Re: Does anyone want an OLTC Driver board

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 19:31 19/05/03 -0600, you wrote:
>Original poster: "Zagarus Rashkae by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <arbitrarily_random-at-yahoo-dot-com>
>
>
>DARN NICE! I would love to build an OLTC, I have a big
>brick, and the thing that put me off was the driver
>board. 30-40 bucks sounds like a great deal
>considering I spent 200 bucks on my conventional TC.
>THe OLTC should build for under 100 bucks.

Mine cost me about $75 most of which was for three IGBTs (I blew one of 
them) The secondary takes a bit more labour than a normal coil. Another 
reason to build a big OLTC because the wire will be thicker and more 
manageable.


>Is it designed to sense and turn off the IGBT on the
>first notch?

Sort of. This part of the design is a compromise. The driver just turns the 
IGBT off during a negative half-cycle of the oscillation to stop it being 
wrecked by kickback. You have to tell it which half-cycle is the right one 
for your coil design. There is a Quenching pot on the driver board that you 
adjust, either with a scope, or running the coil at low voltage and 
adjusting for the biggest spark. This is a set and forget adjustment unless 
you do something that changes the primary-secondary coupling.

I must stress again that these things are still at the prototype stage and 
I won't be selling anything until a few people with well-equipped labs have 
beta tested it. I wouldn't want to disappoint people. In any case, if you 
choose to build an OLTC with a brick, you will be setting off into the 
unknown. We don't yet know how the different makes and models of bricks 
will respond to high-frequency currents. When MMCs were invented, some 
brands of caps worked great, others had a tendency to explode or go on 
fire, and with bricks it'll probably be much the same.

Steve C.