Re: Need a Variac, think solid state

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: stork <stork@xxxxxxxxxxxxxxxxxxx>

Peter,

A very interesting concept.  Also a weight reducer.  How about a 
schematic?  What does the wave form look like?

stork


Tesla list wrote:
> 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.