REFLECTOR: Position Light Wires

Brian Michalk michalk at awpi.com
Thu Jun 27 14:54:34 CDT 2013


For the EI, it's a huge current load all the way to the battery.  I 
don't know your arrangement, but on mine, I have the Autronic control 
three Bosch EI modules.  The signal between the Autronic to the modules 
is just a 5V 20ma trigger, so that's not going to cause any noise.  The 
modules switch the low side of the ignition coils.  The current path 
looks like:

Batt+ -> coil -> ignition module -> batt-

For me, the batt+ to coil wire is twisted with the batt- to ignition 
module wire.  I did scope that wire out, and discovered voltage sags 
down to 4 volts, when measured across the long battery leads, so yes, 
there's a lot of current there causing magnetic fields, which are killed 
by twisting the wires.

Alternator:
Again, current return path.  If you have a large wire from your battery 
to your alternator, it needs a brother to handle the electrons going the 
other way.
I am using my starter ground wire as the alternator ground.  These wires 
are in the left "noisy" duct, and I don't twist them there. Be 
reasonable about it.  you wouldn't want to run them down opposite ducts, 
creating a big magnetic field between your two ducts.  You'd never get 
your compass calibrated.

I do have a panel mounted card compass low and to the left that is 
unaffected by any electrical devices I use.  I tested it with all loads, 
and a battery charger on the alternator post.

On 6/27/2013 2:36 PM, John Dibble wrote:
> For an EI, is it just the wires from the controller to the coil, or do 
> all wires need to be twisted?
>
> For the alternator, does twisting include the large output wire, or 
> just the small ones?
>
> Thanks,
>
> John
>
> On 6/27/2013 2:11 PM, Brian Michalk wrote:
>> Only shield wires that:
>> 1)    radiate a lot of noise (capacitively  -- i.e., have a large dv/dt)
>> 2)    are sensitive to noise
>>
>> Position lights are very quiet, and you don't care if they collect 
>> noise from other sources.
>>
>> Strobes are noisy, so twisting and shielding the power/ground leads 
>> works there.  If your strobe power pack charge pump is RF noisy (bad 
>> capacitors) then, yes, shielding is needed, but IMO, that's treating 
>> the symptom.
>>
>> On my airplane, it's very quiet electrically.  The big offenders: 
>> electronic injectors, coil packs, alternator are all twisted 
>> power/ground pairs.
>>
>> I do not shield ANY of my avionics (not even microphones). They are 
>> quite happy with the arrangement.  Proper grounding is the key to a 
>> noise free airplane.
>>
>
>
>
> _______________________________________________
> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20130627/5593119a/attachment.html>


More information about the Reflector mailing list