Re: Need a Variac, think solid state

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx>

In this electronic age there may be an alternative.....

I lashed up a  small SSVariac tonight using an IGBT out of an inverter 
microwave run by a TL494 at 2kHz.  The tricky part is that it is "inside" a 
bridge rectifier so that it controls AC. This is inserted in one line 
between the mains and the NST.  There is also a snubber of 0.1uF and 400 
ohms that gets pretty hot. I haven't tuned this for long term runs yet as a 
lot of power is still being dumped into a 230V MOV across the IGBT. 
(Fortunately I have 300 of these)

I don't really think that it would be more expensive than a variac for NST 
use of less than 5A 240V.  The main rectifier could be 3A diodes, and the 
IGBT/Mosfet could be almost any one with a 500V rating at 10A. The TL494 
circuit could be a 555 in this situation.  The snubber is going to generate 
a bit of heat and a mains filter is probably wise. A small 12V transformer 
or even old 9V plugpack could supply power. As ususal it depends how much 
can be scrounged up.

If this can be made to work reliably and effectively then it may be of 
interest to those who use NST's.  I have run this on an 12/30 NST so it 
works but has some optimising yet.

Peter




> At 04:44 PM 5/12/2005, you wrote:
> > Original poster: Fucian@xxxxxxx
> > Hello all,
> > I am in need of a variac capable of around 10 amps...
> > Matt