Flyguytki

Flyguytki

Well Known Member
Below are the VP-X instructions on wiring P-Mags, My question is for Scenario 2:

If I am using Toggle Switches for the Mag Switches they would be inline of the 12V to the P-Mags, So what would the P-Lead Switches be? I had always interpreted a P-Lead switch as the Primary on and off switch so in this Scenario why is there both a P-Lead and an On and off switch?

Currently I have it wired like Number 1 but interpreted it wrong thinking the P-Lead switch would power it but apparently not.

Any help would be much appreciated!


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HERE WE GO SEAHAWKS!!!!!
 
The power input to the P-Mag is independent of the P-lead on the P-Mag.

The purpose of the switched power for the P-Mag is so you can test the built in alternator function.

The P-lead works just like any mag. Ground it and it prevents the P-Mag from firing.
 
The "P" lead is what grounds the P-mag and stops it from firing. The power switch provides power for spark before the P-mag comes up to speed (approx 900 rpm). Once the P-mag is up to speed it no longer requires power because it has an internal generator so to kill the P-mag is must be grounded (P lead grounded like conventional mag). Hope this helps.
 
Ok So If Im reading this right then I am still ok, the only thing I am missing is testing the internal alternator.

If I have read this right, the entire post came about because I was doing an volt test on the P-Mag Plug, and the #5 wire (12V Power) was always showing 12V, This is a good thing, and will be grounded/turned on internally when the P-lead switch is thrown. Are there any recommendations on how to test them before the first engine start?

Thanks again!
 
Pre Flight checks

I wonder if youd be better served with a discreet circuit for the each ignition and leave the VPX out of it. I like to pull the breaker and know its running on its internal alternator as part of the preflight. If you have to dig around in the menus to do that it might be something to consider.
Tim
 
Flyguytki said:
Ok So If Im reading this right then I am still ok, the only thing I am missing is testing the internal alternator.

If I have read this right, the entire post came about because I was doing an volt test on the P-Mag Plug, and the #5 wire (12V Power) was always showing 12V, This is a good thing, and will be grounded/turned on internally when the P-lead switch is thrown. Are there any recommendations on how to test them before the first engine start?

Thanks again!
Click to expand...

I think there is still some misunderstanding...

The #5 pin will be hot when the VP-X is making it hot. Either you have the VP-X configured to turn on that pin when you turn on the master (Always On) or you have it programmed to come on when you ground one of the VP-X's switches.

If you have it set to Always On, you will need to use the VP-X menu on the EFIS to turn it off when you want to test the internal alternator of the P-Mag.

If you have it configured to turn on with one of the VP-X's switches, it will work just like a power on/off switch. Turn it off to test the internal alternator of the P-Mag.

The P-Lead switch is a totally separate pin and switch. If you ground it, the P-mag won't fire. If it is open, the P-Mag is hot and will fire if it has power to Pin 5 or it is operating on its internal alternator (above ~650-750 rpm).

My new panel is wired like #3 in the example but I only have 1 P-Mag. The advantage to this method is that you don't have to use the EFIS menu to turn the pin #5 power off to the P-Mag to test its internal alternator. I just flip the switch.

Pin #4 is hooked up and used just like any P-Lead ever was. Use it during your traditional "Mag Check".
 
tim2542 said:
I wonder if youd be better served with a discreet circuit for the each ignition and leave the VPX out of it. I like to pull the breaker and know its running on its internal alternator as part of the preflight. If you have to dig around in the menus to do that it might be something to consider.
Tim
Click to expand...

There is no reason to leave the VP-X out unless you just want to. The VP-X can be used to control the power to the P-Mag either with a switch or by the EFIS menu.

The internal alternator check is not typically done on every flight so even using the EFIS menu option, this is not that big of a deal.

Every EFIS is different in how they implement the VP-X control screen but most of them are really easy and fast to use so occasionally controlling a device that does not have its own dedicated switch is pretty easy.
 
I can tell you that using the VP-X and Skyview with P-Mags (per figure #1) is very simple. Do your runup just like a mag, looking for the proper RPM drop when each P-lead gets grounded.

Then, to test the internal P-Mag alternator:
Press the ENG button
Press the VP-X button
Rotate knob to select which P-Mag you want to test
Press OFF and observe no RPM drop (if the internal alternator is working correctly)
Press the ON button
Rotate the knob to the other P-Mag and repeat

Very simple, and going to the VP-X page during the runup allows you to see that the main electrical alternator is outputting power and the battery is charging correctly.

Not sure if the other EFIS systems control the VP-X in the same manner.
 
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