Input source for HV multiplier

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Dan Knapp
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Input source for HV multiplier

Post by Dan Knapp » Wed Oct 18, 2017 11:29 pm

While using an induction cooktop in a rental apartment, it occurred to me that mass produced spare parts for such cooktops could be a relatively inexpensive source for the input to a Cockcroft-Walton multiplier for a home brew HV supply. These typically operate at 24 kHz and supply high current to the cooktop coil, which, with the cooking vessel, is effectively a transformer. It would seem that the high current 24 kHz supply module might be useful. I have no idea what these cost, but they must be available as mass produced spare parts.

Jerry Biehler
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Re: Input source for HV multiplier

Post by Jerry Biehler » Thu Oct 19, 2017 12:34 am

They make single unit portable versions of induction cooktops as well. Kind of like a modern hotplate.

No idea if you could get it to run something like this, it is probably a closed loop circuit to adjust power and detect the pot. You would probably have a whole lot to redesign.

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Finn Hammer
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Re: Input source for HV multiplier

Post by Finn Hammer » Thu Oct 19, 2017 3:16 am

There is a teardown of an Ikea unit, haven't watched it, but it might be usefull:

http://kaizerpowerelectronics.dk/electr ... ve-part-1/

Hope this helps,

Cheers, Finn Hammer

John Futter
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Re: Input source for HV multiplier

Post by John Futter » Thu Oct 19, 2017 9:34 am

Finn
You beat me to it

Silviu Tamasdan
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Re: Input source for HV multiplier

Post by Silviu Tamasdan » Sat Oct 21, 2017 10:47 am

Having played a bit with the concepts involved in induction heating in the past, and even designed an induction forge for metalworking (but never built it, still on my to-do list, have many of the parts) - I don"t know if the innards of such a device would be useful for building a fusor-grade power supply. Due to the nature of induction heating these operate typically at high currents but relatively low voltages. Which means that a multiplier would have to have a LOT of stages, with all the problems that it causes.

For instance my forge is designed for 200A at approx 20V.
There _is_ madness to my method.

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Dennis P Brown
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Re: Input source for HV multiplier

Post by Dennis P Brown » Sat Oct 21, 2017 4:40 pm

Current alone for the driver supply - while it is a minimum must - is a red herring if one does not have enough capacitance and high enough frequency driving the caps so enough overall power is available from the final cap. While my x-former appeared to be delivering over 40 ma to the stack at a voltage not much different than its rated 15 kV, and adding the fact that my final cap was supplying 50 kV at easily a few mill-amps (at just 60 Hz), this was, of course, zero load.

While someone here has achieved fusion with a voltage multiplier, I seriously doubt this is a good, much less an inexpensive, methodology to power a fusor due to the cost of caps and diodes for a system with enough power. That said, it is a possible methodology to maybe get a large, and nearly high enough voltage x-former to supply a fusor. I'd never seriously try a single NST (possibly two very high end NST's linked for double current would, I'd suspect, be a minimum if one were to try this approach) for such a purpose nor a low voltage very high current source like a stove top supply since no way the diodes and caps that could exploit those high currents would be anything but very expensive. I would think a proper x-ray transformer would still be more cost effective.

Dan Knapp
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Re: Input source for HV multiplier

Post by Dan Knapp » Sat Oct 21, 2017 8:55 pm

The induction cooktop power supply would of course only be a source of high frequency low voltage current. One would also need a ferrite core high voltage transformer between it and the multiplier. Such transformers are sold at reasonable cost by Information Unlimited. With respect to doing fusion with a multiplier supply, essentially anyone who has used a commercial HV supply has done it with a multiplier supply. The big difference between a good commercial supply (e.g. Spellman) compared to a cobbled-together home brew supply is that the commercial supply is carefully engineered with components matched for high efficiency and feedback stabilization of the output. A simple cobbled together supply lacks these features, but you’re talking big bucks difference in cost.
If one has access to defunct replaceable cores for gas lasers (e.g. the widely used Laser Science nitrogen lasers), these are source for high quality HV doorknob capacitors. These are usually potted, so salvaging the capacitors requires some patient cutting away of the potting.

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Dennis P Brown
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Re: Input source for HV multiplier

Post by Dennis P Brown » Sun Oct 22, 2017 2:17 am

I am very aware voltage multipliers are what are generally used in most of those commercial systems; however, many here use powerful single x-formers (with added diodes) to do fusion (my method as well.) Relative to my post, I was solely discussing a home-build and some issues with such a build.

My VM does use door knob caps as shown in my previous posts the last few days on this subject concerning that system.

Also, useful that you noted a method on how to convert such a low voltage high frequency supply into a higher voltage system. This might be a design you could post more on if you believe this could offer a fusion grade supply - many would be interested here (as would I.)

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