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In Need of a Little Help in Designing a Versatile High Voltage Power Supply

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Robert Francis

Fri Sept 18 2009, 07:46PM

Registered Member #2355 Joined: Thu Sept 10 2009, 09:12PM
Location:
Posts: 71

My sarcasm detector just exploded...

Harry, you'll forgive me if I don't just accept that design teams and national budgets are needed to design a C-W generator of high voltage.

You insisted I would need a factory to hold a 1MV transformer and a million bucks when a core about 12" in diameter is all that is needed to get to 1MV if the duty cycle is kept extremely low among a couple other variables like number of primary turns and core stacking factor ratio.

Can you help me out on any of the questions that I asked?
Voltage sag, deliberately inducing voltage ripple, controlling the frequency of the ripple in a C-W?
The maximum flux density of air?

Proud Mary

Fri Sept 18 2009, 09:47PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Oh I really am sorry if you thought I was being sarcastic, Robert, which was not my intention at all. I thought the picture of the 750kV machine an interesting contrast to your own 2MV plans.
Please forgive me if I don't feel able to comment further.

Robert Francis

Fri Sept 18 2009, 10:19PM

Registered Member #2355 Joined: Thu Sept 10 2009, 09:12PM
Location:
Posts: 71

Sarcasm is a form of humor that uses sharp, cutting remarks or language intended to mock, wound, or subject to contempt or ridicule.

You've already made it quite apparent that you think there is no way in hell I can manage to build a transformer or a voltage multiplier capable of delivering 1 megavolt level voltages.

So unless you have made an about face in that opinion, how was your comment not sarcastic?

plazmatron

Fri Sept 18 2009, 11:45PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Ok, I think its time things were calmed down a bit here.

Harry and many others on here, myself included, could more than answer the questions you have asked on CW multipliers, without the need to get into heated debates.

Like others have said on here, you need to start at the beginning, You cant just go out and expect to build a 1 or 2 MV supply that can do what you ask without a lot of experience and a healthy budget.

Here is what I mean by beginning.
You asked how to deliberately induce ripple on a CW multiplier?
All CW multipliers have ripple, quite horrendous ripple actually. The ripple does not dip to 0V, nor could you force a triangle/squarewave through there.

You also ask how to control the frequency of the ripple?
Since CW's are driven off of AC, simply vary the frequency of the input signal !

These are very basic facts of a CW stack, and could be easily googled.

I am sure you have seen a few home-made CW multipliers around on the net? How many have broken 250kV, let alone 1MV?
There are reasons for this, you see, CW multipliers don't scale too well (unless you have the six figure budget someone mentioned). This is why Van-de-Graaf generators are still used today. They are a lot less expensive.

Once you get above 80kV corona becomes a really serious issue, so you can expect an open frame design, like in Harrys picture to be HUGE!

You can go with oil filled CW multipliers (my 150kV multiplier is sunk in oil), but again it is going to be LARGE once you get over 250kV, plus there is the expense and mess of oil, and some more fun problems I'm sure.

These problems are why, for high energy x-ray work, I use a 300kV marx generator. They are simple, robust, and can switch from 0-300kV in nanoseconds, the caveat being, the low repetition rate.

In short, generating 1MV is not trivial, but yes, certainly possible, on a decent budget.

Generating 1MV at 2MHz at a few milliamps, with variable frequency, etc, etc, is highly unlikely, without a team of engineers, and a HUGE budget (like a CERN sized budget!).

Les

Robert Francis

Sat Sept 19 2009, 01:23AM

Registered Member #2355 Joined: Thu Sept 10 2009, 09:12PM
Location:
Posts: 71

Ok, I think its time things were calmed down a bit here.

I agree, tell Harry to cut it out with the snarkiness. What can I say, I appreciate helpful posts like yours, repeated ones from the same person that imply I don't have a shot in hell tend to piss me off. If I was a wiser person I'd just ignore them.

I do know Cockcroft Walton Generators have ripple. I do know that the ripple can be reduced by using larger capacitors at earlier stages.

I wanted to make pulsed voltages so I was hoping I could substantially increase the ripple to essentially make the C-W a pulser instead of constant current.

That equation I was using to calculate ripple in a C-W seemed to suggest it could work but there is a lot I do not know about C-W generators and the fact that I haven't seen any C-W pulsers made me wonder if it was at all feasible to create a C-W pulser.

Aren't the C-Ws like the one in Harry's photo taking in a heck of a lot more current from the outlet than a standard 120V 15 Amp socket can provide? They are used to power particle accelerators. Also government tends to overbuild, they want to make sure they have no problems with the power supply the entire time the particle accelerator is being used.

I've seen the 64 kV one on Bob's High Voltage page, this supposed 120 kV one on youtube, and this supposed 320 kV one.

I figured there aren't many C-W generators above 500 kV because most people don't make the attempt. I have an epoxy resin that at 2" thick has a dielectric strength of over 1MV. I planned on using it wherever corona or other dielectric breakdowns might be a problem.

I looked into a Marx generator but as you said, their pulse rate is slow. I even looked into solid state marx generators for increased switching speed but the cost for MOSFETs or IGBTs would increase very quickly.

I figured with a C-W I wouldn't be able to vary the frequency or waveform.

Proud Mary

Sat Sept 19 2009, 10:58AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I have locked this thread after complaints by members of long standing over some of it's pseudo-scientific content and disagreeable tone,

Harry.

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