[MPaulHolmes]

Perhaps even with pull-down resistors from the mosfets' gate to ground, for a very brief time while the control section is just shutting off (and hence no current limiting anymore), the mosfets could be "on" while the gate voltage drops, allowing power from the batteries to dump through for even a couple milliseconds! murdering them instantly! That's what happened with the bike version awhile back. So, by the time I turned on the controller the next time, the mosfets were already failed shorted.

The controller could have died just by turning it off out of the sequence below...

The smoke could have indicated lots of power through the stuff inside, rather than indicating the moment everything broke.

It's just a guess at this point, but possibly the only completely safe sequence for that version was:

ON:
1. Turn on 12v power.
2. Pre-charge resistor.
3. Close Contactor

OFF:
1. Open Contactor.
2. Turn off 12v power.

It would make me really happy if that's all that the problem is. Man! I love a mystery! By the way, I just ordered all the new parts for the newer, and much more robust and fancy and professional control board section. Ya!

Well, it would be good to incorporate the pre-charge resistor and contactor stuff as Roger suggests. I might have to order from them again to get that stuff. Dang it! hehe.