/Ah, now what if the "wire" was not circular in cross section ?
/Let's say the conductor was of rectangular cross-section, and
/rather thin. In the extreme, if the conductor was very thin,
/the surface area would increase at twice the rate cross-sectional
/area increases, as the width of the conductor was increased.
/In that case, heat dissipation and temperature rise would not
/be the limiting factor; the voltage drop would.
Now you're thinking like an engineer (a process that is not
the sole privilage of engineers . . . in fact, I know lots
of graduate engineers that can't think like one).
/Does that make a case for flat conductors where temperature rise
/might be an issue ? Probably not. They would be a pain to work with.
Sure does. There have been many designs for large powerhandling
systems and components where flat, thin counductors were designed
to minimize temperature rise in conductors. About 15 years ago
I designed a multi-speed trim system for the Learjets. I wanted
to minimize the amount of single strand wiring used and looked
carefully at using as much insulation displacement, flat ribbon
cable as I could inside the black box. Two conductors had to be
capable of carrying 16 amps . . not something you'd normally consider
running through a "bundle" of 26AWG wire! Some simple tests showed
that I could parallel 6 strands of the ribbon cable, and have very
nominal temperature rises at 20 amps.
The reliability of insulation displacement connectors and uniform,
predicable paralleling of multiple conductors in a ribbon cable
allowed me to take advantage of "thin and flat" for power handling.
Although the conductors were short (about 5"), being able to
munch connectors on and solder them to the boards with ZERO
wiring errors was a big help. I'll bet I've got the only
product on the surface of the planet that flys around in high
performance airplanes carrying tens of amps in itty-bitty wires
of a ribbon cable.
/But I have read about some builders using flat conductors
/[bonded to fuselage sides] from their battery. The aim here
/though was to minimise space, and as you say, voltage drop
/under cranking is the issue here, not temperature rise.
If someone wanted to develop the technique for doing so, the IDEAL
way to bring battery juice forward in a metal airplane would indeed
be with a thin, flat conductor bonded to but insulated from the skin.
Super heat rejection and local heat sinking. It's a technique that
would take some very careful integration mechanically with construction
of the skin and it's attachement to formers and ribs. Theoretically
a very attractive idea but pretty labor intensive . . probably more
trouble than the investment would be worth.
/p.s. Bob, I really enjoy your discussions and tutorials.
Thank you, they're fun to do!
Bob . . .
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