Hi Donovan;

I checked an IPC chart and it showed the maximum rated temp for FR-4 to =
be 125 degree C.  If the PCB is in a 20 degree C environment then you =
are allowed a 105 degree C temperature rise form the current.

I'm not sure if a pin is going to be able to carry 20A.  As already =
suggested, you could look in the Canadian equivalent of the National =
Electric Code to determine the "ampacity" of a conductor the same size =
as your pin. Remember to consider the temperature rise from ambient.

glen=20

-----Original Message-----
From: Donovan Parks [mailto:dparks@UVIC.CA]
Sent: Friday, March 07, 2003 2:52 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: [PICLIST] [ELEC]: PCB for High Current (help)


Hello,

I am designing a PCB for a motor controller I have developed for a small =
underwater vehicle being developed at the University of Victoria =
(www.engr.uvic.ca/~auv).  I have a few concerns about putting up to 20A =
through a PCB trace though.  By searching the web I have been able to =
find a nice program by John Brown (http://hampcb.com/downloads.html) =
that calculates the maximum current carrying capacity of a copper trace =
based on the acceptable temperature raise above ambient, trace width, =
and copper thickness.  This is exactly what I am looking for except I =
have been unable to determine what an acceptable temperature raise above =
ambient is.  At what temperature will the copper trace start to peal off =
the board?

This program indicates that with a trace width of 300 mils, an allowable =
temperature raise of 50 degree C, and 1 Oz copper plating I can handle =
21A - does this sound reasonable?

In the same vein, can I put 20A though a throughhole with a pin (i.e. =
through the leg of my MOSFET from on side of the board to the other) =
without taking special precautions? I realize I can't put 20A through a =
simple via, but am not sure if I can do it with a throughole with a pin =
in it.

Sorry for all the questions and obvious lack of knowledge, but this is =
only my second PCB and the first that has carried any serious current.

Thanks,
Donovan

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