Intermitent P-MAG problem

Hi everyone,

I've noticed an intermittent problem on one of my P-MAG>
My setup is: RV-7 with Aeropsort Power IO375, dual P-MAGS and VP-X Sport for the electrical system.
I've also installed two switches on my panel to test the self-power function of the P-MAG and I do the test before each flight.
My procedure:
- 1800 RPM
- both P-MAG power switches OFF (removes ship power to both P-MAGS), P-MAGS are now self powered on internal system.
- One P-MAG switch (P-Lead) OFF, observe RPM drop (typically 50-70 RPM for me), P-MAG switch (P-Lead) ON
- Repeat for other P-MAG
- Both P-MAG power switches ON.

Recently I noticed that my Left P-MAG is intermittently not producing ignition during this test. RPM drop OK with Power switch ON.
I also noticed that the RPM indication on my Dynon Skyview is jumping instantaneously to 2000RPM when this happens, although the engine is cutting off. Note that the RPM indication comes from the P-MAGS.

This problem is intermittent and happens with engine HOT.
Yesterday I did a flight, all good before takeoff. I did the test again after landing and the problem was there.

For troubleshooting I'm thinking to swap P-Mags (Left to right and right to left, if the problem switches side it must be a P-MAG problem, if not it must be an electrical problem but I can't think of what it could be...

Any help from specialists please...

Thank you,

Alain

Just an idea....

How's your blast cooling? Have you checked the temperature sticker on the PMag? Maybe this is a problem that develops when then PMag overheats?

I also have Dual PMags, but never had this problem. I'm curious to help you find answers.

Temp problem

Further to my above message, I now have done the "Pull through test" recommended by emagair and that test was good.

Then I removed my left P-MAG and saw that the thermal trigger sticker has turned grey, which means that the temperature around the P-Mags has exceeded 200 deg F... Same on the right P-Mag. Not good

This leads me to another question: What are you guys doing to keep temperatures inside the cowlings, aft of the baffles at a reasonable level?

I believe that inflight it's OK and the temperature peaks after shutdown on hot days.
I'll keep the habit from now on to open the oil filler door on top of the cowlings after shutdown to keep air flowing in that area.

Anything else you guys would recommend??

Thank you.

Alain.

Send it to Brad at pMag to test/fix it. This is cheap (other than whatever shipping will cost from France). Also good to send it in if you have not updated the firmware.

Carl

Jvon811 said:

Just an idea....

How's your blast cooling? Have you checked the temperature sticker on the PMag? Maybe this is a problem that develops when then PMag overheats?

I also have Dual PMags, but never had this problem. I'm curious to help you find answers.

Click to expand...

Yes I have a blast tube on each P-MAG as recommended by Emagair.

Will overhaul P-Mags

Carl Froehlich said:

Send it to Brad at pMag to test/fix it. This is cheap (other than whatever shipping will cost from France). Also good to send it in if you have not updated the firmware.

Carl

Click to expand...

I will do that...

But now that I know that the temperature exceeded 200F I will have to find a fix for that issue.

Anyone has been faced with this?

If as I suspect the temperature peaks after shutdown installing cowl flaps will not solve that problem as hot air is trapped inside the cowling and has no place to go. As the P-Mags are above the exhausts I think it can get quite hot in there...

Opening the oil door after shutdown could improve things slightly by creating an air flow from bottom to top (hot air rising and exiting through the oil door opening) but I'd like to find a more "permanent" fix...

I'll keep thinking, in the meantime thank you all for your help, keep replies coming

How many hours do you have on your p-mags?
It seems to me that your failure is coming from the internal generator, not the delicate electronics that need to stay below 200F.
I am not sure it is possible to keep them below 200F once the engine is shut down or during post flight taxi; particularly on a hot day.
Send the suspect mag in for service.

pa38112 said:

How many hours do you have on your p-mags?
It seems to me that your failure is coming from the internal generator, not the delicate electronics that need to stay below 200F.
I am not sure it is possible to keep them below 200F once the engine is shut down or during post flight taxi; particularly on a hot day.
Send the suspect mag in for service.

Click to expand...

I have about 130 Hours block on the plane/engine/P-Mags.

I Called Brad at Emagair, he confirmed what I thought: the internal generator is failing.

The light grey colour on the thermal sticker seems to be not too bad and not the issue in this case, this indicates temperatures barely reached 200F.

As suggested by Brad I will send both P-Mags back to Emagair for a free servicing on both units. Great service, thanks a lot Brad.

For now my P-Mag is back on the engine and P-Mag test all good !
Tomorrow (it's almost night here in France now) I'll do a short flight to confirm the problem when the engine is hot after shutdown.

Thanks for all your replies.

Alain.

1 - The generator have internal diodes that can fail if exposed to very high temperatures.

2 - If you have both magnetos feeding the SkyView and one fails, then the SkyView will switch the RPM display to the other mag so you may see a different value.

I agree, it sounds like the internal generator has failed.

As for the temperature issue, most high temperatures are recorded after the engine is shutdown and the aircraft is parked, say for fueling.

You can add additional thermal stickers to see what temperatures you are dealing with.

That or install an EICommander, which can report the maximum and current temperatures.

Remember, the blast tubes are supposed to be aimed at the neck of the P-mags, not the rectangular section.

FWIW it may help to mention blast tube diameter - I use 3/4” inside diameter & no issues with cooling in 550+ hrs to date

Alain,

I had forgotten about this thread until this evening.

www.vansairforce.com/community/showthread.php?t=88012

Take a look at post #8 on the first page and post #12 on the second page. (I can't remember how to point you directly to those posts.)

They highlight the temperature rise and fall after engine shutdown.

N941WR said:

I agree, it sounds like the internal generator has failed.

As for the temperature issue, most high temperatures are recorded after the engine is shutdown and the aircraft is parked, say for fueling.

You can add additional thermal stickers to see what temperatures you are dealing with.

That or install an EICommander, which can report the maximum and current temperatures.

Remember, the blast tubes are supposed to be aimed at the neck of the P-mags, not the rectangular section.

Click to expand...

I'm thinking to install some kind of temp probes in the engine compartment to monitor the temps in the cowling.

jakej said:

FWIW it may help to mention blast tube diameter - I use 3/4? inside diameter & no issues with cooling in 550+ hrs to date

Click to expand...

Blast tubes are 3/4", and are directed at the round part, as recommended by Emagair

N941WR said:

Alain,

I had forgotten about this thread until this evening.

www.vansairforce.com/community/showthread.php?t=88012

Take a look at post #8 on the first page and post #12 on the second page. (I can't remember how to point you directly to those posts.)

They highlight the temperature rise and fall after engine shutdown.

Click to expand...

Thanks for that, I had a look ans some interesting posts there, specially the ones talking about hooking up a temp sensor to the Dynon Skyview