8-stage Cockroft-Walton/Villard cascade multiplier

Something I’ve crafted for the new X-ray experiments: a half wave, eight stage Cockroft Walton multiplier (or a Villard cascade, whichever name you like), submerged in oil, providing a theoretical maximum output voltage in excess of 220 kV with a maximum supply voltage of 10 kV AC, with headroom.

High voltage multiplier, PartsA bunch of capacitors and rectifiers

Sixteen 2.2nF and sixteen 30mA rectifiers, all rated 30 kilovolts, form the 8-stage half wave multiplier. Capacitors need to be rated for the peak voltage + reserve, diodes 2 times the peak voltage + reserve. In my case, as mentioned above, a theoretical maximum of 10 kV AC root-mean-square can be supplied (10*2*1.41, with a 2 kilovolt headroom). The circuit is quite evident from the wiring below:

High voltage multiplier, WiringWhy not?

Theoretical output voltage (that means, when unloaded, input is a sine wave, frequency is sufficiently high and excluding voltage drops on parts) is then calculated with a simple equation:
Uout = 2 * Uin * sqrt(2) * stages
where 1 stage equals to a pair of 2 diodes and 2 capacitors.

High voltage multiplier, OilGood for frying

Of course, the whole setup needs to be submerged in oil, to prevent arc over and corona losses. I have used transformer oil to be on the safe side. Although clean and de-humidified vegetable or mineral oil will suffice.

High voltage multiplier, Submerged in oilUnder oil, leak test proved negative

If you have taken a look at the wiring above, you can say that the output kilovoltage is positive with respect to ground.
However adding a capacitor extra on the “unused end” allows you to change this polarity, if connected in reverse. In my “lunch box design” such an approach is not possible, because that’d need good insulation; to prevent pairs of terminals from arcing between each other.
If your approach leaks, seal them properly, and not with e.g. hot glue, as certain oils (if not all) dissolve it.

High voltage multiplier, output at 3kV ACFat 8 cm spark at 3 kV, 30VA, 12kHz input

The photo above shows the multiplier, fed with a limited square-wave AC input out of this small driver. At load, the supply voltage of such a purposely-low-powered driver drops to approximately three kilovolts AC, estimated by spark ignition distance. Which is good, as this setup was not made with arcs in mind (30 mA rated rectifiers).
This multiplier is used in the (upcoming X-ray setup), coupled with this ZVS driver and a Soviet 8kV AC flyback.

28cm sparks (200 kV)28 cm sparks (approx. 200 kV)
Input is a ZVS-driver-fed 8kV AC flyback


… and again

15 Responses for 8-stage Cockroft-Walton/Villard cascade multiplier

  1. Joshua Frieswell says:

    Is this statement true?

    “I think I understand why [the output voltage remains unaffected]… since the resistor is open to air on one side, no additional “load” has been attached to the multiplier, so there is no voltage drop.”

    I have been trying for weeks to an answer to this type of question, so any help that you might be able to offer me on this confusion would be greatly appreciated. I’m designing a cockroft-walton multiplier that takes a 15 kV peak input (not peak to peak, just peak) from a 30 khz flyback transformer ac output and steps it up to about 100 kV or so. I am planning on initially testing it using spark discharging and I am well aware that some kind of series resistance of very high ohmic value should be connected with the output (I’m placing it on the HV return arbitrarily) to avoid reverse breakdown of the diodes. Basically, I have a few concerns:

    First, will the placement of the series resistor drop voltage? Or simply negate the high-current discharges inherent to sparks across the HV output of the multiplier stack? If the latter is the case, will connecting an arbitrarily capacitive load in series with the resistor and HV output cause a voltage drop?

    I am assuming ohms law could probably be used for these calculations, but when dealing with these high voltage systems I am simply not sure that the same rules apply, which is why I’m getting a second opinion. Thanks again in advance.

