FAQ: Neon transformer wiring diagram - demo fusor

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Richard Hull
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FAQ: Neon transformer wiring diagram - demo fusor

Post by Richard Hull » Tue Mar 02, 2004 4:38 pm

Attached is a diagram on the power supply wiring for a DEMO type fusor using a neon transformer. This supply WILL NOT supply the voltage or power needed to make a deuterium fusing fusor. I show a 12 kilovolt unit in the diagram but a 9kv-15kv neon transformer will work, but the 12kv or 15kv transformers are recommended.

All neon transformers over 7.5 KV are CENTER TAPPED - CASE GROUNDED SECONDARY types. This CENTER TAP connection is made internally to the METAL CASE BODY and is the return path for the two outside HV knobs. The case is always GROUNDED for safety! The knobs, then, relative to ground, are at 1/2 of the rated potential of the transformer.

As shown, the output would be on the order of up to 10kv max with no load. With a 2ufd @ 10kv capacitor, you might expect 7kv @5ma with the voltage lower at higher plasma loadings.

The diodes can be standard microwave oven diodes. These are typically rated at 12-15kv piv @ 250-500ma. Using 4 diodes, (two in series for each diode symbol shown in the diagram), will allow for some extra margin of over volt protection when using 15kv transformers.

NOTE***** The capacitor shown is not absolutely demanded in this simple supply. Consider it optional. However, with a capacitor the voltage is smoothed out and this circuit is especially lethal and can kill instantly. Be very careful to discharge the capacitor before working on the circuit. Without the capacitor the circuit can still kill in certain circumstances, but at minimum it can injure you severely and make you wish you were never born.

The digital panel meters are cheap and can be found from a number of electronic suppliers like Jameco, Marlin P. Jones, etc., for about $10.00 to $20.00 each. You will need to set the decimal point using the instructions supplied with your meter. Metering is not demanded in a demo fusor, but recommended so that you can get a feel for operation at observed voltage and current levels. This trains you for real fusion operation later and you will have to have these later, anyway, if you go beyond the demo system.

The critical 100 megohm series resistor in the voltmeter circuit is a special high voltage resistor (DO NOT USE 10 - 10 megohm common resistors in series!!!! This resistor must withstand the full voltage; common resistors will not! The proper resistor will be a long resistor, (~3" long), designed to prevent arc over.

IMPORTANT! regardless of meter type, please shunt the volt meter terminals with an NE-2 neon lamp and put it where it is visible. If this lamp ever comes on and stays on, your meter is "open", (defective), and you should immediately kill the power as touching the meter might be very dangerous with power applied.

NOTE****

It is very important to use a variac or variable transformer to supply a variable 0-120 volts AC input to the transformer's primary. This will allow a smoothly variable output DC voltage to the fusor ranging from 0 volts to almost 8 kilovolts. The ideal variac is capable of 10 amps with 120VAC input. A 5 amp variac is pushing it, but a 7.5 amp variac will do just fine. Note* A 20 amp variac is overkill, but if you can find one, you will be set for bigger and better experiments later on.

It is also very important that all current metering is done with a low value high wattage SHUNT resistor in the grounding circuit!!!! This is regardless of whether you use an analog or digital meter. NOTE!! The grounding of the transformer case is achieved through the current shunt resistor! If you ground the case directly, the current meter will not work.

All the grounds shown should be connected together with the shortest possible routing and this single connection taken via a short, fat cabling to the fusor chamber body and attached at the same bolt or point on the fusor chamber that your real, super earthed, electrical ground is connected to. (star grounding)

Richard Hull
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Re: FAQ: Neon transformer wiring diagram - demo fusor

Post by Henry Cross » Sat Aug 06, 2011 5:43 pm

Hi Richard,

Is it worth using GFCI outlet or will the transformer disconnect the circuit sufficiently?

Thanks,
Henry

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Re: FAQ: Neon transformer wiring diagram - demo fusor

Post by Carl Willis » Sat Aug 06, 2011 7:39 pm

Henry,

If you observe proper wiring practices, the GFCI should cause you no trouble.

-Carl
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Re: FAQ: Neon transformer wiring diagram - demo fusor

Post by AllenWallace » Sun Aug 07, 2011 2:37 am

Richard,

I know that you are trying to keep the schematic simple and theoretical but perhaps we might add a diode across the voltage meter. If the 100M resistor arcs over, then the diode will protect the panel meter which is typically exposed to the the operator.

Its possible that someone will use common resistors which typically have a max voltage to 150 Volts. A possible but misguided design might use ten 10M resistors in series and these will arc over. Perhaps you could clarify the requirements of the 100M resistor.

Allen Wallace

Edit: I have added a note about the need for a special HV resistor in my original. RH

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Re: FAQ: Neon transformer wiring diagram - demo fusor

Post by charlie_mccartney » Thu Jul 25, 2013 9:40 pm

Sorry if this is a dumb question but if I have a NST that outputs DC do I need all of this and if this is for DC output what do I need for AC.
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Re: FAQ: Neon transformer wiring diagram - demo fusor

Post by charlie_mccartney » Thu Jul 25, 2013 10:07 pm

Also does any of this need to be immersed in mineral oil.
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Re: FAQ: Neon transformer wiring diagram - demo fusor

Post by Carl Willis » Thu Jul 25, 2013 11:30 pm

No neon sign transformer outputs DC. Not all neon power supplies are transformers (NSTs) any more, but all are AC power supplies. DC ruins neon tubes.
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Re: FAQ: Neon transformer wiring diagram - demo fusor

Post by Richard Hull » Fri Jul 26, 2013 2:35 pm

No neon transformer puts out enough voltage to need any form of oil immersion.

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Re: FAQ: Neon transformer wiring diagram - demo fusor

Post by charlie_mccartney » Fri Jul 26, 2013 4:15 pm

Thank you Richard and Carl.
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Re: FAQ: Neon transformer wiring diagram - demo fusor

Post by charlie_mccartney » Thu Aug 01, 2013 9:49 pm

Would this work with a 15kv 30 ma NST and if not what would need to be changed.
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