Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>
I killed a PC power supply (not the whole PC,
fortunately!) running my 25kVA pig as a Jacob's
ladder, sans line filter. I was doing about 15kVA at
the time, IIRC. Since getting a large 75A line
filter, I have observed that the spiking is suppressed
substantially, though. Whenever the arc reached the
top of the ladder and broke, I'd get a 600V (peak)
spike. Nasty!!! I was ballasting with a water
resistor at the time. Not sure, but inductive
ballasting seems likely to make the problem worse. I
did not notice any significant reduction in the spikes
when I used my smaller 15kVA pig, either.
The reason I'd call really big spikes like this
"worse" than RF from a TC is that, to me, they seem
more apt to compromise the insulation in your house
wiring, setting the stage for badness like fires, and
other things that would be really difficult and
expensive to diagnose and fix. Others may have had
really bad experience with RF from TCs...I guess I
*should* have said this: Big Jacob's ladders are
quite able to fry stuff in your house, just like TCs
with no filter. They're not "safe" in any way (to you
*OR* your supply). A lot of people wire up big
Jacob's ladders on a whim. I was one. For posterity:
I recommend a bit more caution these days :-)
Regards
Aaron, N7OE
--- Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "David Rieben"
> <drieben@xxxxxxxxxxxxxxx>
>
> Aaron,
>
> I hope the moderator will allow a little bit of
> latitude here since
> we are talking about Jacob's ladders but this post
> will also ad-
> dress Tesla coils and many coilers build JLs as well
> during the
> "learning curve" toward building a coil. That
> flickr.com JL photo is from
> Clint Dickey, who was a list member at one time, but
> not sure he
> still subscribes. He resides about 55 miles from me
> here in the
> Memphis area and I helped him put a lot of his stuff
> together. I
> assume his "15 kVA" nomenclature is referring to the
> rating of that
> pole pig, which it was, and not to what he was
> actually pul-
> ling from the wall socket.
>
> BTW, I've never experienced any of the "voltage
> spike" problems
> caused by the arc "snapping" at the bottom of the
> rails when it
> starts its "climb" that you mention, although I'm
> sure that under the
> right or wrong circumstances, actually, this could
> be a problem.
> I wouldn't agree that it could be more of a problem
> than
> with a large Tesla coil that draws similar power
> levels, though. I've done
> quite a bit of damage to other sensitive electrical
> components in
> my house in the past from firing a large Tesla coil
> but have never
> damaged anything from firing a JL, even a very large
> and powerful
> one. Maybe the control panel ballasting that I use
> to control the
> input to my 125 kVp, 500 mA x-ray transformer helps
> to suppress
> any of the transient nasties that could try to feed
> back into the house
> wiring by the snap of the arc starting? However, the
> ballasting didn't stop
> damaging kickbacks from the large coil when I did
> something wrong,
> as I use the same ballasting control panel for my
> large Tesla coil that
> I use for the x-ray transformer powered JL.
>
> David Rieben
>
>
> ----- Original Message ----- From: "Tesla list"
> <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Friday, June 23, 2006 1:35 PM
> Subject: RE: Power factor correction
>
>
> >Original poster: "J. Aaron Holmes"
> <jaholmes@xxxxxxxxxxxxxxxxxx>
> >(gettin' a bit OT here, but...)
> >Jacob's ladders are mostly about current, not
> voltage.
> > You need current to generate plasma/heat, and
> heat to
> >make the plasma/arc rise. More current will permit
> >the arc to "stretch" longer. If you have mega-high
> >voltage but virtually no current, then the legs of
> >your Jacob's ladder will be far apart and nearly
> >parallel, since there will be little "stretching"
> >involved, and this in turn will probably yield
> >inconsistent performance (arc frequently giving up
> and
> >restarting at the bottom before it reaches the top,
> >etc.)
> >NSTs make ok Jacob's ladders. A 15/30 can produce
> an
> >arc that self-starts at under an inch but may
> stretch
> >to a couple of inches before breaking and
> restarting
> >at the bottom of the ladder. Fun, easy to build,
> and
> >(relatively) safe. Still, the lack of current in
> the
> >NST case can make ladder peformance inconsistent,
> and
> >placing the ladder in some kind of enclosure may be
> >necessary to allow convection (and thereby the arc)
> to
> >be more consistent.
> >A typical 14.4kV pig is about like a 15/30 for
> >voltage, but can deliver several amps! This has an
> >enormous influence on ladder performance; the arc
> can
> >easily be made to stretch to a foot or more!
> Here's a
> >picture of what that might look like (from some
> >Googling--not sure whose this is, really):
> >http://www.flickr.com/photos/tesla1000/page3/
> >The picture has "15kVA" above it, and "14,400
> volts, 2
> >amps" below it, which doesn't quite add up!! The
> >latter would be about 30kVA, not 15kVA, but
> >whatever... Note, too, that the arc is a totally
> >opaque white flame. There is a big difference
> between
> >a Jacob's ladder running ~15kV at 30ma and 2A!!!
> >BUT (!!!): Beware the Voltage Spikes of Doom!
> Running
> >big Jacob's ladders is a good way to kill stuff in
> >your house just as surely as a lot of RF from a TC,
> >maybe worse! Put some caps across the LV side of
> the
> >tranny to eat these up or you could really have a
> mess
> >on your hands.
> >Regards,
> >Aaron, N7OE
>
>
>
>
>