Re: MY SSTC WORKS!!!!! dead again

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jan Wagner <jwagner-at-cc.hut.fi> 


On Sun, 18 Apr 2004, Tesla list wrote:
 > Original poster: Kreso Bukvic <kreso.bukvic-at-kc.htnet.hr>
 >
 > Ok, so looks like Steve figured out my problem.
 > It looks like i HAVE to use variac.
 >
 > But here is the problem:
 >
 > Im building evrything TIP TOP on acrylic, so all circutry can be seen
 > etc...
 >
 > I would like to buy that small variac for built in purpose
 >
 > Problem again:
 >
 > 1. No variacs like that here
 > 2. I burned my big old variac

Burned?

They can be fixed really easily. I did this a couple of times with some
small <500VA and large >5kVA variacs. The big ones were glued to a
metal+cork board and had to be pried off - that's the only hard part, the
rest is easy.

1 - Open the varic box up, take out the transformer core, brush off the
soot with water+soap or ethyl alcohol etc.
2 - Find the section(s) of windings which has burnt or melt, and remove
that part completely. This leaves a gap in the variac windings.
3 - Put a bit of baking/oven paper around the gap for electrical
insulation.
4 - Solder new magnet wire to one end of this winding "gap", wind as many
new turns as fit there, and when finished solder to other end too.
(logical...)
5 - Take some sand paper, sand off the enamel/varnish of the new wire
section, so that it is blank on the top side where the variac brush moves
along. DON'T sand off too much, very little will do.
6 - Next, take a big hammer. Flatten out the new wire sections so they
are in level with the old, original windings.
7 - Close the variac box up, all done.

 > So i was looking somthing at the internet and some guy used a DIMMER for his
 > 12 kV 60 mA nst
 >
 > Could i use one? It costs only 50 $

For NST's yes. But for bringing up SSTC input voltage gently, not really.

 > What does a dimmer actually do?

Chops up the mains voltage. It is turned on at some point of the mains AC
cycle, and switches off by itself when the current goes to zero. This
repeats every cycle. So the output is chopped mains.

 > Will i also get 0-220 V regulation?

Sort of, yes. But it's not a sine wave you get, but an ugly mess. You
could try rectifying and heavy filtering, though.

Some dimmers are rated for inductive or capacitive loads, though I don't
know which one would work best for testing a SSTC. Capacitive, I suppose,
when its out of tune. Or just build your own with a suitable triac, diac,
capacitor and potentiometer.

cheers,
  - Jan

--
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  Helsinki University of Technology
  Dept. of Electrical and Communications Engineering
  http://www.hut.fi/~jwagner/ - jwagner-at-cc.hut.fi