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Another (DR)SSTC problems thread

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cjk2

Wed May 31 2006, 01:26AM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

Everyone else is building one now so I thought I would try too. I built the driver board using Steve Ward's drsstc 3 circuit(minus the current limiting). I am using a halfbridge of irf460 MOSFET's with a voltage doubler. The driver works fine and will put out a signal to the bridge when a signal generator is fed into the antenna/feedback connection. It will even work on its own noise without a primary coil connected(as in the picture below). The problems all start when I put the primary coil in. The circuit ocillates, but I get no output on the secondary. changing the phasing 180 degrees doesnt seems to do much. It still ocilates, but it draws much more currnet. getting the bridge up to 50vac input doesn't help much either. I have also destroyed 3 ucc37321 chips today probably due to overheating. Using an interrupter should stop this. At this point I an at a total loss for what could be wrong. The only time I got any "first light" was using an antenna for feedback. I wouldn't actually call it first light because the antenna caught on fire and the coil didn't really do anything...

Things I have checked:
-It is grounded in 3 places, line ground, to the water pipe, and to the kitchen sink.
-I have swapped the phases of everything in just about every possible way.
-It is all getting power and will nicely light a 120v bulb with just high frequency while running from its own feedback.
-connections are tight and have been checked.

I say if I can't get this to work in 2 days, I would like to buy a PCB that will actually work. Anyone have a good DRSSTC board for sale? If no one does then I'll just have to spend $60 to have some made...

...

Wed May 31 2006, 02:50AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I am not sure why it isn't working but are you sure that you are atleast close to resonance? If you are too far off it might just refuse to work... The fact that it will run the lightbulb but not the coil seems like it is a tuning problem...

As to making a board... If you give me artwork I would be happy to make one for you; just as long as it is inder 6" by 8". I have double sided 3oz copper stock, various sizes of bits. PM me.

cjk2

Wed May 31 2006, 03:03AM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

I guess the frequency must be totally off, because it is resonating, but I am getting no output. I haven't seen a single spark all day. Using two feedback transformers(cascaded) dosent help. How could it be operating at the wrong frequency but still operating?

Steve Ward

Wed May 31 2006, 07:34AM

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

If you are using primary feedback, be sure to try swapping the actual CT leads (or pass the primary wire through the opposite direction). Or you could swap the inverting and non-inverting gate drivers. SImply swapping the primary coil connections will NOT change the feedback phasing for a primary feedback system (only for secondary feedback, antenna or CT).

The circuit will oscillate if the feedback is backwards, just at a much higher frequency, and this would quite likely destroy the gate drivers if left for long in this condition with a high enough duty cycle.

Also, you must tune the primary circuit to be very close to the secondary resonance, or else you will get lots of primary current, and very little action on the secondary side (no energy transfer).

Good luck. Dont give up so quick!

cjk2

Wed May 31 2006, 10:54PM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

Ok. It seems to be working to some point atleast. I still havent seen a spark, but it will brightly light a florucent bulb, and will create a nice display in a regular bulb. The phasing still seems to be wrong, because if I hook it up one way, it draws a lot of current, and I get no output. The other way it runs at a very high frequency, and I get little output. As for tuning the primary circuit, it is still be operated as a SSTC at this point, so it should self tune, correct? Like I said, It is doing something but it just isnt working well. Even with 340vdc in the bridge, It will not spark (at least it didn't explode).

I am off to try a few things:
-see what frequency it is running at
-try using an antenna again
-wait untill its dark so I can make sure I am not getting any output (wouldn't it be funny if it has been working but I can't see it?)

I'll get some pictures too.

HV Enthusiast

Thu Jun 01 2006, 12:01AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

I would try rechecking all your calculations to make sure your primary circuit at least somewhat matches the resonant frequency of your secondary circuit. I would start here. You can also measure this if you have a signal generator and a few LEDs laying around . . .

cjk2

Thu Jun 01 2006, 01:54AM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

First light! I went to do some more tests on the coil and it worked! It turns out the ground connection had been knocked lose and the coil was operating perfectly without any ground. I think this whole problem must have been caused by me(in my infinite stupidity) winding the primary coil directly on the secondary. While both coils were insulated, I assume the coils became capacitively coupled together and the secondary was "shorted" to the primary. Moving the primary off the secondary to a position slightly under it greatly helped, and the coil now puts out around 4" arcs at 120vdc into the bridge. I am currently using an antenna as I have not bothered to work with the primary feedback system.

I'll make a new primary soon so I can resume testing. Max output so far is about 5" with no real ground(I guess the primary was acting as one.)

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