This my idea for a precharge circuit to eliminate the big spark when I connect the batteries to the controller.

Precharge..jpg

When the key switch is turned on, current will flow through the resister and start charging the controller capacitors. Voltage across the controller will start at 0v and rise as the caps charge. When the voltage across the caps gets high enough, the relay will energize and bypass the precharge resistor. Turn off the key switch and the relay will de energize. This eliminates the need for a time delay relay, the R-C circuit is essentially a timer.

I have not tested this, and it assumes a few things: The relay can energize at less than the full battery voltage, since there will be a voltage drop across the resistor. and assumes the resistor is of a size to have enough current let through to both support the controllers current draw and the relays current draw.