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Re: Large ferrite cores for SSTC work

Original poster: "Steve Rodway by way of Terry Fritz <twftesla-at-qwest-dot-net>" <teslalist-at-legion-elec.demon.co.uk>

Tesla list wrote:
> 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...
	Well, I don't find it that bad, my first ferrite matching
transformer worked fine. Alan sharp has put up a page that
provides a good guide at
With that and some careful planning ( especially of the
insulation from secondary winding to core ) it's not too hard to
produce a functional transformer.

> You get considerably better TC output with a direct primary drive scheme,
> without the ferrite core transformer in between.
	Depends what you're trying to do.

> 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.
	I have to disagree here, because with a larger core, you have a
larger winding window, which allows more turns. More turns on the
coils reduces the flux density the core has to support, which
decreases core losses. 

> 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?
	The core material will be either 3C90 , or more likely 3C94
ferrite, which supports a max. flux of 320mT at 25KHz dropping to
around 175mT at 100KHz (although higher flux densities and
frequencies are possible with increased core losses). Core losses
when running the core at it's maximum ratings are likely to be
considerable, in the region of 200-300W so additional cooling
will likely be necessary for anyone working at high power levels,
either forced air or oil bath. I can't speak for anyone else, but
I will be designing my coils around what cores I can get rather
than the other way around.


* Steve Rodway                              Legion Electronics *
* SteveR-at-legion-elec.demon.co.uk       Tel. +44 (0)1761 300615 *
* http://www.legion-elec.demon.co.uk/  Fax. +44 (0)870 0529740 *
*                                     Pager +44 (0)7661 061026 *