Re: High Voltage but Low Current fuses...Why ? ? ?

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

Original poster: "BunnyKiller by way of Terry Fritz <teslalist-at-qwest-dot-net>" <bunikllr-at-bellsouth-dot-net>

Tesla list wrote:

>Original poster: "Mccauley, Daniel H by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
>
>
>May sound like a dumb question, but can you explain to me why you would
>need a high voltage fuse for tesla coiling?
>If your goal is to provide fusing to the output of a pole transformer or
>similar, then fusing should be placed on the
>input side instead on the 240VAC etc...
>
>Trying to design a fuse (esp. a high voltage one) is a daunting task in
>the least.
>Contrary to most people's belief, fuses are EXTREMELY complex devices.
>Not something you can just take a piece of wire and
>make a simple fusible link out of.
>
>The Captain
>
>
>
> > Hi,
> >
> > Apparently, there is a need for a "Tesla coiling fuse".  The
> > mid-voltage
> > fuses and all are not right for "our stuff"...
> >
> > The key is that we do not need to break a "sustained" 4000
> > amps or anything
> > like that.  A say 5 amp continuous AC current, 0.25 amp,
> > 30,000 volt fast
> > blow fuse is what we need.  Not really hard to make, but none
> > of the big
> > guys seem to make a high voltage fuse that is designed to work with
> > "little" currents...
> >
> > We make take a 4000 amp "hit" from a big impulse cap, but
> > then the current
> > falls to like 100mA in our case...
> >
> > I think I got a new project ;-))
> >
> > Cheers,
> >
> >          Terry
> >
> >
> > At 09:43 PM 7/15/2003 -0400, you wrote:
> > >Chris,
> > >Actually, most standard fuses do fail with time, even when
> > operated within
> > >their specified ratings.  There are microscopic cracks and
> > inhomogenieties
> > >in the fuse bar which get locally hotter than the rest of
> > the material,
> > >thus further propagating the defect.  Eventually, the defect
> > lowers the
> > >functional rating of the fuse, and the fuse blows,
> > frequently with the
> > >turn-on current rush, or just during normal operation.
> > That's one reason
> > >that critical equipment usually has a spare fuse in a holder
> > right next to
> > >the working one.
> > >Dave
> > >
> > >
> > >>I would think that would work here, too, only with pen springs or
> > >>similar.  But that's probably more complex than a simple
> > weight.  The
> > >>weight mustn't be too large or it could promote a premature
> > failure over
> > >>time - copper creeps when hot.
> > >
> >
> >
>
an example I can think of needing hi volt fusing would be in an attempt to 
protect the secondary of the transformer from hi volt peaks from missed gap 
fires, resonate rise on the secodary side...  just to name 
some...  sometimes MOVs arent quite enuf to protect the secondary side 
circuits...

Scot D