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  #1  
Old 11-16-2008, 05:09 PM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
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Posts: 3,752
Default Wiring Mag Switch

I have the Van's A-510-2 keyed ignition switch. I'm using 18AWG shielded wire. Van's drawing shows that the shield is separated from the P-lead at the magneto end but it shows it unseparted at the switch end. (There is only one connection to make at the switch per Van's drawing.)

To put a ring terminal on the switch end, should I just strip the insulation and shielding off and crimp the terminal just as I would with an unshielded wire, or do I need to do something special with the shield at the switch end? (Specifically, I'm wondering if I somehow need to make sure that the shield can't come in contact with the main wire or terminal.)

Thanks.
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  #2  
Old 11-16-2008, 08:12 PM
David-aviator David-aviator is offline
 
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Quote:
Originally Posted by alpinelakespilot2000 View Post
I have the Van's A-510-2 keyed ignition switch. I'm using 18AWG shielded wire. Van's drawing shows that the shield is separated from the P-lead at the magneto end but it shows it unseparted at the switch end. (There is only one connection to make at the switch per Van's drawing.)

To put a ring terminal on the switch end, should I just strip the insulation and shielding off and crimp the terminal just as I would with an unshielded wire, or do I need to do something special with the shield at the switch end? (Specifically, I'm wondering if I somehow need to make sure that the shield can't come in contact with the main wire or terminal.)

Thanks.
Definitely, the shield must not contact the wire it is shielding. If it does the mag will be grounded and not operate.

The purpose of the shielding is to suppress electrical noise that may interfere with radio reception. Some sources recommend that both ends of the shield be grounded, some say one end grounded will do the job.
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  #3  
Old 11-16-2008, 09:04 PM
BillSchlatterer BillSchlatterer is offline
 
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Default Shield use ?

On the 510 switch, the shield on the P-Lead wire attaches at the mag(ground) and to the GRD(center terminal) on the switch end. In the Switch Off position, the shields are used as a ground return for the mags. In the Switch ON position, the shields are protection from electrostatic coupling of the mag noise.

On the switch end, the shield goes to the center GRD terminal on the switch only and not actually to ground at the panel.

See Diagrams Z26/27 and Note 3 in the Aeroelectric Connection for more detail.

Bill S
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  #4  
Old 11-16-2008, 10:42 PM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
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Quote:
Originally Posted by BillSchlatterer View Post
See Diagrams Z26/27 and Note 3 in the Aeroelectric Connection for more detail.
Thanks Bill, but I'm going according to Van's drawings. I saw that Bob Nuckholl's grounds his at both ends, but he seems to be using a different set of switches than Van's A-510-2's. Also, maybe Van's drawings should show the shield grounded at the switch (?) but it definitely does not (at least as I'm reading it).
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  #5  
Old 11-16-2008, 11:26 PM
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az_gila az_gila is offline
 
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Exclamation The Bob N. way is safer....

Quote:
Originally Posted by alpinelakespilot2000 View Post
Thanks Bill, but I'm going according to Van's drawings. I saw that Bob Nuckholl's grounds his at both ends, but he seems to be using a different set of switches than Van's A-510-2's. Also, maybe Van's drawings should show the shield grounded at the switch (?) but it definitely does not (at least as I'm reading it).
This document from AeroElectric Bob does seem to cover exactly the same type of switch that you mention from Vans...
In fact the upper schematic on page 3 uses a Gerdes switch with the same part number you quote....

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

I believe it is a little safer if you follow Bob's wiring - also suggested by Bill S. above.

