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Registered Member #3093
Joined: Mon Aug 09 2010, 11:40PM
Location:
Posts: 68
So I decided to build a clone of steve ward's mini sstc, just for the sake of arcs. (I haven't had much going on lately) And, when I powered it up, crossing my fingers, I was met with only the hum of my now deceased variac. It did not die then, but I was able to do some experimenting. I found out that when I touched the secondary about 4/5ths of the way up, I would get a hum at the frez of the interrupter. I then powered down all my power supplies, and did a thorough triple check of my soldering. The only problem was that I hadn't connected my gdt. (small, right!? ) Anyway, I fixed that. Then, I powered it up again. This time, I scoped the gdt output and saw only very small ripples in the drive, as if the ucc's were not being driven. With the variac set to 24 volts, I 'scoped my entire circuit. And I mean EVERYTHING It was all fine, accept for that the inverter was not triggering from the antenna. There was input present on it (from the interrupter kicking the coil,) but alas, it must have not been enough. So, like an idiot, I turned up the variac to see if I could get enough to start the oscillation. This variac was new, and of medium quality. I had tampered with it before, so as to push down the sliding contact. Unfortunately, an enclosure screw decided to short out two turns, And chaos was set in motion. the variac hummed loudly, then I heard a pop and saw a puff of acrid, electronic smelling smoke, and the voltage readout dropped to zero. As it turned out, the winding literally vaporized. Now i'm out a variac, and my sstc is sitting, sick with an undiagnosed illness. I am considering (Once I get a new, hopefully isolated, if such a thing exists,) variac for christmas, switching to secondary base feedback via ct. Advice or thoughts greatly appreciated.
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
Of course superficially, it sounds like the problem was the variac from the start. IF you can isolate the winding where you got the blown winding and some hemostats you might be able to pull up the ends and solder the blown juncture with an equal-distant piece of same size wire (especially if it's simply a single winding, etc). I once pulled one (a small variac) that had a blown winding and actually got it back to functionality that way. If it looks possible; clean the section and re-coat any burnt lacquered section (of course) on either side & clean the end, pressing it in place only when the soldering has been cleaned smooth & use a micro size brush to paint up any exposed wire(s). Get that screw out of there and grind down the tip so you can put it back with enough room to make SURE it never touches again. But mine had a very obvious blown winding in a very accessible place.I made damn sure all of mine have some form of fuse now.
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poor sstc feedback (?) - Cost me a variac
) Anyway, I fixed that. Then, I powered it up again. This time, I scoped the gdt output and saw only very small ripples in the drive, as if the ucc's were not being driven. With the variac set to 24 volts, I 'scoped my entire circuit. And I mean EVERYTHING It was all fine, accept for that the inverter was not triggering from the antenna. There was input present on it (from the interrupter kicking the coil,) but alas, it must have not been enough. So, like an idiot, I turned up the variac to see if I could get enough to start the oscillation. This variac was new, and of medium quality. I had tampered with it before, so as to push down the sliding contact. Unfortunately, an enclosure screw decided to short out two turns, And chaos was set in motion. the variac hummed loudly, then I heard a pop and saw a puff of acrid, electronic smelling smoke, and the voltage readout dropped to zero. As it turned out, the winding literally vaporized. Now i'm out a variac, and my sstc is sitting, sick with an undiagnosed illness. 
I am considering (Once I get a new, hopefully isolated, if such a thing exists,) variac for christmas, switching to secondary base feedback via ct. Advice or thoughts greatly appreciated. 