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-   -   P-Mag - Requirement for power line switch? (https://vansairforce.net/community/showthread.php?t=114650)

Kevin Horton 06-29-2014 01:58 PM

P-Mag - Requirement for power line switch?
 
I've got one each Slick mag and Lightspeed electronic ignition on our RV-8 with IO-360-A1B6 engine. Yesterday the mag had a major mechanical failure, and I plan to replace it with a P-Mag as soon as I can get one delivered. I'm seeking input on the need for a switch in the power wire to the P-Mag.

I have no room on the panel to install a P-Mag power switch close to the two existing ignition switches. If I add a new switch, it will be in some random location, which greatly offends my sense of order. Or, I could replace my current lever-lock mag switch with a three position switch, but now it would differ from my EI switch, in appearance, feel, and toggle angle when the engine is running. This also offends my sense of order.

Reading the P-Mag installation and operation manual, I see no compelling reason to have a power line switch at all. I could easily check the P-Mag's internal alternator immediately after engine start by momentarily turning off the battery master and the Lightspeed EI. The power switching to set the ignition timing would also be done using the battery master.

Am I missing something here? Is there a good reason to install a P-Mag power line switch?

Thanks,

Bevan 06-29-2014 02:08 PM

Kevin,

Are you going to power the P-mag through a pullable breaker? Or possibly a toggle switch/breaker?

I want to control power to the P-mags.

Bevan

mike newall 06-29-2014 02:11 PM

The switch is to enable you to test the system.

If you have the supply protected via a cb and are happy to test the system in another method then I can't see a problem.

Not conventional but not unsafe - the P-Mag is grounded safe through the P lead.

Kevin Horton 06-29-2014 02:15 PM

Quote:

Originally Posted by Bevan (Post 892895)
Kevin,

Are you going to power the P-mag through a pullable breaker? Or possibly a toggle switch/breaker?

If I don't have a power switch, there would be no means to kill power from the cockpit, unless I shutdown the whole electrical system.
QUOTE=Bevan;892895]Kevin,
I want to control power to the P-mags.
[/quote]
What are the scenarios where controlling the P-Mag power could be useful?

As I understand it, if the P-Mag timing goes wonky, grounding the P-Lead input (wire #4 on their wiring diagram) should kill the ignition. If grounding the P-Lead does not kill the ignition, removing the DC power input won't help, as the ignition will still be powered by its internal alternator.

Kevin Horton 06-29-2014 02:16 PM

Quote:

Originally Posted by mike newall (Post 892896)
The switch is to enable you to test the system.

If you have the supply protected via a cb and are happy to test the system in another method then I can't see a problem.

Not conventional but not unsafe - the P-Mag is grounded safe through the P lead.

I propose to test the system immediately after engine start by opening the battery master, which will remove aircraft power from the P-Mag. The P-Mag power line will have a fuse for protection.

jclark 06-29-2014 02:26 PM

Yet another approach ...
 
Quote:

Originally Posted by Kevin Horton (Post 892899)
I propose to test the system immediately after engine start by opening the battery master, which will remove aircraft power from the P-Mag. The P-Mag power line will have a fuse for protection.

Kevin,

I have been using the *same* (fused) power switch for my P-Mag *and* my ElectroAir electronic ignitions.

I use a keyswitch to check the "mags" as I initially had a magneto.

If I want to test the P-Mag on the ground, I switch to to it alone (keyswitch), power off the EI power and throttle below about 750 (P-Mag stays alive without power being applied if RPM is somewhere around 800 or above.)

This system has worked for hundred of hours.

So I assume that you have a power switch for the Lightspeed EI. If that is independent from your "mag check switch(es)" then your current setup probably could be made to work.

Kevin Horton 06-29-2014 02:35 PM

Quote:

Originally Posted by jclark (Post 892902)
Kevin,

I have been using the *same* (fused) power switch for my P-Mag *and* my ElectroAir electronic ignitions.

Hmm. Interesting idea.

I do have a fused power switch for the Lightspeed ignition. This is a lever-locked switch right beside the lever-locked switch for the mag P-Lead.

I'm not crazy about routing power for both ignitions through one switch though. My plan if the Lightspeed ever goes crazy is to kill its power via that switch. If the P-Mag power was controlled by the same switch, I'd then be relying on the P-Mag internal alternator only if I ever had to kill the Lightspeed. I'd like to keep the two ignition systems a bit more independent.

