FAQ - It is power that does fusion

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Richard Hull
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FAQ - It is power that does fusion

Post by Richard Hull » Wed Sep 14, 2005 2:37 pm

Much of what follows has been discussed over the years, but here it is in a short FAQ that should answer most newbie questions.

Fusion requires power input to make it go. This is true in both a professional and amateur fusion device. This means real power. For the moment, forget voltage and current which will be covered later in this FAQ.

It would be real difficult to do fusion and warrant you had done it below 200 watts input out of the wall outlet. Most good fusors that give easy to measure output require on the order of 400-500 watts. A really first rate fusor with output levels in the range of 10e6n/sec or more demand continuous, 700-1000 rms watts.

Demo fusors, often seen in first pass efforts and science fairs, can easily perform in the 50-100 watt range. Of course, no fusion is being done, but the visual appearance can be similar to a working fusor.

When considering a power supply system for your fusor, you should anticipate your needs not only at present, but for the future as well. This is all part of using your time and money wisely.


The demo fusor supply can be very crude and very underpowered. A really well designed car ignition coil could be used here in an electronic drive circuit, but far simpler would be a common neon sign transformer controlled via a variac.with a simple microwave diode bridge circuit for rectification. The normal range of voltages and currents used in a demo system are from 0-10kv with a current demand of 0 to 50ma.

Higher currents are needed in poor vacuums and at lower voltages to help clean the chamber while dragging the pressure down when pumping. A normal start voltage and current might be 1000 volts at 50ma. This is only 50 watts.

As the vacuum improves, the voltage will climb and the current needed to maintain "glow mode" will fall. Such a working demo fusor displaying a star mode might run or function at 10kv @ 5ma current. This is still only 50 watts!

If you are doing a science fair project or are just dipping your feet into the "fusion pool", a neon sign transformer based supply will allow you to fully explore this demo device and give you hands-on experience with wiring and supply assembly techniques.


This is very serious territory and there are but two options. Make your supply like you did with the demo system or buy a ready to go supply. No matter which way you decide to go, you can never use any more toy efforts involving small transformers like the neon or oil burner type units or any form of flyback or car coil transformer, as all of these are far too weak and ineffective to do real fusion.

Fusion demands "power reserve capacity"!! That is, you need to have latent unused power capacity ready just idling in your supply in the form of larger voltage range and larger current range than you expect to need. This assures that you will not immediately tax or overload your supply, thereby, destroying it in your efforts.

In general, you will need a smoothly variable 0-30kv supply as a minimum with a 0-60kv supply being ideal. This supply must be configured to operate as a POSITIVE GROUND - NEGATIVE VOLTAGE OUTPUT SUPPLY!! The current demand will need to be a bare minimum of 10ma over its entire range of voltage, but 30-50ma would be much better for full performance fusors. This is a range of from a rock bottom low of 300 watts (30kv@10ma) output to as much as 3000 watts output (60kv@50ma). Only you will be the final judge in how well you equip yourself.


This is not for the faint of heart or "first timer". The transformers required are physically large and lethal as will be the finished supply. The absolute best transformer is an x-ray transformer. Quite often, entire old x-ray supplies controlled by a variac are perfect and ready to use.

If all you can get is the transformer, you will need a variac and an appropriate diode array to, hopefully, full wave rectify the voltage output of the AC mains transformer. Such systems are normally tanked under mineral oil to avoid corona. Wiring to the fusor is best carried on at least 50-60kv silicone wire to the feed-through inuslator.

The other alternative when building your supply is to go ultra high tech and custom wind a much smaller HV transformer to output about 5-10kv and drive it with a fully electronic, high frequency, switch mode supply of custom design. The very high frequency, high voltage output of this special transformer is then stepped up with a voltage multiplier circuit to meet the final supply needs. This is probably the most labor intensive and expensive route for supply aquistion, but it will leave you a very knowledgable and capable fellow.

Give up most thoughts of AC mains operated microwave oven transformers (M.O.T s). These DO HAVE THE POWER, but they lack any of the voltage requirements needed for fusion and any cascade scheme coupled with voltage multiplication efforts, at mains frequencies, is dangerous and the required filter capacitors store far too much energy and can damage a fusor's grid when in use via "bumping".


E-bay or LAB-X is the main source of used high voltage supplies. The old caveat of "buyer beware" is a watchword not to be taken lightly. If you find an old X-ray supply or Spellman, Glassman, Hi-Volt or Universal Voltronic HV system, make sure it is complete!! Most of these systems have an output unit and a separate controller unit with a very special cable needed to interconnect them. Also a lot of these monsters need poly phase mains. (Not found or available to the home owner)

Finally, make sure they are functional. A dead, long discontinued supply is close to worthless as the manufacturers may have gone out of business or be reluctant to help in repairing such old units. Schematics to assist in repairs may cost as much as the unit itself!!

Shipping of these systems can be very expensive, requiring truck or freight shipment. Few useable, complete supplies will weigh in at less than 120 lbs. (~50 kilos). It is not uncommon to pay as much for shipping as for the supply itself.

Still, for all the worry and hassles associated with this route, one of these type systems is, in many ways, ideal. All the work is done for you in a safe, sane and professional manner. You have full metering and control capability as well.


Well there you have it. This was not a how-to FAQ but a post designed to inform those considering power for a fusor or fusion project as to the bare minimum needs. It was also designed to put out of the head of those "do-it-yourselfers" any hope of using anything less than the most robust power sources. Yet, many arriving here constantly think that an auto ignition coil, a small neon transformer, a flyback transformer, or ganged CCFl HV supplies will allow them to do fusion. Power does fusion! These small, toy-like sources are just not up to doing easily detected fusion.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: FAQ - It is power that does fusion

Post by sharks63128 » Fri Sep 30, 2005 2:56 pm

So a -20kv 50ma supply would work since it is 1kw supply?

Chris Franklin

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Brian McDermott
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Re: FAQ - It is power that does fusion

Post by Brian McDermott » Fri Sep 30, 2005 3:52 pm

Yes, this is exactly what I had when I first ran my fusor. You will not be able to get huge amounts of neutrons, nor will you be able to pull the full 50mA without melting the grid. It would work fine for an entry-level fusor.

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