Re: High Voltage but Low Current fuses...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi Jim,

At 07:51 PM 7/15/2003 -0700, you wrote:
>Why not use thin aluminum wire... much lower melting point, much faster
>transition from solid to liquid (as anyone who as attempted to weld Al can
>attest)

Oh!!!  I have a large roll of 10mil diameter aluminum wire bond wire that 
was tossed because it was exposed to a finger print or something.

Wire bonding Al has a high silicon content, but we'll just assume it is 
pure...  The fusing current for 10 mil Al is 7.48 amps.  A little high, but 
maybe good enough to play with.  Al has that bad thing about connecting to 
the oxidized wire....

Copper wire is far easier to find...

I = k x d^(3/2)

0.25 = 10244 x d^(1.5)   d== 0.841mil

That falls right off the charts for available copper wire...   Size 43 is 
at 1.057 amps if one can find it that thin...  Very low current fuses use 
either "thin" wire from Heck, or have resistors (and springs) in them to 
"aid" in heating and fusing.

Of course, if we discharge a 7 Joule 20kV cap into it, it's gone!! 
;-))  And that is exactly the kind of "mistake" we may see in real life for 
the differential probe.  I am starting to like MOVs again...  They over 
heat but then "short".  That might be perfect along with a thin wire fuse 
to stop the really bad stuff...

Now I know why these are not "off the shelf" items ;-)))

Cheers,

         Terry