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Shaun

Thu Nov 08 2007, 04:45AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

I'm going to call this my first SSTC, even though I started it long after I started my DRSSTC, because at this rate it looks like I will finish it long before the DRSSTC.

Its Steve's Mini driver, IRFP260 half-bridge, etc... secondary is 9.5" tall by 4.25" wide, 32awg (it would have been 10" tall, but I ran out of wire!).

I am really proud of the driver, though. I don't have the materials to etch boards yet, but I really don't think it could have been made smaller than this without using SMT components, perfboard or not:

It just needs to be connected to a 20V or so transformer on one side, and a GDT on the other.
Oh, and a heatsink on the 12V regulator.

Here are the bridge materials (still waiting for heatsinks), and the secondary.

I plan to make a topload even thought it is not needed; to me coils don't look finished with just a piece of wire hanging off. The R and C of the interrupter I have set to 10M and .1uF, since it is a very low duty cycle for preliminary tests.
Primary and case coming soon.

I will not be here for the next 2 or 3 days, expect updates soon after.

...

Thu Nov 08 2007, 04:57AM

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

Looks good

Although I might note that it is a really good idea to have some low ESR caps (ceramic/tant) of a few at least a few hundred nF in parallel with those electrlytics for the UCCs. The bulk of the work for those caps is right when the gate is being charged/discharged, so you don't need much in the way of capacitance, just a nice low ESR so that you can get the best possible gate waveforms.

I bet that some of the members here *cough matt, waverider *cough could have made the board a bit smaller by putting parts on the bottom of the board and moving them all a little bit closer to eachother, but it is good enough

Just make sure that you make a nice box for it when you are done, or else you can't call it finished

Ken M.

Thu Nov 08 2007, 03:31PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

The Idea of just teh wire hanging off and the arc coming from it with the mini coil of steve's doesn't work too well! I tried that right after I made the coil and got the feedback working, the wire got fried right to where it was point out left a nce black singe mark on the PVC cap!

Shaun

Sat Nov 10 2007, 11:12PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Well I just got back (From Boston; visiting MIT). As soon as I finish typing I am assembling the bridge and primary.

To ... , about those caps across the UCCs: They are tantalum capacitors; 47uF 20V. They do look like regular lytics because they are the military type you can pick up on Ebay, but really its just they don't look like the normal dipped type for consumer use. I hope they perform as well...

As to WhiteArc, thanks for the tip. I don't need my secondary any shorter than it already is.

The two IRFP260s will be mounted top a 3"x3"x3" (roughly) heatsink, with matching fan. Soldering iron is hot now, so here goes...

Edit: oh, and not show in pics is a 200V 820uF filter cap for the bridge.

Shaun

Sun Nov 11 2007, 09:34PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Sorry for the double post, but I'm having some problems here. I did a quick lash-up to make sure everything worked before I put it in a nice box (I'm gonna use an old ATX PSU case), and it is not working.

At a low break rate on the interrupter, I can hear the bridge clicking. No output whatsoever from the secondary.

I took a scope shot of the GDT primary at a much higher break rate (I can't scope the bridge yet-no isolation xfmr). I am getting a semi-clean square wave, but its amplitude seems much less than it should be.

Could it be the feedback? The antenna seems close enough to the coil.

I'm really at a loss as to what to do next...
Here are some picture and a scope shot of the GDT primary:

This last one is 1uS/div and 0.1V/div on GDT primary-no output from coil whatsoever.
Interrupter R and C is 1K and 1nF

Sorry if some pics are blurred..my camera sucks at close ranges.

Dr. Dark Current

Sun Nov 11 2007, 09:51PM

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

Shaun wrote ...

This last one is 1uS/div and 0.1V/div on GDT primary-no output from coil whatsoever.
Interrupter R and C is 1K and 1nF

1k with 1n is really low.. try 10k and 100n.

The coil is not getting feedback. Try reversing the primary.

Shaun

Mon Nov 12 2007, 02:31AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Okay, I made some changes. Interrupter RC is now 10K and 0.1uF, but more importantly, I rewound the primary so that it is now wound in the same direction as the secondary. During tests, the heatsink warms up, so I know power is going somewhere.

Here is a shot of the new GDT primary waveform:

And here is what I can pick up by just attaching the probe to a piece of wire:

More importantly, I was going through the feedback circuit to see what part of it is the problem, and I immediately noticed something was wrong. First of all, probing pin 1 of the 74hc14 severely affects the circuits operation (the bridge stops whistling). It also gives a signal similar to the second picture, but with a sharp bump before the ringing starts.

Probing pin 4 of the inverter gives NO SIGNAL at all. I replaced the chip, twice, with same result each time. I'm pretty sure this is the problem. I'm going to go recheck the circuitry around this IC now; hopefully its just some stupid mistake.

Any suggestions will be greatly appreciated.

EDIT: Remember I said stupid mistake? the inverter's pin 1 was not connected to the filter cap+antenna! Fixing this, of course, did not get the coil working. Now I get a strange, unstable clicking noise from the bridge, a strange 100Hz (that's right, Hz) square wave on inverter pin 4, and strange noises from the primary.

I have NO IDEA where the 100Hz square wave is coming from (we have 60Hz mains), but as for the other problems I suspect primary-secondary arcing. I thought I could get away with winding the primary right on the epoxied secondary, I guess I can't. I'm done with this for the night, tomorrow I will rewind a better insulated primary.

Zum Beispiel

Mon Nov 12 2007, 10:08AM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

The primary should be wound tha same way as the secondary. Have you tried swapping the primary connections around?

Also, try bypassing the interrupter so it runs CW and feeding the bridge with filtered dc (low voltage). See if it can light up a fluorescent light. Try drawing an arc from the breakout point. make sure your antenna clamping diodes are the right way around.

If nothing else works, try running it open loop at low power.

Ken M.

Mon Nov 12 2007, 01:36PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

For really close priamrys to secondary, I suggest going to ur local hardware store, and getting a rubber tube adapter and modifying it to fit your coil (If needed), since the ruber is usually 1\4" thick.

Dr. Dark Current

Mon Nov 12 2007, 03:09PM

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

Shaun wrote ...

...
Here is a shot of the new GDT primary waveform:

...

I have NO IDEA where the 100Hz square wave is coming from (we have 60Hz mains)

...

The 100hz is coming from the interrupter, at least you know its working.

Your coil is still not getting any feedback. The ringy waveform you see on the GDT primary is caused by the DC decoupling cap resonating with the GDT primary winding. With good feedback, the GDT waveform should look like bursts of HF signal repeating at the interrupter frequency.

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