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Bus bar materials

 
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nuckolls.bob(at)aeroelect
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PostPosted: Tue May 08, 2018 7:40 am    Post subject: Bus bar materials Reply with quote

At 10:03 PM 5/6/2018, you wrote:
Quote:
Joe,

Thank you for that calculation. It sounds like thicker material would be better.
I think that I will try flattening a piece of copper tube. Any excuse to play with
a hydraulic press and solder in the same day is a good excuse

On Sun, May 6, 2018 at 9:43 PM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote: --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>
The area of your bus bar is 0.025 x 0.5 = 0.0125 0.0125 equals 12,500 circular mills which is slightly bigger than 10 AWG.

"Circular mills" is a different kind of area. It's simply the diameter of
a conductor in thousandths squared. 10AWG ~ 0.100" diameter
or 100 mills. 100^2 is 10,000 hence the circular mill rating
of 10,000. The real cross section of 10AWG is pi x radius^2
or 0.05 x 0.05 x 3.14 = 0.0078 square inches.

Circular mills are a unit of area PROPORTIONAL to cross
section. The cross section of the cited brass bus
bar is indeed 0.0125 Square Inches which is about
1.5 times the cross section of a 10AWG solid wire . . .
but let us consider another case:

Suppose you have a wire 1.000 inches in diameter (1000 'mils').
The CMA value for this conductor would be 1 million while the
cross section would be 0.5 x 0.5 x 3.14 or 0.785 square inches.
A bar having a cross section of 1.000 x 0.785 would have
an area of 785,000 square mills . . . the same cross section as a
1.000" diameter wire of 1,000,000 CMA.

So when comparing the cross section of the bus with that of
10AWG wire, be aware of the 0.785:1 ratio between square mills
and circular mils.

Another consideration in this thread is the relative conductivity
of the materials being considered. Copper and brass have wide
ranges of RESISTANCE. Resistance is the major driver in a conductor's
ability to (1) transport the energy with acceptable losses and (2)
carry the current while maintaining temperature rise below
acceptable limits.

Silver has a resistance of 1.6 uOhm/cu-cm
Copper is something like of 1.7 uOhm/cu-cm
Aluminum alloys . . . 3 to 6 uOhm/cu-cm
Copper alloys (Brass) . . . . 6 to 10 uOhm/cu-cm

Of all common materials for use as stud-to-stud bar
construction, copper is electrically superior with brass trailing
a distant 4th place.

'Copper equivalent' brass bars may be fabricated
by making the cross section ~4 times that of
the copper one.

Aluminum has been used in production aircraft with
good success and only needs to be 2x fatter
electrically . . . but is thermally superior
for heat conduction . . . so copper and aluminum
are about equal.

The biggest caveat for using aluminum is to strive
for gas-tight electrical joints . . . moisture present
at the interface between differing alloys combined
l with oxygen promotes corrosion which in time can
lead to joint failure. Coating the surfaces with some
robust moisture barrier (DC4 or even WD40) before
making up the joint will impeded moisture/oxygen ingress.

For the instance that germinated this thread, I'll suggest
that an aluminum bar cut from sheet or off the shelf
extrusion is easy to fabricate . . . and the parallel
surfaces go to achieving gas-tight interfaces of the
made up joints. Copper sheet good too. Mashing copper
tube is kinda good if you can really put the mash on
the material between PARALLEL jaws.

If it were my airplane, I'd go for aluminum sheet
with some good 'dope' in the joints. Aluminum is a
whole lot easier to drill!





Bob . . .


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art(at)zemon.name
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PostPosted: Tue May 08, 2018 6:15 pm    Post subject: Bus bar materials Reply with quote

On Tue, May 8, 2018 at 10:39 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
    If it were my airplane, I'd go for aluminum sheet
    with some good 'dope' in the joints. Aluminum is a
    whole lot easier  to drill!


Bob​,
​That's good to know. I have a whole boatload of scrap aluminum.​
When you say "dope," do you mean dielectric grease like this: https://www.homedepot.com/p/CRC-3-3-oz-Technician-Grade-Dielectric-Grease-05113/206843029 ?
    -- Art Z.

--
https://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel


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BARRY CHECK 6



Joined: 15 Mar 2011
Posts: 669

PostPosted: Wed May 09, 2018 7:55 am    Post subject: Bus bar materials Reply with quote

Art:

The term is Electrical DUCK Grease; it is just the opposite of Dielectric
Grease.
It is a CONDUCTOR grease which usually has very fine copper or silver dust
in it.
I doubt if silver is available today as the cost would be ridiculously high


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PostPosted: Wed May 09, 2018 1:06 pm    Post subject: Bus bar materials Reply with quote

Quote:

That's good to know. I have a whole boatload of scrap aluminum.

