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P-Mag questions

wirejock

Well Known Member
I'm installing two P-Mags. IO-360-M1B

Question 1. Top plugs to one mag and Bottom to the other or is there any reason to run a split set up with tops of one side and bottoms of the other to each mag? Sounds weird to me but I ask a lot of stupid questions.

E-mag instructions say..."2. Setup Mode is entered by turning 12 volt bus power ON, WHILE the p-lead switch is OFF (grounded). If the LED is not lit up, you are not in Setup Mode."
Some of us run the Stein Air Honeywell 2TL10-50K, ON/ON/MOM Ign/P-Mag Locking Test Switch. The switch will work great for typical flying needs, but it doesn't have a position for power on while the P-Lead is shorted to ground. I can imagine several ways to accomplish the task. One is to fabricate a test plug for service. The other is to extend the wires into the cockpit under the panel and terminate with a D-sub. A mating D-sub is installed for flight operations with the jumper (if used). The mate is removed and a serial to computer cable plugged in for service. The serial cable has the connections for grounding the P-mag. That solution is great for service but introduces potential connectivity issues that could lead to an energized P-mag.
How do others do it?
 
A locking toggle ignition ON/OFF switch and a pull breaker.

To test the pMag generator, start the engine and open the breaker. Test when you want but I suggest every flight is overkill. I’ve never had a pMag generator test fail in close to 20 years.

Carl
 
A locking toggle ignition ON/OFF switch and a pull breaker.

To test the pMag generator, start the engine and open the breaker. Test when you want but I suggest every flight is overkill. I’ve never had a pMag generator test fail in close to 20 years.

Carl

My panel is built. Switches mentioned are installed. Testing the internal generator is not a problem. Flip the switch to "Test" (momentary).
The question is how do folks with my setup put the mags into "Program" mode.
 
I'm installing two P-Mags. IO-360-M1B

Question 1. Top plugs to one mag and Bottom to the other or is there any reason to run a split set up with tops of one side and bottoms of the other to each mag? Sounds weird to me but I ask a lot of stupid questions.

E-mag instructions say..."2. Setup Mode is entered by turning 12 volt bus power ON, WHILE the p-lead switch is OFF (grounded). If the LED is not lit up, you are not in Setup Mode."
Some of us run the Stein Air Honeywell 2TL10-50K, ON/ON/MOM Ign/P-Mag Locking Test Switch. The switch will work great for typical flying needs, but it doesn't have a position for power on while the P-Lead is shorted to ground. I can imagine several ways to accomplish the task. One is to fabricate a test plug for service. The other is to extend the wires into the cockpit under the panel and terminate with a D-sub. A mating D-sub is installed for flight operations with the jumper (if used). The mate is removed and a serial to computer cable plugged in for service. The serial cable has the connections for grounding the P-mag. That solution is great for service but introduces potential connectivity issues that could lead to an energized P-mag.
How do others do it?

Question #1 - if you wire one mag to the top and the other to the bottom, your mag RPM drop will be materially different when doing your mag check. Assuming both mags are running properly, it probably doesn't matter, but Lycoming says to stagger them.
 

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My panel is built. Switches mentioned are installed. Testing the internal generator is not a problem. Flip the switch to "Test" (momentary).
The question is how do folks with my setup put the mags into "Program" mode.

Note that you are not installing the pMag per the installation instructions. The pMag “kill” switch should not be on the pMag power switch - as you have discovered. The diagram on page 26 is germane.

I suggest you keep it simple. A locking toggle for ignition kill, and a pull breaker for power. Power is applied when whatever buss you are feeding the breaker has power. Set timing with the kill switch off, and power to the pMag.

While I’m sure you can come up with some work around with jumpers and such, I would think the simple approach would be best.

Carl
 
SteinAir

Note that you are not installing the pMag per the installation instructions. The pMag “kill” switch should not be on the pMag power switch - as you have discovered. The diagram on page 26 is germane.

I suggest you keep it simple. A locking toggle for ignition kill, and a pull breaker for power. Power is applied when whatever buss you are feeding the breaker has power. Set timing with the kill switch off, and power to the pMag.

While I’m sure you can come up with some work around with jumpers and such, I would think the simple approach would be best.

Carl

I'm using the Stein Air method. I had the discussion with Brad as well.
LT-005-DPDT-3-POSITION-LOCKING-P-MAG-SW-Rev-A.pdf
 
Plug wiring

Question #1 - if you wire one mag to the top and the other to the bottom, your mag RPM drop will be materially different when doing your mag check. Assuming both mags are running properly, it probably doesn't matter, but Lycoming says to stagger them.

