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P-mag wiring question

pa38112

Well Known Member
I am a little confused on how to wire my p-mags. The instructions say to put them on a dedicated switch for testing the internal alternator, but they also mention shutting off the buss for ignition testing. I don't really want to kill my other electronics when testing the p-mag alternators.
Are most of you running these on their own switch or on the main buss switch?
 
Two switches per P-mag....one to supply 12v power to the mag, one to provide the “control” circuit (P-lead on a conventional mag) to the P-mag to actually turn it on/off.

I used a 3 amp switch like this to supply bus power to the P-mag:

https://www.aircraftspruce.com/catalog/elpages/pbcircuitbrkr2.php

For the P-lead circuit a good quality SPST “On/Off” switch will work.

Page 5 of the install manual tells you about the using the old P-lead circuitry (if it exists) under Note 1 after Step 4.

Step 5 on page 5 tells you about the (unsupplied) switch or circuit breaker that’s needed.

Testing the P-mag won’t require you to shut bus power off to everything else if it’s wired this way.

Edited to add: EACH p-mag should be wired this way. DON’T power BOTH mags off a SINGLE switch or breaker...it becomes a single point of failure that way.
 
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I use a locking toggle switch for control, and a reachable pull breaker for power. One set for each pMag. Breaker is normally in - only open the pull breaker for the periodic check that the pMag internal generator if functioning properly.

Carl
 
Push button

I wrestled with using the CB to remove 12v power for the P-Mag internal power test. I decided to us a normally closed push button next to each mag switch.

During mag check when on single mag I just push the button momentarily to check mag internal power.

The push buttons I used are metal and use the same size hole as the toggles.

If you CBs are easy to reach that is a good way to do it, I only test the internal power occasionally. I don?t test it every mag check.

Picture at this link from my log

http://www.mykitlog.com/users/display_log.php?user=rvg8tor&project=403&category=4901&log=93280&row=96
 
Emag thinks everyone is using a key switch for starting and their mags.

If you use a pushbotton, then you can use a three way switch to manage your P-mags.

In my case, down is grounded and unpowered, the middle position is ungrounded and unpowered, and all the way up is ungrounded and powered.

With this setup, if the switches are up, you are ready to fly. If they are down, then don't fly.

This setup also requires individual circuit breaks, one for each igntion. It is not recommended to use one breaker for both ignitions.

Here is how I perform my pre-flight ignition check. It takes longer to read than to perform:

pmag%20preflight.jpg
 
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pmag wiring

Here's how I did it - I think I captured all the requirements. Many threads on this topic, for sure!

PMAG Wiring.png

My switches are exactly as Bill shows above.

2 x 3 position switches, and one 2 position switch to activate the "maintenance mode".
 
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Be careful with momentary switch. With one P-Mag off and the other firing, testing the internal power, if it fails the engine will shut down. LET IT.

If you let go of the momentary switch and ignite all that unburnt fuel air in the exhaust pipes with engine still turning, you will get a BOOM.
 
I use a switch (with a green LED) for power, fused, direct to battery.

Typical "keyswitch" for control.
 
After a long discussion with Brad at EMagAir, I simplified my wiring. I was using a 2-10 switch arrangement, combining test, power, and p-lead functions into one switch (each).

I ended up with pullable breakers and simple single pole plead switches. The test function is performed by pulling the circuit breakers, which have a life span similar to switches (10,000 operations).

The reason I simplified it was for a rare boundary case... hand propping an engine with a flat battery! In this case, the p-leads must be turned on (opened) before power is applied. This defeats the Mags' internal 3-rotation start delay, allowing the ignition to fire immediately.

While hand propping is an unlikely event, it does benefit from the P/EMags' ability to fire even with a low battery voltage that may not crank a starter motor.

Brad alluded to other benefits, but convinced me that a simple, conventional wiring arrangement would be best. YMMV

V
 
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