I hate to waste good stuff but also understand caution is in order.
Jerry
james_s:
Swelling is an indication of damage, but it doesn't necessarily mean the cell is bad or needs to be replaced. I have a load of LiPo packs I use in my RC aircraft and I've had a few that puffed a bit either due to manufacturing defect or abuse, provided it's minor I just keep using it. If a pack puffs up badly then it's time to retire it. I would not try to replace a single cell in a pack unless you *know* the protection circuitry is well designed. Discharging a cell below a certain point damages it, and over charging a cell much beyond 4.2V will cause it to burst into flame. IMO it's not worth the risk.
Audioguru:
There are new Li-PO cells now (Lithium Ferro Phosphate) that have iron in them instead of the original Cobalt and their voltage is lower.
Lithium Cobalt is fully charged at 4.20V, has a storage charge of 3.7V to 3.8V and is about 3.2V when its load should be disconnected.
The new lithium cells with ferrous might have a fully charged voltage of 3.6V.
Your puffed lithium cell is worn out or has been abused and all three cells are in series therefore have the same age or had the same abuse so the entire battery should be replaced.
grizewald:
Damaged Li-Po cells are a liability and I wouldn't even entertain keeping those indoors. While it is rare, damaged cells can burst into flames all of their own accord. Once they start to burn, you can't put them out either.
Examine the top of the cells where the wires come out to see if they have a protection board or not. Then note the dimensions of the cells and look for replacements. The numbers on the cells often reveal nothing, but in the end, one Li-Po cell is much like another. They either have a protection board or they don't. If they do have a protection board, it prevents the cells from being either over, or under discharged. The fact that these cells became damaged in use tends to suggest that you won't find a protection board.
Just because some of the cells look OK is no reason to trust any of them. Dispose of them properly!
hobbyking.com is probably a good place to look for replacement cells, or even better, a replacement pack.
A replacement pack removes the need to work with soldering a pack together yourself. Even when the cells are at 3.7V storage charge, accidentally shorting one is something you won't forget! :D
james_s:
While it is rare, pristine undamaged cells can burst into flames too, it's just the nature of the beast. My observation has been that the vast majority of LiPo fires occur during charging due to defective or improperly configured chargers that allow one or more cells to over charge. The next most common cause is crashes, a couple years ago I saw someone crash a large electric heli and it made an impressive fireball when it went in. Lots and lots of people fly slightly puffed cells without issue, it's a sign of degradation but doesn't mean a cell is finished.
I *never* store fully charged LiPo batteries no matter what their condition, and I never charge them indoors unsupervised. Normally I charge one set as I'm packing up my gear and then set up my charger at the field.
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