fmidgett
Jun 12, 2006, 07:04 PM
As I have been learning the characteristics of Lipos over the past several years I have come to realize that four key things cause a premature decline in pack capacity and output:
1) Overdrawing
2) Heat
3) Too high voltage
4) Too low voltage
My basic question is, which of these is the most damaging?
More specific questions:
1)Does overdraw hurt the cells provided it is kept in short enough bursts not to cause heat build up? For example if I severely overdraw a pack during a bench test for just a few seconds will there likely always be some degradation? Let's assume we demand 50 amps from an 30 amp max pack. If I did that 10 times for 5 seconds, 10 minutes between tests, would the cells remain good as new?
1a) Similarly, if I know a setup is overamping the battery slightly, can I protect my batteries by flying only part of the pack capacity thus keeping the temperature in check? For example, say I would end a 10 min flight with a temp of about 130 degrees. I fly for 4 minutes and only hit 110 degrees. Am I doing no damage with the short flight strategy because there I'm not building up heat, even though I am technically overdrawing the battery? Or will I do some damage anyway, even though the cells never get really hot?
2) Is heat inherently bad, no matter how it is generated? I left a pack in my locked car it the sun. The silver liner on the cells puffed up (like a tight bag of potato chips) but the underlying cells appear to still be flat. Did the heat from the sun do the same kind of damage as if I had over-amped them to generate that heat? Some damage but not as much? No damage just puffed up the encasement?
3) My Triton charger fills my 3 cell packs to a voltage of 12.6. My other less expensive chargers fill until the green light appears. If I then read these on the Triton they go as high as 12.8. Is this slight overcharge doing damage? If I immediately balance is that better, or is there damage done to a cell the minute it hits 4.21+v?
4) If I run my pack to the end I sometimes hear the motor begin to pulse. If I hear the pulse of a depleted pack, does that mean I have degraded to pack a little bit, or if i heed the sound and kill the throttle will the cells survive this momentary undervoltage OK?
Again, I understand that all of these things are bad. I attempt to avoid them. I just want to understand which things are the worst to be sure I have my priorities straight to maximize pack life.
-Fred
1) Overdrawing
2) Heat
3) Too high voltage
4) Too low voltage
My basic question is, which of these is the most damaging?
More specific questions:
1)Does overdraw hurt the cells provided it is kept in short enough bursts not to cause heat build up? For example if I severely overdraw a pack during a bench test for just a few seconds will there likely always be some degradation? Let's assume we demand 50 amps from an 30 amp max pack. If I did that 10 times for 5 seconds, 10 minutes between tests, would the cells remain good as new?
1a) Similarly, if I know a setup is overamping the battery slightly, can I protect my batteries by flying only part of the pack capacity thus keeping the temperature in check? For example, say I would end a 10 min flight with a temp of about 130 degrees. I fly for 4 minutes and only hit 110 degrees. Am I doing no damage with the short flight strategy because there I'm not building up heat, even though I am technically overdrawing the battery? Or will I do some damage anyway, even though the cells never get really hot?
2) Is heat inherently bad, no matter how it is generated? I left a pack in my locked car it the sun. The silver liner on the cells puffed up (like a tight bag of potato chips) but the underlying cells appear to still be flat. Did the heat from the sun do the same kind of damage as if I had over-amped them to generate that heat? Some damage but not as much? No damage just puffed up the encasement?
3) My Triton charger fills my 3 cell packs to a voltage of 12.6. My other less expensive chargers fill until the green light appears. If I then read these on the Triton they go as high as 12.8. Is this slight overcharge doing damage? If I immediately balance is that better, or is there damage done to a cell the minute it hits 4.21+v?
4) If I run my pack to the end I sometimes hear the motor begin to pulse. If I hear the pulse of a depleted pack, does that mean I have degraded to pack a little bit, or if i heed the sound and kill the throttle will the cells survive this momentary undervoltage OK?
Again, I understand that all of these things are bad. I attempt to avoid them. I just want to understand which things are the worst to be sure I have my priorities straight to maximize pack life.
-Fred