Re: [TCML] Any one using a 7200 V pole pig?

["Roger Smith" <rwsmith@xxxxxxxxxxxxxx>]

Hi Charlie,  I got a 7200 volt, 5kva pole pig out of oil that I use to run 
my large DC resonant charging  Tesla coil.  The pole pig drives a DC voltage 
doubler circuit so the Tesla coil gets about 15000 volts.  One nice thing 
about this set up is that the charging choke takes all the abuse so your 
rectifiers and pole pig will last forever.     Another thing you could do 
with it would be to get something like a 3CX10000A3 triode and build a large 
vacuum tube Tesla coil.

           I couldn't resist looking you up in the ham radio call book and 
I see you live in Bethesda Md.  Cool, I use to live in Silver Spring 
Maryland but I am livening in Ohio now.

Roger ,  KC8FTQ
----- Original Message ----- 
From: <cbroring@xxxxxxx>
To: <Tesla@xxxxxxxxxx>
Sent: Saturday, March 06, 2010 7:18 PM
Subject: [TCML] Any one using a 7200 V pole pig?


I've been messing with my first Tesla coil for several weeks now.  It
has a 3.5" x 20" secondary, two OBITs in parallel for power, a sucker
gap, and 13nF beer bottle salt water primary capacitor.  After fiddling
with it a lot,  I managed 28 inch strikes between the break out point
and a metal tool chest, my official measuring technique.

Today I replaced the OBIT's with an old 7200V pole pig that weighs
nearly 100 pounds and has been out of it's oil for years..  I used 4.7
ohms resistive ballast, and ran it off 120V with the low voltage
windings paralleled..  I had to reduce the spark gap to about half of
what I was using with the OBIT's to get it to fire.  The result was 8
inch streamers and a screech from the spark gap.  I added another 6 nF
to the primary capacitor, re-tuned the primary coil, and the streamer
length doubled. The spark gap also sounded more normal.  The ballast
resistors are rated at 450 watts and didn't get all that hot so I
wasn't putting much power through the system.

I think I understand whats going on here.  The OBIT's were running near
resonance with the 12 nf capacitor and along with the wide spark gap
setting I was seeing much higher voltages across the primary capacitor
then I have with the pole pig.  Now I have low voltage and lots of
current available now so I need a lot of capacitance and a small
primary inductor with high current capacity.  It's also going to be
harder to cool the narrow spark gap.

My question is whether a 7200 V pole pig is worth using?  I see that I
am going to have some issues to work around using this low voltage.
Also going to have to drink a lot more beer to provide bottles for
capacitors.  I'm thinking it may be a better approach to find a higher
voltage transformer or even just a few more OBIT's

Any comments or suggestions?

Charlie
K3YA
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