I have 15 aircraft that have been converted from nitro to electric, and on each and every aircraft there is a spark when connecting the Dean connector. If you plug the connector in all the way nothing gets hot and there are no more sparks. The spark only happens when they touch on plug in. Want to know why?

Even when the switch is off, electrictiy is still flowing and there is a completed circuit. The current that is flowing is not strong, but there is a demand and therefor a spark when the connection is made. If you fail to disconnect the lipos from the BEC when you are finished flying, this small demand will deplete and ruin the lipos. While I am typing this post I have several packs of lipos in the garage charging. I left them connected and the voltage dropped from 11 volts down to 7. The charger thought they were 2S packs instead of 3S and wouldn't charge. I am trying to restore them back to the correct charge, but, previously I failed at this.

I guess what I am trying to say is simply this. The switch does not shut off all electric power, it just shuts it off to the receiver. The motor doesn't run when the switch is off because the receiver is not sending to the controller, however power is still going to the controller via the BEC.There is still a slight demand, thus, a spark when re-connecting after a disconnect.

Think about this, the lipos are connected to the controller, the controller is connected to the motor. That is a compelte circuit. The BEC is tapped off of the controller, runs to the switch, then to the receiver. So turning the switch off does not disconnect the power to the controller or motor. There still is a completed circuit between the batteries to the controller to the motor. The only thing missing is the imput from the receiver to tell the controller to start the motor, but the current is still there, and when you connect the dean connector, the current want to jump and complete the circuit.

Hope this helped.

Al G