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  #21  
Old 03-11-2017, 03:15 PM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by Xkuzme1 View Post
Or turn the fuel selector off...
Ah, yes...I should have thought of that, too... doh!

But with the mags ungrounded, the engine is always "hot", so just watch that prop and don't touch it lest it decide to fire :0 Plenty of videos out there of what can happen.
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  #22  
Old 03-11-2017, 09:59 PM
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Thanks for all the replies gents:

Turns out it was a P-lead issue. Disconnected them today and it fired 3rd blade. Taxied around for a bit too, a huge milestone!

Next session will be to figure out where it's grounding. I'm suspect of the switch- I've been through the diagrams 100 times (I'm sure I wired it correct) and we verified it wasn't the shield ground. Rumor has it these ACS switches are prone to this issue....

Will report back!

Cheers,
DB
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  #23  
Old 03-12-2017, 09:48 AM
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Quote:
Originally Posted by Dave Bernard View Post
Thanks for all the replies gents:

Turns out it was a P-lead issue. Disconnected them today and it fired 3rd blade. Taxied around for a bit too, a huge milestone!

Next session will be to figure out where it's grounding. I'm suspect of the switch- I've been through the diagrams 100 times (I'm sure I wired it correct) and we verified it wasn't the shield ground. Rumor has it these ACS switches are prone to this issue....

Will report back!

Cheers,
DB
I'm glad you found the problem, this is about the 10th time I've heard of this! When you hear the sound of hooves, think cows; not camels. There was a few years ACS had an incorrect dwg in the their catalog and supplied with the switch. Locate an old Bendix drawing for the proper pin-out.

First start on a new plane is indeed a big milestone; congratulations.
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Last edited by deek : 03-12-2017 at 01:44 PM.
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  #24  
Old 03-12-2017, 02:12 PM
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Welp, I'm still miffed over here.

I pulled the switch out and checked it's continuity and didn't find anything wrong as far as I know. With the key off, both mag terminals ground. In L, the right terminal grounds. In R the left terminal grounds. In Both, neither ground. In the start position, the right terminal grounds itself through the jumper, the left does not ground. The body of the switch does not ground to itself from the rear ground terminal.

My ground wire grounds to the fuselage.

Neither p lead wires nor their shields ground while disconnected from the switch and the p leads. I have verified the p leads go to correct wire that connects to the switch.

The P lead terminals on the mags both ground while disconnected from the p leads.

Could it still be the switch even though it tests as I expected? What am I missing?
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  #25  
Old 03-12-2017, 02:37 PM
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Originally Posted by Dave Bernard View Post

The P lead terminals on the mags both ground while disconnected from the p leads.
Huh? What does this mean?
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  #26  
Old 03-12-2017, 02:51 PM
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This is confusing to me as well. With no pleads hooked up, the plead terminal on the magneto has some continuity to the airframe- i.e. I get a beep from my ohmmeter. I understand this is because of the inner workings of the magneto, but that's the extent of knowledge here!!
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  #27  
Old 03-12-2017, 03:06 PM
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Quote:
Originally Posted by Dave Bernard View Post
The P lead terminals on the mags both ground while disconnected from the p leads.
Not so fast, my friend. With the points closed, the resistance will only read 0.5 ohms - not a direct short but close enough to make your continuity checker beep. (Ask me how I know...)
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  #28  
Old 03-12-2017, 03:09 PM
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Default Return grounding...

Quote:
My ground wire grounds to the fuselage.
Hi Dave, Great to hear you got her running!

It sounds to me that wiring your ground terminal on the switch to the fuselage ground would be a problem. From what I gather, it should be sent back thru the wiring shield, by the starter contacts, to ground out at the mags. Electrical radio interference would also be an issue...

Hopefully this wiring diagram will clarify as well as this thread link...

http://www.aeroelectric.com/articles...tchOptions.pdf

Thanks to Gil Alexander.

http://www.vansairforce.com/communit...ad.php?t=36272

Sorry......don't know where that bottom quote link comes from.....




Best Regards,

T.C.








Quote:
http://www.aeroelectric.com/articles/MagnetoSwitchOptions.pdf
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  #29  
Old 03-12-2017, 03:11 PM
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Correct- this is what it reads. Well, .7 anyways. Thanks for the clarification.
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  #30  
Old 03-12-2017, 03:41 PM
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Thanks for the reply tommy.

I know this is a can of worms, but here goes:

The ACS switch diagram says the center ground post grounds to "nearest structural member", not the shielding.

I have read in numerous places that the shielding is only grounded at the ground post on the magneto. My shielding ends prior to the connection that hooks up to the mag switch.

The Lycoming mechanic I had here yesterday asked me specifically if my shielding was only grounded on the mag side, he was happy that it was.

Perhaps this is the problem... But I'd hate to rewire the leads just to find out it wasn't.....
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