Re: sstc as a transformer?

["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>


> Original poster: "Laurence Davis by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <meknar-at-hotmail-dot-com>
> would it be attainable to use a sstc as a transformer?

Well, as a very high voltage but low current transformer, yes.

> I would guess not because the coil would react differently
> while loaded as opposed to unloaded.

SSTCs are just one "brand" of resonant switch mode power supplies,
unregulated output. If you really are after a suitcase sized pole pig,
then have a look at:
 http://ece-www.colorado.edu/~ecen5817/Lecture_schedule.html
And be warned... It's hard to get these right. Expensive and
highly frustrating. ;-)

For the lightweight route, you could have a look at TV flybacks or car
ignition coils. There's a wealth of circuits on the web, very simple and
inexpensive to build. Output power levels are somewhere around 50W, or
less.

A flyback can be run as a SSTC. That is, self-resonant.


> Reading about the sstc coils makes me want to build one,
> but I'd like to do it small, if possible. I don't want to waste
> alot of expensive mosfets or igbts (and neither does my bank account.)

You don't have to! :)

See schematics at for example
 http://misty-dot-com/people/don/sst.html
 http://tacashi.tripod-dot-com/elctrncs/ssstc/ssstc.htm

You may use a TV flyback transformer, or a "real" TC secondary and a
helical primary with one or two feedback windings (with a couple of
turns).

I've never built an air-cored, biplolar transistor SSTC like these (i.e.
I always had a gapped ferrite core xfmr like TV flyback, or xenon flash
tube non-gapped step-up xfmr), but, these SSTCs _do_ work.
 www.google-dot-com
    car ignition coil driver
    tv flyback solid state tesla

They're very nice for doing cool plasma globe demos

 http://tacashi.tripod-dot-com/elctrncs/splglobe/splglobe.htm

or Kirlian photography

 http://www.hut.fi/~jwagner/tesla/kirlian2.htm

TV flyback "streamer" output can be 1-3cm of a high frequency flame. Looks
like a blowtorch. If the TV flyback has an internal rectifier and stuff,
you can get 5-7cm arcs. 30kVDC-50kVDC??

You can make a real TC secondary, too. Just a lot of thin wire on a
(non-PVC!! maybe a 1.0liter polyethylene soda bottle or something) coil
former, resonant freq below 300kHz. Output similar to TV flyback, <3cm
flame, likely no streamers.


> Plus a small coil I might be able to measure the secondary without
> serious risk to equipment. right? or am i right back to the first
> question/answer: that loading will affect the output.

You have an oscilloscope for measuring the output?

Then all you have to do is hold the scope probe near to the SSTC secondary
topload, and the probe will pick up the field. From that, you can
estimate into what range the output voltage falls. Granted, not very
precise... :o)

If you don't have an oscilloscope you can get an even less precise
estimate by calculating like this:

Power in P_in = U_in * I_in. Power to the resistor R_test, power P_out, is
less than P_in. For simplicity let's say P_out==P_in.

 P_out = U_out*I_out = U_out*(U_out/R_test) = (U_out^2) / R_test

Now, using the (wrong ;o) assumption of P_out=P_in we get

  U_out = square root ( P_in * R_test )
  U_out = square root ( U_in * I_in * R_test )

You know U_in and R_test, and measure I_in. From these you get U_out.
Again, this is just a _very_ very crude estimate, whether you get into
the 100V or kV or 10kV range.

R_test can be infinitely large but there will be other factors limiting
the output voltage, so you don't really get infinite output voltage. Which
would be fun, of course... ;-)

You could make a real measurement with series high voltage resistors (3kV,
TV repair shops) accross the TC secondary, in resistive voltage divider
fashion. Then measure with an oscilloscope, or ultrafast diode rectifier
+ small capacitor ("sample and hold" style) and cheap digital multimeter.
But HV resistors aren't cheap...

cheers,

 - Jan

--
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 high voltage at http://www.hut.fi/~jwagner/tesla
 Jan OH2GHR