FAQ - Demo fusor feed through under $20

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Richard Hull
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Re: FAQ - Demo fusor feed through under $20

Post by Richard Hull » Sun Sep 05, 2021 7:04 pm

This is a demo fusor FAQ. Demo fusors never have current flow in them. Thus, the feed through need only handle 10kv or a maximum of 15kv. Most demo fusors use a neon transformer and are themselves self current limiting and voltage limiting. A zero resistance feedthrough might be great for use in ion implanters, etc. where ampere curent levels at low voltages of 5kv at 1 ampere are demanded. A 5k ohm resistor at 15kv would only offer voltage loss issues at above 30ma. This current is well outside of the demo fusor range.

Never use spark plug wiring unless it is pure copper wire! (racing wire) All stock spark plug wire is highly resistive being carbon on silk or polymer fibers. (Reduces RFI for car radios and electronics.)

Finally, if you make an SS fusor body for your demo and plan on moving onto real fusion, do not consider a spark plug for a feed through at all!! You will just have to discard it to do fusion. We deliberately throw resistors in the power line of our fusors to limit current in some instances. Why worry about 5k resistance in a demo spark plug insulator when you have a 10k ohm DC resistance in a neon transformer secondary of huge inductance and a shunted magnetic path already there to limit current?

Only demand a zero resistance plug when you are going to demand amps to flow through it. Worry far more about the air insulating capacity of the plug and the behavior in a vacuum of the base electrode/insulator combo.

Joe's comment about a spark plug boot to avoid sparking is wise. I used one on my early iteration of fusor III in 1989 and did limited fusion with it. I cut it short to just lock over the top of the plug, but first slathered the top with silicone HV putty and let the boot encase it to avoid air paths to the base. Ultimately, above 25kv, it had to be replaced with a real vacuum rated HV feed through.

Richard Hull
FIII spark plug.jpg
First finished image of fusor III used a well done implementation of a spark plug
FIII spark plug1.jpg
Later fusor III has a nice shielded proper insulator installed. Much better!
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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