On Sun, Jan 22, 2006 at 09:18:38PM -0500, Peter Todd wrote:

Well, I got some boards back with my PCB fuses design etched into
them... Results are as follows:

http://petertodd.ca/persist/2006-02-04/pcb_fuses.jpg

The holes are standard 0.1 grid spacing. The fuse traces were 8mil wide.

Sure enough you guys were right, the shortest fuse, the extreme left
and right, didn't blow very well at all, it's heat getting conducted
away from the wire. The best results were obtained with the longest
fuses.

I didn't accurately measure current/energy used, but for what it's worth
I used 20V from a large power supply for each one. On almost every one
the current meter on the supply moved about half an amp, of course peak
currents were probably high all the same, but it's a good sign. The
longest traces blew with a bit of a spark, pretty much instantly.

Testing with 4mil traces could prove interesting... And I'll find myself
some low-ESR caps to properly measure the energy used sometime.

> Thanks!
> 
> Geezus, that's really scary, 5.12 amps for a 6mil dia wire...
> 
> The chart looks accurate to me though. I've got some #32 stainless steel
> wire for another project. According to your chart, iron fails at 2.21
> amps. In my experience, SS is about 2.5A Not the exact same material of
> course, but that's close.
> 
> I wonder if it's possible to get circuit boards that have *just* tin as
> the conductive layer? Tin's fusing current is one-fifth that of copper.
> 
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> pete@petertodd.ca http://www.petertodd.ca
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