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gdaub(at)cox.net
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 Posted: Wed Apr 08, 2009 3:50 am Post subject: Brass vs copper |
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Whem building bus bars and ground points, are there any significant reasons to use one over the other?
Thanks,
Gene
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nuckolls.bob(at)aeroelect
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| Posted: Wed Apr 08, 2009 4:43 am Post subject: Brass vs copper |
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At 06:46 AM 4/8/2009, you wrote:
| Quote: |
Whem building bus bars and ground points, are there any significant
reasons to use one over the other?
|
Brass comes in a variety of alloys and can have an
electrical conductivity of perhaps 20% that of
pure copper. But brass is generally easier to work
with in terms of drilling clean holes. It's also
a bit less reactive and subject to corrosion than
copper.
That relatively low conduction value is significant
if you were making wire . . . and needing to efficiently
carry energy long distances. But for compact parts like
bus bars, either material can be considered. While
making the same part from copper might offer 1/5th
the electrical losses, losses in a copper bus bar
are very small . . . and 5x very small is still small.
How are you intending to build ground blocks?
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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longg(at)pjm.com
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| Posted: Wed Apr 08, 2009 6:00 am Post subject: Brass vs copper |
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Gene,
Both B & C and Stein sell brass buss bar stock (what do they know?). The thought is that copper is softer and may give under torque loads. Personally I find copper to be a solid alternative. If you look at the buss on the electrical panel in your house (and everyone else's), you find mostly aluminum, albeit rather thick aluminum. The panel in your house doesn't normally move or vibrate, so that is a primary reason for using brass in airplanes which has good torque ratings.
If we took a class in metallurgy, we would likely find there are not yet tried superior metals. You would also find that the service life of one over the other will extend long after we're gone. I took calculus and we applied it to metal failure in widgets (makes you feel like it's really useful in life). The difference between copper and brass used on a tool over their life were something like 10 log -> 2 power as applied to charted figures. This basically meant you would never outlive the life of either if you rubbed it 100 times a day for the rest of your life. Interesting stuff.
Silver is a great conductor, but too soft to torque bolts too. Aluminum is also thought to be too soft. Back in the sixties the old guys tried aluminum in house wire, but later found the mice had screwdrivers and were always loosening the connections.
One nice thing about brass is that if your really worried the mounting bolts can be brazed (lightly) such that they will never come loose.
Glenn
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rparigor(at)SUFFOLK.LIB.N
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| Posted: Wed Apr 08, 2009 1:49 pm Post subject: Brass vs copper |
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As Bob stated brass does not conduct very good.Copper 101 or 110 does not machine very good.Now that is not the case for copper 1451 It machines terrific.Go to www.mcmaster.comsearch: "about copper""copper 145"Here is technical info:http://www.mcmaster.com/#8964kac/=1czbjrAlthough not quite as conductive as 101, not bad.Ron Parigoris [quote][b]
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Thu Apr 09, 2009 5:00 am Post subject: Re: Brass vs copper |
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You guys do know that you are discussing resistivity differences
in milliohms or tenths of a milliohm between copper and brass on buss
strips, right?
Aluminum is a particularly bad choice because of rapid AlO2 corrosion forming a tough skin almost immediately, and consequent resistive
losses and heating
Use unprotected copper in the engine compartment and with the heat
and reactive Nitrogen combustion species floating around, you can watch
it corrode before your eyes. Lets not even mention work hardening
from vibration loads on the connection tabs.
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Ira N224XS |
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jimw_btg(at)earthlink.net
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| Posted: Thu Apr 09, 2009 5:58 am Post subject: Brass vs copper |
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Typically Brass is 88% plus copper with tin/silicon and other elements to
alter the grain boundaries' and molecular structure so Ira is right you are
splitting hairs when discussing resistivity. You pick up strength corrosion
resistance and modulus with Brass with the exception of leaded brass which
was used for bearing materials. If you add nickel and aluminum to the tin
and silicon you change brass into bronze. Still all maintaining around 88%
plus copper. Brass and cost are the two considerations. Take care.
Jim Wickert
Vision #159
Tel 920-467-0219
Cell 920-912-1014
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rob(at)hyperion-ef.com
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| Posted: Thu Apr 09, 2009 8:22 am Post subject: Brass vs copper |
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Just to be sure we understand the science correctly….
Contrary to the direct relationship between composition and conductivity implied in your message, the effect on electrical conductivity of trace elements and alloying elements is significant for any of the usual metals used as conductors (Ag, Al, and Cu), and in the case of brass here’s how conductivity changes with the addition of zinc.
[img]cid:image001.gif(at)01C9B8EB.991E60A0[/img]
A mere 1% of tin (in the absence of any other elements besides Cu) will reduce conductivity by about 50%.
Your conclusion is of course correct. In this case brass is as good as pure copper.
Best regards,
Rob Housman
Irvine, CA
Europa XS Tri-Gear
A070
Airframe complete
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nuckolls.bob(at)aeroelect
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| Posted: Thu Apr 09, 2009 8:38 am Post subject: Brass vs copper |
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| Quote: | You guys do know that you are discussing resistivity differences
in milliohms or tenths of a milliohm between copper and brass on buss
strips, right?
