New H bridge driver for AC fusor drive

Things at the limits.

Re: New H bridge driver for AC fusor drive

Postby Doug Coulter » Sat Jan 20, 2018 1:01 pm

The painful experience of burning up my ion grid coil has taught me to be extra careful with this especially arc-y HF stuff. The reason it worked so well as a drive for the ion source was just this property - with DC voltages of 40kv not being "willing" to light it off, this HF did it with ~ 10kv. But - there's no free, and it also arcs more easily in air and plastic.

So...before I stress test the big boy sigificantly, I'm doing the same upgrade to the basic mechanicals I did for the ion grid supply. A big thick plexiglass (because I have it and it's real machineable) disk to "guard" the somewhat conductive ferrite core from the HV so it doesn't arc to that, and the probably the primary winding, letting the magic smoke out of the semiconductors - which is actually less of a problem to replace than this coil would be (I can make another, but that means making tools to make this sexy coil form and on and on).

I have one more step before mixing the epoxy for this - making a centering jig. The darn hole in the existing coil form is 1.995"...and of course, the rest are 2.00? inches. So I'm going to turn down a piece of plastic rod I can wax up as a mold release to hold the coil form and disk centered while the epoxy sets. After all, I might even need to make a corona ring to glue to the inside side of this disk at some point, this looks like it'll make 100kv without breaking a sweat - quite the little Tesla coil if I wanted that - and it would act the same - nasty arcs to nowhere (pretty but not wanted here).

Arc guard

I'd have made a vid showing how I made that thing - it needed a little cleverness to do with home-gamer machine tooling. Maybe I'll ask Joe Pie to do one, my shop is a bad example to anyone with a modicum of neatnik in them. Too cold to hang out in there and clean things up, it's just do things and get out, not even taking off your coat just now. A whole new meaning for "let the chips fall where they may" I guess.

Glued in place, waiting for terminal block

Now I'll fab an all-insulating plastic terminal for the inside side of this to capture the HV wire from the coil and the HV wire going out to the world, using a plastic clamp screw, glued into this ring.
I hope that works(!).
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
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Location: Floyd county, VA, USA


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