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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.
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...
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.
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,
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. ;)
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