A coiled wire will get much hotter than a straight wire for a given
current, always. However, I disagree that you should care how hot it
gets. It can go through phase changes which will reduce the springiness
if it gets too hot. I don't have phase diagrams for BeCu, so cannot give
you a max. However, BeCu is precipitation-hardened at about 300°C for
most usual alloys, so I feel it would be unwise to exceed ~200°C,
depending on the % of Be.

Brian

Jack C. Olson wrote:
> 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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