    Second, how is one to calculate the required value of the resistor to safely produce spark discharges without incurring harm to the multiplier rectifier diodes?

    Third, as far as the power rating of the resistor, should it be rated for a significantly high wattage as well as ohmic resistance?

    Thank you very much for your input.

    • Jay says:

      Your HV resistor does not need to be high in wattage. If you are merely drawing a few sparks. However, it NEEDS to have large size (I placed 20 20Kv, 100kOhm resistors in series, zigzagged them to conserve space, and encased in wax).

      If you do not encase in wax, then you need a physically large resistor, or the voltage will jump over the resistor to avoid being ‘resisted’.

      Also, to calculate the resistance, look up the data sheet of your diodes. Mine are 2CL2FL resistors, rated for 100ma continuous current. Their PEAK is a 10A burst. So, in theory, if your multiplier outputs 400,000 volts like mine, use Ohms law: 400,000 = 10A X resistance, or, Resistance = 40kOhm. This would be the MINIMUM resistance to meet your diode’s max surge. However, you never want to reach your max surge. Try to limit a diode’s surge to 10% of its max, and it will last forever. I personally limited surge current in my multiplier to 0.2 amp sparks, as I am paranoid about wear and tear. Long story short, my multiplier used this equation: 400,000 = .2A X resistance. This gave me 2M ohm of resistance.

      Scale everything to your multiplier voltage output, and, your diode’s surge rating.

      Happy Shocking,


  2. nikhil says:

    hello ,
    I am doing this as a project in our college . Initially i have planned of doing 5stage multiplier with 230v ,50hz as input .So that i can generate around 1kv neglecting the losses that takes place. But i’m in a trouble because cant understand which capacitos (i.e their type and ratings ).. Will you pleae suggest me with the capacitos to be used?

    • nikhil says:

      sorry i have mentioned 230v but it is 100v input

    • Jozef says:

      That also depends on the output load current you want. Use at least 300V rectifiers (since it’s 50Hz, 1N400x series can be used) and for e.g. an 1mA load, I’d suggest a 4-stage multiplier with 4M7 200V non-polarised caps. More on this here .

  3. Anonymous says:

    how to decide the no. of stages to b used

  4. jay says:

    Brilliant results man. I just finished a 10 state multiplier myself. It works great at only 1kHz input. Cant wait to build a higher frequency input!

    I have a question: have your caps ever degraded / your spark performance degraded over time? Basically I’m curious if running the sparks without a current limiter will damage the caps?

    • Jozef says:


      Drawing sparks won’t harm your caps, but you ought to use diodes with a bigger surge current rating. Some folks use fast 1kV/1A rectifiers (BA159, UF4007 etc) stacked in series as one HV rectifier in the bridge. Of course they’re soaked in something non-conductive, or are rolled inside some plastic tube so the corona losses are minimized.

      As this multiplier was originally planned for more X-ray experiments, my rectifiers were rated 30 mA only.


    • jay says:

      Thanks for the comments. I am currently using 100ma, 30kv diodes. They work great. They have a surge rating of 10A, but I try to keep spark amperage at 5A. I only use a 20KOhm water resistor on the output. Does spark length increase or decrease with increased resistance on the output?

    • Jozef says:

      I presume your 20k resistor is in series with the multiplier output – the output kilovoltage measured at open circuit (“spark jump distance”) won’t be affected much.

    • jay says:

      I think I understand why… since the resistor is open to air on one side, no additional “load” has been attached to the multiplier, so there is no voltage drop.

      Great. Cant wait to make an even larger multiplier.

  5. Deepak kamble says:

    Will You plz let me the the diodes that you have used. as in like UF4007 or 1N4007.

    • Jozef says:

      Those were HVRL300’s. However if you plan to build it for arcing and stuff, you’d better use beefier diodes.

  6. Γεώργιος says:

    Awesome setup I have 20 – 10 amp 100kv diodes ( monster sizes) and i have been wondering what to do with them… now I know!

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