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-   -   P-Mag - Requirement for power line switch? (https://vansairforce.net/community/showthread.php?t=114650)

SmilingJack 06-29-2014 05:58 PM

Kevin, Here is my setup for 4 switches. Turn the 2 outboards off and after they check good turn them back on and then turn the 2 inboard switches off...if they check good, Internals are check and ready for flight!

They are at the very bottom on my panel on the left hand side under the radio stack.


Bavafa 06-29-2014 06:24 PM

Quote:

Originally Posted by LARCO (Post 892920)
Because the P-Mag loses internal power below about 750 RPM I installed a DPDT switch with 2 slow blow fuses. Reason-----One day I turned off the P-Mag switch to check the internal power during the run up, got distracted and forgot to reenergize the circuit. Got to destination and on roll out with idle power engine quit! So now I have a light to indicate when the switch is OFF! Just another way of doing it. :-) Larry

For this reason, I have a simple warning light that illuminates when the power to PMAG has been switched off.

N941WR 06-29-2014 07:24 PM

Quote:

Originally Posted by Kevin Horton (Post 892945)
Did the internal alternator fail completely, so the engine would not run at any rpm if there was no ship's power? Or, did it have a partial failure so that it would generate power at some rpm higher than the normal 800 rpm cutout?

The internal generator was toast. Once I removed it, you could turn the shaft but it was "crunchy".

When running on the faulty ignition, it would operate fine as long as it had ship's power. Once I turned off the power to it but left it ungrounded, it died. (Step 5, below.)

I wired mine slightly differently:


This allows me to perform a preflight by doing this:


One other thing, with the jumper in, your timing starts at 26* BTC. Without the jumper, it is around 30* BTC. Depending on your engine, you may want to connect to it with a PC and the EICAD program and adjust the timing to match your engine / needs. If you make any adjustments with their program, you must leave the jumper out as that program only lets you change the "B" curve.

Canadian_JOY 06-29-2014 07:59 PM

A very good discussion was had on this topic in the following thread.
http://www.vansairforce.com/communit...t=p-mag+switch

With the right switch, a progressive transfer switch, one can achieve the desired result. This same switch could be used for the Lightspeed ignition, thus meeting your requirement for the same switchology between the two ignition systems.

Ironflight 06-29-2014 07:59 PM

No disrespect to anyone (and I mean that), but simple is almost always better! I have flown airplanes that had so many switch combinations that only the designer/builder could figure out how to operate them. I guess that is an effective anti-theft design at least.

I flew a couple of airplanes recently where the power and engine systems were far from intuitive - I had several minute briefings on each in order to understand them - and these were single-engine, simple airplanes. I don't see much need for that!

I want to be able to "ground" each mag for a mag check, and I want to be able to kill power to them. That requires a mag switch for each, and a circuit breaker if I am a minimalist. I've flown aerospace craft that were extremely complex because they needed to be - ours don't.

N941WR 06-29-2014 09:01 PM

Quote:

Originally Posted by Ironflight (Post 892991)
No disrespect to anyone (and I mean that), but simple is almost always better! I have flown airplanes that had so many switch combinations that only the designer/builder could figure out how to operate them. I guess that is an effective anti-theft design at least.
...
I've flown aerospace craft that were extremely complex because they needed to be - ours don't.

So true!

Someone I know purposely made his -6A overly complex because that was how he remembered his days in the USAF back in the 60's. There were guarded switches, buttons, etc. scattered all over the place.

If he every had an "issue' while flying, I think the stress would keep him from figuring anything out.

Keep it simple!

MarkW 06-30-2014 08:28 AM

Kevin,
I also like simple. I have two P-Mags. Standard ignition switch that grounds p-leads for testing on run-up. For testing P-Mag internal alt. I kill master power while above 1000 rpm. I run my P-mag power off a fuse under the panel. If need be I can pull the fuse for testing. I never saw a need for a tach. while testing the internal alternator.

Bevan 06-30-2014 12:34 PM

Quote:

Originally Posted by MarkW (Post 893112)
Kevin,
I run my P-mag power off a fuse under the panel. If need be I can pull the fuse for testing.

Keep in mind that Emagair suggests a resettable circuit breaker, NOT a fuse for power.
Bevan

DeltaTango 06-30-2014 01:17 PM

I used a 3 position switch for my master. The bottom position is "off". The middle position is ships power to everything except the Pmag. The full up position is ships power to everything including the Pmag. During the run up, I position the master to the middle position and then check each side of the ignition system. Upon completion of the check I reposition the master to full up to provide the Pmag with the ships power backup. As with all designs it's not perfect. It would be possible to forget and leave the master switch in the middle position thus causing the Pmags to shut off below 650-800 rpm. However that would normally occur post run up.

A friend had an idea of putting a push button type switch on the panel that would remove power to the Pmag during run ups. The procedure would be to turn one ignition off then press and hold the button. Should see no change in operation. Next turn the first ignition back on and then second ignition off and repeat the push button test.

Just a couple of ideas.

David

Larco 06-30-2014 01:22 PM

Quote:

Originally Posted by Bevan (Post 893207)
Keep in mind that Emagair suggests a resettable circuit breaker, NOT a fuse for power. You should contact them for an explanation but I believe it may have had to do with a crow bar over voltage circuit inside the P-mag.

Bevan

FYI Brad said that a slow blow fuse was just fine and they have worked fine for many hours in our RV. Larry


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