>> > Yesterday, I sat down to figure out if my busses were adequate.
Current
>> >plan is to use 1/2" strips of .031" silver. The busses are little and
>> >short, so I was mostly worried about temperature rise, less about voltage
>> >drop.
Temperature rise and voltage drop go hand-in-hand . . . loss
of energy due to voltage drop converts directly to heat. However,
thin strips of bare metal have the BETTER heat rejection than
insulated wires of the same cross section. Further, because
the strip is bolted to the terminal posts of circuit breakers
every inch or so, you can probably get by with a very thin
foil . . . buss bars tend to be thick for the purpose of making
them mechanically favorable to work with.
>> Silver? Talk about overkill! Trust me, it isn't an issue.
>>
>*** Yeah, well, I was going to make them of copper ( "Gee", said my IA, "all
>the busses in my Bonanza are copper" ) but the FSDO inspector wanted me to
>put in inspection requirements for the copper. Something like
>
> "Inspect for corrosion at annual. If corrosion is found, remove bus and
>burnish it off. Use Swiglet special tool PAQ-FIBS-1 for burnishing. Bus is
>adequately burnished when it looks like new copper. Replace bus if, after
>burnishing, it is less than 0.XX inches thick or less than 0.XX inches
>wide."
This statement probably grew out of a paragraph in AC43-13 wherein
a suggestion is made for "periodic cleaning of buss bars for
corrosion" or something like that. EAA asked me to comment
on the rewrite of AC43-13 about two years ago, I pointed out that
properly assembled hardware attaching bus bars to breakers uses
multi-tooth lockwashers or at the least, properly torqued fasteners
that create GAS TIGHT joints. If properly assembled, very corroded
bus bars can have perfectly good electrical properties because the
place where breakers and screws hit the bar are SEALED from
environmental effects. Most copper production bus bars are
tin or solder plated to retard corrosion of bare copper surfaces.
However, when clean hardware is assembled with internal tooth
lockwashers under properly torqued fasteners, that joint is
good for a lot more years than you're going to own the airplane.
The science of crimping terminals to wires calls on the same
conditions for getting two pieces of metal into intimate contact
with each other.
None-the-less, after EAA comments were forwarded to
the FAA, -and- the document went back to the techwriters
for another two years worth of work, AC43-13 is still loaded
with poorly crafted suggestions and requirements that receive
further bastardization when invoked by ignorant people with
power.
> ...Since I used silver, I was able to say something more like
>
>"Since busses are solid silver, they should remain free of electrically
>significant corrosion for the life of the airplane".
Silver is about as reactive to atmospheric stresses as copper.
Why would we need "silver polish" for the family heirlooms
were it not so? However, assembled with proper hardware and
techniques, a silver bus bar will perform no better or worse
than its copper brothers.
>...I had the silver sheet just lying around, anyway. My dad was an amateur
>jeweler, and when he died, I got all his stuff. That silver has been in the
>closet for 15 years. I'd kept it because I thought it might come in handy
>for RF projects.
I've got a couple of silver bars that I bought about 20 years
ago to silver-plate the inside surfaces of VHF antenna duplexer
cavities I was building out of copper clad etched circuit board
material . . . here's where a few molecules of silver laid
on top of the copper was really worth the effort. Don't anyone
run out looking for silver strip to "update" your airplane's
bus bars . . . anyone who suggests it's either necessary or
useful simply doesn't understand the physics involved.
Bob . . .
////
(o o)
< Independence Kansas: the >
< Jurassic Park of aviation. >
< Your source for brand new >
< 40 year old airplanes. >
http://www.aeroelectric.com
|