Re: Big x-ray transformers and Jacobs Ladders.

["Tesla list" <tesla@xxxxxxxxxx>]

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

Jim, David,

I agree with David to a point. Yes, current is more of what de-
termines the maximum arc length attainable in a Jacob's ladder than
voltage, but I've gotten very good results from an x-ray transfromer
driving a Jacob's ladder. I power my "ladder" with a 150 kV,
600 mA rated x-ray tranny and get self starting arcs with about
a 5" spacing at the "start". The rails spread to about 18" or so
at the top. The transformer stands about 3 ft high and the pole pig
bushings adds about another 10" and I only have 8 ft high ceilings in
my garage, and I don't want the arc hitting the ceiling at the end of its
travel. All of these factors pretty well limit my arc travel distance
but I can still feed the transformer with over 100 amps from my
huge custom control panel that also feeds my Green Monster
coil, and I get some very impressive and wicked looking arcs ;^)
BTW, I've never been able to get the x-ray transformer's outer
tank case to reach any perceivable warmth above ambient tempe-
rature, even after several minute non-stop runs of 120+ amps!
X-ray transformers are truly beasts! Also, like I said above, you
will have NO problem getting the arc to start with the 100 kV+
voltages available to start the arc. With only 10 to 15 kV, it seems
like the rails almost have to "touch" to start the arc, especailly if the
rails are rather large in diamater, which increases the radius of
curvature and consequently, the breakdown voltage!

David

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Sunday, April 22, 2007 10:32 PM
Subject: Re: Big x-ray transformers and Jacobs Ladders.


Original poster: David Speck <dave@xxxxxxxxxxxxxxxx>

Jim,

It's my understanding that the arc length of a JL
is primarily dependent upon the current
available, not the voltage. Once the arc is
established, the voltage drop across it is only a
few hundred volts, if that much. Supplying it
with more voltage doesn't do anything to increase
the arc length. Other list members have reported
that X-Ray transformers have made disappointing
JLs, because they can supply relatively little current.

How much current is your current pole transformer
rated for? If you go for a higher rated
transformer, and can supply it with enough
current, then you should be able to get longer
arcs. However, JLs are hungry beasts, and you do
need a lot of current to drive them. Ed Wingate's
JL draws a maximum of nearly 100 amps at 240 VAC.
I'm not completely certain, but I think he was
driving it with at least a 10 or 15 KVA
transformer to get about 24 - 36" arcs at the final break.

I'll have to dig through my reference books about
the GE flaming 20 foot three phase arc display at
the 1939 NY world's Fair. Although they were
billed as "Million volt" transformers, the
leakage inductance of the transformers made them
function like giant self ballasting NSTs,
according to the retired GE employee I once
talked to about them. They were driven by big
motor gensets onsite, rated for a great many
horsepower. It was the high current available to
them that made the spectacular continuous arcs.

Dave

Tesla list wrote:
>Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>
>
>Hello List,
>
>I am considering purchasing a Big box x-ray
>transformer, somewhere near 100kv at >150ma
>single phase 240v 60hz for a large Jacob's
>ladder. What has been anybodies' experience with
>these? It is presently DC out but I would remove
>the diodes and filters and put a flat plate on
>top with (2) 14,400v horns on it. Evidently
>others are doing this without arcing to the grounded case.
>
>Here's the question: how big of arc could I
>expect to draw on a dry, windless night. I have
>not been able to get much more the 12-14" with our usual 14400 driven hard.
>
>.A bit off topic, but hopefully of interest.
>
>Thanks,
>Jim Mora
>
>