Re: Large ferrite cores for SSTC work

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

Original poster: "rob by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rob-at-pythonemproject-dot-com>

Tesla list wrote:
> 
> Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jwagner-at-cc.hut.fi>
> 
> >       I'm starting to resume my work on my solid state Tesla coils at
> > the moment, and I am looking at getting in some large ferrite
> > transformer cores for the main matching transformer. I've spoken
> > to a few other people who are also after ferrite cores, so I
> > thought I'd see if there is enough interest to organize a bulk
> > buy.
> 
> Just thought I'd add my 2 cents: the hassle with ferrite cores isn't,
> at least IMHO, worth all that trouble of designing, winding and isolating
> an array of test-transformers. It requires a stunning amount of xfrm
> expertice to get working properly at all, not to metion all the maths you
> have to wade through...
> 
> You get considerably better TC output with a direct primary drive scheme,
> without the ferrite core transformer in between.
> 
> Furthermore, the size of the core is quite irrelevant!! The most
> important things are it's material characteristics: heating losses vs
> frequency, permeability, cross section, power handling capacity.
> 
> You must have a look at the core material-specs sheets in order to decide
> whether or not a particular core is suitable for your intended frequency
> ranges, and whether or not it can handle the desired power without
> saturating. Bying "just any ferrite core" may work out ok, but then, it
> also might not.
> 
> The core - is it 3C85? N27? Other material?
> 
> cheers,
> 
>  - Jan
> 
> --
> *************************************************
>  high voltage at http://www.hut.fi/~jwagner/tesla

Actually, a transformer based feed with one wire going to a magnifier
coil has a very important advantage.  If wound so that its self
resonance is much higher than that of the coil, the driver only draws
large current at coil resonance.  Whereas the direct primary approach
looks like a short circuit everywhere but at resonance, unless you use a
huge number of turns, in which case the whole scheme is sort of
useless.  There won't be much step-up in voltage.  You can see my old
design on Alan Sharp's page.  He considerably improved upon it.  Rob.

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