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Full wave Cockcroft-Walton voltage multiplier

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RogerInOhio

Sun Nov 15 2009, 01:26AM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

I have spent a lot of time playing around with Tesla coils for the last few years and I was kind of missing High voltage DC which is a whole different experience. Van de graaff generators can be kind of sensitive to humidity so I decided to drive a Cockcroft -Walton voltage multiplier with a 15kv /30ma neon sign transformer and try to get enough voltage to feel an ion wind, get corona to come off of my finger tips and make hair stand up on end.

This involved some trial and error but I ended up going full wave with 5 stages, the last four are in a glass tube filled with transformer oil that Bert Hickman gave me when he was cleaning out his garage. The capacitors in the first stage are .003uf at 30kv and the capacitors in the other stages are .002uf at 30kv. All the diodes are rated for 20kv at 100ma and I use them in pairs connected in series. There is about 1.5 meg worth of resistors hooked up in the top of the tube to protect the diodes from current surges. Enjoy the pictures.

rp181

Sun Nov 15 2009, 02:24AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

very nice construction, the glass tube looks great! where did you get the tube?

Mads Barnkob

Sun Nov 15 2009, 09:26AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Looks good, clean construction and good results ;)

How do you find the performance of those capacitors? They look like some I bought long back from a china ebay'er, was wondering if you got yours from a similar place.

RogerInOhio

Sun Nov 15 2009, 10:53AM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

very nice construction, the glass tube looks great! where did you get the tube?

I got the glass tube at an arts and craft store called Hobby Lobby. It was meant to be a flower vase and it is closed at what is now the top so I had to drill a hole for the output electrode. The bottom is sealed to the base with silicon rubber caulking.

How do you find the performance of those capacitors?

You are right. The capacitors are from China and I got them off of Ebay. They work just fine.

Proud Mary

Sun Nov 15 2009, 12:34PM

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

Hello Roger, do you know what the sag under load is?

brtaman

Sun Nov 15 2009, 12:54PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Great work, roger. The construction is top notch, looks as if it was built commercially! The gold hue of the transformer oil really sets it off.

RogerInOhio

Sun Nov 15 2009, 02:23PM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

Thanks guys for all the complements.

Hello Roger, do you know what the sag under load is?

I don't have any figures but I can say it sags a lot. If you connect something to it that has a lot of sharp points the corona losses are so great that the voltage drops down to a fraction of what it normally is. The girl in the bottom picture doesn't have too many sharp points on her (most of her points are nice and round) and if you where to try to touch her hand you would get hit by a three or four inch long spark.
I would say that if you where going to make something like this to drive an x ray tube or a partial accelerator you would want to design it to have a lot less sag than what I'm getting.

Electroholic

Sun Nov 15 2009, 05:29PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

how fast are the diodes? maybe pumping it at higher frequency will help?

Proud Mary

Sun Nov 15 2009, 06:43PM

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

Hello Roger,

if you could specify V(in), f, C, and number of stages, performance under load can be easily estimated, (i.e. before corona and other leakage losses)

Stella

RogerInOhio

Sun Nov 15 2009, 10:00PM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

how fast are the diodes? maybe pumping it at higher frequency will help?

The number on the diodes is 2CL2FM and the recovery time is 100ns. I suspect that is fast enough that I could increase the pumping frequency quite a bit and I might want to do that sometime but it seems a little hard to do. Do you have any suggestions on how I might raise the frequency?

if you could specify V(in), f, C, and number of stages,

Frequency is 60 hz voltage in is 7500vac , 5 stages first stage uses .003uf caps. The other stages use .002uf caps.

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