Toobuilder 06-29-2014 02:35 PM

I'm guessing you are going to run the new 114 series which runs on internal power most of the time. In this case you really only have a test switch, so using the ships master is an acceptable way of doing the self test.

This was my original plan for our -8 as well, but I have 113's, and I found it useful to be able to "force" the ignition onto internal power with an accessible switch (or CB, in my case). The 114's are a whole different animal, so no reason for the switch, IMHO.

Kevin Horton 06-29-2014 02:37 PM

Quote:

Originally Posted by Toobuilder (Post 892906)
I'm guessing you are going to run the new 114 series which runs on internal power most of the time. In this case you really only have a test switch, so using the ships master is an acceptable way of doing the self test.

Yes, this will be a brand new 114 series P-Mag.

jclark 06-29-2014 02:42 PM

Define "goes crazy" ...
 
Quote:

Originally Posted by Kevin Horton (Post 892905)
Hmm. Interesting idea.

I do have a fused power switch for the Lightspeed ignition. This is a lever-locked switch right beside the lever-locked switch for the mag P-Lead.

I'm not crazy about routing power for both ignitions through one switch though. My plan if the Lightspeed ever goes crazy is to kill its power via that switch. If the P-Mag power was controlled by the same switch, I'd then be relying on the P-Mag internal alternator only if I ever had to kill the Lightspeed. I'd like to keep the two ignition systems a bit more independent.

My thinking is that the P-Mag (114 Series), once fired up is "on it's own" so to speak. Whether I have power to it or not. If I want to take it out of firing for the engine then my action is the SAME as if it was a mag that I wanted to remove.

I have not yet envisioned a power problem that would apply to the P-Mag but not to the "other" EI. So if I have smoking EI wire then I need to turn the power off to BOTH and LAND ASAP.

Probably not within your risk profile but that is how I think about it.

James

Kevin Horton 06-29-2014 03:10 PM

Quote:

Originally Posted by jclark (Post 892909)
My thinking is that the P-Mag (114 Series), once fired up is "on it's own" so to speak. Whether I have power to it or not. If I want to take it out of firing for the engine then my action is the SAME as if it was a mag that I wanted to remove.

I have not yet envisioned a power problem that would apply to the P-Mag but not to the "other" EI. So if I have smoking EI wire then I need to turn the power off to BOTH and LAND ASAP.

Probably not within your risk profile but that is how I think about it.

James

By "goes crazy", I mean fire the spark plugs at the wrong timing, so the engine runs rough or quits.

If there is smoke in the cockpit, my thinking is that it will be pretty much impossible to quickly identify the source. My Smoke in the Cockpit procedure is to open the battery master/alternator switch, which will kill the whole electrical system, except the Lightspeed EI and my turn and bank, both of which are fed from an always-hot battery bus.

Larco 06-29-2014 03:10 PM

Because the P-Mag loses internal power below about 750 RPM I installed a DPDT switch with 2 slow blow fuses. Reason-----One day I turned off the P-Mag switch to check the internal power during the run up, got distracted and forgot to reenergize the circuit. Got to destination and on roll out with idle power engine quit! So now I have a light to indicate when the switch is OFF! Just another way of doing it. :-) Larry

Ironflight 06-29-2014 03:35 PM

No power switches for any of our P-Mags Kevin - they are powered through pull-able breakers in order to test when needed. SInce I added them well after the -8 was flying, I also didn't have a good spot for the breakers on the norma panel - I put them on the inboard face of the left gear tower where I can reach them. It made adding the wires easy as well - buried them in the gear tower.

krw5927 06-29-2014 03:59 PM

One possibility would be to ditch the lightspeed and get 2 pmags, each with its own three-position switch. Your sense of (dis)order would not be offended.

Andy Hill 06-29-2014 04:02 PM

We have 2 P-Mags with a CB for each for Power.

Only use the CBs for the "once every so often" self-generating test. I would say not having this ability might not be ideal in a Dual P-Mag installation? But cannot see an issue in a single installation if you are willing to kill all ship's power.

When you kill all power, do you still have RPM indications? The full test is to remove power from the P-Mag, having removed the other ignition system - then gently slow engine and note RPM at which self-generating stops.

