Hi Chris,

Can I know, when the copper pour is done, do you do it for the GND or the
Vcc or the track that is carrying the huge current? I have done an
automotive project that has an onboard relay. The relay carries huge
current, ~40A and we have practically done all that is mention. ( short
track, track on both side of the pcb and increase the width). I am
wondering, for the sake of long term usage, is it advisable that we just use
those external relay or can the board withstand the current and still
function well?

Thanks.

Pang



----- Original Message -----
From: "Chris Loiacono" <chris@MAIL2ASI.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, March 08, 2003 7:31 AM
Subject: Re: [ELEC]: PCB for High Current (help)


> I have used this calculator before. prior to that I had a hand-written
list
> that was compiled from experience. Now I use both plus some common sense.
>
> My 2 cents:
> If you have the time & $$, use 2 oz Cu or more.
> I also use the piggyback wire to trace trick - have done so for close to
20
> yrs.
> Keep the high current runs as short as possible and in open areas as much
as
> is possible. If they are beneath a transformer or some such place, they
will
> have more of a tendency to cook.
>
> Also this is a good place to do copper pours in your CAD layout - even if
> you still have some narrow points in the run the extra copper makes a nice
> heat sink which helps somewhat.
>
> Another good idea is to save enough room on the board to copy one layer to
> the other, effectively doubling the ampacity. A few extra vias evenly
spaced
> may make you feel better, but I don't kow that they actually do much -
can't
> hurt though. I regularly do 35 to 40A on all commercial board materials
> without any probles seen in many years - just by these simple means - in
> fact just finished one that is now out for fab that has a pair of 35A
paths
> on it to & from an alternistor. - was 'poured' in Eagle, mirrored on both
> sides and will be wired with some bare copper Monday!
>
>
> Don't sweat it - it was wise to look inot this, but 20 Amps is very
do-able.
>
> Chris
>
> > 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.
> >
>
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