Death of a A123 Cell

[Big House]

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.

[brushlessboy16]

better then needing a new car

[killjoyken]

Originally Posted by Big House

Had this been a regular lipo, my car would be up in smoke.

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

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

[Big House]

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

[killjoyken]

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.

[BL_RV0]

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

[sleebus.jones]

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

[Big House]

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.

[suicideneil]

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.

[Big House]

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.

[roweder]

Originally Posted by Big House

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.

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 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.

[suicideneil]

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

I wish thee luck....

[snellemin]

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.

[snellemin]

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.

[Big House]

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.