Aluminum is a particularly bad choice because of rapid AlO2 corrosion
forming a tough skin almost immediately, and consequent resistive
losses and heating
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<snip>
Gentlemen,
We're getting our ties wrapped around the axles of
insignificant fact . . .
The FIRST job of any conductor is to take part in
getting the effects of electron motion piped from one
place to another. One consideration is conductivity of
the material. This speaks to efficiency . . . every
Joule of energy waste in raising the conductor
temperature doesn't help run your electro-whizzies.
The second consideration is an evaluation of processes
necessary to secure gas-tight connection between various
pieces. No matter how badly a conductor SURFACE corrodes,
the INTERFACE BETWEEN PIECES of the conduction path are
still capable of carrying energy relatively unimpeded.
The third consideration goes to issues of mechanical
robustness - a study of S/N ratios: How many times
can this material experience a predicted level of
operating stress and not develop stress-cracks?
The last consideration goes to cost of manufacturing
that looks at material cost, $time$ and processes
needed to do the best we know how to do in fabricating
the parts.
Consider these examples of bus structures:
http://aeroelectric.com/Pictures/Grounding/Grd%20Bus%20Sys1.JPG
http://aeroelectric.com/Pictures/Grounding/Forest_of_Tabs_Ground_Kit.pdf
http://aeroelectric.com/Pictures/Grounding/Avionics_Bus_3.jpg
These are SYSTEMS that blend the functional capabilities
(and limits) of raw materials, fabrication techniques,
off-the-shelf components, and the skill of both designer
and installer to meet design goals.
Bar copper bus bars will look butt-ugly 10 years
from now . . . but where they're mashed against
terminals on wires can still be performing as-
new.
Brass bus bars might need to be thicker/wider
to accommodate the higher resistance of the
material but they'll LOOK nicer and they're easier
to build due to machineability of brass versus copper.
Nonetheless, it's where the terminals grab the bus
structure that controls future performance.
Aluminum can be considered too as long as you don't
need to solder to the bus and you've taken measures
to control voltage drop to tolerable levels. Further,
you need to insure integrity of the joints that
are gas-tight today, tomorrow, and ten years from
now.
I'm aware of no bus structure on a TC aircraft where
the weakest links in the chain had anything to do with
mechanical stress of the bus bar material or its resistance
to surface corrosion. Lack of gas-tightness and structural
integrity of individual connections account for the vast
majority of ALL conductor failures whether or not they're
trying to keep a grip on a bus or any other component
of the system.
This product:
http://aeroelectric.com/Pictures/Grounding/gnd_bus.jpg
Combines PLATED BRASS tabs, SOLDERED to BRASS bus
and assembled with alloy BRASS BOLTS, and intended
to accept BRONZE terminals crimped onto COPPER wires.
Irrespective of choice of materials, there are
a variety of conditions that could precipitate
a failure of one or more conductors attached to
this bus.
Inattention to a host of potential toe-stubbers can
contribute a failure factor that has little
if anything to do with selection of copper, versus
brass or even aluminum as ONE OF MANY elements of the
system. Successful and enduring bus structures have been
fabricated from all of these materials. Each was
the preferred material for the designer for reasons
that are now known only to him.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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nuckolls.bob(at)aeroelect
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| Posted: Thu Apr 09, 2009 9:34 am Post subject: Brass vs copper |
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At 04:44 PM 4/8/2009, you wrote:
| Quote: | As Bob stated brass does not conduct very good.
Copper 101 or 110 does not machine very good.
|
"very good" is non-quantified. if you're doing
a ground bus like:
http://aeroelectric.com/Pictures/Grounding/gnd_bus.jpg
. . . just how large are anticipated voltage drops
for any accessory's ground point with respect to
the rest if the conductivity of the base material
is say 1/20th or even 1/50th that of copper?
When we're talking about hundreds of amps in
the cranking circuit, short lengths of poor
conductivity can produce significant voltage
drops . . . say in excess of 100 millivolts.
However, at the current levels comprised of the
sum total of panel mounted hardware spread over
the sheet resistance of a brass base, I'll suggest
that the voltage drops are insignificant.
| Quote: | Now that is not the case for copper 1451 It machines terrific.
|
So should we recommend that everybody endeavor
to acquire this material for the fabrication
of their bus bars? More importantly, are products
offered by B&C for this purpose to be avoided
as falling short of compliance with design goals?
Keep in mind that all the overhead wires that
carry power across the countryside are aluminum
and steel. Would we wish they were "better" conductors?
Sure. Are all copper conductors even possible much
less practical? Probably not. Has the recipe
for success been "tuned" for the best we know
how to do? Don't know . . . but in honorable,
competitive, free-market endeavors, you can
bet the most successful players have paid due
diligence to fine tuning.
The recipes for success should take consider
capabilities and limits for ALL ingredients
against the design goals. But the recipe may
NOT get better because we've sliced and diced
the comparison between competing materials.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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