Re: Magneto switch and Rotax
Larry,
I wouldn't worry about your mag switch.
There are some sites that say a “standard” mag switch cannot handle AC current from the ignition shorting wire on the Rotax 912. This is probably not correct.
In fact, any switch designed for DC can handle a much higher voltage and current when used in AC. The limiting factor on switches is arcing of the contacts. When a DC switch opens the current continues to flow across the gap until the air resistance is high enough to break the connection. It is the continued arc that causes switch contacts to burn or pit.
In AC circuits the current is constantly reversing. Each time the current reverses the voltage drops to zero. When the voltage drops the arc is temporarily stopped. Restarting the arc takes a much higher voltage for a given air gap, thus the arc is broken sooner than it would be with a DC circuit. Less burning and less pitting with AC.
A switch can often handle 10 times the voltage and 50 percent higher amperage on AC that it could on DC. Many switches have voltage rating printed on them. A typical rating might be AC 250 volts at 6 amps and DC 28 volts at 4 amps.
The Rotax “kill” wire shorts the low voltage input side of the ignition module, not the high voltage output. That voltage is about 40 volts at maximum which is comparable to a magneto P lead voltage.
The Magneto ignition P lead is not pure DC either. It is pulsed, starting at zero and rising to peak then falling back to zero on each opening of the points.
The contacts in a “standard” magneto key switch are very robust and can handle AC voltages far in excess of anything put out by the Rotax dynamo. If you install toggle switches, you may actually end up with a switch that is less reliable than what you have now.
I would continue to use your magneto key switch with confidence.
John Pitkin
Greenville, Tx