magudaman
10 kW
So I have some new cells I am testing out to check for cycle life, cell heating, and confirming the C rate specifications. The cell I am testing is a 10ah LiMn pouch cell that is supposed to be able do 5c continuous 10c intermittent.
My cycle testing just reached 100 cycles at .5C charge, 30 minute rest, 2C discharge 100% DOD, 30 minute rest @ 20c ±3c ambient, the battery looks to have lost around 4% but I have not graphed it yet to see if that is a linear loss or not. I hope not since they are supposed to do around 800 cycles to 80%. Of course their charge setup in cycle life varies from the English spec sheet verses the Chinese specs. But both are discharging the cell at 5C but the recharge seems to be .2c on Chinese and 1c on the English. The English discharge also seems to have a discrepancy in that is says continue cycling until the discharge time is less or equal to 41 minutes. Well a 5c discharge should only take 12 minutes so not really sure what was happening there, unless the orginal discharge for 800 cycles was 1c
I did some open air testing and the temperature results were decent. Even at 50 amps the cells was doing about a 17C rise over ambient. But it turns out it is dissipating quite a bit of heat in open air.
One concern I have is that these batteries are are going to be configured in a pack at some point. Most likely will be flat up against another cell and in turn won't dissipate the same amount as I saw in my open air test. So I did try a 52 amp discharge with 1/2in syrofoam up against the cell and just my thin thermal probe. From an starting temp of around 20C the cell reached 55C at which point it was at 95% DOD and I terminated the test early due to temperature. The temperature rose about another 0.3c after stopping then started to slowly cool. So this makes me think I may want to consider putting some thin veins in between each of of the cells for some extra cooling or possibly a thin aluminum heat sink of sorts. Especially for hotter climates with much higher starting temperatures. On average even riding as hard as I can, I don't drain my 900wh pack faster than 40 minutes, so I end up with an average of around 30a continuous 200a intermittent @ 50v.
So the questions.
Is it right to assume that a cell against another cell would not really get any cooling?
When doing C rate tests I am looking at voltage drop at a given amperage rate and capacity output, is this a pretty good determination of cells C rate handling?
Any voltage lost from nominal (at the tabs) (x)times the amps is the watts of heat being produced inside the cell?
Any good Limn batteries out there that aren't 2ah or smaller ?
My cycle testing just reached 100 cycles at .5C charge, 30 minute rest, 2C discharge 100% DOD, 30 minute rest @ 20c ±3c ambient, the battery looks to have lost around 4% but I have not graphed it yet to see if that is a linear loss or not. I hope not since they are supposed to do around 800 cycles to 80%. Of course their charge setup in cycle life varies from the English spec sheet verses the Chinese specs. But both are discharging the cell at 5C but the recharge seems to be .2c on Chinese and 1c on the English. The English discharge also seems to have a discrepancy in that is says continue cycling until the discharge time is less or equal to 41 minutes. Well a 5c discharge should only take 12 minutes so not really sure what was happening there, unless the orginal discharge for 800 cycles was 1c
I did some open air testing and the temperature results were decent. Even at 50 amps the cells was doing about a 17C rise over ambient. But it turns out it is dissipating quite a bit of heat in open air.
One concern I have is that these batteries are are going to be configured in a pack at some point. Most likely will be flat up against another cell and in turn won't dissipate the same amount as I saw in my open air test. So I did try a 52 amp discharge with 1/2in syrofoam up against the cell and just my thin thermal probe. From an starting temp of around 20C the cell reached 55C at which point it was at 95% DOD and I terminated the test early due to temperature. The temperature rose about another 0.3c after stopping then started to slowly cool. So this makes me think I may want to consider putting some thin veins in between each of of the cells for some extra cooling or possibly a thin aluminum heat sink of sorts. Especially for hotter climates with much higher starting temperatures. On average even riding as hard as I can, I don't drain my 900wh pack faster than 40 minutes, so I end up with an average of around 30a continuous 200a intermittent @ 50v.
So the questions.
Is it right to assume that a cell against another cell would not really get any cooling?
When doing C rate tests I am looking at voltage drop at a given amperage rate and capacity output, is this a pretty good determination of cells C rate handling?
Any voltage lost from nominal (at the tabs) (x)times the amps is the watts of heat being produced inside the cell?
Any good Limn batteries out there that aren't 2ah or smaller
?
