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uzzors2k

Tue Jun 10 2008, 08:39AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Just a little something I whipped up over the last few days. I'm not sure if I should be calling it a CW, Greinacher or Villard cascade, but it's a voltage quadrupler at any rate. (seriously, is there a difference? look at the schematics.

) I used 4 strings of sixty RGP10M diodes, and four capacitors made by Mate's recipe. All in all it should be good for about 20kV AC input and 80kV DC at a few kW. All I'm missing now is a decent source of 20kV AC power...

Construction was pretty straight forward. First I made the capacitors with tin foil and overhead transparencies. I made sure to give at least 4cm clearance from the sides so it wouldn't arc over.

Then I moved on to the diode stack. 240 diodes, and they all had to be chained together. It took a few hours from I started until they were all linked together in strings.

Here the diodes are wrapped around a thin PVC pipe to give them some structure and voltage stand-off in a smaller package. Beside them is the pipe they will soon be fitted into.

..and the finished multiplier! Some duct-tape really eases construction.

1213085450 95 FT0 Finished Multiplier Back

1213085450 95 FT0 Finished Multiplier Front

I can't wait to try it out! I did some early tests with an ignition coil, but 400Hz is too low for 1.3nF caps. It made some sparks though. I'm considering an upgraded ignition coil driver, homemade flyback or the SLR inverter (once I finish it).

aonomus

Tue Jun 10 2008, 02:01PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

I'm almost tempted to try and remix a song so you can have 'Unchained Diode' for the next time you make one of these.... :D

Mates

Tue Jun 10 2008, 02:35PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

This reminds me my old doubler project

and a bit my CW project

The ignition coil works very well for this concept, but you need to switch it in KHz frequencies (3-6KHz works the best)

The only thing I do not understand is why your caps have such small capacitance. For 20KV DC you need like two transparencies sheet separtion only (three is already overkill but you can use it to be sure) which should give close to 7nF. Why you use so many transparencies? Remember, one sheet can stand 14KV DC.

And BTW, there is a big difference in quadrupler and two stage CW despite the output voltage is the same. Remeber to put as the lower stage caps with much higher capacitance (twice is minimum)...

Good luck and keep us updated!

uzzors2k

Tue Jun 10 2008, 09:34PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Your multipliers have been a source of inspiration Mates. About your ignition coil driver, what duty cycle do you run it at while doing 6kHz offline?

I still don't see any difference whatsoever between a two stage CW and a voltage quadrupler, am I suffering from some delusion? Is there any non-historical reason that seemingly alike multipliers have different names? At any rate the capacitors need to be rated for 2x Vin, and with some overhead you quickly land around 60kV, which is what the diodes can ideally stand. I used 5 sheets in my capacitors, hence the low capacitance. However, over 10kHz or so they can still supply a few kW of power so the low capacitance isn't much of a hinder.

Mates

Tue Jun 10 2008, 10:25PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

here is a scheme of quadrupler... you see it's a different concept (it gives more power than CW)

Those five sheets - you are right, it's better to be on the safe side... Hope you will not have to deal with side sparking.

My iggy driver is rather special - it's powered straight from the mains (pumping 300V DC into the primary!) and I'm not sure whether you would have any use for that concept (it gives minimum 50KV AC and sucks 600W from the wall). Not every iggy and transistor can stand that...

In case you are interested I'll post the scheme...

BTW: I like the idea of the tube in tube design... Only thing is the way you have connected your diodes together - it looks you will have huge corona losses. The joits should be like pearls...Maybe you could solve an oil bath between the walls of those two tubes???...

uzzors2k

Wed Jun 11 2008, 01:26PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I sort of remember what your flyback/ignition coil driver looked like, lots of TVS diodes and heavy IGBTs. Running low duty cycles should be safe though, and with all the primary inductance an ignition coil has the primary current won't rise too high. Do post a schematic though.

I made no attempt at corona suppression because I'm wasn't sure if corona losses would be much of a problem. Do they really drain lots of power? Filling the tube with oil is quite possible, but it would take several liters of oil, and require a redesign. Putting the diodes in a smaller tube, put the capacitors on the outside, then put another tube around the whole setup, and then flood it all with oil. Come to think of it, it wouldn't have taken much extra work if I had thought of it earlier...

Oh, that quadrupler schematic is just a 2 stage CW/Villard/Greinacher fed in the center, a bipolar multiplier of sorts. I see that gives more power without the need for larger capacitors though. Still, the difference is so negligible that I think naming is just a matter of preference.

Mates

Wed Jun 11 2008, 11:33PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

Uzzors wrote ...

I sort of remember what your flyback/ignition coil driver looked like, lots of TVS diodes and heavy IGBTs. Running low duty cycles should be safe though, and with all the primary inductance an ignition coil has the primary current won't rise too high. Do post a schematic though.

here is the latest version - easy to build

Firefox

Thu Jun 12 2008, 12:43AM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

Mates is right, if you organize the two circuits, a two stage CW Multiplier, and a Quadrupler with the capacitors along the same lines, it becomes apparent that they are not the same circuit, though there are similarities
QuadruplervsCW

Steve Conner

Thu Jun 12 2008, 09:36AM

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

The quadrupler circuit is just two Villard doublers

one wired for a positive output, and the other for negative. They have their inputs in parallel and outputs in series.

As far as I know, I introduced this circuit to HV hobbyists when I used it in my Tesla-2 coil

It gives more power than a 2-stage C-W multiplier (which is, as someone pointed out, also made of two Villard doublers cascaded) built with the same capacitors.

From Firefox's drawing, it seems that the only difference is one connection. The top right-hand capacitor is fed directly from the transformer in my circuit, whereas it's fed through the top left-hand capacitor in the 2-stage C-W. So maybe the difference in output power isn't that great, although I remember simulating both circuits in PSpice and liking mine more.

uzzors2k

Sun Dec 28 2008, 10:17PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Well, it's complete.

And I must say well worth the trouble, despite taking about 6 months to acquire a suitable power supply. With my big-mofo xrfmr in working order I have been able to use this 2-stage CW (I'll surrender to the naming convention to avoid misconceptions) at near maximun rated power. Taking pictures of acrs at their longest is always tough, so I'll let a video do the talking.

A picture of the current setup. I'm running out of table space!

I think the arc had just struck in that picture. As for the sparks, they're created while driving the CW from my homemade xfrmr at 10kV. It was ballasted at the time too, which prevented arc formation unless the leads were brought within close proximity to eachother.

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