flathill wrote:Well we know this pack can put down 436 hp at the wheels on a first gen P85. Figure inverter and motor and other losses add up to 20% at full power. That means the pack is putting out maybe 523 hp. 523/16 module=32 hp per module or 27kW
OK lets say 3.5 V (sag) * 6 * X amps peak * 74 = 27000 W
X=17 A per cell peak
So you are right. 15-17A per cell seems perfectly safe. I'm sure there is a little more headroom though before the cell fuse breaks.
For drag racing you might be able to push much more than 20 A per cell if you don't care about cycle life. It would be interesting to test when the cell fuse blows vs time vs amps.
The cell level fuse is only supposed to trip during short circuit
"the potential hazard regions represent possible current levels for internal short 255 that may be present in a band below the fusing current of any such fusible components and above a current required to cause hazardous overheating of components including battery cells. This range may be from approximately a 2 C discharge to an 8 C discharge in some high energy battery packs for electric vehicles. The range may be higher, such as 10 C to 30 C for higher power battery packs used in plug-in hybrid electric vehicles. Fusible components often have short thermal time constants. Long time constant fusing devices require large thermal mass and are heavy and expensive and are thus undesirable in electric vehicles and the like."
According to this Tesla patent we can expect the cell fuse to blow probably at at a minimum of 26A if we assume 8C? Seems kind of low
I've got an 8-channel battery cycle tester on order from China so everyone can benefit who buys these cells from cycle test data.
It maxes out at 10A, but I can set any custom charge/discharge routine to see how different loads and conditions affects the life of the cells.
I have a little programmable DC load i've been using, but it's too hard to get consistent results as I have to baby sit the charging...
I don't think there's a fuse... I am pretty sure they remove both the PTC and fuse to maximize performance of these cells...?
I know I had one shorted for a good 5 sec and it's fine. Must have been 50-80A.
I will charge these cells up and do some serious torture tests. (short, overcharge, smash, etc.)