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Jan 02, 2004, 05:56 PM
Crash Site Instigator
sheerLuck's Avatar

LiPo cell imbalance causes what kind of problem ?


Lots of great information lately on at least 2 good ways to prevent imbalance in lithium packs. However, for me, these still appear to be solutions in search of a problem. Has anyone done any research, or even have any incidents to report, where even a gross imbalance has been shown to cause some kind of problem ? All the threads I've seen seem to assume that this is a problem and that everyone knows it.

If we had some pictures of fires cause by imbalance, or even "I destroyed 2 cells by having the 3rd out of balance", then I'd be much more inclined to rip my packs apart to allow monitoring or separate charging - or to only buy packs configured with multiple leads in the future.

My wife says I have to be hit with a baseball bat in order to pick up on what she really means. I guess the same is true here.

Would really appreciate some solid info on what the issues are in lithium pack cells being out of balance. Not solutions, but issues. If one cell is low, do the others get overcharged, with the potential for a fire ? Or does it just cause a weak pack - then everything is hunky dory after the low cell is recharged or replaced ? Or does it damage the low cell ? Or what ?

Thanks.....

Larry
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Jan 02, 2004, 07:51 PM
Registered User
tekochip's Avatar
The problem is that if you charge in series, then the cell with the highest voltage drop will get the most power. Since this cell is already full, or even overcharged, you get a runaway situation; the cell's voltage gets higher, it soaks more power, and so on, until you get energetic disassembly (a line from the Three Mile Island final report).

So the cell that blows is the high cell, not the low cell. The cell balancer Suzanne (check my spelling) posted will do a great job of keeping things in check. You can also wire the cells in series in the model, but charge them in parallel. This means lots of wires and lossy connectors.

I hadn't thought about all this when I bought my first pack, so I'm living on the edge right now. My plan is to build a balancer in my next charger, rather than in the cells, just to keep the rewiring down.
Jan 02, 2004, 07:54 PM
EDF Head
Haldor's Avatar
Search for "lipo fire" here in these threads and you'll see what imbalance can cause, mainly when recharging.
Thats a bat for ya