Re: How much current can a PCB handle?


John Woodgate wrote:
In message <1155652891.579330.12840@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, dated
Tue, 15 Aug 2006, Andrew <xxragexx@xxxxxxxxx> writes
Are you saying it depends on where the connections are, within the
trace?

I think when you get the message, you will kick yourself.

Think about wire instead of copper foil. I have this copper wire which
is 0.5 inches square and four inches long. It has a resistance from one
end to the other (4 inches) of X ohms.

Now I have this copper billet, which is 4 inches wide by 0.5 inches
thick and 0.5 inches long. It has a resistance from one end to the other
(0.5 inches) of Y ohms. Y is not equal to X!

Yes, unless the board conductor is a geometrically-square ***, the
resistance does depend on where on the edges you connect to it. Even
with a square, it does vary a bit if you have only point contacts.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

So where the connections are matter *alot*. I get it now, I think.

The "from one end to the other" phrase you list is the key component.
The ends meaning where the connections are made. You could take the
same copper billet and place the connections (ends) the "long" way and
it would be the same as the copper wire, right? If so, I understand
completely.

I just didn't realize how important the closeness of the connections
was for current capability, when talking about an entire copper area or
plane.

Would this be correct to say as well: That the resistance is
determined by the closeness of the connections. The copper that
expands outward (width) is for heat sinking.. ?

If so, is there a point where the width stops affecting thte
resistance, at least significantly enough to consider?

(Sorry if these are ridiculous questions, but I've never considered how
resistance is affected by shapes and where connections are, etc)

.

Quantcast