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4hv.org :: Forums :: Tesla Coils
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Problems with MiniSSTC

 1 2 3 
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HV Enthusiast
Thu Apr 13 2006, 10:30PM
HV Enthusiast Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
I think the first thing to do is find out why the 7812 died. These regulators are pretty bombproof and the fact that you killed one leads suspicion that you have something very wrong with your circuit. Firstly, i'd check the input voltage to the regulators. You don't want too high a voltage otherwise your regulator will burn up, or even kill it if it exceeds ratings. I'd start there.
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Mike
Thu Apr 13 2006, 10:57PM
Mike Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317
Well the last board was crapily made and now I've taken time on this one. I know its working fine, and even the GDT seems to be good I think. I disconnected power from the bridge, and disconnected the primary TC from the bridge, and just let it run on feedback, i got 6-7khz on the bridge outputs, and touching the antenna made em jump down. So it is obviously working, except for when i add power and hook it to the TC. Then I get nothing.
Any ideas?
Mike
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HV Enthusiast
Thu Apr 13 2006, 11:02PM
HV Enthusiast Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Use an oscillator to drive your gate drive chips at the expected operating frequency, and check each point, step by step.

1. Gate driver chips
2. Secondary of GDT (no load)
3. Secondary of GDT (with capacitor for load)
4. Secondary of GDT with actual device (no power)

Connect each component step by step until you see where the problem is.
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Mike
Fri Apr 14 2006, 01:11AM
Mike Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317
Okay, seems I've got it working again. The hex inverter was messed up, when input to was 80khz , itwas giving 40khz out, so i switched it with another and I now have some tiny arcs with 12v 3A.
I am tempted to hook it up to 120vac but I should probably use some type of light dimmer ?
Thanks, Mike
Edit:
Another thing, after arcing 2 or 3 times with a screw driver to the secondary output, it stops arcing, I figure that the antenna lost the signal, and at the moment the antenna is like an inch from the output ( at low power it should be fine to be near it) so does it loose the signal because of the lower power input to the coil?
thanks, Mike
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HV Enthusiast
Fri Apr 14 2006, 02:47AM
HV Enthusiast Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
wrote ...

I am tempted to hook it up to 120vac but I should probably use some type of light dimmer ?

If you have a modulator (i.e. interruptor) with adjustable pulsewidth, you don't need a variac or light dimmer, etc...
Simply use the pulsewidth as your power control. Start at 0 pulsewidth, and increase slowly.

Of course, you should have most bugs fixed by this point as even with the pulsewidth setting quite low, you still have all that energy stored in your DC bus capacitors, so any shoot through or fault condition has the potential to be quite spectacular.

If you are truly unsure of the operation of your fullbridge, then power control through a variac or similar. If you have full confidence, than use the pulsewidth adjustment.
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vasil
Fri Apr 14 2006, 12:35PM
vasil Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506
Verify again your 74HC hex.
Use 0.1 uF ceramics and 10-20 uF tantals between the +/- rails on each chip on the board to better protect them.

I am using a little neon lamp to see if it is oscillating even if the spark output is not present.
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Mike
Tue Apr 18 2006, 10:24PM
Mike Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317
So I tested it a little while ago, and something odd happened, I turned it on, a streamer shot out, and then there was an arc from one of the .68uF capacitors (the plastic case of it) to the bread board.
And i turned it off and the UCC's, hex inverter, and igbt's were dead. I got around to replacing it all, and replacing the clamping diodes on the antenna. It seems to be working. With no coil connected and no power on bridge, the antenna shows in shows .09khz (freq of my interrupter), the pin 4 output of the hex shows .17khz (not sure about that) and then the output off the ucc21 shows .15khz.
Also touching the antenna changes the freq slightly, which should mean its working. I am not sure whats going on. The bridge also shows .15khz. And I have tested it on 113khz on the antenna and i get 113khz on pin 4 output, and on outputs of uccs and bridge output.
I am kinda lost at the moment here.
Mike
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vasil
Wed Apr 19 2006, 07:24PM
vasil Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506
Do not put antenna near the coil. It can develop corona on top, or it can be invisible discharges between topload and antenna, so the driver (clamp diodes) can broke. Put some distance between coil and antenna (around 20-25 inches would be better), as you see in the picture:

http://www.geocities.com/livvasil/Mini8.jpg

With enable, it will oscillate even at low voltage input.

...or better go to secondary feedback.
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Mike
Wed Apr 19 2006, 09:51PM
Mike Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317
the antenna isnt that close to the coil, When I said i touched it, I ment with my finger, so the freq change which meant it was working. I was told maybe i should try new capacitors, and I am soon, but i dunno how these would be broken, they still read the same capacitance on the dmm..

Mike
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ragnar
Thu Apr 20 2006, 12:46AM
ragnar Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
If the antenna is close to the coil, you get RF burns when you touch it whilst it's running... not to mention a very impressive corona spray that melts the insulation, and some smokin' 1N4148s.

I'm not sure what you're saying.. have you replaced all this stuff and run it at 113kHz, but you're not actually getting breakout?
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