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I have two microwave transformers in series connected to a Cockroft Walton voltage multiplier. This allows me to generate well over 1 million volts (measured by spark gap) at high current (it looks like a flame due to heat.)

I want to manually manipulate the output.

I intend to use a buck converter to control the voltage and a variable resistor to control the current (with the combination of both tuning methods obviously controlling watts.)

However, I can't find affordable components with ratings anywhere near these power and voltage levels, does anyone know a way around this? Either a source for cheaper/different components or some other or DIY solution.

BTW, there's no need to worry about my safety, I'm very careful, and one hand is always in my pocket!!

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    \$\begingroup\$ A buck converter at the output seems ridiculous, since you are dealing with a million volts. If I were you, I’d try to find a way to control the input voltage, to regulate output voltage. As for the current, that’s a different question. An input fuse? DIY wire wound resistors and inductors, in some plaster/gypsum? Not sure. Secondly, even though you mentioned safety, please be careful. You would not be the first dying from this, disconnect power always before working on your contraption. \$\endgroup\$
    – Ananas_hoi
    Dec 15, 2020 at 22:30
  • \$\begingroup\$ @Ananas_hoi, thank you for the input; I always disconnect and Discharge (!) before touching anything (lol!). I do kind of agree on regulating the input; I have seen what are essentially bucks that handle pretty high voltage, but they cost a great deal and none are at my voltages thusfar. Any further input would be great! Thanks. \$\endgroup\$
    – SR999
    Dec 15, 2020 at 22:37
  • \$\begingroup\$ I assume you are using. AC at the input, so using a transformer like a potentiometer might do the trick. You might be able to wire your own, with thin heating pipe. I am no expert whatsoever on this subject, my only source is from 2 years EE and online subjects, take this with a grain of salt and conduct some more research. About discharging, I figured there would be almost no capacitive load, so it wouldn’t be too important. Better to be safe, any charge is really gonna hurt at these levels. Edit: instructables.com/DIY-Power-Resistor This might be handy \$\endgroup\$
    – Ananas_hoi
    Dec 15, 2020 at 22:41
  • \$\begingroup\$ @Ananas_hoi , thank you for the help! Yes, AC. I will do further research. Thanks once more! I do get some discharge, I'm not sure why? But, I definitely don't want to make contact with it, lol. \$\endgroup\$
    – SR999
    Dec 15, 2020 at 22:48
  • \$\begingroup\$ If there is stray capacitance in the transformers, and you just disconnect the live wire, there is a good chance the voltage was non-zero and that same voltage might still be on the line. (Amplified). On the transformer, you might be able to use an Autotransformer. \$\endgroup\$
    – Ananas_hoi
    Dec 15, 2020 at 22:56

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As Autistic suggests, you control the output voltage by controlling the input voltage.

As you've noticed, high voltage anything is expensive. I'm not even sure you can make semiconductors that will work at 1 million volts - let alone be able to make a buck converter in a practical size at that voltage.

A variac should do the job for the voltage.

The current is a tougher nut to crack.

You can manage the current on the low voltage side just like you can the manage the high voltage output from the low side.

You've got two problems there, though:

  1. Reducing the current going in will also reduce the voltage.
  2. It takes a lot of current to drive those microwave oven transformers, so you'll have to handle amperes of current going into your transformer.

One way to handle it would be to put a large coil in series with the transformer input. Use a moveable core to vary the inductance - core out is low inductance and maximum current, core in is high inductance and low(er) current.

You could reduce the maximum current by using smaller value capacitors - the output current of a Cockcroft-Walton voltage multiplier is very sensitive to the impedance of the capacitors and the number of stages. That's a kind of permanent thing, though. You could reduce the maximum current to something less dangerous that way, but you can't dial it up and down for experiments.

In any case, changes to voltage will change the maximum current and changes to the current will change the maximum voltage.

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You could buy a VARIAC. This is a variable transformer. Such a device takes in AC mains and can output anything from 0 to 110% of the incoming mains voltage. The devices that I have seen have an internal toroidal single layer winding in a ring core and have a dial that moves a brush along the winding. Check the rating of your MOT pair and rate the variac accordingly. Confirm your mains voltage and mains frequency and specify the variac. These devices are simple, robust, easy to use and quite heavy.

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Doing almost anything at a million volts is going to present a serious challenge, because it will simply arc across the components.

Instead, recognize that what you've built is a big boost converter. The multiplication factor is fixed. So by controlling the amount of energy you put in, either in sinusoid or pulse form, you can control the voltage and power of the output arc.

It's never going to be particularly precise. What form of control are you aiming at and what's the ultimate purpose of the system?

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