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.
>>
>
>
>
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