CW Multiplier

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Alex Peterson
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CW Multiplier

Post by Alex Peterson » Wed Sep 24, 2014 11:06 pm

for the past few months i have been looking for a power supply will any of these supplies work that i found on ebay
Image
Image
http://www.ebay.com/itm/100-KV-DC-High- ... 259532fb62
http://www.ebay.com/itm/100-KV-DC-High- ... 23406e9610

John Futter
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Re: CW Multiplier

Post by John Futter » Wed Sep 24, 2014 11:53 pm

Alex
These multipliers are but a small part of a high voltage supply.
you still need the high frequency inverter stage that feeds 5-10kV AC into the multiplier at somewhere between 20 kHz and 74 kHz

then of course you still need the metering and control electronics to save it all going up in smoke at the first accidental discharge

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John Taylor
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Re: CW Multiplier

Post by John Taylor » Thu Sep 25, 2014 4:08 am

Alex,
I have used the bottom type of multiplier and part of that effort has recently been posted in the images du jour area. If you use that multiplier, you will have to put capacitors across the outer portion of the board where the little l-shaped metal pieces are screwed to the through holes or vias. It will then make an 8-stage full wave cw multiplier. The existing capacitors are .001 uf at 30kv. If you intend to use it as a full wave cw, you will have to feed it from a center-tapped secondary. Since the caps are so small, you will want to use a fairly high frequency. I feed mine with 240khz at up to 15000 volts. I can help with a diagram if you want. By the way, you'll want to have it under oilat those voltages.

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Richard Hull
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Re: CW Multiplier

Post by Richard Hull » Thu Sep 25, 2014 5:23 am

John, why don't you upload an image of the schematic for the HF driver that you use.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Alex Peterson
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Re: CW Multiplier

Post by Alex Peterson » Thu Sep 25, 2014 11:42 am

Could i feed this with microwave oven transformers alligned in parallel?

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John Taylor
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Re: CW Multiplier

Post by John Taylor » Thu Sep 25, 2014 12:57 pm

Alex,
While you could connect two paralleled MOTs to feed this multiplier, you would be better off to think of something else,in my opinion. First, as this is 8 stages, you would probably not have enough voltage output to easily detect fusion and, since MOTs are iron-core, their maximum frequency is probably going to be limited to relatively low frequency requiring the filter capacitors on that multiplier to be relatively large (read as expensive). An online calculator for voltage multipliers will quickly show you that ripple will be excessive unless fairly large caps are used. The inrush current for such large caps will likely exceed the rating of the diodes on that multiplier with out current limiting.

Richard,
I am not at home right now so I can't draw a schematic with a drafting program, but I will scan in a hand-drawn schematic and post it today. I have not finished my driving circuitry yet, but am just driving the base of 4 paralleled ECG 2533 (1200v NPN Horizontal output transistors) with balancing reisistors(ballasts) on the emitters. I have a 20 ohm resistor in series with the base of each and am feeding these from the 50 ohm output of an older HP signal generator with appx 6v peak square wave. I am currently feeding this into the bases with a short piece of coax with BNC connector.

I just adjusted the frequency output until I got maximum output from my handwound ferrite core transformer which has the 7-turn primary connected between a 0-700v dc power supply and the collectors of the four transistors. Granted, this is not a perfectly-matched rf driver circuit, but it is working okay at around 240khz with a fairly steep dropoff on either side of this frequency. This transformer outputs around 15,400 volts with 700 volts input.

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John Taylor
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Re: CW Multiplier

Post by John Taylor » Thu Sep 25, 2014 5:06 pm

I'm attaching my driver circuit that I am currently using for testing my power supply. I have modified the above-mentioned CW multiplier and it can be seen in my recent post in the "images du jour" section of this forum. I will eventually drive this with a commonly available PWM (Pulse Width Modulation) integrated circuit. I used the Horizontal Output transistors because I had them in my parts drawer from back in the CRT type monitor days. It would probably make more sense to use MOSFETS for switching transistors, but right now I just threw this together without much regard for capacitances, inductances and other nasties that will be important to design a better driver circuit at higher frequencies than a lot of switch mode power supplies. Of course, this will probably need good shielding to tame the RF noise this thing will make using square waves at higher power.

Photos of some of the components are in the "images du jour" section as mentioned above.

Even with the obvious design flaws and inefficiencies here, I am able to get to about 50kv unloaded (other than bleeders and voltage divider) with the multiplier in dry air. After I finish a suitable container from 6" PVC pipe and submerge this in oil, I will be able to test it to higher voltages.

I still have only a limited idea of what my final configuration will be. My objective is to build a low-cost power supply using as many cheaply scrounged and easily available parts as possible. I also want to build something with plenty of capability that can be built by others on a limited budget. Of course I'm also trying to keep the design process as simple as possible as well.
After finalizing the high voltage portion, I will try to get the switching part completed. I am hoping to be able to mount all except the transformer and multiplier/divider in a 19" rack mounted cabinet of approximately 10"tall.
Attachments
drivercircuit.pdf
(326.29 KiB) Downloaded 222 times

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Richard Hull
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Re: CW Multiplier

Post by Richard Hull » Thu Sep 25, 2014 6:59 pm

John sounds like something I would try..... cobble & test. Great effort and thanks for the schematic.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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