Today's Message Index:
----------------------
1. 01:17 AM - Inflight load return wire size (Stuart Hutchison)
2. 04:57 AM - Inflight load return wire size (Ben Boatright)
3. 05:48 AM - Re: Inflight load return wire size (ROGER & JEAN CURTIS)
4. 07:19 AM - Re: Inflight load return wire size (Robert L. Nuckolls, III)
5. 09:00 PM - Re: Inflight load return wire size (Stuart Hutchison)
Message 1
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Subject: | Inflight load return wire size |
G'day Bob,
I have an all-metal aircraft without much room for large diameter wires,
especially two. I recall reading that it's a good idea to have power and
return lines of the same size for small systems, but is it really necessary
to have a return wire to the battery of the same size as the starter wire?
In other words, I have # 2 AWG CCA fatwire from the battery (down aft) to
the starter contactor at the firewall, but I would like to use a # 6 CCA
fatwire for inflight currents? I was thinking of grounding the engine to
the airframe, but using an # 6 CCA fatwire for return to the battery
(insulated from the airframe - to which normal inflight loads [lights,
avionics etc] would be connected). Is this idea OK?
Cheers, Stu
Message 2
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Subject: | Inflight load return wire size |
There was a very good article in one of the aviation magazines recently that
discussed grounding. The article pointed out that your ground wire should be
as large as (or larger) than your positive wire.
Keeping the size to those rules should minimize and/or eliminate any ground
feedback looping.
Ben
J. Ben Boatright
-----
benboatright@gmail.com
-----
Member, AOPA and EAA
On Mon, Jun 13, 2011 at 4:13 AM, Stuart Hutchison <
stuart@stuarthutchison.com.au> wrote:
> stuart@stuarthutchison.com.au>
>
> G'day Bob,
>
> I have an all-metal aircraft without much room for large diameter wires,
> especially two. I recall reading that it's a good idea to have power and
> return lines of the same size for small systems, but is it really necessary
> to have a return wire to the battery of the same size as the starter wire?
> In other words, I have # 2 AWG CCA fatwire from the battery (down aft) to
> the starter contactor at the firewall, but I would like to use a # 6 CCA
> fatwire for inflight currents? I was thinking of grounding the engine to
> the airframe, but using an # 6 CCA fatwire for return to the battery
> (insulated from the airframe - to which normal inflight loads [lights,
> avionics etc] would be connected). Is this idea OK?
>
> Cheers, Stu
>
>
Message 3
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Subject: | Inflight load return wire size |
I have an all-metal aircraft without much room for large diameter wires,
especially two. I recall reading that it's a good idea to have power and
return lines of the same size for small systems, but is it really necessary
to have a return wire to the battery of the same size as the starter wire?
Cheers, Stu
I own a "tin" T/C aircraft (Cessna Cardinal) and it has the
battery in the rear. The negative terminal is connected directly to the
airframe with a short cable. There are no other cables going to the
negative side of the battery. This seems to work well for Cessna, in that
they use the whole airframe as ground reference. When you use this method
always be sure that you have a substantial ground strap from the engine to
the airframe.
Roger
Message 4
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Subject: | Re: Inflight load return wire size |
At 04:13 AM 6/13/2011, you wrote:
><stuart@stuarthutchison.com.au>
>
>G'day Bob,
>
>I have an all-metal aircraft without much room for large diameter wires,
>especially two. I recall reading that it's a good idea to have power and
>return lines of the same size for small systems, but is it really necessary
>to have a return wire to the battery of the same size as the starter wire?
>In other words, I have # 2 AWG CCA fatwire from the battery (down aft) to
>the starter contactor at the firewall, but I would like to use a # 6 CCA
>fatwire for inflight currents? I was thinking of grounding the engine to
>the airframe, but using an # 6 CCA fatwire for return to the battery
>(insulated from the airframe - to which normal inflight loads [lights,
>avionics etc] would be connected). Is this idea OK?
I'm not getting a good mental image of your proposed ground
system architecture. How long are the wires in question?
If you take the approach illustrated in Figure Z-15 View -A-
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z15K1.pdf
. . . you can consider the option of taking a same-size battery
ground wire to the single-point, firewall ground -OR- grounding
the battery locally
http://aeroelectric.com/Pictures/Grounding/Local_Battery_Grounds_1.jpg
2AWG wire may be somewhat oversized too. Unless you have a
really big engine or the battery is a long ways away from
the starter, 4AWG wire might be adequate to the task.
But I do suggest you review your grounding philosophy in
light of suggestions offered in Z-15 and chapter 5 of
the 'Connection.
Bob . . .
Message 5
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Subject: | Inflight load return wire size |
Thanks Bob,
Yes, I have an IO-540 with the starter about 10 feet ahead of the battery.
This configuration is needed A) due to space limitations and B) for weight
and balance. I understand the need for a big cable to carry start current
and planned to ground this current via the airframe to a local bonding strap
next to the battery. However, after start, normal inflight currents will
obviously feed via the same big cable to the hot pole of the starter
contactor, then to the busses and I would like to ground via a dedicated
return to the battery post that is only 6 AWG and is insulated from the
airframe. I don't understand why we need an return cable the same size as
the starter wire when only 60-70A max is passing through this during flight?
Z-15 shows the engine bonding strap connected to a 2 AWG return all the way
to the battery, but I propose not to do this, since high currents are only
required during start and can be grounded via the airframe for that short
period. I would have thought any noise generated during start would be
acceptable, because it is temporary? Perhaps different sized power and
return wires cause noise regardless of whether they are both quite able to
carry the current .. I don't know?
Kind regards, Stu
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: Tuesday, June 14, 2011 12:01 AM
Subject: Re: AeroElectric-List: Inflight load return wire size
--> <nuckolls.bob@aeroelectric.com>
At 04:13 AM 6/13/2011, you wrote:
><stuart@stuarthutchison.com.au>
>
>G'day Bob,
>
>I have an all-metal aircraft without much room for large diameter wires,
>especially two. I recall reading that it's a good idea to have power and
>return lines of the same size for small systems, but is it really
>necessary to have a return wire to the battery of the same size as the
starter wire?
>In other words, I have # 2 AWG CCA fatwire from the battery (down aft)
>to the starter contactor at the firewall, but I would like to use a # 6
>CCA fatwire for inflight currents? I was thinking of grounding the
>engine to the airframe, but using an # 6 CCA fatwire for return to the
>battery (insulated from the airframe - to which normal inflight loads
>[lights, avionics etc] would be connected). Is this idea OK?
I'm not getting a good mental image of your proposed ground
system architecture. How long are the wires in question?
If you take the approach illustrated in Figure Z-15 View -A-
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z15K1.pdf
. . . you can consider the option of taking a same-size battery
ground wire to the single-point, firewall ground -OR- grounding
the battery locally
http://aeroelectric.com/Pictures/Grounding/Local_Battery_Grounds_1.jpg
2AWG wire may be somewhat oversized too. Unless you have a
really big engine or the battery is a long ways away from
the starter, 4AWG wire might be adequate to the task.
But I do suggest you review your grounding philosophy in
light of suggestions offered in Z-15 and chapter 5 of
the 'Connection.
Bob . . .
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