x-ray transformers - was Re: Power factor correction

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>

Aaron,

I use a 125 kVp, 500 mA rated x-ray transformer to power my Jacob's 
ladder. You are correct in that an x-ray transfor-
mer should NOT be operated completely open circuit on its
secondary, high voltage output. However, beyond that little
caveat, x-ray trannies, at least the old 60 hz input style ones,
are NOT fragile! Since >100 kV can easily jump several inches, a 
typical Jacob's ladder setup will NOT overtax the internal insulation 
of an x-ray transformer, unless your closest approach of the rails 
where the arc starts is over a foot apart!
I can run mine drawing 80 to 100 ballasted amps, at
around 200 volt input for as long as I please without being
able to "feel" noticable warmth above ambient temperature by touching 
the outer tank case of the transformer. And it's
nice to be able to "self start" the arc at the bottom without
needing a capacitor or a sharp point, or having to "stick" something 
across the electrodes to start the arc, as is often
the case with sub-20 kV voltages. The big disadvantages of
typical 60 hz input x-ray trannies with 100 to 150 kVp at 300 mA or 
more output is that they are very heavy (usually well over 300
lbs and often in the 500 to 800 lb range), they require exter-
nal ballasting, you must have the matching Federal male
receptacle plugs with cables to access their HV output,
and you will need to open them up and remove the internal
rectifier diodes to use them as a Jacob's ladder driver
( this requires an engine hoist or ratchet hoist and is an oily
mess), as the short circuit currents, even ballasted, will eventually 
burn out the diodes. And while you have it opened up, you might
as well go ahead and remove the low voltage filament transformer(s)
and their associated wiring as they will just be extra dead weight 
for this purpose. So an x-ray trannie powered Jacob's ladder makes 
for quite an impressive climbing arc but they are a bit
of a pain tio set up and they atr NOT portable!

David Rieben


----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, June 21, 2006 1:26 PM
Subject: RE: Power factor correction


> Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>
> I've heard (though I may be wrong) that the PF of a
> Jacob's ladder isn't that bad, since it's a short
> circuit.  Isn't PF a bigger issue for large but
> lightly-loaded transformers, motors, etc.?  Now I'm
> gonna have to go do a bunch of reading...damn!! :-))
> The biggest problem I've observed with large Jacob's
> ladders is the voltage spikes created every time the
> arc breaks and returns to the bottom.  You need a big
> cap in *parallel* with the transformer, or you can
> damage your home wiring and any plugged-in electronic
> devices pretty easily.  These spikes are also hard on
> the transformer's insulation, but I've never heard of
> a pig dying this way.  At 15kVA, my pig was generating
> 600V (peak) spikes every time the arc broke!  When I
> saw that on the scope, I stopped playing with large
> Jacob's ladders :-(
> At 15kVA, my pig-based ladder didn't go "bzzzz" at
> all.  It made a very warm 60Hz tone that you could
> "feel".  The output was a pure white, totally opaque
> flame.  This was 14.7kV at nearly an amp.  I'm
> guessing the sound has a lot more to do with current
> than voltage, but I could be wrong about that.  I'm
> thinking that an x-ray tranny will be more "bzzzz",
> but a much longer initial arc (probably won't stretch
> much, though, due to low current).  I've been told,
> however, that x-ray trannies tend to ofen have high
> open-circuit voltages (above their rating), and that
> running them full-bore in a Jacob's ladder-type setup
> can cause them to flash over internally and croak.
> Anybody want to confirm or deny that?  I have the
> opportunity to pick up an x-ray tranny, but they've
> always sounded a bit fragile to me.
> Regards,
> Aaron, N7OE
> --- Tesla list <tesla@xxxxxxxxxx> wrote:
> > Original poster: "Dave Halliday" <dh@xxxxxxxxxxxxxx>
> >
> > He is not talking "modest"
> >
> > Your Jacobs Ladder makes a nice bzzzzzzrt,
> > bzzzzzzrt, bzzzzzzrt sound
> > (at 3,000 Watts) while I bet that his sounds like a
> > large wolverine in
> > heat. I have one from a 15KV 60MA (9,000 Watts) neon
> > transformer that
> > sounds wonderful and I can only imagine what
> > something running at 34KW
> > would be like.
> >