Pilots flying w/ P-mags ? Do you check the internal generator prior to each flight?

The P-mags are a great ignition and with the ability to seamlessly transfer between ship?s power and their internal power, they have brought a number of people home safely after the ship?s electrical system failed.

I?m curious how often pilots test their P-mags for operation under ship?s and their internal power. This test can be done by pulling the breaker, if wired according to E-mag Ignition?s wiring diagram, or, if running 114 P-mags, by turning off the P-mags one at a time and letting the idle drop below 800 RPM, at which point the 114?s will switch back to ship?s power. (113 series P-mag run off of ship?s power, regardless of RPM, unless they detect a loss of ship?s power.)

Hi Bill

Late getting to this poll but I check mine every flight after start but use the test in the manual at constant RPM whilst the engine warms up...

"You can check the internal alternator operation on the P model during a ground run-up (900+ rpm) by switching to the P model ignition and cutting buss power (not the p-lead switch) at the breaker. If the built-in alternator is working, the engine will continue to run. If it is not working, the engine will quit"

Hi Bill,

I check my everytime by manually cutting the ships power to each one during the standard mag check. So, my mag check has 4 steps to do, not just 2. Fist the P leads one at a time and then the ships power one at a time. I have also killed the ships power at idle to check the low end of the P mags ability so I know they are working.

Not using P-mags, but I voted anyway. My Precision Eagle EMS is tested off of battery power only after every engine start. I have two batteries, and the system will consume 1 amp per side at WOT. So after the engine start, I shut down the alternators and all power to ensure the dual back up batteries are keeping my electronic ignition going.

pmccoy said:

Not using P-mags, but I voted anyway. My Precision Eagle EMS is tested off of battery power only after every engine start. I have two batteries, and the system will consume 1 amp per side at WOT. So after the engine start, I shut down the alternators and all power to ensure the dual back up batteries are keeping my electronic ignition going.

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Peter, do you change out your backup batteries every "X" years? How do you know that your backup battery will last long enough to fly for 15, 30, 45, 60, whatever minutes?

Peter, do you change out your backup batteries every "X" years? How do you know that your backup battery will last long enough to fly for 15, 30, 45, 60, whatever minutes?

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Bill, yes I plan to switch out one battery per annual. That will keep both batteries at most 2 years old. As for how long the system will run... I have two alternators and two batteries. If I am down both alternators (Plane Power 60, B&C 20) and just running on battery, you can bet I would have pushed the nearest airport button by then. At max 2 amp draw with two batteries, I should be able to go longer then required. I also have an emergency E-bus that just puts power to the primary EFIS, radio, boost pump and flaps. All other electrical is turned off.

I am still in phase 1 testing with dual P-mags so I have not developed a habit yet. I understand that this portion of the P-mag is so reliable that I will probably test once a month.
I have problems doing a standard mag check since with dual P-mags I usually don't get a rpm drop at all. I look for a small increase in EGT then when I put the mag back on line it drops again.

Just to let you know about my screw up with a pmag so no one repeats it. My pmags had been flawless for 120 hours until one developed an rpm oscillation.
I took both off and sent them to Brad at pmag to look at them. He found the problem and had a one day turn around. Fantastic service. Thanks Brad!

He found a significant anomaly was the drive gear. It appears
that at installation the drive gear was positioned with the woodruff key out
of alignment with the slot on the gear taper. As the gear was drawn down
onto the shaft by the castle nut, the woodruff key was deformed and
partially conformed to the space available. The key was substantially
flattened, but still raised well above the tapered conical shaft shape. In
short, it was not locked to the shaft and was likely able to rotate -
causing a timing shift. Initially, it might have been secured by friction
alone, but as it eventually worked loose, we can imagine it finding a degree
limited movement back and forth (i.e. oscillation). The gear could not have
been centered on the shaft because of the raised woodruff deformation, so
it's somewhat remarkable it operated at all, or did not self-destruct
shortly after going into service.

Install procedure check

Did Brad suggest a way to validate the installation of the gears,like backing the nut &washer off to see if the key is seated? I know there is a variance in pressure if you blow in different hoses setting the timing.I'm glad to hear this was caught on the ground and not in the air.
RHill

I just put mine on and it appeared to go on without a problem but I will have to take a closer look. My problem is that I can't get the gear off my slick mag. I have tried several pullers and even put it in a press and it won't budge.