Very helpful. THX
 
Hey Larry. Traditionally mags have been set up to fire top plugs on one side and bottom plugs on the other side because of the tendency for bottom plugs to foul more readily.

I.e. if a mag fails the you only lose 1/2 of your “good” top plugs.

As I’m sure you know, pmags have a much hotter spark and I believe are also a wasted spark system. Those things are popping off like crazy all the time so it’s hard to imagine there would be much opportunity for fouling unless a guy was just completely incompetent in leaning but I don’t really know.

Having said all that, I’m still planning to wire mine in traditional lycoming criss cross fashion because even though I don’t think it will make much difference, it certainly can’t hurt anything.

I’m doing the stein air switches as well. Sounds like I’m probably about a month behind you on engine stuff
 
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I’ve got a very simple reason for using the “staggered” plug wire setup - that’s the way that the plug wires Brad supplies with the P-Mags fit best! The lengths you get in the kit work out to be the same as standard Mag wiring, so I just go with the flow…..

Four dual-PMag Lycomings on our hangar, all wired that way.
 
Yep, I would let the plug wires dictate that decision. Doesn't matter either way. Look how many of us are running one mag on top/bottom and 1 pmag on top/bottom.
 
Question

Thanks everyone.
New question
How did you secure those flimsy MP tubes?
Not at the ends. There's clamps provided.
I mean in-between. Adel seems over kill.
 
Test when you want but I suggest every flight is overkill. I’ve never had a pMag generator test fail in close to 20 years.

First prebuy I did on a P-mag equipped airplane turned up a failed generator, but I don't think it proves anything...except they should be checked every time. The previous owner was also dismissing the need, but he didn't have the backup he thought he had.

Question #1 - if you wire one mag to the top and the other to the bottom, your mag RPM drop will be materially different when doing your mag check.

Dual EI here, plugs all top, all bottom, about 40 drop each.
 
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Thanks everyone.
New question
How did you secure those flimsy MP tubes?
Not at the ends. There's clamps provided.
I mean in-between. Adel seems over kill.

Small section of thicker/stronger tubing with same id as mp od. Then zip tied. Works great and tube doesn't collapse.
 
Question #1 - if you wire one mag to the top and the other to the bottom, your mag RPM drop will be materially different when doing your mag check. Assuming both mags are running properly, it probably doesn't matter, but Lycoming says to stagger them.

They do, but not for the reason you likely think they are. Mags alternate polarity every other ignition cycle (they use AC and not DC, like EI) and the polarity determines which part of the plug wears. Lyc recommendation leaves differently polarities top and bottom to make it easier for the mechanic to swap plugs for wear balance (just swap top for bottom on each cyl) without fully understanding the details. EI systems will fire all plugs with the same polarity, so no need to balance.

Lyc cylinder head chambers are quite symmetrical and should see very little RPM difference top to bottom. Most of what is observed are timing differences. I do top and bottom with dual EI on the 10 and see about a 10 RPM difference during runup. Mine are timed while running with a timing light, so very close in actual timing between the two.

Larry
 
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First prebuy I did on a P-mag equipped airplane turned up a failed generator, but I don't think it proves anything...except they should be checked every time. The previous owner was also dismissing the need, but he didn't have the backup he thought he had.

...
I wired mine as Bill suggested in the other thread, so I test the generator during every runup. Super easy to wire, to test, and to maintain. If I had a nickel for every time I heard about a problem with the "standard" ignition switch, I'd have a dollar or so! Toggle switches are so much easier and they make your panel look like it belongs on the Space Shuttle. :D
 
E-mag instructions say..."2. Setup Mode is entered by turning 12 volt bus power ON, WHILE the p-lead switch is OFF (grounded). If the LED is not lit up, you are not in Setup Mode."

Larry,

I was confused about that statement as well. By that statement it seem would that it would be exactly that state that my PMAGs would be powered up in every time since I have normally on momentary switch(s) for the PMAG power. I actually called Emagair and asked them about it and they said that the configuration is fine. I never quite understood the subtleties of this statement but I believe your configuration is fine as well. There are many people who use similar configurations and they seem to be fine.

Maybe someone who has some direct PMAG experience could explain what is meant by this statement or how Setup Mode is actually entered.
 
Larry,

I was confused about that statement as well. By that statement it seem would that it would be exactly that state that my PMAGs would be powered up in every time since I have normally on momentary switch(s) for the PMAG power. I actually called Emagair and asked them about it and they said that the configuration is fine. I never quite understood the subtleties of this statement but I believe your configuration is fine as well. There are many people who use similar configurations and they seem to be fine.

