FAQ - Voltage Multipliers

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Richard Hull
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FAQ - Voltage Multipliers

Post by Richard Hull » Thu May 01, 2014 6:12 pm

Go here for go design data

http://www.voltagemultipliers.com/html/multdesign.html

http://www.voltagemultipliers.com/pdf/M ... deline.pdf

(Thanks to Dennis Brown on the second URL)

I am loathe to go to any real depth on this subject as so very few are equipped to do a creditable or acceptable job on this. To a degree, any success is based on what you start with regarding you selection of transformer or the capabilities of any HF switcher output you might create or stumble onto.

It is always simpler and far less hassle to get a normal 60hz x-ray or other high tension trasformer capable of the full high voltage you need and then half or full wave rectify it and use no capacitor in the circuit, controling power with a variac. No voltage multiplication, no stored energy, no electronics. Keep it simple and rapidly move on to other issues in doing fusion.

If you fail to locate a proper 60hz mains transformer, you are in for a bit of a ride...... There are two options

1. 60 mains operation with a lower High Voltage (HV) transformer than desired and voltage multiplication to achieve higher voltages.
2. High Frequency (HF) switcher supply construction and voltage multiplication to the desired level.

It is assumed you will use the simple half wave series multiplier.

There are advantages and disadvantages to both options listed above.

60 hz standard iron core transformer..........

Larger, heavier and more bulk in the finished supply. Large, very high voltage and very expensive capacitors are needed. Dangerous stored energy in the multiplier capacitors. The old way to get HV with multiplication. But, putting safety aside, a bullet proof supply that can be made self ballasting without resistors. You will need to fully understand basic electronics related to your transformer selection.

Note that the little design program in the above URL relates to high frequeny multipliers, but the schematics are good. A good HF supply will need .001ufd 20kv caps, while a 60hz system might call for .1 ufd or higher caps at the same voltage!

High Frequency Swither with multiplier............

This is the up to date, totally modern, all electronic solution to your high voltage needs. You can't use a normally availalble transformer and you are often forced to purchase a ferrite core and wind your own transformer. Modifying a current microwave oven "switcher type HV system is a kind of useful work around on this. All of this effort from beginning to end is a concentrated learning course in modern electronics. Are you up to it?

The advantages of an HF switcher are many and wonderful. The capacitors in the multipliers are small, inexpensive and there is little stored energy at the output. Such a supply can be made in a very small, light weight cabinet compared to the 60 hz system above. For advanced electronics buffs, this is the way to go. For the guy who has difficulty repairing a toaster, you are on a very, very steep hill.

The disadvantage to the HF switcher is that you can blow semiconductors up with arcs or bizarre transients that would not phase a 60hz supply.

Regardless of which method you employ, if going via voltage multiplication, you can only use so many stages of multiplication in the supply before you are defeated by diminishing returns. Fusors that fuse to a level of easy detection and proof of fusion, demand a minimum of 30kv negative DC voltage at a suppply current of 15ma minimum continuous feed.

It is best to limit the multiplication to a tripler or quadrupler at most!

Whether you choose 60 hz transformer or HF switcher to feed your multiplier, it must offer a minimum of 10kv alternating current at a power capability of 500 watts to the multiplier network. That is 10kv at 50ma RMS minimum! Don't even start until you have this bare necessity in hand.

60hz neon sign transformers, old microwave oven transformers and such are just not in the running to make good 30-40kv supplies that don't have some major safety issues. Try and forget about them unless you wish to create very hazardous conditions.

Above certain voltages in 60 hz iron core transformers, one end of the secondary or the center of the HV secondary will be grounded to the iron core. Center tapped systems are more common and make full wave rectification easy, but will limit your final voltage to a bit over one half the transformer's voltage rating and require more stages. End grounded transformers are better, but very rare.

The HF supply is ideal if you are willing to design your own switcher and wind your own transformer from scratch or modify a Microwave oven switcher and rewind its ferrite transformer.

This is the limit for now of this FAQ. Make sure to use the design data at the URL supplied above. (hope it doesn't go away in future.) Use its schematics as your base. It is up to you to get that all important front end, be it a nice used HV 60 hz mains transformer or cobble up a suitable HF switcher. Remember, to start a voltage multiplier system, you need a minimum of 10kv at 50 ma RMS, preferably more!

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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Dennis P Brown
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Re: FAQ - Voltage Multipliers

Post by Dennis P Brown » Mon May 05, 2014 2:16 pm

Here is a site (if it stays up) that allows most parameters of a voltage multiplier to be calculated using a few known parameters as inputs (#stages, driver voltage and frequency,required current output, and capacitance of the caps used):

http://www.extremeelectronics.co.uk/cal ... oltage.php

This yields the voltage and ripple of the voltage multiplier and the required driver current needed to achieve these values

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