Death of a A123 Cell
 

I took my converted Super RS4 out last night for some wide open runs. Towards the end of the run I reached the limit of the battery powering the MM 7700. I heard two small subdued pops and I brought it in. Looking to see if andthing was broke and seeing nothing, I took a whiff inside the body and a resin like odor was coming from the car. I disconnected the battery and to my surprise, the shrink wrap had melted and the cells had popped open, and leaked the contents of the pack out. Had this been a regular lipo, my car would be up in smoke. My hats off to A123, but now I need a new battery.

better then needing a new car :yes:

Or....had that been a good lipo, your car would still be running. :lol:

What setup were you running that would cause your A123s to pop?

Mamba 7700, 2S1P A123 battery. I guess the motor could not keep up with the appetite of the Mamba.

Since you were doing speed runs I'm guessing that you're not geared conservatively, plus the 7700 can pull some serious amps. Your A123 pack can deliver 69 amps continuously, while a Trakpower 4900 can deliver 122.5 amps. You should be running a 2s2p at least.

I'd run 2s3p if weight was not an issue. Or a 6900 and 3s2p.

Yep, I'd say you're drawing (or trying to!) 115A+ from that pack with a 7700.

Max volts for Mamba 7700
 

I know the Castle limits the 7700 to 2s or 8 cells, my question is this, could the 7700 motor handle 2 3S1P 9.9V A123 packs in parallel. I do believe the death if my first pack was due to power demand. I figure I run these two packs with a continuous rating of 69A each, together to equal a continuous 138A. Thanks.

7700kv motor is for 2s only really, thats way too many rpms with a 3s setup- you'd have to drop to slower motor. 2s2p is the way to go.

I figure if you can do 8 NiMH cell @ 1.2 that equals 9.6V. A123 cells have a nominal voltage of 3.3 and 3 * 3.3 equals 9.9. I figure the .3V is not a material difference. I am going to test the 8 NiMH cells first to see. If all goes well and the motor stays in one piece, I will go with the two 3S1P in series.

7700kv x 9.9v (nominal at that) = 76,000rpms+.

I wish thee luck....

4s lipo is used in the extreme class in dragracing which only last 1.3 seconds with the 7700kv motor. I have ran 4s1p A123 with the 7700kv motor and heated the batteries pretty good. 3s2p is doable, but be aware of your gearing with that motor. It's best to add a cap to the esc when running high kv motors.

remember though, that's the nominal voltage, I don't know too much about A123 cells, but li-pos will crawl way above their nominal voltages, their nominal voltages are 3.7v per cell, but they usually end up at 4.18v at fully charged, that's almost a .5v difference, and x3:surprised: I think you'll find that A123's are pretty similar, and a 3s A123 will probably crawl much higher above it's nominal voltage than a 8s Ni-Mh pack, plus A123's and Li-Po's have much greater power density and will hold their voltage better and longer, considering all this it doesn't sound like a good idea, but, you could see what castle creations says.

With the right motor choice, you can run 6s1p A123 with the mamba max. Just remember to disable the LVC. I ran it with a 6L c40 hacker motor in a rustler geared pretty high.

By "LVC" do you mean the red wire or what ever color it is on the ESC. If so copy that...just got to get the right motor.