Today's Message Index:
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1. 01:08 AM - Re: Aluminum bronze - conductivity (Stuart Hutchison)
2. 06:28 AM - Re: Aluminum bronze - conductivity (Robert L. Nuckolls, III)
3. 07:30 AM - Re: Hour meter ground (Richard Girard)
4. 08:19 AM - Re: Aluminum bronze - conductivity (Eric M. Jones)
Message 1
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| Subject: | Aluminum bronze - conductivity |
Thanks guys.
I've made lots of aluminum and stainless parts for underwater photography
and yes, the galvanic corrosion between them can be brutal immersed in an
electrolyte liek sea water. Ultra Tef-Gel from B&C Specialty helps, but I
suppose aluminum adjoining stainless is very common at the firewall and
doesn't seem to present too many problems without an electrolyte ... I could
be wrong, but that area stays pretty dry and I haven't witnessed much
corrosion at the firewall on aircraft. I'm less worried about the aluminium
bronze oxidising - a gas tight seal is obviously important because all the
usual metal options oxidise, but there must be tens of thousands of aircraft
with ground wires bonded direct to aluminium. I guess I'll just use
di-electric grease to keep the air out at the point where the stud meets
with the firewall, or perhaps make a phenolic bush to insulate it from the
stainless, then bond the stud to a substantial part of the aluminum
structure on the inside (such as an engine mounting bolt).
Kind regards, Stu
F1 Rocket VH-FLY <http://www.mykitlog.com/RockFLY>
http://www.mykitlog.com/RockFLY <about:www.teamrocketaircraft.com>
www.teamrocketaircraft.com
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Henador
Titzoff
Sent: Thursday, May 03, 2012 1:11 AM
Subject: Re: AeroElectric-List: Aluminum bronze - conductivity
With copper and aluminum, it's bound to be extremely low resistance, but the
aluminum will corrode on the surface to form alumina, which may interfere
with good connections. Why not send that puppy off to Eric at Perihelion
Design to get it copper plated? Or better yet, why not go with copper bar?
It's relatively cheap and known good material. Beats ripping out something
that didn't work that well.
Henador Titzoff
_____
From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
Sent: Wednesday, May 2, 2012 10:18 AM
Subject: Re: AeroElectric-List: Aluminum bronze - conductivity
At 05:33 AM 5/2/2012, you wrote:
G'day Bob,
Do you reckon aluminum bronze is suitable to be used in place of brass for
the main firewall ground ? It has plenty of copper in it, but are there any
known nasties when it's used adjoining stainless steel - I'd like to turn a
custom large-flanged firewall passthrough for the engine ground.
Hmmmm . . . I have no reason to believe it's
any worse. Brass isn't the greatest of conductors
but the way we use it (large cross-sections and/or
short lengths) the electrical resistance doesn't
raise concerns. I don't know any specifics about its
reactivity with other metals but I think anything
against stainless is pretty low risk . . .
Perhaps others on the List have experience foundations
from which to advise you further . . .
Bob . . .
href="http://www.matronics.com/Navigator?AeroElectric-List">http://w=======
Message 2
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| Subject: | Aluminum bronze - conductivity |
At 03:06 AM 5/3/2012, you wrote:
Thanks guys.
I've made lots of aluminum and stainless parts for underwater
photography and yes, the galvanic corrosion between them can be
brutal immersed in an electrolyte liek sea water. Ultra Tef-Gel from
B&C Specialty helps, but I suppose aluminum adjoining stainless is
very common at the firewall and doesn't seem to present too many
problems without an electrolyte ... I could be wrong, but that area
stays pretty dry and I haven't witnessed much corrosion at the
firewall on aircraft.
Agreed.
I'm less worried about the aluminium bronze oxidising - a gas tight
seal is obviously important because all the usual metal options
oxidise, but there must be tens of thousands of aircraft with ground
wires bonded direct to aluminium.
