[Beowulf] Interesting google server design
Lux, James P
james.p.lux at jpl.nasa.gov
Thu Apr 2 12:01:49 PDT 2009
> However, I would imagine this is a trivial amount at 12 VDC
> vs 5 VDC and the incredibly short distances the electricity
> travels on a PCB trace.
Actually, it's a non-trivial amount. Consider that a processor that draws 100W at 3.3V is drawing 30Amps.
If you're using 2oz copper (typical for a high power application), and you allow a 10C rise, the trace, if inside the board, needs to be 1.7 inches wide. A 3 inch long trace will have a loss of 0.4W (which is small).
If you can put the trace on the outside of the board, it can be about half the width, but you'll lose a watt in a 3" long trace.
Drop the current to 10A, and you're down to a .4" trace inside the board, and .15" wide outside.
You could let it get hotter, but that gets you into junction temperature problems and/or thermal distortion issues.
Play around here
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