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06-29-2014, 01:58 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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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,
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06-29-2014, 02:08 PM
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Join Date: Sep 2007
Location: BC
Posts: 1,674
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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
__________________
RV7A Flying since 2015
O-360-A1F6 (parallel valve) 180HP
Dual P-mags
Precision F.I. with AP purge valve
Vinyl Wrapped Exterior
Grand Rapids EFIS
Located in western Canada
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06-29-2014, 02:11 PM
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Join Date: Jan 2005
Location: Yorkshire, England
Posts: 2,052
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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 add a little excitement, a little spice to your lives, and all you do is complain!" - Q
Donated in 2020
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06-29-2014, 02:15 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by Bevan
Kevin,
Are you going to power the P-mag through a pullable breaker? Or possibly a toggle switch/breaker?
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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.
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06-29-2014, 02:16 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by mike newall
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.
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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.
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06-29-2014, 02:26 PM
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Join Date: Jan 2005
Location: Columbia, SC
Posts: 804
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Yet another approach ...
Quote:
Originally Posted by Kevin Horton
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.
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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.
__________________
James E. Clark
Columbia, SC
RV6 Flying, RV6A Cowling
APRS
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06-29-2014, 02:35 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by jclark
Kevin,
I have been using the *same* (fused) power switch for my P-Mag *and* my ElectroAir electronic ignitions.
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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.
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06-29-2014, 02:35 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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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.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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06-29-2014, 02:37 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by Toobuilder
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.
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Yes, this will be a brand new 114 series P-Mag.
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06-29-2014, 02:42 PM
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Join Date: Jan 2005
Location: Columbia, SC
Posts: 804
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Define "goes crazy" ...
Quote:
Originally Posted by Kevin Horton
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.
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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
__________________
James E. Clark
Columbia, SC
RV6 Flying, RV6A Cowling
APRS
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