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Re: [TCML] Crock Croft Walton Voltage Multiplier



Having built a CW stack, and used a very lightly doped mixture of deionised water with Copper suphate, be very careful.

Be aware of what you use as the electrodes, over time the metal will leach into the water and can alter the resistance of your resistor.

Make it HUGE ... What ever size you think it needs to be, add some. Remember to account for skin effect, contamination and especially humid conditions.

I had a CW stack running at about 160KV with a 400mm long water resistor made from 2M of silicone piping, space wound around a 30mm dia PVC tube

After using this resistor to discharge the stack, it arced over from end to end. Very impressive, but it took out some diodes in the process.

I decided that using this or a bigger alternative as a safety resistor was out of the question as you can't guarantee its performance.

I'd suggest multiple commercial resistors in a large oil filled tube , but it soon gets expensive and heavy for the top of the stack for a good safety margin.

    Derek


On 04/05/2012 14:53, Bert Hickman wrote:
Although it may be possible to make an aqueous resistor using a long length of small flexible vinyl tubing, I wouldn't recommend it since the resistance may vary significantly over time or with temperature.

A better choice would be a string of commercial high voltage resistors connected in series to achieve the desired resistance and hold-off voltage (with a significant - say at least 50%+ - safety margin). New HV resistors can be pricey, but you can sometimes find them on eBay at relatively low cost.

For example, following are some possibilities where the vendor is also offering sufficient quantities:

http://www.ebay.com/itm/260719938778    (200 Meg, 11 kV)
http://www.ebay.com/itm/251009542782    (100 Meg, 15 kV)

Bert


Neon Tesla wrote:
Thanks for all the great ideas on construction, anyone
have any Ideas for resistors of that size (could you build
one)?
On Thu, May 3, 2012 at 10:23 AM, Kurt Schraner<k.schraner@xxxxxxxxxxx>wrote:

Hi,

of course Cockrroft and Walton are the famous Nobel winners for using this
device:

http://en.wikipedia.org/wiki/**Cockcroft%E2%80%93Walton_**generator<http://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator>

but why should it not be mentiond, that it was invented long time before
by :

http://en.wikipedia.org/wiki/**Heinrich_Greinacher<http://en.wikipedia.org/wiki/Heinrich_Greinacher> ... the Greinacher cascade

...just a Q, this is no AC vs. DC war! ;-) ... and I'm not too much of a
patriot.
Bert: I enjoy happily your explanations to the device: super!

Regards,  Kurt


-----Ursprüngliche Nachricht----- From: Bert Hickman
Sent: Thursday, May 03, 2012 5:39 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Crock Croft Walton Voltage Multiplier


Just about any HV capacitors will work, including Power Factor
Correction (PFC) caps. However, PFC caps contain internal bleeder
resistors that will reduce the overall output of your CW multiplier.

The rated DC voltage of the stage capacitors must be at least as high as the peak HV input voltage, and the HV rectifiers must be at least 2X the
peak HV input voltage. Add 20% - 50% to this to provide a degree of
design margin. Use fast recovery rectifiers if you'll be driving from a
high frequency source (see below). You can stack a series of identical
lower voltage rectifiers to create higher voltage rectifiers.

Although a CW multiplier can be used for "hair raising" experiments,
this is really NOT recommended unless you know EXACTLY what you are
doing... especially if you're storing significant energy in your CW
stage capacitors. This trick is done by connecting a series chain of
high voltage resistors (Gigaohm(s)) between the CW output and your
volunteer to severely limit maximum current to no more than 10's of
microamperes. If your volunteer suddenly decides to step off the
insulated platform, or if the platform flashes over, the HV resistor
chain MUST safely withstand the full voltage of your CW without breaking down. Your volunteer's life may very well depend on YOUR engineering and
construction skills.

Give serious consideration to the total amount of energy stored within
the stage capacitors before arbitrarily selecting large valued stage
capacitors. Consider powering your CW from a high frequency (20 - 25
kHz) HV source. This will allow you to reduce the stage capacitance and
total CW energy. Also, remember that short-circuiting the HV output will
likely destroy some (or all) of your rectifiers.

Some good design information for half-wave and full-wave CW designs can
be found here:

http://blazelabs.com/e-exp15.**asp<http://blazelabs.com/e-exp15.asp>
http://home.earthlink.net/~**jimlux/hv/cw1.htm<http://home.earthlink.net/~jimlux/hv/cw1.htm>

Good luck and play safely,

Bert
--
Bert Hickman
Stoneridge Engineering
http://www.capturedlightning.**com<http://www.capturedlightning.com>
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Neon Tesla wrote:

              Im not sure if this is of topic but;
I wan't to build a voltage multiplier but I have seen very little on the practical construction of large units, my 3 main questions of construction
are, firstly what type of capacitors would work, would high voltage
distribution PFC's be suitable? Secondly what are the values that should
be used for the Capacitors and Diodes in relation to the power source,
should the parts be over rated? And last I've seen Crock Croft  Walton
multipliers used in the same way as a Van De Graff in hair raising stunts,
should or could this safely be attempted?




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