- Wed Oct 25, 2006 11:14 pm
#21039
Those were intentionally overcharged. The thing is, you CAN charge Lipos with NICD/NIMH chargers, but you need a volt meter, an ammeter, and the patience and attention of a saint. You have to sit there the WHOLE TIME watching first the volt meter then the ammmeter, AND know where to turn off the blasted contraption.
Now, the thing about R/C lipos. They charge them fast, so they tend to get hot. They charge them constant, so the lipos tend to get warm as they age (internal resistance goes up). Fast charging ages them faster, as does high current drains.
When I first started looking at R/C lipos, the current cell balancing multitap systems weren't available. It was plug and pray, and knowledge that even with a well designed lipo charger, you were still talking about when the battery pack was going to fail, not if. You usually hoped it was during charging, where you could contain the damag,e not during in-plane discharge. Many a good model fireballed because of that. It's still a concern on discharge if you don't have a lipo level sensor onboard. Lipos have a very steep discharge rate at the end, so the last 10% can sneak up on you while airborne. The normal hope if that you get the warning, throttle back, and bring her home while you still are in the safe range. If the warning isn't recieved, burn and crash. I think some speed controllers may now have a detector and automatic soft stop (50% power to allow for a controlled landing?). Still, danger lurks.
Modern multitap RC packs, when used with the correct hardware, now will diagnose and not charge bad cells and alert you to the imminent failure, so you don't have a fireball.
All commerical LION/Lipos are supposed to have the safety circuitry built in. However, if the parameters aren't entered correctly (say, too large a maH rating or maybe the wrong type of anode selected), you get a Sony battery.
Technical Alchemy
Strange ideas, rambling technical thoughts
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