Key Ignition vs. Toggle Switches

[Dave S]

John P - Regarding the photos of the burned contacts

Were you able to determine exactly what kind of metal the contacts are made of? Almost looks like aluminum??? I know photos often don't show the colors well; but, on the photos of the contacts they certainly don't look like copper, brass or gold to me.

Also - was there any type of lubricant on the contacts when it was originally opened up?

Thanks,

Dave S

[jtpitkin06]

The contacts in the ACS switch appear to be silver plated brass. The switch shown is notable in that it is one of the later manufacture dates with the identifying red paint in the screw heads. It is not subject to the AD for periodic lubrication but it did have lube inside.

I have the same switch in my Cessna. It too is a later model and I have a diode in the start circuit. The AD requires that I check the switch is functional in the OFF position. I may open the Cessna switch on the next annual just to have a peek at the contacts.


John Pitkin

[jrevens]

A recent series of conversations with a friend & fellow builder, have brought this issue to mind again. I'm probably just beating a dead horse at this point, but I have a couple of thoughts/theories on this subject that I'd like to share with the group.

Regarding the possibility of these ACS keyed switches somehow causing the failure of a sensitive ignition module - since these switching contacts are located in the same enclosure & relatively close to each other, I wonder if there is a possibility of the high voltage back emf, produced when a non-diode protected starter solenoid coil is de-energized, "jumping" the gap or perhaps following a slightly conductive "trace" (caused by previous arcing) from the starter coil contact to one of the ignition contacts, effectively "zapping" an ignition module.

The second thing I'd like to present is that having a switch with a high enough current & voltage rating does not always make it an ideal choice for a low voltage, low current application (such as, perhaps, an ignition grounding switch). It is fairly common to have cadmium-silver plated contacts on high quality switches, and these contacts are sometimes not recommended for use with low voltage &/or current. The reason is because there is not enough (or any) arcing that occurs during use, and some arcing has been found to be desirable or necessary to keep these contacts from slightly oxidizing & creating an abnormal amount of resistance when "closed". This is probably not the case with the ACS switches, since they have a sliding contact action... I don't know.

I'm using a small key switch for start, & 2 toggle switches for ignition (similar to the way that Van's does it with the RV-12) on my Kitfox.