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Barry,
If you are using a metallic conduit then I would ground the conduit at
one location. Power or signal. I do not think running an exposed shield
would have any effect or offer any EMI protection. Avoid all ground loops. One point grounds on all shielded wire.
Incidental grounding can create loops depending on contact area. Not
likely a problem in a composite airframe. Keep signal / radio ground isolated from motor grounds return leads,
lights, etc, where possible. On your ground / return buss you can
connect the negative return / ground lead in the middle. Connect the
clean stuff to one side of the buss bar and the dirty stuff to the other
side so the clean stuff has a clean path to ground. Make sure signal cables and power cables are not twisted or mixed
together. Signal cable woven between large power cable can get dirty. Bobby -----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Barry Gardner
Sent: Thursday, February 16, 2006 11:03 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Radio noise saga
Bill and other knowledgable folks,
Is there any value in running a braided shielding inside the conduit
that will carry the power leads? I'm building a plane like Buly's and
want to know if that's something I should just build into my electrical
raceway. Thanks.
Barry Gardner
Wheaton, IL
Bill Dube wrote:
The separated power leads radiate noise quite well. They are a giant loop antenna that is transmitting any ripple on the current to the battery. Alternator whine, motor whine, ingnition system input ripple all will radiate from such a loop.
This is a very common problem on homebuilt electric vehciles. With the
large battery pack, folks often fine it convienient to run the power leads up one side of the car and back on the other. The hash from the motor controller and/or the charger make it impossible to use anything
electronic inside the car if you wire it that way. Sometimes, the motor controller throttle input will pick up the output hash from such
a loop and make the car undrivable.
Always run power leads as a pair. Keep the "presented area" low to reduce the transmitted noise.
You have found the problem.
Twisted pair only reduces noise in signals transmitted THROUGH the wire, and it only works if the receiver uses a differential signal.
It doesn't help with power wires. The curious can drop by:
http://www.duxcw.com/digest/Howto/network/cable/cable4.htm
It's a fairly good, brief description of what goes on. You'll usually
only find twisted pair in LAN cabling.
Regards,
Chad
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