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SSTC: lots of heat, small sparks

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william L

Mon Sept 06 2010, 05:08AM

Registered Member #3093 Joined: Mon Aug 09 2010, 11:40PM
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Posts: 68

So, I have built a clone of http://stevehv.4hv.org/SSTC5.htm. When I first built the coil, It worked well with thick, hot sparks. Then, I soldered in the Filter capacitors for the bridge backwards, and the thing went up in smoke. luckily, it was only the capacitors and my variac's fuse. (they didn't explode, luckily) I immediately removed them. Though, after turning on afterwards, the sparks were very short and the mosfets, drivers, inverter, and 12 volt regulator got very hot. I decided to replace the mosfets, and got the same result. So, I tried using an external interrupter, with small sparks, one again. then, I accidentally let the spark get to the interrupter through my hand and everything but the interrupter and the 5 volt regulator died. several component samples later, Small sparks are still running, and everything is getting hot. the gate drive waveforms look very messy, and I get a high pitch whine, the frequency of the interrupter (who's wave is square and fine) I don't know what to do. please help.

Steve Conner

Mon Sept 06 2010, 03:20PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

You said you removed the filter caps, but you didn't say that you installed fresh ones. And a complete lack of filter caps would explain your symptoms.

I assume that you did install fresh ones though, in which case, it's most likely that you forgot to reconnect some important wire when you put the thing back together. A MOSFET gate lead, a RF ground, etc. Or maybe you got the phasing the opposite way to what it was before.

william L

Mon Sept 06 2010, 06:47PM

Registered Member #3093 Joined: Mon Aug 09 2010, 11:40PM
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Posts: 68

Steve McConner wrote ...

You said you removed the filter caps, but you didn't say that you installed fresh ones. And a complete lack of filter caps would explain your symptoms.

I assume that you did install fresh ones though, in which case, it's most likely that you forgot to reconnect some important wire when you put the thing back together. A MOSFET gate lead, a RF ground, etc. Or maybe you got the phasing the opposite way to what it was before.

Well, I will look for loose wires. The filter caps I broke were the bridge filters. My 12 and 5 volt regulators are well filtered.
thanks for the wiring reminder though.

Duality

Mon Sept 06 2010, 08:28PM

Registered Member #1951 Joined: Sun Feb 01 2009, 01:59PM
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Posts: 105

if you can't find any lose wire's check your other caps two. unless you already did that :)

sometimes they die from the shock, without you knowing, happened to me ones.
real pain in the @as if you don't know that some caps are short circuiting.

william L

Mon Sept 06 2010, 09:13PM

Registered Member #3093 Joined: Mon Aug 09 2010, 11:40PM
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Posts: 68

I think you might be right. the 12 volt filter capacitor lowers in resistance when connected to the multimeter as does the 5 volt one. They are still connected to the voltage regulators, but this still seems like odd behavior. they don't seem to be shorted though.
EDIT: the resistance settles out at 5.01 k still weird that it starts out high

Duality

Tue Sept 07 2010, 01:14PM

Registered Member #1951 Joined: Sun Feb 01 2009, 01:59PM
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Posts: 105

william L wrote ...

I think you might be right. the 12 volt filter capacitor lowers in resistance when connected to the multimeter as does the 5 volt one. They are still connected to the voltage regulators, but this still seems like odd behavior. they don't seem to be shorted though.
EDIT: the resistance settles out at 5.01 k still weird that it starts out high

correct me if I am wrong, but caps don't have resistance.. right?

william L

Tue Sept 07 2010, 01:49PM

Registered Member #3093 Joined: Mon Aug 09 2010, 11:40PM
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Posts: 68

well, as I learned it, caps start out with a resistance of 0, (discharged) then there capacitance starts rising gradually as the capacitor charges.

Dr. Dark Current

Tue Sept 07 2010, 03:28PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

maybe the cap was charged

william L

Tue Sept 07 2010, 10:33PM

Registered Member #3093 Joined: Mon Aug 09 2010, 11:40PM
Location:
Posts: 68

Dr. Kilovolt wrote ...

maybe the cap was charged

unfortunately, that wasn't the problem either. It does look increasingly like it was the capacitors, because a quick scope of the mosfet gates revealed that the ucc's were only making very short pulses (even though the antenna and inverting buffers were picking up the signal fine.) I guess that they were rapidly discharging the blown capacitors.
The second bit that supports all that is that my variable power supply for powering the logic side was frequently being over currented even though It would only draw ~ 500ma when the coil was properly working.

EDIT: I installed new filter caps. DIDN'T help at all.

Dr. Dark Current

Wed Sept 08 2010, 07:55AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

If your logic (driver) side draws too much, most likely one of the FETs is dead or damaged (leaking or shorted gate), or one or more of your driver chips are damaged.

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