Pushing a CW Multiplier

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Matt_Gibson
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Real name: Matt Gibson

Re: Pushing a CW Multiplier

Post by Matt_Gibson » Sat Nov 13, 2021 4:25 pm

Hi Rex,

I made an offer that was accepted. The seller had a link to a university website with the manual that this multiplier went in. It doesn’t look like it was designed for oil. I’ll have to take it apart so you guys can see the insides, they are pretty beefy!

My 40kV 15mA glassman was also a low bid surprise. I had to replace the mA scale, reverse the diodes and jumpers, but it works well other than that. 600W ought to be plenty, no?

I was sorry to see that 75kV negative Glassman go so high…

-Matt

Matt_Gibson
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Re: Pushing a CW Multiplier

Post by Matt_Gibson » Fri Nov 19, 2021 8:44 pm

Here are some pictures of my 100kV @ 1mA Glassman multiplier, opened up. Pretty beefy looking!
54B74646-0D3A-4B44-A2BF-DBA415567568.jpeg
29AA8D18-5BCB-4F1A-9E1F-9517A774691F.jpeg
C5FC63EF-0A07-4339-8B0A-1E77C71F44E2.jpeg
ED9454D8-E002-41D2-8CF1-5BBEFD4B2974.jpeg

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Dennis P Brown
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Re: Pushing a CW Multiplier

Post by Dennis P Brown » Sat Nov 20, 2021 8:47 pm

I am familiar with simple voltage multiplier circuits but don't recognize some of those components. It appears to be full wave but the purpose of the resisters isn't clear to me. Could you explain a bit about each picture and for others (besides me) a bit on the function of the entire system, maybe? What frequency does it need and current/voltage?
In any case, thanks for sharing the images.

Matt_Gibson
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Re: Pushing a CW Multiplier

Post by Matt_Gibson » Sun Nov 21, 2021 4:58 pm

While I am by no means an expert, I’m pretty sure it’s just a half wave multiplier…I wish it was full wave, more power!

I don’t know, for sure, what the series resistors (in series with the 0.015uF capacitors) are for, but would guess for current limit/protection.

The other resistors/capacitors are for voltage and current metering.

Don’t know the intended frequency either.

Once I have more time, and been successful with my 40kV supply, I’ll design/build a proper switching supply for this 100kV multiplier so that I can see how hard I can push it. I’m guessing that it is more capable than 1mA.

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Dennis P Brown
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Re: Pushing a CW Multiplier

Post by Dennis P Brown » Sun Nov 21, 2021 11:39 pm

Thanks - guess the frequency matches most their std. commercial units.

I built a rather powerful 120 kV voltage multiplier (used very beefy door knob caps and high current diodes) and charged it a quarter way (I thought but either it was over charged or had a far higher upper limit - my calculations always errored on the under values.) When my 45 kV probe went full scale and I was still 5 cm from the unit - the field effects by the small discharge sphere (under oil!) convinced me it was far too dangerous to be near this unit. It is in an attic unused. Maybe someday (I tell myself) I'll have the nerve to try it again and with a better (safer) methodology to charge and test it.

So be careful at these very high voltages - as I learned (and can tell the tale) they get rather squirrelly and their behavior can be unpredictable.

Matt_Gibson
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Re: Pushing a CW Multiplier

Post by Matt_Gibson » Mon Nov 22, 2021 3:36 am

I also have a homemade multiplier that I have put away…

It’s a 4 stage using 0.068uF 6kV capacitors in series (so 0.034uF and 12kV). Under oil. I need a safer setup as it is very hard to control and has gunshot level discharges when it bypasses whatever resistor I try to throw at it :-) A lot of spraying and then BANG!!! It’s also for a future path that I may take along this journey:-) For now, my 40kV glassman is the man.

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Dennis P Brown
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Re: Pushing a CW Multiplier

Post by Dennis P Brown » Tue Nov 23, 2021 11:44 pm

Here is my old voltage multiplier without its vertical oil tank. If I recall, the diodes were 20 kV. I intended the unit for a corona field generator - not for current. Used the wrong caps but was rather ignorant of design of those devices. The driver was 3 kV, high current x-former (close to an amp) that also had a single stage multiplier of its own but no need for that section to be under oil.
Attachments
VoltageMultiplier.JPG
Eight stage using 15 kV door knob caps

Matt_Gibson
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Re: Pushing a CW Multiplier

Post by Matt_Gibson » Wed Nov 24, 2021 5:29 pm

I have some 40kV 2nF doorknobs that I was going to use but decided to save them for a Marx generator.

How did this multiplier perform? Did you get some current/voltage measurements? I abandoned the idea of using the doorknobs when I saw how bad the voltage ripple was going to be at just a few mA.

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Dennis P Brown
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Re: Pushing a CW Multiplier

Post by Dennis P Brown » Wed Nov 24, 2021 6:01 pm

I tried to measure it but the field generated was too intense - even with the multiplier's top electrode under oil (about a cm), my 45 kV probe pegged when it got to within 5 cm while still in air. Worse, the oil surface was moving towards the probe! I calculated the stack could hit (with a better HV supply) 120 kV - 140 kV safely (for the components, not necessarily me, apparently) and assumed it would max to 100 kV with the reduced supply I was using. However, the variac was only at half scale so I thought I was within the limits of the HV probe - apparently not. That was just too dangerous so I abandoned the linear accelerator and built a normal fusor.

Matt_Gibson
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Re: Pushing a CW Multiplier

Post by Matt_Gibson » Thu Nov 25, 2021 5:08 pm

Sounds like you need a good “dummy” load for the multiplier?

I’ve been meaning to put one together, but will save that for fusor 2 once I outgrow my 40kV Glassman.

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