Maybe someone who has some direct PMAG experience could explain what is meant by this statement or how Setup Mode is actually entered.
Hi Ray, It's important that you understand this, since you will need to get into setup mode to set your timing safely.

Setup mode means that the device has 12v and the mag is grounded. This is why the recommendation on the switchology is to move from 12v off/grounded to 12v off/ungrounded to 12v on/grounded - this eliminates accidentally getting into setup mode. Using a MOM switch to turn off the 12v probably can work, and seems to work for some people, but it's not the way that seems to be recommended by the experts.

If you look in this thread, you'll see some diagrams that explain this.

https://vansairforce.net/community/showthread.php?t=170343


I wired a "maintenance" toggle switch to both pmags which just sends 12v to both pmags putting them in setup mode. This switch is out of harm's way to the right of my panel. If it's on or off in the air it makes no difference - with the pmags hot (ungrounded) the pmag won't go into setup mode. If setup mode is on when everything else is off (pmags grounded), my pmags are in setup mode, and I can set the timing.
 
Mickey,

Thanks for the information. Based upon your switching sequences I think I have it. I guess the instructions lack the interrelationship of the switches. I have a key-switch which makes is a little clunkier. So with a key-switch, the normal start sequence would preferably be:

1) Key-switch Off Both(grounded), PMAG Power Off
4) Key-switch Both (ungrounded), PMAG Power Off
3) Key-switch Both (ungrounded), PMAG Power On
4) Key-switch Start, Both (ungrounded), PMAG Power On

I can certainly change my test switches to non-momentary to resolve my current situation to allow the Pleads to be ungrounded prior to applying power to the PMAGs.

I get what you are suggesting and it makes perfect sense, but I'm not sure how folks with just a breaker don't have a problem or why Emagair would say it was ok (unless they really didn't understand what I was doing).
 
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Starting Order

It seems like there are many ways for the PMAG ignitions to be used successfully. This is directly from the manual provided by E-MAG:

Screenshot 2023-01-23 at 9.00.56 AM.png

Based on this instruction it seems that powering up the ignition in Setup mode is standard practice during normal starting procedure.
 
I just went back and reviewed the Emagair docs and saw those exact statements and see why I originally selected the switch method I did.
 
I just went back and reviewed the Emagair docs and saw those exact statements and see why I originally selected the switch method I did.
The switching method I put in place was recommended by Bill R, who probably knows more about these devices than anyone outside of Emagair.

I know that there was a "bug" in the software that could allow the timing to change due to the suggested "power up first, then ground the pmag" switching that you see in the documentation. Not 100% sure how they fixed it, but it seems strange to put the device into setup mode at every boot. The switching that I use avoids this, but requires a separate switch to activate the setup mode.
 
P-mag tip

I discovered a P-Mag "Gotcha".
There is no way to squeeze the MP tube clamp with the mag installed. Plus, it's really easy to install it incorrectly.
The tube cannot be pushed on where it's flush to the case. The fitting won't allow it. However, the little plastic clamp CAN be installed flush to the case. If it's done that way, it will be half on the tube. Notice in the photo. Be careful. I made a shim to hold the clamp at the correct position so it is holding the tube.

Also, if you remove or install a mag, leave the bottom nut and clamp snug till the top nut and clamp are removed. You don't want parts falling into the engine.
20230123_134159.jpg
 
Dual EI here, plugs all top, all bottom, about 40 drop each.

I got around 100/30 when I wire all top/all bottom, and staggering pursuant to the Lycoming manual yields 40-50 rpm drop on either mag. Another friend running dual p-mags had a similar experience and staggering was also his remedy. I didn't come up with the solution!

Wondering if you are running a hotter plug or if you lean at all prior to run-up?

Brad's wire lengths work well either way. I only ended up cutting one wire a very small amount.
 
I got around 100/30 when I wire all top/all bottom, and staggering pursuant to the Lycoming manual yields 40-50 rpm drop on either mag. Another friend running dual p-mags had a similar experience and staggering was also his remedy. I didn't come up with the solution!

Interesting. Perhaps the difference is combustion chamber swirl pattern, parallel valve vs angle valve.
 
Interesting. Perhaps the difference is combustion chamber swirl pattern, parallel valve vs angle valve.

Another data point - I did the change from Top/Bottom to Staggered to try to balance the mag drop and it made no difference. Parallel valve IO-360, FM-200, Superior Cold Air Sump.
 
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