Re: DIY HV transformer

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Christoph Bohr" <cb@xxxxxxxxxxxxxxx>

Hello Mike

> Well, you already wound it , but the way I'd wind it for built-in limiting
> is use an E-I core ( or a rectangular I-core fore less weight if 1 is
> handy) with the Primary in the center and the 2 secondaries (midpoint
> ground em for 1/2 the insulation needed) on either outer leg.

Well, I would have chosen that way too, but this was the only big core I
had at hand. Using this core as normal E/I core would not work, as all
3 legs have the same cross section. A pic of the original core can be seen 
here:
http://www.luebke-lands.de/pics/trafo1.jpg
I removed the center leg, use one original winding as 160 turns primary and
on the opposite side there sits the HV coil I wound.
When I take this core with a primary in the middle and two HV windings
on the outer leg, I only have half the magnetic flux density there, resulting
in only half the induced voltage which would require twice the number of turns.
>From insulation standpoint certainly still worth it, but 20K was just to 
many...
I feel like at 14KV I can get away with it when I run it under transformer 
oil....

> As long as
> the total magnetic path length seperating the pri/sec is at least 1/2  the
> total length and there's enough primary turns to keep the core from
> saturating with the given voltage, it'll be limited like an nst (open
> circuit voltage drops to about 1/2 under short circuit). No extra iron for
> shunts/ external ballast needed.

Alex Boekeler from the GTL just gave me more insight into this topic today
and I will carry out some tests when I assemble the core tomorrow
(still have to weld new mounts for the dowel pins to add some clearance to the
secondary coil).

Thanks for you input.
best regards

Christoph