N941WR 06-29-2014 04:47 PM

The 114's switch to internal power around 800 RPM, which works seamlessly. However, I had one of my 114's internal generators go bad and the only way I found it was to pull the power on them, one at a time, because it was running on ship's power.

So, yes, you want a way to kill the power on them.

Kevin Horton 06-29-2014 04:49 PM

Quote:

Originally Posted by Andy Hill (Post 892936)
When you kill all power, do you still have RPM indications? The full test is to remove power from the P-Mag, having removed the other ignition system - then gently slow engine and note RPM at which self-generating stops.

That's a great point. No, if I killed all power, I would no longer have an RPM indication. That is definitely a point against my draft plan.

Kevin Horton 06-29-2014 04:54 PM

Quote:

Originally Posted by N941WR (Post 892942)
The 114's switch to internal power around 800 RPM, which works seamlessly. However, I had one of my 114's internal generators go bad and the only way I found it was to pull the power on them, one at a time, because it was running on ship's power.

So, yes, you want a way to kill the power on them.

Did the internal alternator fail completely, so the engine would not run at any rpm if there was no ship's power? Or, did it have a partial failure so that it would generate power at some rpm higher than the normal 800 rpm cutout?

Larco 06-29-2014 05:27 PM

Quote:

Originally Posted by N941WR (Post 892942)
The 114's switch to internal power around 800 RPM, which works seamlessly. However, I had one of my 114's internal generators go bad and the only way I found it was to pull the power on them, one at a time, because it was running on ship's power.

So, yes, you want a way to kill the power on them.

And this is why I installed a switch as per P-mag recommendation. To ensure that the internal power mechanism is operating properly before flight. Not a big deal until it becomes one. :-)

GalinHdz 06-29-2014 05:48 PM

Quote:

Originally Posted by N941WR (Post 892942)
The 114's switch to internal power around 800 RPM, which works seamlessly. However, I had one of my 114's internal generators go bad and the only way I found it was to pull the power on them, one at a time, because it was running on ship's power.

So, yes, you want a way to kill the power on them.

I echo that you really want a way to kill power to the 144 mag for testing. If panel space is tight then a combination CB Switch is the way to go.

:cool:

SmilingJack 06-29-2014 05:58 PM

Kevin, Here is my setup for 4 switches. Turn the 2 outboards off and after they check good turn them back on and then turn the 2 inboard switches off...if they check good, Internals are check and ready for flight!

They are at the very bottom on my panel on the left hand side under the radio stack.


Bavafa 06-29-2014 06:24 PM

Quote:

Originally Posted by LARCO (Post 892920)
Because the P-Mag loses internal power below about 750 RPM I installed a DPDT switch with 2 slow blow fuses. Reason-----One day I turned off the P-Mag switch to check the internal power during the run up, got distracted and forgot to reenergize the circuit. Got to destination and on roll out with idle power engine quit! So now I have a light to indicate when the switch is OFF! Just another way of doing it. :-) Larry

For this reason, I have a simple warning light that illuminates when the power to PMAG has been switched off.

N941WR 06-29-2014 07:24 PM

Quote:

Originally Posted by Kevin Horton (Post 892945)
Did the internal alternator fail completely, so the engine would not run at any rpm if there was no ship's power? Or, did it have a partial failure so that it would generate power at some rpm higher than the normal 800 rpm cutout?

The internal generator was toast. Once I removed it, you could turn the shaft but it was "crunchy".

When running on the faulty ignition, it would operate fine as long as it had ship's power. Once I turned off the power to it but left it ungrounded, it died. (Step 5, below.)

I wired mine slightly differently:


This allows me to perform a preflight by doing this:


One other thing, with the jumper in, your timing starts at 26* BTC. Without the jumper, it is around 30* BTC. Depending on your engine, you may want to connect to it with a PC and the EICAD program and adjust the timing to match your engine / needs. If you make any adjustments with their program, you must leave the jumper out as that program only lets you change the "B" curve.

Canadian_JOY 06-29-2014 07:59 PM

A very good discussion was had on this topic in the following thread.
http://www.vansairforce.com/communit...t=p-mag+switch

With the right switch, a progressive transfer switch, one can achieve the desired result. This same switch could be used for the Lightspeed ignition, thus meeting your requirement for the same switchology between the two ignition systems.

