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LANDING CHECKLIST PMAG EXTERNAL POWER ON

BMW_X6M

Active Member
If you are running dual PMAG's or any kind of all electronic ignition your landing checklist should include the PMAG external power verified ON.

GUMPS check when you get to Switches would be a good time to verify that the external power is ON prior to the engine RPM getting low for landing. Remember the PMAG runs on internal power until the RPM gets too low, and then it switches to EXTERNAL POWER or DIES if the power is OFF.

I have connected both PMAG external power circuits to the Dynon EFIS which monitors the voltage and produces an aural and visual alarm if it is OFF.
 
I have connected both PMAG external power circuits to the Dynon EFIS which monitors the voltage and produces an aural and visual alarm if it is OFF.

I assume you used one of the extra inputs to do this. Did you then change the configuration inside Dynon to tell it that it was a voltage monitor and what it was for so the screen displayed that info?
 
How would one successfully start a dual pmag setup without at least one mag powered? Do you routinely turn power off to one or more p mags in flight? I love checks as much as the next guy, but this seems a bit excessive.

Maybe I'm missing something, my wife would say that's pretty common...
 
I have a miniature toggle switch for the PMAG power. They can easily be flipped to the off position by mistake, if your hand accidently hit them. For that reason, I have installed a LED that will come on if the power is turned off. That is for my sanity check.
 
I assume you used one of the extra inputs to do this. Did you then change the configuration inside Dynon to tell it that it was a voltage monitor and what it was for so the screen displayed that info?

Actually I described it incorrectly. DYNON is looking for a ground on the contact inputs, so I used two small relays. When de-energized they produce the ground for the contact inputs. The screen shows indicator lights.
 
Actually I described it incorrectly. DYNON is looking for a ground on the contact inputs, so I used two small relays. When de-energized they produce the ground for the contact inputs. The screen shows indicator lights.
Not necessarily. It depends how you configure your color ranges.

I connected two inputs to the Pmag power inputs at the PMag itself. 0-4.5V = Red (Problem). 4.5V-5.0V = Green(OK). You can put 14V into a 5V input without damaging the EMS module, according to Dynon.

According to EMagAir, you supposedly cannot measure PMag internal voltage with an external voltmeter when the PMag is running because it is diode-isolated, but the Dynon doesn't lie. I can turn ships power off to the PMags in flight and the Dynon reports >4.5V on the PMag power pin. I am guessing it is similar to the VP-X installation manual caution, that notes you will observe close-to-bus voltage on a VP-X power pin that is "OFF" if measured with a voltmeter, but apply any kind of load, and it will show 0V.


EDIT: Apologies, BMW, you clearly stated contact inputs. I used GP inputs for my PMag power inputs.
 
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I once forgot to switch Ign Pwr back on after runup and didn?t read my T/O checklist thorough enough. So after a normal flight the engine stopped on rollout after landing.
I have Ign Pwr in the T/O checklist and Abnormal Checklist. May be a warning light is a good idea as well.
 
monemtary switches

I just used a 3 position switch, bottom: grounded and powered, center:ungrounded and powered, and top:momentary ungrounded and unpowered. Can't stay in the momentary position unless you hold it there
 
I just used a 3 position switch, bottom: grounded and powered, center:ungrounded and powered, and top:momentary ungrounded and unpowered. Can't stay in the momentary position unless you hold it there

Same here. 600+ hours with this setup.
 
Mine is exactly like engineerorange too. Both Pmags powered through pullable circuit breakers, which stay in unless I?m checking them a couple times per year. I check the momentary position (ships power off) on every takeoff when above 1000 RPM. If ships power failed in flight, I wouldn?t know it until I turned off the runway and RPM dropped below about 750 RPM.
 
Complexity vs reliability

I have pondered adding NC push buttons to the PMag 12v supply so I don?t have to kill my master to test the onboard source of the Pmag. Whether a 3rd switch contact ( previous comments) or sp push button, it is added points of failure.

Are contacts really a WEAK link at these power application .
 
I have pondered adding NC push buttons to the PMag 12v supply so I don’t have to kill my master to test the onboard source of the Pmag.
This is exactly how I have my dual P-Mag setup. With NC push button switches the power is off only when I have the button pressed. So impossible for me to forget or get it wrong.

FWIW; I push each switch before engine start to make sure they actually disconnect the power to the mags. Then I push each switch with the engine running to make sure the internal generators are working correctly. I monitor the power status to each P-Mag via my DYNON EMS display.

66a5.jpg


:cool:
 
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If they are a weak point then you could just pull the circuit breaker (if so equipped) to accomplish the same thing. Pullable circuit breakers are not meant to be switches, so I would assume their failure mode would be shorter than a switch, push button or otherwise. If your push button failed to the open position then you wouldn?t be able to start the engine. If it failed closed then you wouldn?t know it unless you are checking low RPM cut out. If the mag doesn?t shut down at very low RPM while holding the button in, then it has failed closed. Am I getting that right? I?m assuming a normally closed momentary push button switch. With dual Pmags this is a little easier to check without having the engine shut down and having to restart. Just make sure you ground the mag in this situation before re-instating power to the dead one.
 
It seams to me that if your P-mag switches are not on the Ship's Power & Ungrounded position for landing, then you missed something on your pre-takeoff checklist.

I have mine configured so that if the three position switches are all the way UP position, then you are ready to go. Simple ergometric panel design. Down is off, and the middle would be test. Everything is up and you are ready to go.

A push button switch to momentary drop power to the P-mags is a simple solution but takes more panel space.

Just a couple of things to think about as you design your panel.
 
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It seems to me that if your P-mag switches are not on the Ship's Power & Ungrounded position for landing, then you missed something on your checklist.

I have mine configured so that if the three position switches are all the way UP position, then you are ready to go. Simple ergometric panel design. Down is off, and the middle would be test. Everything is up and you are ready to go.

I'm using this solution with locking toggle switches to prevent inadvertently turning one off in flight. They're also on the side of my panel where it's unlikely that I would bump them.
 
I'm using this solution with locking toggle switches to prevent inadvertently turning one off in flight. They're also on the side of my panel where it's unlikely that I would bump them.

I used a recessed sub-panel to keep the switches organized and out of the way. (Probably won't work on an -8.)

Here is an old, pre SkyView, picture of what I'm talking about. It has turned out to be a GREAT setup!

(Click to enlarge)
 
Actually I described it incorrectly. DYNON is looking for a ground on the contact inputs, so I used two small relays. When de-energized they produce the ground for the contact inputs. The screen shows indicator lights.

You could also use a double-pole switch. One set of poles for the mag power, second set switched to ground for a contact input.
 
Never mind all that! Only one burning question, dangling for ages, matters in P-Mag world:

When will the 6-cylinder model actually come to market?
 
Never mind all that! Only one burning question, dangling for ages, matters in P-Mag world:

When will the 6-cylinder model actually come to market?
I'd say they're too late now. Surefly have their 4 and 6 cylinder EI magneto-hole-mount replacements out now...$1500USD each, and STC'd for the certified crowd too.
 
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