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Re: Solid-state coil (gate xfrmr question)



Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Carl,
         I strongly suggest you avoid using ring cores from SMPS 
because most are iron powder. They are undesirable because:

- they have a distributed airgap with consequent very low
  permeability (they were *not* design as transformer cores)

- they are very lossy with high flux swings (probably less of an
  issue if you follow the suggested guidelines of high winding
  inductance which will be difficult to attain because of the low
  permeability). Such cores are designed to carry a high level of DC.

You can use ring cores designed and used for common mode filters. 
These have a very high permeability. You can recognize them as you 
typically see a bunch of wires running through the centre (they are 
commonly used in video monitors to stop hash getting out through 
external connecting leads).  

Regards,
malcolm

On 6 Nov 2001, at 14:31, Tesla list wrote:

> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<cwillis-at-guilford.edu>
> 
> 
> Hi Eddie, Ed, Malcolm,
> 
> Thanks for your most informative responses.  I just sent out another post
> to the list with the same questions because I thought my e-mail was down
> and not because your answers did not suffice.  I also put photos and some
> more description of the current state of this SSTC setup on the web at
> www.angelfire-dot-com/electronic/cwillis/sstc.html.  I have some photos of the
> oscillosope while the coil was running as well, so you can comment on how
> good / bad the setup is doing from an FET survival standpoint.  The biggest
> question still outstanding to me is why I get such a high drain voltage
> (about twice the DC supply voltage) on the pulses.
> 
> Eddie's suggestion that my ferrites were too small, wrong type and wound
> with too few turns sounds exactly like the case.  Although I don't know
> what types of ferrite these all were, at least one was a ~0.6" OD,  0.1 -
> 10 MHz tiny little thing and I only had ten turns on it.  I'll follow your
> advice and sack a few old switching supplies for their toroids.  Malcolm
> corroborated what you said also.
> 
> In regards to Malcolm's question about power supply, I am using rectified
> and filtered AC line power (and, until I'm really sure of myself, a
> variac.)  And finally, Ed, the setup is a conventional tesla coil and not
> an ignition coil.  I admire the GMHEICSLR (?) efforts very much but I just
> don't have the nerve to try to get 6"+ out of one of those things! 
> 
> Thanks, y'all!
> 
> Carl
> 
> 
>