PMAG Problem

[NROBB]

Originally Posted by N941WR

With the shorting described by the OP, the system was being grounded, which puts it in setup mode. (Powered but grounded is setup mode.)

Allow me to backtrack a little on this; my understanding of the OP is that his power line was the issue, meaning voltage spikes and/or high rate of off/on situation on the +ve line coming out of the Alternator.

This should not affect the p-lead to become grounded. So IMHO, his PMag could have been powered and unpowered at a high rate in a short period of time along with voltage spikes on the line (depending on the quality of his battery acting as a buffer) but the P-lead would not be grounded. So its more like (Powered & Unpowered with ungrounded P-lead)

If setup mode can't be entered with p-lead ungrounded, so my first guess would be that its not the Setup mode + MAP line that changed the timing but could have been circuit leak due to the spikes that changed the value of the timing at the EEPROM register. Would have been interesting to read the value stored after this incident. If its circuit isolation issue, the value could be random or the max HEX value that register can store.

If anyone comes forward with a timing issue for V40, depending on their luck of having similar alternator line failure or spikes then a preventive hardware solution is called for maybe by using a small circuit in series with the power line feeding the PMag to cut spikes and regulate/clean up the line.

Rob

[Brantel]

Originally Posted by ChiefPilot

Frankly, I'm skeptical that such a failure could cause the timing issue and think maybe switchology might have been involved otherwise it's not clear how a powered-and-ungrounded PMag could revert it's timing.

Originally Posted by NROBB

Allow me to backtrack a little on this; my understanding of the OP is that his power line was the issue, meaning voltage spikes and/or high rate of off/on situation on the +ve line coming out of the Alternator.

This should not affect the p-lead to become grounded. So IMHO, his PMag could have been powered and unpowered at a high rate in a short period of time along with voltage spikes on the line (depending on the quality of his battery acting as a buffer) but the P-lead would not be grounded. So its more like (Powered & Unpowered with ungrounded P-lead)

If setup mode can't be entered with p-lead ungrounded, so my first guess would be that its not the Setup mode + MAP line that changed the timing but could have been circuit leak due to the spikes that changed the value of the timing at the EEPROM register. Would have been interesting to read the value stored for after this incident. If its circuit insolation issue, the value could be random or the max HEX value that register can store.

If anyone comes forward with a timing issue for V40, depending on their luck of having similar alternator line failure or spikes then a preventive hardware solution is called for maybe by using a small circuit in series with the power line feeding the PMag to cut spikes and regulate/clean up the line.

Rob

I also can't reconcile the theory that the P-Mag was grounded or somehow forced into setup mode with the supporting statements. How can a failure of an external alternator control wire cause the P-Mag's P-Lead equivalent to become grounded?

We must also keep in mind that anytime the P-Mag is above 800-900 rpm and the internal alternator is working properly, the P-Mag is self powered. My understanding is that the P-Mag uses a simple diode isolation circuit between the two power sources and the internal alternator is designed to be the winner in a typical experimental airplane's power system. The only thing I can think of would be abnormal random voltage "spikes" hitting the P-Mag (not sags or no power) at a voltage "higher" than that of the internal alternator but this does not explain how the P-Mag could enter setup mode....

Bet there is more to this story and I am not sure that V40 is the pixie dust that prevents whatever the true failure mode ends up being.

[6 Gun]

Yes Brian that's my take when the OP is at 7500 in cruise and Emag on own power what happens when you turn landing light on it causes a flux?
Bob

[Carl Froehlich]

Originally Posted by 6 Gun

Yes Brian that's my take when the OP is at 7500 in cruise and Emag on own power what happens when you turn landing light on it causes a flux?
Bob

Bob,

A landing light flux? As in photon flux or what?

Carl

[Canadian_JOY]

Flux as in expanding and contracting magnetic field around the power-carrying wire. Start arcing a contact and you're getting something like random Alternating Current so those fields could be changing rapidly. So yeah, flux, of one sort or another.

Now where did I put that flux capacitor?!?! *grin*

[Raymo]

For the benefit of future readers and me:

Did the PMAG have the latest software (40) that *should* have precluded this issue?

Dual PMAGS in my future...

[Jesse]

It is my understanding that Pmags always use ship's power until it loses it and then reverts to the internal alternator.

[Toobuilder]

Originally Posted by Jesse

It is my understanding that Pmags always use ship's power until it loses it and then reverts to the internal alternator.

The 113's yes, the 114's no.

The 114's alternator is primary once up and running.

[Carl Froehlich]

Originally Posted by Jesse

It is my understanding that Pmags always use ship's power until it loses it and then reverts to the internal alternator.

Not correct according to the pMag install manual:

"Series 114 ignitions will transition off of aircraft power (and onto internal power) as the internal power rises. Somewhere around 1200 to 1500 rpm P-model ignitions should be operating totally on internal power. At this point, internal power is the ignition?s primary power supply and the aircraft power is the backup. Transitions to and from the aircraft power supply are managed automatically by the ignition. There is no need for operator action of any kind. If you loose external power, your P-model ignition is capable of providing emergency power down to 900 rpm, and sometimes less."

Carl

[thinkn9a]

I am one of those "in the zone", and most likely would not have looked until condition inspection, which is still some months off. Hopefully now that it is flagged, no one else will have to find out "the hard way"

I know Doug flags notes/bulletins fron Van's, maybe that can broaden out, or a special area could be created, and hold info for a few months, getting input from forum.