I understand using a mosfet to protect the switch contacts when pulling a higher current, or to allow fancy firing control (3-round burst etc). In effect the mosfet is being used as a relay.
My understanding is the cause of arcing at the switch is not related to the closing of the switch, but it’s opening. There is insufficient voltage to cause a breakdown of the air and cause arcing during a switch closing. When opening a switch on a inductive load you can see very high voltages, which causes the arcing.
A motor is an inductive load (ie has a magnetic field) and when opening the switch contacts the energy within the magnetic field needs to be dissipated somewhere, hence arching at the switch. See the below formula;
v=volts
L=inductance
di=change in current
dt=change in time
Based on a everything being equal, a small change in time (ie opening the switch) will result in a high voltage spike and this high voltage leads to arching across the switch contacts.
I have been involved in industrial electrical engineering for ~13 years, and we always install a free-wheeling diode across relay coils (another inductive load) on DC circuits. A free-wheeling diode should work the same on a DC motor, and I believe this would be a simpler fix then installing a mosfet circuit.
I have searched google and have found no mention of installing just a free-wheeling diodes on a AEG. Has anyone consider or installed just a free-wheeling diode?
Reference links;
http://en.wikipedia.org/wiki/Flyback_diode
http://en.wikipedia.org/wiki/Inductance