Re: Large ferrite cores for SSTC work

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

Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>


> If the transformer core is heating up and you have corona, then you have
> a misdesigned transformer.

Yeah, that's true, but despite everything I tried, it just didn't work out
to un-misdesign the transformer... :( 

Maybe I got the formulas wrong, somehow. I've a design sheet up at
http://www.hut.fi/~jwagner/tesla/SSTC/SSTC-Designer.xls which I used for
calculating the number of turns required. Maybe you could have a quick
glance and check whether or not the numbers seem to be in the ballpark? 

(i.e. for a fullbridge with 5cm^2 e-core 3c85, 150kHz, 350VDC in, 1400
Gauss delta-B, 32 pri turns is the real minimum?)

> It is there simply to match the FET driver to the input of the
> magnifier.  If you have < 2:1 SWR into the magnifier, then most of the
> available power will go to the magnifier and sparks produced.

By "match", you probably mean a current the driver can deliver at which
it does not yet blow up? At this (and smaller) output current, the driver
and coil impedances will always be "matched". I don't know about SWR -
there shouldn't be any, unless the fets once again decide to blow up or
the driver goes to PWM/PW limiting.

> 1:10 ratio is on the high end.   Rob.

*ouch*! I did built a couple with >1:20 ratio (about 6kVac), although I
started with 1kV. 10cm was the best streamer length achieved...
subjectively impressing, objectively not. :o(

many thanks,

 - Jan

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