Neon Sign Transformer (Remove centre Tap OR pot it)

[gsmsslsb]

I want to use a neon sign transformer to run a cockroft walton cascade and I have some questions about the cantre tap.
The bottom of the cascade is grounded so that means one end of the NST is also grounded with the secondary winding of the NST centre tapped to ground this means I will be shorting out one half of the NST  RIGHT?
So either I have to remove the centre tap or why cant I build a box around the whole thing and pott it.
From what I have heard the problem with removing the centre tap is that the transformer core is connected to the case therefore grounded. So the voltage between the HV ends of the secondary and the core is constrained to half the HV output. If I remove the centre tap and ground one end of the HV winding then the voltage between the other end and the core will be the full HV output which the insulation will not handle. right?
So if I build a plexiglass box and pot the whole transformer and just bring the HV ends and the 230 volt supply out then I should be able to ground one end of the HV and have the core and case floating at half the full HV output and have the full HV output to apply to the CW cascade.
Am I thinking right someone let me know.
Thanks GSM

[Staffman]

You have the right idea. I built one of these many years ago. My setup was two 5 stage CW multipliers, one for Positive DC and the other for Negative DC (think 'reverse the diodes'). I used two NST's. I'll drag that thing out if you need me to, to see how I had it wired up. I don't quite remember how I have it grounded... probably to house ground. You can also use a separate grounding rod. I will tell you one thing, if you don't choose the correct components, ie capacitors and diodes, the output will not be what you wanted it to be. Also, you may have to put the multiplier in mineral oil to prevent arcing between nodes. I used my setup to test lifters. These things are dangerous. I had an assistant always on standby near the power outlet just in case something went wrong. One day, out on the patio both pos and neg leads touched the concrete. It shocked the crap out of me, I could not move or talk. I didn't realise that concrete and stone was conductive to hv. Thankfully my assistant yanked the cord out of the wall. I thought several minutes went by before my assistant yanked the cord, but in reality it was only about one second! I haven't touched the thing since.

[z.monkey]

It shocked the crap out of me, I could not move or talk.

You're quite lucky it didn't kill you...
Is gsmsslsb still around?

[CompuTutor]

gsmsslsb,
All the above are correct of course.

But there is more to consider.

The point of the center tap is to
half the potential between the ground,
and any winding including primary
as far as potential arc over internally.

And keep the average mean voltage
cancelled to zero by having one leg
positive equal to the negative of the other.

Running sign's on humid days
would really suck otherwise...

May I suggest you utilize that aspect.

Use the two cathodes of
two high voltage diodes
on each leg of the NST
to a common postitive.

You retain the safety aspect
designed into the transformer.

Using one of the legs as a common
puts the house mains neutral
at half the HV potential of the secondary.

And of course as result,
the common of your project,
the same unsafe potential
from your entire enviroment !

Unwise if avoidable...

Unless you need the full voltage ?

A variation on staffman's idea
would retain a neutral enviroment
with balanced cancelling HV,
and only shifted by one half of
the mains voltage instead,
but provide all the HV needed.

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