Minimum Voltage for a Demo Fusor

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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Tom Davies
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Minimum Voltage for a Demo Fusor

Post by Tom Davies »

Hi,

I'm building a demo fusor for a school project, and I was wondering what the minimum voltage needed was? Putting two microwave oven transformers in series and then rectifying the output should give me about 4000 VDC. Would that be enough?

Tom Davies
Ross Moffett
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Re: Minimum Voltage for a Demo Fusor

Post by Ross Moffett »

AllenWallace
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Re: Minimum Voltage for a Demo Fusor

Post by AllenWallace »

I have seen star mode with a flyback transformer. it was not very bright, but distinct. You don't need very much voltage for plasma.
I'd recommend a NST (neon sigh transformer) for a demo fusor.
Your comment about putting 2 MOTs in series concerns me, do you understand the break-down voltage problem? There is no safe way to use two MOTs in series.
JakeJHecla
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Re: Minimum Voltage for a Demo Fusor

Post by JakeJHecla »

MOTs are a terrible idea. Please, for your own safety and the financial wellbeing of your life-insurance company, use a NST. While you certain can employ MOTs to power a fusor (using several chained together with a multiplier on the output), they are exceptionally dangerous.
Tom Davies
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Re: Minimum Voltage for a Demo Fusor

Post by Tom Davies »

Thank you for your fast response with the link, and thanks also for the warnings about MOTs.
I was thinking of MOTs over NSTs for the sake of cost (I can fairly easily scavenge some MOTs) but I will look into getting an NST now.
I hadn't heard of the breakdown voltage problem but thanks for the pointer, I am still very much in the research phase of this project at the moment.
Tom Davies
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Re: Minimum Voltage for a Demo Fusor

Post by Tom Davies »

Is there somewhere where all the FAQ forum posts are accessible together? I may be being stupid but I can't see such a place, and searching FAQ's or similar doesn't really give useful results.
Ross Moffett
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Re: Minimum Voltage for a Demo Fusor

Post by Ross Moffett »

When you entered the High Voltage forum, and pressed "New Topic?" Immediately above that. Different set of FAQs in each forum, for each subject.
Tom Davies
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Re: Minimum Voltage for a Demo Fusor

Post by Tom Davies »

Thanks
Dan Tibbets
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Re: Minimum Voltage for a Demo Fusor

Post by Dan Tibbets »

MOT are dangerous due to the current they can output. It can be deadly. NSTs are less likely to kill you because of the current limited to lower levels (typically 30 mA). Also, hooking up MOts in series is bad. There are ways to wire MOTs together, but not in simple series. One MOT with the diode and capacitor from the microwave oven will provide ~ 3.3 KV. Again , the current can kill. A MOT with a primary side ballest to limit current (to safer levels) and a diode or better yet a bridge rectifier will provide ~ 1700 volts. This is the way to go if you cannot use an NST. You can use voltage multipliers (1/2 stage like above) or 1,2,3 stages. But again, the capacitors store a lot of current so that you are vulnerable to fatal shocks even with the appropriate primary ballast.

A modest NST might be rated at ~ 6,000 to 12,000 volts. Two diodes and you have DC voltage of ~ 4,000 to 8,000 volts. This is the simplest and relatively safest approach. Old oil burner transformers is another option.

As for the voltage required, a faint glow may be seen at only 300-400 volts. Brighter at higher voltages.

Also, don't forget the Variac (variable transformer ) to control the voltage.

Dan Tibbets
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