The legacy process involves putting a tin-plated copper
terminal down on a brightly buffed area of aluminum and
applying lots of pressure with the attach hardware. The
surface areas in gas-tight contact are, as you suggest,
not subject to environmental stresses. The outside of the
joint can get pretty cruddy with age without having the
connection go bad.
I guess I'll just use di-electric grease to keep the air out at
the point where the stud meets with the firewall, or perhaps make a
phenolic bush to insulate it from the stainless, then bond the stud
to a substantial part of the aluminum structure on the inside (such
as an engine mounting bolt).
I think clean, grease and lots of pressure are key. Additional
bonding is not useful.
Bob . . .
Message 3
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| Subject: | Re: Hour meter ground |
On Wed, May 2, 2012 at 11:13 PM, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> nuckolls.bob@aeroelectric.com**>
> The tach has its own signal wire.
None of the Rotax wiring diagrams for the various regulators has an AC
> going to ground.
As pointed out, the note on the drawing for the hour meter says if one of
> the AC feed wires is grounded that wire is used for pin 5 on the meter.
> Otherwise the two AC wires feed the meter and it makes no difference which
> goes to the meter connections.
Rick
> At 02:46 PM 5/2/2012, you wrote:
>
>> Bob, Yes, as you can see they show one side of the AC leg going to ground.
>>
>> Rick
>>
>
> Hmmm . . . separate winding for the tachometer. Your
> AC power to the rectifier/regulator cannot be grounded
> on one side so that you can have full-wave rectification.
> This tach coil is a very low power source. Do you have
> an electronic tach reading this output too? In any case,
> exactly where it grounds (if at all) is of little
> consequence. These two systems are neither potential
> antagonists nor victims. Does your tach wiring call out
> grounding of one side of the signal wire?
>
>
> Bob . . .
>
>
--
Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
Message 4
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| Subject: | Re: Aluminum bronze - conductivity |
> Why not send that puppy off to Eric at Perihelion Design to get it copper plated?...Henador
The copper clad aluminum I sell is not plated. This wouldn't be good, plating always
has pinholes and wears off. The Super-CCA I sell is "clad" which is a process
where copper and aluminum are fused together. 10% of the diameter of the
crossection is actually copper. Copperweld Inc., historically made lots of different
stuff clad with copper by this process. It is important to know that
there is a long history of aluminum wiring problems, but essentially NO HISTORY
of CCA problems. The wire behaves very much like copper
Some notes of metals:
1) In many applications the conductivity of the metal is less important than the
surface reactivity with atmospheric oxygen (or in the case of titanium only,
with nitrogen). Impure aluminum oxide is the same as sapphire or corundum and
is quite insulating. Copper oxide looks bad but still conducts electricity well.
Same for silver. It can turn black and conduct well. Stainless steel, nickel,
chrome and aluminum looks great initially but turns into an insulator. This
usually happens slowly. Battery contacts made of stainless steel were once
the bane of cheap electronics.
2) See: http://aerospacedefense.thomasnet.com/Asset/MIL-F-14072.pdf Finishes for Ground Based Electronic Equipment. There is probably an aircraft-version of this but it is all the same chemistry.
3) Gold has zero reactivity with the atmosphere. Gold is only a fairly- good conductor
but is great for low voltage electrical contacts. Silver is the best conductor
followed by copper, then aluminum.
4) Aluminum has over TWICE the conductivity per unit mass of any other metal. So
learning how to use it can save weight. The electrical power industry uses far
more aluminum than copper outside the home. Aluminum wiring in houses (that
used electrical plugs and switches designed for copper) were retrofitted by adding
a short pigtail of copper with special grease in a wirenut or crimp connector.
5) Galvanic corrosion depends on the Electrode potential in the electro-chemical
series AND presence of an electrolyte--saltwater perhaps but water will do.
If you put dissimilar metals together, but keep them air-tight and dry, there
is no problem.
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=372337#372337
Attachments:
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