When you say "dope," do you mean dielectric grease like this: https://www.homedepot.com/p/CRC-3-3-oz-Technician-Grade-Dielectric-Grease-05113/206843029 ?

I checked the SDS on this stuff . . . it's a very
close cousin to the Dow Corning product I mentioned.
It would be fine.


Bob . . .


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PostPosted: Wed May 09, 2018 1:28 pm    Post subject: Bus bar materials Reply with quote

At 09:34 AM 5/9/2018, you wrote:
Quote:
Art:

The term is Electrical DUCK Grease; it is just the opposite of Dielectric Grease.

We're talking different materials that serve
two different purposes. There are useful materials to
add to joints in rigid components common to high
power technologies like submarines, sub-stations
etc. These not only exclude moisture, they contain
electrically conductive enhancements for crossing
voids that cannot be closed with tension in the
bolts.

Then there are treatments intended to fill tiny gaps
between mated surfaces to prevent ingress of water/oxygen
that progressively degrades the joint. I have a tube
of Dow Corning DC4 that has lasted about 40 years
. . . it doesn't take much. It's used to thinly coat
mating surfaces of DUCTILE terminals. Any DC4 caught
in the squash on the two metals is simply extruded out.
But the tiniest voids in the interface will remain
completely filled with DC4. Other, non-reactive
materials would work too. Axle grease is better
than nothing. The CRC product cited is good.



Bob . . .


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art(at)zemon.name
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PostPosted: Wed May 09, 2018 6:19 pm    Post subject: Bus bar materials Reply with quote

Bob,
Thanks for the info. I will opt for the CRC from the local Home Depot instead of paying shipping for DC4.
Cheers,
    -- Art Z.


On Wed, May 9, 2018 at 4:27 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 09:34 AM 5/9/2018, you wrote:
Quote:
Art:

The term is Electrical DUCK Grease; it is just the opposite of Dielectric Grease.

  We're talking different materials that serve
  two different purposes. There are useful materials to
  add to joints in rigid components common to high
  power technologies like submarines, sub-stations
  etc. These not only exclude moisture, they contain
  electrically conductive enhancements for crossing
  voids that cannot be closed with tension in the
  bolts.

  Then there are treatments intended to fill tiny gaps
  between mated surfaces to prevent ingress of water/oxygen
  that progressively degrades the joint. I have a tube
  of Dow Corning DC4 that has lasted about 40 years
  . . . it doesn't take much. It's used to thinly coat
  mating surfaces of DUCTILE terminals. Any DC4 caught
  in the squash on the two metals is simply extruded out.
  But the tiniest voids in the interface will remain
  completely filled with DC4. Other, non-reactive
  materials would work too. Axle grease is better
  than nothing. The CRC product cited is good.



  Bob . . .


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BARRY CHECK 6



Joined: 15 Mar 2011
Posts: 669

PostPosted: Fri May 11, 2018 5:16 am    Post subject: Bus bar materials Reply with quote

Bob:
The question that Art brought up is due to inconsistency in terms; you used the term 'dope'.  
From Art's question I gathered he wanted to do two things:
1 - Insure electrical contact and
2 - Prevent corrosion due to the elements and dissimilar materials.
I agree we, are talking two different products.
Dow Corning DC 4 is a Dielectric Grease.
By definition and manufactures recommendations it is used to COAT a joint in preventing contact by the elements.
Dielectric means INSULATE. 
It does NOT improve the conductive properties of metals or dissimilar metals.
It protects them from the elements.  Which is a good thing if that is all you want to do.
The product which has the industry nickname DUCK GREASE does BOTH - Protect and Ensure electrical conductivity, especially between dissimulator metals.  
Personally I think this particular coating process is just a bit beyond normal requirements.
Why?  Well, I would have to ask:  Is the owner going to REPEAT the exact same process every Annual/Safety Inspection?
Remove/open the entire connection, clean the mating areas, replace the lock-washers and re-coat the area [with what ever process he deems acceptable]?
Human Nature and 20+ years working on peoples planes, says: No!
Considering how DUCK GREASE is used, it does not require replacement and it is used between mating parts.  BUT!  I still think it is Belts & Suspenders and Shoelaces.  
Many of the certified planes out there are around 40 years old.  They nBarryow have a history.  Those connections were NOT opened every Annual/Safety Inspection.  Yet!  They continue to work!
If the additional coating process extends the unknown life of the connection / plane ...  GREAT!  We will see in 41 years.  LoL!
And Art...  If you want to obtain Dielectric Grease it can be purchased at Auto Stores, it comes in a Yellow Packet, packaged by Permatex.  Cost: About $1.00.
Duck Grease is not as easy to find.  Electrical Supply Outlets - It comes in a squeeze bottle usually with a red label and white writing.  
Barry


On Wed, May 9, 2018 at 5:27 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 09:34 AM 5/9/2018, you wrote:
Quote:
Art:

The term is Electrical DUCK Grease; it is just the opposite of Dielectric Grease.

