Brian,
Does the coiled wire get hotter due to the proximity of adjacent coils,
the concentration of heat in a small space, or a combination of both?
Or do they sound like the same effect expressed differently?
The straight wire and the coiled wire, if they have the same properties,
should dissipate the same amount of power in watts, correct? It is the
proximity and space constraints that cause the temperature to increase.
Thanks,
Blair
>>> [log in to unmask] 10/08/03 02:42AM >>>
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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