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First Light, Full Power? Mini SSTC (Steve Ward)

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coillah

Wed May 27 2009, 05:55PM

Registered Member #1517 Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304

I have nearly completed construction of my version of Steve Ward's Mini SSTC. I am very tempted to turn it all on at once, with full power, but I am not so sure that this is a great idea.

Has anyone here been confident enough in their design to turn it on full power for the first light?

I left my variac in chico... so I would have to wait until monday next week to attempt to light it up...

here are some pics, tell me what you think:

Pics folder:
Here

Pylon

Wed May 27 2009, 06:54PM

Registered Member #2065 Joined: Sun Apr 05 2009, 06:32PM
Location:
Posts: 26

If you have step down transformer with suitable power you can use it for first light, the 30V should be ok. Then you can supply your sstc from AC line with huge lightbulb or high power resistor as a current limiter (with rectification of course). I think that is a better idea than running SSTC on full power for first light. Do you have properly isolated mosfets from heatsink?

coillah

Wed May 27 2009, 07:36PM

Registered Member #1517 Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304

Thanks pylon that sounds like a good idea.

As for the isolation. I have read mixed opinions on that. I planned on using the same heatsink with thermal compound for both mosfets. Is this a bad idea? I can just take a hacksaw to the center of the heatsink to isolate them...

syntroniks

Wed May 27 2009, 07:52PM

Registered Member #1530 Joined: Tue Jun 10 2008, 03:34PM
Location:
Posts: 32

Pardon my asking - Where'dja get the driver board?

Dieu

Wed May 27 2009, 08:00PM

Registered Member #1730 Joined: Thu Oct 02 2008, 08:12AM
Location: Poland
Posts: 35

Is yours drivers board buyed somewere? For me buying this kind things is like berying myself. Sheme yourself.

Pylon

Wed May 27 2009, 09:01PM

Registered Member #2065 Joined: Sun Apr 05 2009, 06:32PM
Location:
Posts: 26

Thermal coupound should solve insulation problems. I think connecting heatsink to earthground is a good idea. When I have seen thermal compound in my micro sstc i notice a burned surface near the screw. Probably if the heatsink are not grounded there can induce high voltage thats break down the compound or air betwen to-247ac case and heatsink.

Btw. the board is very nice

coillah

Wed May 27 2009, 10:21PM

Registered Member #1517 Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304

LOL.

No I made the driver board myself in eagle, then sent it to a boardhouse.

I also designed my halfbridge in eagle, but I etched that one myself.

I'll be sure to coat the fets in thermal grease.

I make nearly all my stuff myself.

ty for the kind compliments

Myke

Wed May 27 2009, 10:29PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

I wouldn't use just thermal compound for isolation. You would need something like mica for insulation (in addition with the compound). Sil pads work to some degree but they aren't meant for withstanding large potential differences.

I don't know if you are using mica or sil pads as you haven't mentioned them.

coillah

Wed May 27 2009, 10:54PM

Registered Member #1517 Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304

I did not know that I would need that kind of isolation. It is sounding like taking a hacksaw to the heatsink is the best idea. That way I can just forgo the insulation pads and whatnot...

Quick question, anyone know the typical current draw of the SSTC bridge?

SeanSpark

Thu May 28 2009, 03:25AM

Registered Member #2082 Joined: Fri Apr 17 2009, 03:59AM
Location: USA
Posts: 3

Nice work Coillah, I've just built the same project. When I started I planned using one heat sink, from a GM stock radio, looked cool an all with the purply grey going on, lol, but I found the IGBT and the diodes I was using had common leads with the mounting tab, rats, so I got seperates ones for all. As far as the compound alone, no way in heck, when you mount the chip and tightened it down a bit, the edges will dig right in, mica is cool but it will slow cooling down a bit, learn that from audio amp work, we need all the cool we can get with the lightning machines.
I fired it up with a variac, running a larger coil (24"x4" 22awg) it came to life, but not too impressed by the spark size yet. Got bout 4" angry purple feeders using .47uf on the 555, at bout 110V, they were cool, they growled !
As far as current draw, lol, I've learned my new BK369B clamp on ammeter is useless! Ooops, the RF is driving it nuts, I've should have known.. I was thinking Ah, no big shunt resisters, no direct connect, ya, perfect, .. clamp on.. WRONG! It was bouncing aroung 200 to 400+ amps while the coil was running. Even tho I had only a 10 amp fuse in line, it didn't blow. I have a automotive style amp gauge, but I don't think it reads right either at the freq it's pulling out amps, it was bareley budging. I ran it for a few minutes at a time thru out the few days, and the coil and IGBT's were only slightly warmer than me after each run. I wan't to audio modulate it, but I blew the IGBT's trying with a TL494 circuit instead of the SchmTrig sounded distorted, messing with the duty cycle, poof! Anyone have a good clean audio mod circuit to drive the Mini SSTC {by Steve Ward}?
]mini_sstc.wmv[/file]

1243481155 2082 FT70273 Sparks N Arcs 048sm

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