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SSTC: base feed transformer

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Marko

Wed Dec 26 2007, 06:45PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

The coil didn't work too well after I wound an air core primary back - actually it worked, but output was very poor and I didn't want to run it longer than few seconds like that.

I messed with the circuit and CT arrangements unsuccessfully until my fuse blew..

And then I disassembled the bridge:

The plastic insulation around the hole is scorched down to copper substrate.

I guess I should keep this pad as a reminder...

Marko

Tue Jan 01 2008, 11:00PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

This'll be my next attempt of a base feed transformer...

I think this is a quite evil transformer.

I potted the secondary the way it's floating completely in resin. Output studs have a large bent wire soldered on them firmly so they can't move once covered by resin.

I'm only sorry I didn't put some sorts of bushings on the outputs, but still I expect the transformer to take the pounding.

I count the most on now high pri-sec coupling, less place for high resonant voltage to be induced.

If this thing blows up I think it will be a quite big nail in the coffin of this idea.

I'll post more construction pics if anyone gets interested...

Marko

Dr. Drone

Tue Jan 01 2008, 11:38PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
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Posts: 1673

Marko

Wed Jan 02 2008, 12:20AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Allright, all pics for chris.. I should probably have taken more than this!

Firstly I tried to secure the secondary by superglue and wooden sticks, but didn't work too well, the high-thickness glue I used dried slowly, and then I ripped the wire as I tried to remove toothpicks.

Then I made some putty with talcum powder and resin, and secured the secondary in carefully so it doesn't touch neither PVC tube. Sorry but didn't photograph that :(

Not too much of it as I didn't want any air to be left in. I used non-drying putty to seal the other end while resin sets.

uzzors2k

Wed Jan 02 2008, 11:32AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

That transformer is unbelievably awesome Marko! I'm looking forward to seeing how it works in a TC. What ratio did you wind it for?

Marko

Wed Jan 02 2008, 01:35PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Primary has 10 turns now so ratio is about 1:22, which should be about 3.5kV with halfbridge.

At 500kHz even fullbridge will work for this primary so I'm only troubled with insulation, despite the single-layer winding and all the resin.

And yes, I believe coupling is very important, as any leakage inductance becomes like a part of secondary coil and give resonant voltage rise which will make the transformer very unhappy.

Last transformer had rather poor coupling compared to this,

Marko

Wed Nov 09 2011, 03:37AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hey guys,

I felt like raising this long-dead thread as new ideas sprang up...

The basic idea of this was pretty much a fail, as it's practically impossible to make a transformer that will even have a self resonant frequency lower than the tesla coil itself, and this is made hopelessly worse by increasing the transformer size.

The solution? Use diode split transformers - diodes do excellent job of de-qing their secondary windings from resonant rises and removing the self-capacitance problems. You might wonder how is one going to drive a tesla coil using DC - well, we're going to use two transformers, in antiparallel (or better, one transformer with two diode-split windings).

Since each winding would be carrying DC in this configuration, effects from self-capacitance would be pretty nullified (depending on how dense diodes are placed).

Even better thing is, one would not need the diodes to stand a full transformer output voltage, but just a fraction of it since potential across the diodes is actually very low in the off state - so it seems like just a bunch of schottky's spread over the windings would do the trick.

I don't have the time myself but if someone has a handy diode-split CCPS or whatever transformer laying around, this could be tried out. If one wants to be silly even two DC flybacks in antiparallel could work for an experiment.

I actually ended up using a step down transformer for my SSTC, driving a series tank and a normal primary... kind of wishing again this all could be avoided and use a transformer alone. ;)

Marko

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