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  #11  
Old 01-18-2019, 05:45 AM
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N941WR N941WR is online now
 
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Quote:
Originally Posted by Scott Hersha View Post
Bill - why can’t both Pmags be grounded to the same case bolt? It seems like two case bolts on the same case, just a few inches apart, would be electrically the same. I’m pretty sure both of mine are grounded to the same bolt on the accessory case.
Electrically it is the same; however, if that one bolt comes out, you run the risk of both ignitions failing.

Addition:

Why take two completely independent systems and make them dependent on one bolt or a single ring terminal, which are known to fail?

Should that one bolt back out, the P-mags will continue to fire; however, when you land at some "away" airport in the middle of a "dark and stormy night" and your RPM's drop below that magic 800 RPM self powering threshold, your engine will die on the runway and you will be scratching your head as to why. (This scenario has happened before, but not on a "dark and stormy night".)
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Last edited by N941WR : 01-18-2019 at 06:03 AM.
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  #12  
Old 01-18-2019, 05:48 AM
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Bill Boyd Bill Boyd is offline
 
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I'm sure the answer is to avoid a single point failure that would result in engine stoppage if one bolt shears/backs out.

EDIT - beat like a rented mule.
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  #13  
Old 01-18-2019, 08:13 AM
Scott Hersha Scott Hersha is offline
 
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I guess I didn’t consider a bolt falling off the engine as a risk - but anything is possible. I’ll check mine to see if I’ve done that. The more likely failure point is the wire/connector and I have separate ring terminals on each Pmag. If the connector fails, it wouldn’t matter what bolt it was attached to - it would still fail. The reason for my question was to see if there is some grounding issue with both ground wires going to the same point and I’m not sure I did that, I was just curious as to the why. Pretty easy to move it over if I did.

Here’s another question concerning grounding - just for my own understanding of the system...... If the ground wire on the connector fails, I’m not sure the engine will quit when the RPM drops below 800. Wouldn’t the chasis of the Pmag still provide a ‘not very good’ ground? It’s not an excuse to not install a ground wire, and disregard the installation instructions, but I think the ground wire in the Pmag connector is there to provide a reliable ground due to poor conductivity of anodized aluminum on the Pmag chasis. If that fateful bolt fell off the engine, you may not know it until you have the cowl off next time and discover it. Isn’t that the way it works? - again, I’m not saying anyone should do that, and I’m not saying anyone should trust a single grounding point on the case for two separate mags, but it seems like the wire is providing a reliable and redundant ground for each Pmag. If so, and it’s redundant, you might not know you had a wire/connector or bolt failure unless you checked it when the cowl was off. Is that correct?
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Last edited by Scott Hersha : 01-18-2019 at 08:23 AM. Reason: Added question
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  #14  
Old 01-18-2019, 08:35 AM
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N941WR N941WR is online now
 
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Scott,

The P-mags will ground through their case, as you mentioned; however, there are electronics in the P-mags that would really like a clean ground signal.

If that wire fails for any reason, the P-mags will still fire as the path is out one plug and back through the other.

Because of how our EICommander determines if there is a firing angle difference between the two ignitions, it must have a clean signal and we have found that wiring them per the manual eliminates extraneous noise that the EICommander picks up as a timing divergence error.

This is your ignition you are wiring, I cannot express strongly enough that they should be installed exactly as described in the manual.
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  #15  
Old 01-18-2019, 03:01 PM
Scott Hersha Scott Hersha is offline
 
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Thanks Bill, and yes I did install them exactly as the manual suggests. I was just questioning the failure mode if the ground wire were to fail, either in the wire
/connector itself, or the attachment to a case ground bolt. You answered my question - there is a redundant ground path in case of one of those types failures. Good to know.
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  #16  
Old 01-20-2019, 03:15 PM
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swisseagle swisseagle is offline
 
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Default Case is anodized ... also non-conductive ... how is it grounded through their case?

Hello Bill

Cans you explain this a bit deeper?

Quote:
Originally Posted by N941WR View Post

The P-mags will ground through their case,
How is this done?

The case is anodized aluminium, this is electrical non conductive!?

Aluminum Anodizing is an electrochemical process that creates a thin aluminum oxide film on the surface of aluminum substrates. The resulting anodized film is electrically non-conductive, protects the aluminum against corrosion and is resistant to wear.

If I where Emagair, I would just cut away the layer of anodisation on the place where the clamps from the two brackets hold them to the engine case. So that there is the first and strongest ground. Maybe change the aluminium alloy to a not so corrosion reactive type.
The benefits would be:
- Two grounds per Pmag
- Fire resistant for many minutes
- If Pmag is mounted correctly, it is grounded
- Bullet prove
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  #17  
Old 01-20-2019, 04:11 PM
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Quote:
Originally Posted by swisseagle View Post
Hello Bill

Cans you explain this a bit deeper?

How is this done?

The case is anodized aluminium, this is electrical non conductive!?

...
You really must ask Emag as I am not on their design team.

I do know the P-mags are insulated from the case by the gasket; however, the path may be through the hold downs. Check with Emag.

Also, there is a ground path through the sparkplugs, as I also mentioned.
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Build the plane you want, not the plane others want you to build!
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Last edited by N941WR : 01-20-2019 at 06:25 PM. Reason: Corrected some wording.
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  #18  
Old 01-20-2019, 04:49 PM
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the hold downs will usually scratch the surface

On a flat surface, this will not happen ... inside an anodized thread, if you tighten the screw fairly well, then you have a ground ... but not a proper one ... take at least two screws.

If you want to have this on a flat surface, then the clamping element must have some sharp edges/spikes that break the oxide.
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