Power Supply

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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Eldarion
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Power Supply

Post by Eldarion » Sat Nov 22, 2008 9:48 pm

I am just starting out and was wondering, would it be possible to use a power supply that I built, or do you have to use one made by a company because of safety issues? It is basically a voltage multiplier hooked up to a transformer and gives a variable power output from 0-50Kv.

Attached is a basic schematic of the power supply.
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myID
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Re: Power Supply

Post by myID » Sat Nov 22, 2008 10:04 pm

Hi-

if you want a useful current on the output you need rather big caps for your multiplier when you use just 50Hz from the mains... Usually multipliers are used with higher frequency devices, some kHz- otherwise caps get really big! Modern Xraytanks (often multipliers in there) use some 10kHz for example- they are nice- small and powerful but you need a bridge switched with high frequency to drive them (and to build one of those for high powers, high reliability and good output control is not too easy (at least for me...)) It will be pretty much the same for every high voltage device with a multiplier I guess. (OK in microwaves you have a multiplier but that one is for "low" voltage so the cap is not too big...)

Greets

honickmonster
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Re: Power Supply

Post by honickmonster » Sat Nov 22, 2008 11:54 pm

You would need some monstrous capacitors to make the voltage multiplier put out an kind of reasonable current at 60hz mains frequency, almost all voltage multipliers utilize high frequency (10khz-50khz) and thus are able to use much smaller capacitors. Also, in your schematic you lable the main transformer with the abbreviation OBT, if that refers to Oil Burner ignition Transformer, then you will will need to find a more powerful transformer, as an OBIT does not have the current capacity to power even the most basic fusing fusor.

Matthew Honickman

Eldarion
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Re: Power Supply

Post by Eldarion » Sun Nov 23, 2008 1:10 am

The capacitors used are 20Kv ceramic capacitors, which I can get for a little over $40. Also, the transformer used in my revised version is a 10Kv neon sign transformer.

Thank you for speedy reply

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Carl Willis
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Re: Power Supply

Post by Carl Willis » Sun Nov 23, 2008 2:45 am

Hi Nelson,

Richard Hull has done a "FAQ" in this forum about neon sign transformers and their close cousins, the oil burner transformers. Do a search for it. Almost any conceivable question about them is answered there.

Your schematic shows a somewhat unusual though not unheard-of variation in which the OBIT is not center-tapped. Most I've met are center-tapped, though, as are all neon transformers. If you use a center-tapped transformer, you cannot ground one end of the secondary; you'll have to use a full-wave multiplier or only use half the secondary.

Your other commenters recommended bigger caps, but these alone will not get around the fundamental limitations of the NST/OBIT's magnetic shunt ballasting. As the FAQ explains, drawing any current from these transformers dramatically lowers the delivered voltage. For fusor use, they make OK "demo"-class power supplies, but you'll have to upgrade for an easy shot at neutron-producing fusion.

Also note that as drawn, your multiplier is delivering positive HV. Fusors generally use negative HV.

-Carl
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Eldarion
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Re: Power Supply

Post by Eldarion » Wed Nov 26, 2008 4:55 pm

Does anyone know how to reverse the polarity to negitive???

Dustinit
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Re: Power Supply

Post by Dustinit » Wed Nov 26, 2008 10:32 pm

Reverse the direction of all the diodes in the CW multiplier (assuming it is made of discrete components).
Dustin.

zhgreader
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Re: Power Supply

Post by zhgreader » Thu Nov 27, 2008 3:54 am

Its vague of your problem.
If you wish to get a negtive application for a positive output. you can reverse the output terminal. means use positive voltage as groiund while the gnd as negtive ouput.
although it s not recommanded

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Carl Willis
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Re: Power Supply

Post by Carl Willis » Mon Dec 01, 2008 3:20 am

Dustin provided the correct explanation for how to reverse the polarity of a multiplier.

Before you get too far ahead (and into dangerous territory), spend some time reading Wikipedia, our "FAQ" posts, Google results, etc., and play around in your lab with more modest components and voltages. Be a self-directed learner, and do not rush the learning process. Make sure you have a firm understanding of what you are doing before you do it. This is very important with the type of electrical equipment used for fusors.

-Carl
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zhgreader
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Re: Power Supply

Post by zhgreader » Tue Dec 02, 2008 3:04 am

oh, what I did is may dangerous.
right way is revers diodes.

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