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wire for mags

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mojavjoe

Joined: 23 Dec 2013
Posts: 64

Posted: Sat Dec 31, 2016 1:56 pm Post subject: wire for mags

What gage wire is correct to connect mags to mag switches? And am I correct that the switches connect to ground?



Thanks



Joe

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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Sun Jan 01, 2017 8:43 pm Post subject: Re: wire for mags

The gauge is irrelevant. Anything will work. Literally. Yes, they do connect to ground. If you plan to use a radio, then you need to use a shielded cable, the cheapest and sufficient is microphone cable, it is two insulated wires plus a ground wire inside a metal foil sheath inside a plastic sheath. If you have dual mags, you can use one insulated wire for one mag and the other insulated wire for the 2nd mag. 

If you have an older engine with one mag, then you use one insulated wire for the mag and the other insulated wire for the tach. 

The basis for this is that the ignition pulses are AC, and they will mess up your radio, so you ground one end of that wire/sheath to either the engine or the frame, but not both ends. Only one end gets grounded. I am not knowledgeable enough to explain it, but you don't ground both ends, only one end. 

Now you have 2 insulated wires running through the grounded sheath. If both of those wire go to your two coils, then you ground those two wires to  your two  kill switches and then to ground. If you have an older type engine with only one ignition system, then you use one of the wires to ground your ignition coil - kill switch, and use the other one for the tach.

TL,DR - wires that carry pulsing AC will mess with your radio, and you want them inside shielded cable, of which one end is grounded.

If you are planning to use a radio, you have to use shielded cable, one end of which has to be grounded, but not both ends. As long as you observe this protocol, you can make your radio work.

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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

ceengland7(at)gmail.com
Guest

Posted: Mon Jan 02, 2017 9:08 am Post subject: wire for mags

For some reason, I never got the       original poster's message. But for wiring magnetos ('conventional'       aircraft mags):

       Suspend normal thought about shields when looking at magnetos.

       

       The shield helps minimize radiated 'noise' (RF energy) from the       mag while it's operating, and is grounded only on the mag itself       while operating. The shield is the return path to short out the       mag when the mag switch is 'off' (note the quotes). 

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

       (Note that the .pdf shows many more 'bells&whistles' than are       needed to simply control a magneto; try to mentally strip away all       the extra functions & just look at the wiring to the mags.)

       

       Center conductor to the points in the mag (P lead terminal),       shield grounded to the mag case.

       

       At the other end, center conductor to one terminal of your mag       switch, and the shield to the other terminal. When the switch is       *closed* (continuity across the terminals), the mag is *off*. When       the switch is *open* (off, in normal terminology), the mag is       *on*. The other end of the shield should not be connected to the       airframe; only to the 2nd terminal of your mag switch.

       

       Wire gauge is non-critical; anything 22awg or bigger for center       conductor is fine (smaller is just too mechanically fragile).

       

       Using a 'spare' wire that's in the same sheath as the P lead might       work fine for something like a tach signal. Or it might not. If       something's not working normally, how do you troubleshoot?

        	  Quote: 	
		  Charlie

	
       

       

       On 1/1/2017 10:43 PM, Richard Pike wrote:

     

      	  Quote: 	
		          	  Quote: 	
		  --> Kolb-List message posted by: "Richard Pike" <thegreybaron(at)charter.net> (thegreybaron(at)charter.net)



Yes, they do connect to ground. If you plan to use a radio, then you need to use a shielded cable, the cheapest and sufficient is microphone cable, it is two insulated wires plus a ground wire inside a metal foil sheath inside a plastic sheath. If you have dual mags, you can use one insulated wire for one mag and the other insulated wire for the 2nd mag. 

If you have an older engine with one mag, then you use one insulated wire for the mag and the other insulated wire for the tach. 

The basis for this is that the ignition pulses are AC, and they will mess up your radio, so you ground one end of that wire/sheath to either the engine or the frame, but not both ends. Only one end gets grounded. I am not knowledgeable enough to explain it, but you don't ground both ends, only one end. 

Now you have 2 insulated wires running through the grounded sheath. If both of those wire go to your two coils, then you ground those two wires to  your two  kill switches and then to ground. If you have an older type engine with only one ignition system, then you use one of the wires to ground your ignition coil - kill switch, and use the other one for the tach.

TL,DR - wires that carry pulsing AC will mess with your radio, and you want them inside shielded cable, of which one end is grounded.

If you are planning to use a radio, you have to use shielded cable, one end of which has to be grounded, but not both ends. As long as you observe this protocol, you can make your radio work.



--------

Richard Pike

Kolb MKIII N420P (420ldPoops)

Kingsport, TN 3TN0



There are only two kinds of people in the world. Those who say to God; &quot;Thy will be done.&quot;

And those to whom God says ; &quot;OK then; have it your way.&quot;

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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Mon Jan 02, 2017 11:45 am Post subject: Re: wire for mags

Good point, my bad. I was only thinking "Rotax." And having only ever wired up 2-cycle Rotax engines, some of what I said might not be right for the 912/etc versions. Or an HKS. Sorry.

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Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

baberdk

Joined: 23 Jan 2014
Posts: 53
Location: East Moline, Il

Posted: Tue Jan 03, 2017 7:53 am Post subject: wire for mags

I agree with the wiring description and it is electrically correct. But since we have the center conductor attached to the mag, and the mag is producing the electrical interference, wouldn't it be safer to connect the shield at the switch end so the shield on the cable follows the plane ground instead of the mag ground?



Respectfully,

Dennis Baber

(305) 814-7218

baberdk(at)gmail.com (baberdk(at)gmail.com)

Stay Curious

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ceengland7(at)gmail.com
Guest

Posted: Sat Jan 07, 2017 6:06 am Post subject: wire for mags

On Tue, Jan 3, 2017 at 9:53 AM, Denny Baber <baberdk(at)gmail.com (baberdk(at)gmail.com)> wrote:

 	  Quote: 	
		  I agree with the wiring description and it is electrically correct. But since we have the center conductor attached to the mag, and the mag is producing the electrical interference, wouldn't it be safer to connect the shield at the switch end so the shield on the cable follows the plane ground instead of the mag ground?



Respectfully,

Dennis Baber

[url=tel:(305)%20814-7218](305) 814-7218[/url]

baberdk(at)gmail.com (baberdk(at)gmail.com)

Stay Curious









 

 	


Hi Dennis,

Sorry to take so long to reply; for some reason this entire thread ended up in my gmail spam folder.

The P-lead shield should *always* be connected to the case of the mag. The mag is the source of the noise, so you're grounding the shield at the ground reference of the noise source. But for me, an even more important point is that the shield is how you turn the mag 'off'; it supplies the ground path to short out the coil of the mag when you turn the mag off. If it has to find its ground path through the airframe back to the mag, what happens if a tech is doing maintenance around the engine and removes the battery negative lead(s)? Depending on how the ground wires are arranged from airframe to battery and from engine to battery, it can leave the mags 'hot' without the tech realizing it (he hasn't touched the mags or mag switches). That can be deadly.

There's also some chance that if you route the shield's ground path through the airframe, you may inject the noise into the ground path of other electronics in the a/c, similar to what happens when the strobes' "whoop...whoop" sound is heard in the intercom.

Charlie

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