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Two Cockcroft Walton Gens powered by a Neon Sign Transformer

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Robert Francis

Wed May 02 2018, 04:55PM

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

Hi guys,

I have a question. I originally was going to power a single cockcroft walton generator with a flyback transformer. But the flyback does not have a HV negative or ground terminal on it.

As a result I decided to scrap the power supply > buck booster > flyback - and swap in a neon sign transformer. But I have read that neon sign transformers use a positive and negative voltage on their HV output. Easier to insulate than making the positive doubled and negative ground.

So I decided I would have 2 cockcroft walton gens, the positive NST feeds a positive cw and the negative would feed a negative CW.

My question is do I follow a standard CW for the negative one or do I reverse the diodes? I know if I was dealing with a positive voltage and needed a negative one I would reverse the diodes but with the NST negative it is already negative and doesn't need to be flipped. So do I not need to reverse the diodes?

Thank you,
Bob

hen918

Wed May 02 2018, 05:17PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

You could not reverse the diodes and have a fullwave CW generator like this:

The input voltage to this one would be the voltage across one half of the centre-tapped secondary, but the advantage to this one is reduced ripple voltage, allowing you to draw a higher current.

or you could make two separate CW multipliers, one with reversed diodes, using the centre point of the transformer as the common connection. Your output would be double that of the previous case, but only half wave rectified.
a third option would be to only use the centre-tap as common, connecting a normal CW generator to the + and - terminals, this would be similar to the second option, but would require diodes rated to at least 4 times the peak voltage from centre-tap to positive rail, whilst the other two only require diodes rated at 2x.

Robert Francis

Tue May 08 2018, 07:46PM

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

I bought a couple solid state NSTs off of ebay. There is a paper that came with them saying they will not work with Tesla coils. A little research on Google said it was due to the gfci circuit in the NST.

Is it possible they will work with a cockcroft walton generator that leads into a Marx gen?

Robert Francis

Sat May 12 2018, 05:48PM

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

I have another question, the NST I have puts out +7500V and -7500V. In an ordinary CW gen if the CW was one stage would the output be +21kV or +42kV?

I am wondering if the output voltage is based off the +7500V or if it is based off of the difference between the positive and negative leads off the NST, therefore 15kV.

Here is a CW calculator if that helps:

hen918

Sat May 12 2018, 06:07PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

See my post above. That depends on how you wire it.

Robert Francis

Wed May 16 2018, 07:35PM

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

I apologize, but I am hoping you could clarify some things for me.

How do I access the center point of the NST. Do I have to open the NST case and run a wire to the outside of the NST case? I ask cause as far as I can tell on my NST there are only 2 high voltage connection points, +7500 and -7500. I don't see any other way of accessing the center point in the middle of the high voltage transformer.

There is a case ground of course but I don't think you are referring to that as that is for household electrical ground along with voltage in and neutral.

hen918

Wed May 16 2018, 09:15PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

The case of the NST will be ground / 0 V assuming it's an old, electrical type.

Robert Francis

Thu May 17 2018, 01:26PM

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

So its safe to connect the CW gen to the ground on the case?

Robert Francis

Mon May 21 2018, 03:53PM

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

Is it safe to connect the CW gen to the ground on the NST case? I need to know.

hen918

Mon May 21 2018, 04:42PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

It will be safe to do so, but it might have a built in RCD / GFI which will trip if current flows though ground. Hopefully you don't have one of those. If you do your only options are either remove/disable it (I don't think that will be easy) or make a multiplier like the third option.

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