  We're talking different materials that serve
  two different purposes. There are useful materials to
  add to joints in rigid components common to high
  power technologies like submarines, sub-stations
  etc. These not only exclude moisture, they contain
  electrically conductive enhancements for crossing
  voids that cannot be closed with tension in the
  bolts.

  Then there are treatments intended to fill tiny gaps
  between mated surfaces to prevent ingress of water/oxygen
  that progressively degrades the joint. I have a tube
  of Dow Corning DC4 that has lasted about 40 years
  . . . it doesn't take much. It's used to thinly coat
  mating surfaces of DUCTILE terminals. Any DC4 caught
  in the squash on the two metals is simply extruded out.
  But the tiniest voids in the interface will remain
  completely filled with DC4. Other, non-reactive
  materials would work too. Axle grease is better
  than nothing. The CRC product cited is good.



  Bob . . .


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PostPosted: Fri May 11, 2018 8:51 am    Post subject: Bus bar materials Reply with quote

At 08:14 AM 5/11/2018, you wrote:
Quote:
Bob:

The question that Art brought up is due to inconsistency in terms; you used the term 'dope'.
From Art's question I gathered he wanted to do two things:
1 - Insure electrical contact and
2 - Prevent corrosion due to the elements and dissimilar materials.

I agree we, are talking two different products.

Dow Corning DC 4 is a Dielectric Grease.
By definition and manufactures recommendations it is used to COAT a joint in preventing contact by the elements.
Dielectric means INSULATE.
It does NOT improve the conductive properties of metals or dissimilar metals.
It protects them from the elements. Which is a good thing if that is all you want to do.

That IS all I want and expect it do to . . .

Quote:
The product which has the industry nickname DUCK GREASE does BOTH - Protect and Ensure electrical conductivity, especially between dissimulator metals.
Personally I think this particular coating process is just a bit beyond normal requirements.
Why? Well, I would have to ask: Is the owner going to REPEAT the exact same process every Annual/Safety Inspection?
Remove/open the entire connection, clean the mating areas, replace the lock-washers and re-coat the area [with what ever process he deems acceptable]?

Yeah . . . AC43.13 used to have a paragraph or
two about "inspection of bus bars . . . with
recommendations for refurbishment on condition.

If any combination is assembled to specs and remains
tight, then there is no reason to 'inspect'. This applies
to every rivet in the airplane, all the fasteners in
the engine, etc. etc.

Quote:
Human Nature and 20+ years working on peoples planes, says: No!
Considering how DUCK GREASE is used, it does not require replacement and it is used
between mating parts. BUT! I still think it is Belts & Suspenders and Shoelaces.

When you simply twist two strands of freshly
exposed wire together in the classic 'Western
Union" telegraph splice . . . that joint is
presently as good as it will ever be. The
telegraph guys didn't solder them because tension
on the suspended wires maintained gas-tight
connections where the forces peaked on the
interfaces. Solder was later used to enhance
integrity from environmental stresses . . .
an excellent encapsulation that protected
the edges of the regions of gas-tightness.

DC4 or any other material used in the interface
of devices on threaded fasteners does the same
thing. The day that the assembly is made up
brand new . . . is as good as that joint is
ever going to be. Now, if the fastener stays
tight and DC4 (or other good stuff) protects
the boundaries of gas-tightness . . . the join's
integrity will not degrade with age.

Quote:

Many of the certified planes out there are around 40 years old.
They nBarryow have a history. Those connections were NOT opened
every Annual/Safety Inspection. Yet! They continue to work!
If the additional coating process extends the unknown life of the
connection / plane ... GREAT! We will see in 41 years.

My point exactly. We did not use ANY goops, greases,
magic juice or pixie dust in the assembly of
production airplane. The goal was to create joint
with a life expectancy longer than the airframe
itself . . . with, what you have observedis a
high degree of success.

DUCK grease may well be belt, suspenders and shoe
laces . . . but DC4 (or equal) is at least belt and
suspenders and probably useful in the most exposed
joints . . . like those ground screws on an antenna?


Bob . . .


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