RE: Re: T-24 Hours Until New (Really Bright 10KVA) Light...

["David Dean" <deano-at-corridor-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Ryan,

The element should not melt down, it should have an over temperature safety
switch on it somewhere that would open if it got too hot. That is based on
all the dryer elements I've seen. Of course, the safety switch may be
missing, or you might not have it hooked into the circuit...  Also, some of
the newer dryers use a different type of element, more like an oven element,
that would be enclosed in a tube that is bent into some kind of shape. Some
of the newer furnaces also use that kind of element, RUUD uses a curved rod
type element that slides down into the blower housing right by the blower
wheel. In cases like that, the safety switch is on the housing that the
element is mounted in. I just assumed that you had one of the old style
elements that is made of nichrome wire held in some kind of fixture with
ceramic insulators. Those types of fixtures are designed for the fan to blow
air through them at a pretty high velocity. I have one of those in the back,
it is rated 5400W at 240V. That would draw about 22.5A, and have a
resistance of 10.667 ohms by calculation. Unfortunately, the element has
been "repaired", that is it was broken in two places and tied back together,
so there is too much resistance in the junctions to get an accurate
resistance reading with an ohmmeter. BTW the safety switch is a round, disk
shaped thingy with a clamp or head on it that is oval in shape and has two
holes for mounting screws. It will have two 1/4" blade terminals on it for
the wires to connect, and should be in a place where it could be easily
serviced. Some dryers would also have a thermo fuse. I used furnace
elements, otherwise known as heat strips. They have both thermo switches and
thermo fuses.

With a static gap, you will find that the element gets just about as hot as
it does with a Jacobs ladder. Once you get set up and running, you will want
to lower the resistance a bit, that can be done by cutting up the element
into smaller pieces and connecting them in parallel. 8 ohms cut in half is 4
ohms, 4 ohms in parallel with 4 ohms is 2 ohms, for example.

The first test I did on my pig when I got it, was to flash it across one
120v side with a lawn mower battery and jumper cables. It would put out a
spark across a 1/4" gap between the high voltage terminals. Then I hooked up
the 120V winding to the output of a welder. That gave enough juice to power
a 4' long Jacobs ladder. Got about 10" to 12" arcs at the top of the ladder,
starting at a bit less than 1/4" near the bottom where the arc started. Then
I put a furnace element in series with the low voltage windings and powered
up with 240V. The element got real hot real fast, so I put a fan across it.
That kept the element cool enough, but disrupted the arc too much to get up
the copper tubing. Then I replaced the element with the welder primary. That
resulted in a not so stable arc. Something about Jacob ladders, they don't
seem to like inductive ballast. That is counter intuitive, as normally a
fine Jacobs ladder can be made with a NST and a couple of brass or copper
rods. When I hooked up the Tesla coil with the static gap blown by an air
compressor, the element did not get as hot as fast as it did with the Jacobs
ladder, but it still needed fan cooling. Only after migrating to a SRSG was
I able to get rid of the resistance altogether and just use inductance for
current limiting. My little welder goes down to 30A on the low range, and
does not have enough inductance to limit the current as well as I would
like. I run the secondary open, as when I short it, the current goes up, and
so do gap losses. To much loss in the gap does hurt T.C. performance. With
insufficient current limiting, you will find that the coil will not work as
well as with a "wimpy" NST. Even a 5HP two stage air compressor cannot put
out enough air to quench a power arc in a gap that has too much current
through it. Another problem I had with an air blown gap was when moisture
condensed in the air line, and a bubble of water got in the gap. Rather than
shorting the gap, as one would expect, it insulated the gap causing the
voltage to rise too high and blew a NST. (was running in reso. mode at the
time) I did not see that one comming, but I did see it happen.

I guess I've rambled on enough about nothing, so I'll just let it go now.
Will be interested to see the results.

later
deano

> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Saturday, September 16, 2000 1:17 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Re: T-24 Hours Until New (Really Bright 10KVA) Light...
>
>
> Original poster: "Ryan Ries" <spud-at-wf-dot-net>
>
> 	I ran the pole pig just last night, not on my Tesla Coil,
> but just to
> light it up in a Jacob's ladder.  I was using only the 8-ohm element,
> because I could not get ahold of my friend who had the arc welder. :) The
> element got burning hot only after a second, and I wonder how
> long it would
> last before meltdown.  I didn't test it, but I suspect that there
> was quite
> a voltage drop because the spark wasn't incredibly long, but it was many
> times brighter and hotter than anything I had ever seen before. (500
> milliamps)  Hopefully tonight I'll have the welder.  And oh yeah, I am
> completely suffering with my capacitor.  It is poorly constructed, ugly,
> and underrated.  It's made from MMC caps, but if anyone out has a ~.02µf -at-
> 20Kv or thereabout capacitor to sell, please let me know! :)  And thanks
> for all the information/help.
>
> 	Ryan Ries
>
> ----------
> > From: Tesla list <tesla-at-pupman-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: RE: Re: T-24 Hours Until New (Really Bright 10KVA) Light...
> > Date: Friday, September 15, 2000 3:15 PM
> >