Actually Jack you could push a lot off current through a short cooper
spring, the temperature rise is easily calculated at 50 degrees c the
current would be 7.5 to 10 amps At a max of near red hot it would be about
18 to 20 amps. The short length means there will be no adjacency heating
effect so to whole wire spring will be even in temperature. A long pcb track
will be much hoter in the center then the end's due to the fact more
temperature will be present at each point along the track from the heat
before it.. Ie the ends of a track only have heat  generated to produce
temperature from one side. Hope that helps.
BEst regards Robert tarzwell   megadawn.com

----- Original Message -----
From: "Jack C. Olson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, October 07, 2003 12:56 PM
Subject: [TN] Max Current Brain Teaser


> Does anyone out there enjoy brain teasers?
> I was asked an interesting question today.
>
> We need to have current traveling across a spring.
> The spring connects a connector pin to a SMT pad.
> We don't care how hot the spring gets as long as
> it doesn't melt the board.
> When the spring is compressed it is only 20 mils
> away from the board, but the current may have to
> travel around the circumference, so the distance
> may be more like 200 mils.
> The spring material is berrillium copper and the
> thickness is equivalent to AWG26. So even though
> a wire of this thickness may be rated 1.7 amps:
>
> What is the maximum current we can push
> through this short distance continously?
>
> We have been discussing the fact that even though
> the wire in your house may be rated for 10 amps
> and it won't get hot even on a 200 foot run, how
> much current can you drive through a half-inch
> piece? Especially if you don't care if it gets hot?
> Nothing I found on Doug Brook's site (temp calc
> and fusing current study) seemed to help.
> ( http://www.ultracad.com )
>
> thanks,
> Jack
>
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