A detailed thread is here...

http://www.vansairforce.com/communit...magneto+switch

Check my post #5 in the linked thread for my reasoning.
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Last edited by az_gila : 11-16-2008 at 11:31 PM. Reason: update
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  #6  
Old 11-16-2008, 11:49 PM
mike109g6 mike109g6 is offline
 
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Default P-Lead

Steve,
I had the same confusion. After countless inquiries, talks, reads, etc., the 510-2 switch the shielding should be grounded on the mags and grounded on the central ground terminal of the switch. Bob at Aero Electric shows it and you should really read this:
elippse Join Date: Dec 2006
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--------------------------------------------------------------------------------

The "P", "primary" lead, is connected to the primary of the spark coil. Under high power conditions, the voltage pulses on that lead may be in excess of 100V. Any current which flows from a source must return to that source, by whatever path is available. The voltage pulses in the shielded wire will couple to the shield, electrostatically and electromagnetically, and so the current in the shield must get back to the return side of the spark coil primary. The shield should be connected at the magneto case and at the ground terminal of the switch, AND NO WHERE ELSE! If you connect the shield to the aircraft "ground", these currents will then use the aircraft skin to go to the engine and then back to the magneto, radiating electromagnetically all along the way. This is where you get spark noise into your radios. When the current only flows back through the shield, the current flowing in both directions will effectively cancel as far as radiation is concerned. And whatever you do, please don't install a "filter" in the "P" lead circuit. The reason you had ignition noise is because you didn't have a properly shielded and grounded circuit, and the filter just adds another alternate current path
Hope that this solves the confusion,
Mike H 9A/8A
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  #7  
Old 11-17-2008, 11:04 AM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
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Thanks Mike and Gil-
I'll look into it some more. Sounds like good reasoning to ground at both ends. I wonder why Van's doesn't suggest this in their drawings?
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  #8  
Old 11-17-2008, 11:38 AM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by alpinelakespilot2000 View Post
Thanks Mike and Gil-
I'll look into it some more. Sounds like good reasoning to ground at both ends. I wonder why Van's doesn't suggest this in their drawings?
...use Vans wiring, but while it works, it's not optimum.

My Tiger uses Vans approach, but many more joints are involved, and one wire then affects both mags. One hot mag is bad, but two might be worse.

One item that I found when researching this on other brands of certified planes was finding the actual wiring schematic for the key switch.

The magnetos "belong" to the engine in the maintenance manual, and seem to be ignored in the "electrical" section with the actual 12 volt wiring diagrams - I checked 2 Piper and one Cessna Maintenance manuals, and could not find a specific wiring diagram that showed shields for the magnetos.

Hence a lot of A&Ps wire it up their own way when the P-leads break (I've seen lots of poor connections to the shields here) which is a relatively frequent repair.

Heatshrink for support is good here - again Bob N. shows how. Twisting an exposed length of shield and crimping a terminal on the end almost guarantees a future break at the point the shield exits the cable - but this is the way I've seen many done.
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  #9  
Old 11-17-2008, 12:30 PM
noelf noelf is offline
 
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Just as another data point...

ACS has a picture / drawing of this switch in their catalog, as well as on their web site. Bob Nuckolls also provides a picture and the switch and position / function chart in his Z-27 drawing. And, if you order the switch from ACS, you will get a small slip of paper packed with the switch which "identifies" the terminals on the switch.

I found that none of the drawing of the switch agreed with each other. There is a subtle difference between them. I think it was the location of the BAT and S terminals were reversed. For my implementation, it did not matter, but it did cause me to double check everything to be sure there were no other issues.

Just check your switch against your implemented wiring scheme.
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  #10  
Old 11-17-2008, 03:02 PM
alpinelakespilot2000 alpinelakespilot2000 is offline
 
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Quote:
Originally Posted by az_gila View Post
...Hence a lot of A&Ps wire it up their own way when the P-leads break (I've seen lots of poor connections to the shields here) which is a relatively frequent repair.

Heatshrink for support is good here - again Bob N. shows how. Twisting an exposed length of shield and crimping a terminal on the end almost guarantees a future break at the point the shield exits the cable - but this is the way I've seen many done.
Is this the easiest, best way, then Vern?
http://www.aeroelectric.com/articles...l/pigtail.html
I wonder if trying to solder the sheild to a wire will tend to melt the insulation on the main conductor??
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