P-Mag Test Switches, necessary?

[RV8R999]

I don't think so. The P-lead switches ground the P-mag to prevent and/or allow spark generation. No matter what the source of power is to the P-mag if the P-lead (ignition) switches are off the P-mag will not spark. The test switches only provided the ability to disconnect aircraft power from the P-mag. For the lager models this test would need to be done at low RPM (below 900 rpm) otherwise as you state, the internal gen will maintain power to the p-mag.

[RV7ator]

Ken,

I may be making a mountain out of a mole hill, as this thread's starter doesn't address whether he has a P-lead switch or not; if he does, all's well, and I'll just back out of this thread 'cause I don't care what kind of switch/breaker/test switch is on the +12. Otherwise, my comment applies. Then, the picture of the pushbutton installation doesn't show a P-lead switch. Hopefully, there's one somewhere else on that aircraft.

So we agree. The test switch depicted is in the +12 line. If the P-mag is running on internal alternator, the only was to kill it is to ground the P-lead, or reduce power to idle (or less than 900 or so when airborne - good luck!). Brad at E-mag told me that the only thing the P-lead does is shut down spark; the electronics are unaffected.

John Siebold

[apkp777]

I am still trying to wrap my head around the P-mag principal of operation. Seems that when the P-mag detects a loss of ships power and the engine RPM is over 800, the P-mag internal alternator is activated thus self-powering. The test switches disconnect ships power as would pulling the circuit breaker. There would be no difference in the effect on the P-mag. If the P-mag suffered an internal fault the test switches or circuit breaker would kill ships power and isolate the mags from ship power. The P-lead should kill the P-mag through the ignition switch. You can kill Left or Right P-mag selectively through the ignition switch. Am I mis-understanding this. The ignition switch must provide the isolation of run-away P-mag otherwise there would a major design flaw.

[RV8R999]

from the P-mag perspective you are correct in that if breakers and test switches are in series then it wouldn't matter which one you used to disconnect power to the P-mag. The issue then becomes one of reliability of using breakers as switches. The later model P-mags (114s) above 800-900rpm are always running on the internal gen even if aircraft power is still available.

And I agree with the earlier post, if P-lead switches are not installed then spark would occur no matter what you did above 800-900 rpm (provided the internal gen was functioning). Although this set-up would be contrary to the installation instructions and am not sure why anyone would do that?

[apkp777]

Still comes back to how often do you need to test the p-mag. Here is the endurance info for model 7274 breaker from www.klixon.com:

2500 cycles ................................. 120 VAC, 400 Hz Inductive
5000 cycles ................................. 120 VAC, 400 Hz Resistive
2500 cycles ................................. 30 VDC, Inductive
5000 cycles ................................. 30 VDC, Resistive
5000 cycles ................................. Mechanical, no load

Assuming the worst case you would be able to use the breakers about 2500 times before rated failure (probably get 5000). Probably just change the breakers at engine overhaul.

[RVG8tor]

If you look at my picture again you will see there is one toggle and one push button test switch for each mag. The toggle controls P-lead (spark) and the push button is a momentary switch to remove ships power for the internal alternator check.

If I need to disable a mag due to lost timing the I can turn it off with the toggle. I cam also permanently remove 12v ships power bu pulling the respective CB.

Funny I thought my labels spelled out the operation clearly but then I guess you have to understand how the P-Mag works.

Cheers

Originally Posted by RV7ator

Ken,

I may be making a mountain out of a mole hill, as this thread's starter doesn't address whether he has a P-lead switch or not; if he does, all's well, and I'll just back out of this thread 'cause I don't care what kind of switch/breaker/test switch is on the +12. Otherwise, my comment applies. Then, the picture of the pushbutton installation doesn't show a P-lead switch. Hopefully, there's one somewhere else on that aircraft.

So we agree. The test switch depicted is in the +12 line. If the P-mag is running on internal alternator, the only was to kill it is to ground the P-lead, or reduce power to idle (or less than 900 or so when airborne - good luck!). Brad at E-mag told me that the only thing the P-lead does is shut down spark; the electronics are unaffected.

John Siebold

[apkp777]

Originally Posted by RV7ator

Ken,

I may be making a mountain out of a mole hill, as this thread's starter doesn't address whether he has a P-lead switch or not; if he does, all's well, and I'll just back out of this thread 'cause I don't care what kind of switch/breaker/test switch is on the +12. Otherwise, my comment applies. Then, the picture of the pushbutton installation doesn't show a P-lead switch. Hopefully, there's one somewhere else on that aircraft.

So we agree. The test switch depicted is in the +12 line. If the P-mag is running on internal alternator, the only was to kill it is to ground the P-lead, or reduce power to idle (or less than 900 or so when airborne - good luck!). Brad at E-mag told me that the only thing the P-lead does is shut down spark; the electronics are unaffected.

John Siebold

Yes, I have a standard ACS ignition switch. And you're right there would be no-way to kill a runaway P-mag without.

[apkp777]

Originally Posted by RVG8tor

If you look at my picture again you will see there is one toggle and one push button test switch for each mag. The toggle controls P-lead (spark) and the push button is a momentary switch to remove ships power for the internal alternator check.

If I need to disable a mag due to lost timing the I can turn it off with the toggle. I cam also permanently remove 12v ships power bu pulling the respective CB.

Funny I thought my labels spelled out the operation clearly but then I guess you have to understand how the P-Mag works.

Cheers

Your panel looks great. And yes, your P-mag set up is textbook.

[N941WR]

Originally Posted by apkp777

I am still trying to wrap my head around the P-mag principal of operation. Seems that when the P-mag detects a loss of ships power and the engine RPM is over 800, the P-mag internal alternator is activated thus self-powering. The test switches disconnect ships power as would pulling the circuit breaker. There would be no difference in the effect on the P-mag. If the P-mag suffered an internal fault the test switches or circuit breaker would kill ships power and isolate the mags from ship power. The P-lead should kill the P-mag through the ignition switch. You can kill Left or Right P-mag selectively through the ignition switch. Am I mis-understanding this. The ignition switch must provide the isolation of run-away P-mag otherwise there would a major design flaw.

Tony,

This is true for the 113 series. The 114's switch to self power whenever they produce enough power. Usually above 800 rpms. Check the electrical page of my web site for how I test my 113's.

For 114's here is how I would test them.
Power on both.
1800 rpm
Turn left off, back on, turn right off. Note rpm drop.
With only the left mag on throttle back until below 800 rpm. (You just tested both internal and external power on the left.)
Turn the right on and left off while still below 800 rpm. Bring it up above 1000 rpm. (You just tested the other Pmag on both ship's and internal power.
Turn on the other mag and go fly.

[apkp777]

Originally Posted by N941WR

Tony,

This is true for the 113 series. The 114's switch to self power whenever they produce enough power. Usually above 800 rpms. Check the electrical page of my web site for how I test my 113's.

For 114's here is how I would test them.
Power on both.
1800 rpm
Turn left off, back on, turn right off. Note rpm drop.
With only the left mag on throttle back until below 800 rpm. (You just tested both internal and external power on the left.)
Turn the right on and left off while still below 800 rpm. Bring it up above 1000 rpm. (You just tested the other Pmag on both ship's and internal power.
Turn on the other mag and go fly.

Bill - Is there any noticeable engine indication when the P-mag switches from self to ships power?

Are you using "test" switches? Your procedure above looks to be a fully functional test of the P-mags with no test switch.