E-mag / P-mag Ground Maintenance switch
 

In Bob Nuckolls' AeroElectric book there is a diagram of how to wire in a ground maintenance switch for a duel pmag set up.

I do not like the idea of having a ground maintenance switch on my panel so in its place I will install a 1/8" audio plug up under the panel and use a "shorted" matching male plug with a long "remove before flight" streamer as the "switch".

What do you think of this idea? Anything concerns that you can think of?

under panel switch
 

Bill,

I put the switch up under the panel - and an indicator LED on the panel. Works as advertised.

Your idea sounds good, too.

In order to put the P-mags into set-up mode, you have to power them before ungrounding the P-lead. So your plug idea is going to have +12V on one side and a connection to the P-mag power on the other? Sounds ok to me, but a little bit funky. Hiding the switch behind the panel or on the subpanel is another option. You won't have to carry around your special plug that way.

Just happen to be installing mine this a.m. Switch and light are on a small bracket riveted to the forward side of the firewall, near the top and right of center (but not so right as to block lifting the battery for removal). Rationale: (1) I'm only going to be doing maintenance with the cowl off. (2) I can reach in through the oil access door to turn it on/off for hand propping. (3) No way on God's green earth can it be inadvertantly activated from inside the cockpit.

John Siebold
-7 & -7

Is a maintenance switch needed?
 

Perhaps I'm just being dumb, but I don't see the need for this switch. I turn the master on, E-mag is powered up, set the timing, turn it off. There is some stuff that comes on with the master, but not that much. Power draw is small, timing doesn't take that long. What am I missing? Additional switches and connectors are just additional failure points.
Pete

I can't remember which is which (pmag/emag), but on whichever unit has it's own generator, isn't having things powered of the master going to prevent checking the self-power feature during run-up?

Also, if I remember correctly, there is no danger in activating the service switch in flight, since the unit is already powered up anyway. The only real "danger" is in leaving the switch on after timing (drain the batt)

Steve,

The Pmag is the self powered unit. You need a three way switch to test them. In my -9 UP will be for aircraft power, MIDDLE will be self power mode, and DOWN will be off. The preflight will work something like this: Both mags UP (Starting position so they should already be there.), 1800 RPM, right mag OFF, left mag MIDDLE, both MAGS UP, left mag OFF, right mag MIDDLE, both mags UP. That sequence will test each mag on the ship's power and their self power feature.

Make sure you don't try turning off power to an Emag. According to the manual:

NOTE: Do NOT turn 12 volt power OFF and ON to E-MAG (non-alternator)
model ignition while the engine is running.

I'm planning the same set up and test procedure. (I copied this idea from somebody else, so I still only owe you 2 beers Bill :) ) At first I was concerned, because the manual I have says the run mode delay option (to avoid blowing out the Ryton sumps) is selected by applying power before or after enabling the P-mag. But I think they now have that selectable via a jumper.

Putting the P-mag into setup mode is going to be such a rare thing. I might just leave out the extra switch and just have some sort of jumper behind the panel (tip-up canopy). You basically just need to keep the P-lead grounded while applying power to get into set up mode.

Dave

Chuck, its not that bad, you wouldn't want to do it all the time (as it makes the enngine run rough for a few seconds while it figures out what is going on), but it won't cause any damage. From the horse's mouth at the factory. I think they're going to re-word the manual.

Pete