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nuckolls.bob(at)aeroelect
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 Posted: Sun Nov 19, 2023 8:08 am Post subject: Power, signal, and Coax - How should they be bundled? |
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| Quote: | | Menzimer . . . Actuonix . . . . etc |
These actuators are about as EMC friendly
as any motor driven accessory can be. Actuators
with 2500 pounds of push drawing 10+amps
and themselves weighing 10 pounds are
similarly free of EMC concerns.
They are not potential victim or antagonist
in the aircraft environment. You can route
their wires with impunity. Spent a goodly
portion of my career working with such
devices on all manner of trim systems from
Lears, Beechjets etc down to the T6 and Bonanzas.
Not one of those systems required any special
treatment for during runs through
the EMI/EMC gauntlets during certification.
The itty-bitty devices popular in our projects
are no different.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
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nuckolls.bob(at)aeroelect
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| Posted: Wed Nov 22, 2023 7:59 am Post subject: Power, signal, and Coax - How should they be bundled? |
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| Quote: | Your point seemed to be that there is never a problem running power
and signal lines together so just do it. My point is that this is
true most of the time, but not all of the time. |
Recall that 'power' conductors are potential antagonists
that do their dirty work via magnetic coupling to parallel
conductors. 'signal' conductors are potential victims never
vulnerable if (1) ground loops are designed out of the
system and (2) shields are properly terminated. They are
otherwise vulnerable to electro-static coupling.
For a power conductor to be a nuisance, it must carry
LOTS of 'bumpy current'. The b-lead on an alternator,
a power feeder for hydraulic landing gear pump or really
honky flap system MIGHT be a potential antagonist . . . but
how likely is it that any of these leads might become bundled
with lines carrying micro/millivolt signal levels which
are in turn, poorly configured for noise immunity?
In my whole career, I've encountered only two such
events. One on a car I purchased in OSH where a major
bus feeder got bundled with a speaker lead. I could
barely hear alternator whine in the speaker whether
the radio was on or not. Separating the power lead
by a few inches fixed the problem.
The other was on a Hawker 800 where a cooling blower in the
tail was powered from a source in the cockpit. The
single conductor ran the length of the airplane
sharing a bundle with wires that were signal inputs
to a terribly conceived annunciator system. Inrush
currents to the little blower would cause several
annunciator to illuminate momentarily. Had to tack
some capacitors to the annunciator system inputs
to fix this one.
Energy coupling between parallel conductors is
exceedingly weak so it takes some extra-ordinary
conditions of two or more errors of design
for the problem to manifest.
In our projects, worrying about such things
is not useful.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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Voyager
Joined: 30 Jun 2020
Posts: 77
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| Posted: Wed Nov 22, 2023 8:34 am Post subject: Power, signal, and Coax - How should they be bundled? |
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I think we are generally in agreement. I never suggested “worrying” about electrical noise, I simply suggested designing it out where it is nearly free to do so. Gently twisting wires has a huge effect on noise generation and susceptibility. Professor Van Doren demonstrated that 1 twist per inch in a pair of 22 awg wires decreased the mutual inductance by 43 dB compared to untwisted wires. This is 11 dB better than the same untwisted wires in a steel conduit (32 dB improvement over baseline)! Since gently twisting wires is easy to do, I do it as a matter of course. And SteinAir sells twisted pair red and black wires ideal for power circuits in aircraft at almost no price premium compared to the wires bought separately. To me, this is just a no-brainer thing to do. If this required significant effort, I wouldn’t bother.
Same with separation of power and signal wires. In my airplane, it is very easy to run power down the left side of the fuselage and signal down the right side. No worry required, just a simple precaution that costs virtually nothing in either dollars or time. So why not? In my case it is actually easier as I would need to make larger holes to run everything together down one side. If there was a case where only one hole existed, then I’d run everything through that hole and not lose much sleep. However, if it is equally easy to separate power and signal, I will do that every time.
As I mentioned earlier, my RANS home built is my first aircraft electrical system design as my experience was in industrial control and data acquisition systems. So, I claim no specific aircraft design expertise. I have, however, been a pilot since 1978 and have flown a variety of Cessna and Piper aircraft and my experience has been that such aircraft are terrible in regards to electrical noise management. I have not flown one yet that didn’t have some popping, hissing or static in the headsets. Not a single one. So, it isn’t obvious to me that aircraft designers have paid much attention to noise mitigation. My automobiles have been far superior to any GA airplane I have flown or owned in this regard. I think the only vehicles where I ever had significant noise issues were made in the 1970s or earlier.
Matt
Sent from my iPad
| Quote: | On Nov 22, 2023, at 11:01 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:
 | Quote: | Your point seemed to be that there is never a problem running power
and signal lines together so just do it. My point is that this is
true most of the time, but not all of the time. |
Recall that 'power' conductors are potential antagonists
that do their dirty work via magnetic coupling to parallel
conductors. 'signal' conductors are potential victims never
vulnerable if (1) ground loops are designed out of the
system and (2) shields are properly terminated. They are
otherwise vulnerable to electro-static coupling.
For a power conductor to be a nuisance, it must carry
LOTS of 'bumpy current'. The b-lead on an alternator,
a power feeder for hydraulic landing gear pump or really
honky flap system MIGHT be a potential antagonist . . . but
how likely is it that any of these leads might become bundled
with lines carrying micro/millivolt signal levels which
are in turn, poorly configured for noise immunity?
In my whole career, I've encountered only two such
events. One on a car I purchased in OSH where a major
bus feeder got bundled with a speaker lead. I could
barely hear alternator whine in the speaker whether
the radio was on or not. Separating the power lead
by a few inches fixed the problem.
The other was on a Hawker 800 where a cooling blower in the
tail was powered from a source in the cockpit. The
single conductor ran the length of the airplane
sharing a bundle with wires that were signal inputs
to a terribly conceived annunciator system. Inrush
currents to the little blower would cause several
annunciator to illuminate momentarily. Had to tack
some capacitors to the annunciator system inputs
to fix this one.
Energy coupling between parallel conductors is
exceedingly weak so it takes some extra-ordinary
conditions of two or more errors of design
for the problem to manifest.
In our projects, worrying about such things
is not useful.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
|
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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