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RE: OLTC II Even bigger arcs

Original poster: "Adam Horden" <ath-at-blueyonder.co.uk> 

Hi All,

I got some excellent photos of Steve Conners OLTC as well.

The page is here:


I got some shots of ground arcs as well.

I even got one of it arcing to the primary.

Adam Horden

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: 03 June 2004 15:09
To: tesla-at-pupman-dot-com
Subject: OLTC II Even bigger arcs

Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>

Hi all

Some of you might remember the OLTC II, the large solid-state disruptive
coil that I have been working on for almost a year now. It is basically
same as a classical coil, but with an IGBT "spark gap replacement".

I just demonstrated it at the UK Teslathon and it worked great, giving
strikes up to 73". This was using a bang energy of ~8J at 400bps. It
produced a couple of ground strikes (which we sadly never got pictures
and even struck its own primary coil, triggering the overvoltage
circuit. Luckily the protection circuit did its job, as changing an IGBT
a half-hour job with a socket wrench, and cheap replacements are getting
bit harder to find.

The IGBTs are currently running at 2500A peak each. This is twice the
maximum pulse rating but I expect they will take up to 8000A each. So it
should be possible to get even more output from this coil by just using
bigger toroid and more tank capacitance.

But it will need a new primary circuit with lower resistance, as the one
using just now, made from copper pipe and twelve coax speaker cables in
parallel, runs dangerously hot. The MMC bank, IGBTs, and secondary coil
get slightly warm.

Here is a great pic taken by James Pawson

There are more pics from the UK Teslathon on Mike Harrison's website

And you can read technical details of the OLTCII here (look for Tesla

A big thankyou to Terry Fritz who built the original OLTC, and donated
to this project too.

Steve Conner
Head of Power Electronics Misapplications
"We start with the absolute max ratings and work our way up"