The high voltage transformer FAQ

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
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Finn Hammer
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The high voltage transformer FAQ

Post by Finn Hammer »

All,
I have written a FAQ about the high voltage transformer, and it is available here:
viewtopic.php?t=14502

It does not seem to show up on the board index as a new entry in the FAQ register, so this is meant as a commercial for it.
I cover the basic issues of core saturation and how to calculate the turns count, and I have thrown in a measure of explanations and warnings to put these issues into context.

Cheers, Finn Hammer
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Richard Hull
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Re: The high voltage transformer FAQ

Post by Richard Hull »

A very nice FAQ, Finn! Thanks for the very nice explanation and example. This should help all of those looking to "roll their own" HV supply who have the skills to tackle such a project. In a follow-up you might include a simple schematic of the half bridge and full bridge hookup and multiplier examples. I know that the full wave is ideal. I assume you are talking about a single transformer with a large multiplier of a lot of stages and suitable filtering. (6-8 stages as noted) This is how Hi-Tek and others do it.

I own the stack block shown. It has one giant flyback style transformer in the base. The full wave pies are doublers with caps, complete. They are just stacked however high you care to purchase them. Mine is positive output 60kv rated at 60ma. I have no driver but it outputs about 6-7KV at 25khz at fearsome energy from an H bridge. I have acquired 3 negative pies. Sheer idleness and a functional X-ray supply keeps me from constructing a 220 volt full H bridge system to drive it. 220 power supply X 1.414 = 310 vdc drive to the H-bridge.

Richard Hull
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Finn Hammer
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Re: The high voltage transformer FAQ

Post by Finn Hammer »

Thanks, Richard

I have updated the post with a dimensional chart of the transformer cores of choice, as well as a hookup schematic of the transformer to multiplier junction.
I also added these few words of wisdom :-)
I am trying to keep this FAQ very basic. Covering every aspect of transformer theory has created many shelf-meters of books. Creating a functioning transformer has been considered a black art, which it is to some extent, and there are many reasons for that point of view. For one, there are the different units of magnetism, a lot of the litterature relies heavily on math, few sources want to reveal the simple fact that all you need is the basic transformer formula.
With that at hand, it all comes down to actually starting to wind some coils.
If winding these coils gives you a sense of satisfaction, you could get hooked, if not, just forget about it and go buy what you desire. This is not for everybody, but it has given me great satisfaction over a period of 25 years.

Cheers, Finn Hammer
Matt_Gibson
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Re: The high voltage transformer FAQ

Post by Matt_Gibson »

Thanks, Finn! I knew this was easier than my professors made it back in college (calculus all over the place).

I really love these sort of projects where, for example, increasing frequency is beneficial up until you begin to see significant losses in the core based on your material choice…

It’s like a puzzle where one design choice affects one, or more, other choices, but with limits (core material and diodes for example).

-Matt
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Finn Hammer
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Re: The high voltage transformer FAQ

Post by Finn Hammer »

I found it interesting too, and a humbling experience to go through the iterations that landed the design at 35kHz.
The higher frequencies herald the promise of smaller magnetics, but this is beneficial only to a point, because of the need for voltage standoff in the high voltage transformer.
Additions to a FAQ don't seem to be announced on the board index, so in case you missed it, there is now an excell spreadsheet for download, where you can plug the numbers to get the turns.

Cheers, Finn Hammer
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