Homebrew HV transformer help

• To: tesla-at-pupman-dot-com
• Subject: Homebrew HV transformer help
• From: "Jon Lagler" <rockcrawl-at-netzero-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Sat, 11 Mar 2000 19:40:37 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hello,
 I'm working on rewinding a transformer for TC use. The core is from an old
welder and has a variable current shunt, or at least I think it's a current
shunt. If I'm correct, this will work like the shunts in an NST, and no other
current limiting will be needed. The total core size is 8x8x4.5 inches, and it
is basically an EI core, but with just E's butted together in the center. I
have uploaded a picture to
<http://www.fortunecity-dot-com/silverstone/impala/403/trans.jpg>http://www.for
tunecity-dot-com/silverstone/impala/403/trans.jpg . Sorry, my camera died before I
could take more pics. My question is how to configure the secondary. Do I need
a center tapped secondary? Because of the moveable shunt laminations, there is
only room for two coils, unlike a neon which has three. I'll be using the
original plastic bobbins. Here are a few layouts I have come up with:
 
1. Primary wound on one bobbin, secondary wound on separate bobbin with no CT.
 
2. Primary wound on one bobbin, secondary wound on separate bobbin with CT at
1/2 of total turns.
 
3.Split primary between two bobbins, split secondary wound on top of primaries,
with CT obviously between the two separate coils.
 
As it is now, the transformer has the primaries for 208 and 230 on the top
bobbin, with multiple secondaries on both bobbins. It (the welder) is rated for
230 volts at 30 amps. I used the equations at
<http://members.aol-dot-com/tesla00/hbt.htm>http://members.aol-dot-com/tesla00/hbt.htm
to design new windings for a 230 volt primary and 12kV/500mA secondary. The
formula tells me primary current should be 25 amps. I expect to have to run
this swine under oil.
 If my core is larger than needed, will it not work?, what will be the effects?
I can imagine a gearmotor attached to the screw shaft to adjust the output from
the control panel. This is all a lot of work, considering I could probably buy
a pig for $100, but this is much more fun and something to be proud of (if it
works).
 Sorry for the semi-long post, I've tried to supply enough info to get my
questions answered. Any comments/suggestions are welcome and appreciated.
 
Thanks,
Jon Lagler
PA, USA

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