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Pmag internal generation check procedure

Larry DeCamp

Well Known Member
My Pmags are powered from the main buss ( master switch). To check internal gen function, I assured 1,000 RPM, switch off the master and listen, then turn on the master. This reboots any functions already powered from the master :mad:

There are numerous options offered here on VAF for switches and push buttons to interrupt power for this confirmation, and most draw some objection for complexity, additional single point failure etc.

A wise contract pilot suggested to me after I discovered a dead mag at run up before take-off, that he did mag checks taxing to the hanger so he knew in advance of "show time", if maintenance was required. So I have amended my protocol, hope this is useful:
Radios,avionics etc off.
1,000 or more RPM for you 100LL fans to clean the plugs.
Master off
Mag check
Mixture cutoff
 
I have mine off the master also but I have 2 individual breakers, I do the same except instead of powering the master down I just pull the breaker for the pmags . Very simple
 
Power source

I believe after a certain firmware level the Pmags are only powered off your bus for start or any time the RPM falls below the internal generator limit. As long as you have sufficient RPM the Pmags are powered internally with external (bus power) as a backup. The test procedure on mine has me turn off power to the bus while the engine is running on the ground (1000 RPM works) and then slowly reduce RPM until the ignition fails causing the engine to quit making note of this RPM value. Pmag says that while this value may be above your ground idle RPM, you will not be able to get RPM this low in flight (without a stall).
 
I have found that following the manufacturers recommended installation process works best. So I installed a normally closed push button switch right after the circuit breaker. I test the power before very flight and it works great.

E-mag%2520P%2520Model%2520wiring.JPG


:cool:
 
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I have mine powered directly from the battery bus (not through the master switch) through a fuse. During run up, after I check the P lead connections, I then shut the both power switches to the pmags off. If it continues to run (and it always does), then I know the internal generators are working. Yes, if I left one or both of my pmag power switches on, I'd come back to a dead battery even if the master is off, but I like the simplicity of going directly to the battery
 
Stein wired my p-mags with temporary interrupt switches for ship’s power. 1850 rpm, right mag with key switch, right interrupt switch, key back to both, left mag with key switch, left interrupt switch, back to both. Easy. I only check the minimum rpm operation once a year or so. My check sequence was suggested by the P-mag guy at Oshkosh. MED
 
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I plan to use the same arrangement as Gailn. The test switches (dual PMAGs) are normally closed and only opened as part of my preflight checks. That arrangement makes it pretty simple. Some just pull the breaker but I like the switch better.
 
Is the "Test Switch" left open when the aiplane is shut down?
If you are asking about my arrangement, the test switch is spring loaded to always be closed (normal closed). Power to the magnetos is only removed when I push and hold the button down, so if I don't do anything the magnetos always have power.

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It is impossible for me to unintentionally switch the power off.

:cool:
 
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Clean

If you are asking about my arrangement, the test switch is spring loaded to always be closed (normal closed). If I don't do anything, power is always supplied to the magnetos. Power to the magnetos is only removed when I push and hold the button down.

2844.jpg
e7e2.jpg


It is impossible for me to unintentionally switch the power off.

:cool:
Pretty clean way to do it, Galin. I don't have a key switch, so I just used toggle switches, but with a key switch, this looks nice, and is super clear for the next pilot.
 
VP-X example

I do my P-mag checks using the VP-X menu on my Dynon Skyview EFIS. No external switches needed to accidentally hit.
I just go ENGINE->VP-X, scroll down to Pmag Left ON/OFF, then next to Pmag Right ON/OFF. Easy and quick before every flight to check. I can run the idle down lower than 850 RPM and usually turning one P-mag off will get an indication of roughness showing that the internal power is not being sufficiently generated.
 
Functionally ok, but I assume you picked a switch that has adequate rating, silver contacts, etc.

Many of these push button switches are cheap China junk.

For me a pull breaker on each pMag is simple, and does both the function of the breaker as well as a way to test the internal pMag generator from time to time.

Carl

If you are asking about my arrangement, the test switch is spring loaded to always be closed (normal closed). Power to the magnetos is only removed when I push and hold the button down, so if I don't do anything the magnetos always have power.

2844.jpg
e7e2.jpg


It is impossible for me to unintentionally switch the power off.

:cool:
 
Functionally ok, but I assume you picked a switch that has adequate rating, silver contacts, etc.

Many of these push button switches are cheap China junk.

For me a pull breaker on each pMag is simple, and does both the function of the breaker as well as a way to test the internal pMag generator from time to time.

Carl
Hence the rating of 100,000 actions MTBF. Since it is a normally closed switch even IF it fails, it is designed to fail in the closed position which keeps power to the magnetos forever. You will discover the failure on your next magneto power check.

A pull breaker is ok but they are not designed to be pulled and reset on a continuing basis, like you should be doing before every flight in this application. I try to use things to do what they are actually designed for. It enhances component reliability. YMMV

Pretty clean way to do it, Galin. I don't have a key switch, so I just used toggle switches, but with a key switch, this looks nice, and is super clear for the next pilot.
IMHO as long as they are spring loaded toggle switches, like bkervaski posted, then that is also a great way to go. Eliminates the possibility of unintentionally leaving the switch in the OFF mode, which I know I would eventually wind up doing.

:cool:
 
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