P-Mag switches

[RVG8tor]

I am getting my wiring started and have a question on how some of you with P-Mags wired your systems. There are two tests for th P-Mag as I understand things. One is just like a traditional magneto check, you turn off (ground the p-lead) and check for mag drop. The other check for a P-Mag is to turn off the 12v power to the P-Mag to check that the internal alternator keeps the magneto running. The check of the internal alternator does not seem like something that needs to be check each flight. I am considering just pulling the CB for each P-Mag to make this check rather than wiring a switch to serve this purpose.

What have others done with regard to this, I don't want to use a switched breaker, I will just add the switch if it is required? My thinking is to just pull the breaker. We pull breaker on the B-767 at the end of each flight to turn some equipment off while the plane sits between flights, so I don't think there is an issue of waring out a breaker. I am thinking a monthly check of the internal alternator would be sufficient. Thanks for any pointers.

[N941WR]

Mike,

You will still want switches so you can ground them. Also, don't forget that you will need to have some way to put them into ground service mode so you can set the the timing.

As for me, I used the Bob Nuckolls Z-33 drawing to wire mine. One note about this setup, Emag does not recommend it.

[Bob Ellis]

Originally Posted by N941WR

Mike,
As for me, I used the Bob Nuckolls Z-33 drawing to wire mine. One note about this setup, Emag does not recommend it.

Bill can you enlighten us to why Emag do not recommend it?

Bob
www.rv-8.co.uk
Rivetting fuselage skins

[RVG8tor]

Originally Posted by N941WR

Mike,

You will still want switches so you can ground them. Also, don't forget that you will need to have some way to put them into ground service mode so you can set the the timing.

As for me, I used the Bob Nuckolls Z-33 drawing to wire mine. One note about this setup, Emag does not recommend it.

I plan a switch which will control the spark part of the P-Mag, the switch just goes from the P-Mag terminal thru the switch to a ground. What I want to use a CB for is the 12V power from the power bus to the P-Mag. I talked to Brad, he though pulling the CB would work fine rather than have a switch since it does not need to be tested each flight. I was just wondering what others have done. To be clear there a two things which can use a switch, one is the function of the ignition to the plugs and the other is the function of the P-Mag internal alternator, you have to remove the 12V power to the P-Mag to check internal alternator. I propose to do the 12V check by pulling the CB that controls 12V power to the P-Mag. There are two tests, one controls spark to the engine and the other controls power to the P-Mag, which tests P-Mag internal power.

In my book Z-33 in for dual power path for a battery contactor, I don't see anything related to P-mags.

I think Bob N. recommended wiring the E-Mag to the always hot battery buss there by keeping power to the mags with the main bus off line. With P-mags the internal alternator takes care of back up power so I plan to wire mine to the main buss IAW the int install manual. There might be reason why they don't want it wired to the battery but I can't think of what it is, maybe the mags draw power even with things are off?

[Ken]

Mike,

I used on/off toggle switches for the P-Lead (kill switch). Then I used push buttons (normally closed/spring loaded to open) for the test switch. At run up just push and hold the appropriate button to check the internal alternator.

Ken

[N941WR]

Mike,

It sounds like you are on the right path. What you propose should work just fine.

Bob,

Emag did not like the way Nuckolls wiring schematic dropped power, they attributed it to some early lost timing issues. (Including the one I had.) Check with Emag for details. However, Emag has changed the software since then and I have left my wiring untouched and haven't had an issue in 250 hours. Should I lose a timing mark two things are going to happen; 1. The EICommander will let me know and 2. I'll identify the offending P-mag and shut it down.

For details of how I wired it, go to the Electrical Page of my web site and scroll to the bottom. There is also a diagram of how I do my preflight P-mag checks.

Originally Posted by RVG8tor

I am getting my wiring started and have a question on how some of you with P-Mags wired your systems. There are two tests for th P-Mag as I understand things. One is just like a traditional magneto check, you turn off (ground the p-lead) and check for mag drop. The other check for a P-Mag is to turn off the 12v power to the P-Mag to check that the internal alternator keeps the magneto running. The check of the internal alternator does not seem like something that needs to be check each flight. I am considering just pulling the CB for each P-Mag to make this check rather than wiring a switch to serve this purpose.

What have others done with regard to this, I don't want to use a switched breaker, I will just add the switch if it is required? My thinking is to just pull the breaker. We pull breaker on the B-767 at the end of each flight to turn some equipment off while the plane sits between flights, so I don't think there is an issue of waring out a breaker. I am thinking a monthly check of the internal alternator would be sufficient. Thanks for any pointers.

I used four separate SPST switches. Each P-mag has two switches: one for the 12V power and one for the spark (traditional P-lead). The power wires were fused at the battery bus. This way you can control any aspect of each P-mag independently.

I had read of a lot of instances where people tried to combine the switches for these things into multi-function devices and get fancy with the wiring, and many of these people had problems (at least initially). I opted to keep it simple, and I had absolutely no problems at all.

My run-up checks were simple as well:

1) Turn off the 12V power to both P-mags simultaneously. If something happens, investigate further. Otherwise you just tested internal power on both of them.
2) Turn off the spark (ground the P-lead) for each one independently. Check for RPM drop. If nothing happens, investigate further. Otherwise you just tested the spark making ability for each of them and confirmed no fouled plugs.
3) Turn the 12V power back on to both of them. You're done.

Obviously if test 1 or 2 above results in something unexpected, you'll have to delve deeper into the system by manipulating the switches in different ways. Personally, I never encountered any problems in 100 hours of operation.

[RV7ator]

I've used Nuckolls' progressive-on switchology and most recently the four spst switches E-mag wants you to use. The Nuckolls' deal works, but it lacks the flexibility to actually check P-mag performance.

"mag check" is simply grounding one then the other. All's well if no change. What you're doing is telling one mag to stop making a spark to proof the other mag, yet the internal electronics remain booted up. The Nuckolls method, or any instance of removing power, means the mag might reboot while the engine's running; it must boot, time, and spark immediately - a demanding task that E-mag doesn't support (yet it works out). But, by causing a reboot, you've invalidated your test of its prior boot, ad infinitum. You can't get around this with Nuckolls set-up.

The latest firmware uses the internal alternator full time once above idle speed, so removing ship's power shouldn't matter - maybe. Ask E-mag. But, there's no longer a need to kill ship's power. The P-mag is obviously working, running on its own juice, when it's partner isn't making spark.

Go the 4 spst route. It's really the simplest and most flexible in practice.

John Siebold

[RVG8tor]

Is this switch recommendation from Emag, I just looked over my install guide and this is not what I saw. I just received my guide in July when I downloaded the it and wonder where this is coming from.

As you say the pulling 12V power does not make sense since they are self powered a little above idle, seems like leaving the 12V power lead unswitched makes sense since pulling the CB would not do anything. So you have one switch per P-Mag and this switch just cut the spark for that mag, do I have this correct?

[N941WR]

Mike,

I would think you would still want to know if the ship's power is reaching the P-mags.

On starting I suspect you have both turned on, so if you have a bad wire/connector/whatever going to one, you won't know it unless you do a low RPM power test.

BTW, I have 113's in my ship, thus they only go to self power when they can't get any juce from the ship. For those reading this thread, that was changed with the 114's. The 114's self power all the time above idle, as pointed out earlier.