From: tomb@hplsla.hp.com (Tom Bruhns)
Subject: Re: Trace size for a 15 Amp supply
Organization: HP Lake Stevens, WA
Lines: 34

acollins@uclink.berkeley.edu (Andy Collins) writes:

>How thick do I need to make a PCB trace for 15 Amps of current? and
>Does anybody have any other thoughts on the process (what kind of PCB
>to use, materials, thickness of copper, any advice graciously accepted)?

In four replies, I've seen no hard numbers, so here goes:  For traces
on the outside (not inner layers), expect, in 1 oz copper, at 15 amps,
the following temperature rises versus width.  This is from Sams'
"Reference Data for Engineers," seventh edition, Pg 5-30, which claims
in turn to be from MIL-STD-275C...

    width   Temp rise
    inches  degrees C
    ------  ---------
     .125	100
     .15	 75
     .17	 60
     .20	 45
     .24	 30
     .33	 20

At 10 amps, the rise for the .125 width is only about 30 degrees.
Power goes as square of the current, plus the copper resistance goes
up as temperature goes up...  Certainly .20" (~5mm) traces should be 
ample for what you want to do.  And 2 ounce copper almost cuts the 
required width in half.  (I'd do 2 oz at about 0.08" width myself, 
I think...given that the _rated_ current is 10 amps and the 15 is
a transient or fault condition.)

(There's another question: will the voltage drop be low enough?
But you should be able to figure this one out with wire tables or
just the resistivity of copper.  Keep traces short and use separate
sensing traces where appropriate, as mentioned by another poster.)