Ironflight 06-29-2014 07:59 PM

No disrespect to anyone (and I mean that), but simple is almost always better! I have flown airplanes that had so many switch combinations that only the designer/builder could figure out how to operate them. I guess that is an effective anti-theft design at least.

I flew a couple of airplanes recently where the power and engine systems were far from intuitive - I had several minute briefings on each in order to understand them - and these were single-engine, simple airplanes. I don't see much need for that!

I want to be able to "ground" each mag for a mag check, and I want to be able to kill power to them. That requires a mag switch for each, and a circuit breaker if I am a minimalist. I've flown aerospace craft that were extremely complex because they needed to be - ours don't.

N941WR 06-29-2014 09:01 PM

Quote:

Originally Posted by Ironflight (Post 892991)
No disrespect to anyone (and I mean that), but simple is almost always better! I have flown airplanes that had so many switch combinations that only the designer/builder could figure out how to operate them. I guess that is an effective anti-theft design at least.
...
I've flown aerospace craft that were extremely complex because they needed to be - ours don't.

So true!

Someone I know purposely made his -6A overly complex because that was how he remembered his days in the USAF back in the 60's. There were guarded switches, buttons, etc. scattered all over the place.

If he every had an "issue' while flying, I think the stress would keep him from figuring anything out.

Keep it simple!

MarkW 06-30-2014 08:28 AM

Kevin,
I also like simple. I have two P-Mags. Standard ignition switch that grounds p-leads for testing on run-up. For testing P-Mag internal alt. I kill master power while above 1000 rpm. I run my P-mag power off a fuse under the panel. If need be I can pull the fuse for testing. I never saw a need for a tach. while testing the internal alternator.

Bevan 06-30-2014 12:34 PM

Quote:

Originally Posted by MarkW (Post 893112)
Kevin,
I run my P-mag power off a fuse under the panel. If need be I can pull the fuse for testing.

Keep in mind that Emagair suggests a resettable circuit breaker, NOT a fuse for power.
Bevan

DeltaTango 06-30-2014 01:17 PM

I used a 3 position switch for my master. The bottom position is "off". The middle position is ships power to everything except the Pmag. The full up position is ships power to everything including the Pmag. During the run up, I position the master to the middle position and then check each side of the ignition system. Upon completion of the check I reposition the master to full up to provide the Pmag with the ships power backup. As with all designs it's not perfect. It would be possible to forget and leave the master switch in the middle position thus causing the Pmags to shut off below 650-800 rpm. However that would normally occur post run up.

A friend had an idea of putting a push button type switch on the panel that would remove power to the Pmag during run ups. The procedure would be to turn one ignition off then press and hold the button. Should see no change in operation. Next turn the first ignition back on and then second ignition off and repeat the push button test.

Just a couple of ideas.

David

Larco 06-30-2014 01:22 PM

Quote:

Originally Posted by Bevan (Post 893207)
Keep in mind that Emagair suggests a resettable circuit breaker, NOT a fuse for power. You should contact them for an explanation but I believe it may have had to do with a crow bar over voltage circuit inside the P-mag.

Bevan

FYI Brad said that a slow blow fuse was just fine and they have worked fine for many hours in our RV. Larry

N941WR 06-30-2014 01:33 PM

Quote:

Originally Posted by DeltaTango (Post 893214)
....
A friend had an idea of putting a push button type switch on the panel that would remove power to the Pmag during run ups. The procedure would be to turn one ignition off then press and hold the button. Should see no change in operation. Next turn the first ignition back on and then second ignition off and repeat the push button test.

Just a couple of ideas.

David

I considered a pushbutton switch then thought about there failure rate and went with the setup described above.

Just keep in mind that this is your ignition you are messing with!

Josef 09-11-2015 09:29 AM

problem with ignition switch
 
hi there,
fired it up my P-Mags today and now I have this question:

I have the ignition switch from Van's Aircraft installed ( OFF - R - L - BOTH - START ), used that for the Slick magnetos. Now when I fired up the P-Mags strangely enough I can switch to right or left P-Mag, but when I turn the key to "both" the engine goes dead. Anything I overlooked in the installation manual ? Obviously I do have to change the wiring of the ignition switch ? Any advise ? Thanks a lot in advance !

best regards,

Josef
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