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Steve Ward

Mon Apr 30 2007, 05:06AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Have anyone of you guys ever had the problem I had with the interupter? Or know what values to stay away from?

Shouldnt matter since SSTCs can usually operate up to 100% duty cycle. I go for the lower pulse frequencies since they are more pleasing to hear than a high pitched squealing.

CT2

Mon Apr 30 2007, 05:18AM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

Thanks Steve, I guess something else caused the problem...For this coil I'll be using one of your circuits, so far I have the mini SSTC circuit running producing 18" sparks on my coil. I was wondering though if maybe your SSTC 1 or 2 are better/more reliable? I don't think I've had any problems with the mini circuit, but I thought I'd ask anyways since you are here, thanks.

Steve Ward

Mon Apr 30 2007, 06:09PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Reliability tends to always go down as size and power go up. Since you are pushing 18" sparks (half-bridge? full-bridge?) you are getting into an area where getting really good reliablity becomes a bit of an art. My SSTC-1 never (and i mean never) blew a mosfet, and i used it a lot (often running for 30 minutes at a time). The design is completely taken from hvguy.com (though their new site is lacking content currently). The mini SSTC is just a variant of that, and it too had a good record when it was in my hands. So i dont really know if one or the other is more reliable, they all worked fine for me for the most part. As i said, reliability tended to go down as spark length went up (likely because the higher power designs werent as overdesigned as the small ones could be).

CT2

Mon Apr 30 2007, 08:16PM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

I'm using a full-bridge on my coil and will also be using one on this coil. Thanks for letting me know, I'll just stick with the mini circuit I have then because it seems to do the job just fine. Time to wind another coil...

Thomas

Tue May 01 2007, 02:26AM

Registered Member #120 Joined: Fri Feb 10 2006, 07:07AM
Location: Westchester New York
Posts: 83

Just to add to the conversation, I think over heat protection can be very helpful. I added some of these chips in my later SSTC and flyback drivers. I use the TC622.
Datasheet
Basically it can be screwed into the heat sink the FETs are mounted on. This will however, not guard against over current. But hey when things are running at a high current they get hot so it can shut down the h-bridge with are relay or anything you choose.

CT2

Tue May 01 2007, 04:44AM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

Hey thanks for that part! I was thinking it'd be good to add some sort of temp sense circuit, I had no idea it was as easy as a single chip. I'll try and find one and include it on the bridge (hopefully the local store has them...).

Effilcdar

Thu May 03 2007, 03:00AM

Registered Member #655 Joined: Wed Apr 18 2007, 10:23AM
Location:
Posts: 14

Hey for soft turn on for any AC powered project I recomend a pannel mount variac. Also known as a variable auto transformer they would be a much better idea than a variable resistor for heat concerns. I have used these with great success my coil gun. My one recomendation is that you be carefull that you have a thin enough pannel to mount on. The lexan I used was almost too thick to thread it on.

CT2

Thu May 03 2007, 05:08AM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

Hey thanks for the idea, I don't have a variac though so I can't do that, I'm just going to go with Steve's soft start circuit at full power.

Marko

Thu May 03 2007, 11:58AM

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

A simple triac-based dimmer can be used

for regulation and can be easily modified for soft-start if required.

You only need an additional series inductor to limit the peak current and reapir PFC.

It's usually in range of several MH and can be wound on a core of smaller (100Va or so) transformer with airgap.

Very similar setup seemed to work well with steve conner's large OLTC so it's sort of tested out.

CT2

Fri May 04 2007, 12:22AM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

Hey Firkragg thanks for the link, I was already looking at that and had posted that link in my original post. I just wasn't sure exactly which circuit to use? I was thinking either circuit C on page 11 or the one on page 10... the one on page 11 is much simpler and I would prefer it if possible, also the one on page 10 is for 220V and this coil will be run off 110V so I don't know how the values should change.

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