Voltage Multipliers

If you're trying to build a high voltage power supply, a 'voltage multiplier' may sound like just the thing you're looking for. Voltage multipliers take AC voltage, and multiply that voltage by some factor giving a larger DC voltage. In order to build an effective and SAFE voltage multiplier, you need to have a transformer to isolate the circuit from the main power source. This site is about building coilguns, which require very large capacitor banks to be effective. This means that you need to have a high power, high voltage power supply. If you choose to build a voltage multiplier in order to get a high voltage, you need to have a high power transformer. High power transformers can be quite expensive, which is why I recommend building a switching power supply instead.

The Greinacher voltage doubler

This is the Greinacher voltage double, and is widely accepted as the simplest AC voltage doubler. The only necessary components are a transformer, two diodes, and two capacitors, it's that simple! Because this circuit simply doubles the input voltage, it's important to consider that you may have to implement additional controls if you want to charge your capacitor bank to a certain voltage then stop. If the input AC voltage is too high, the output voltage could become too high and cause your capacitors to explode violently. Before building a voltage doubler, be sure you know the exact ration of the transformer, the input voltage, etc.

Also, I apologize for the poorly drawn schematic. I usually write them by hand, not via software.

Villard Cascade Voltage Multiplier

What if you want to more than double a voltage? Don't worry, you could always build a villard cascade voltage multiplier. Like the Greinacher voltage doubler, I highly suggest you use a transformer for the AC input voltage to isolate the circuit from your home wiring. The good thing about the villard cascade voltage multiplier is that you can have as many stages as you'd like, giving you the opportunity to build up tremendous voltage. I build a voltage pentupler (pictured below) which used the villard cascade voltage multiplier. A word of caution: with each additional stage, you significantly reduce the amount of total power this circuit produces!

This is my villard cascade voltage quadrupler. As you can see, it if very compact, simple, and easy to build. The only necessary materials are wire, capacitors, diodes, and a prototype board. The prototype board and wire came from Radioshack, and the capacitors and diodes came from Jameco. Each capacitor is 10 uF rated for 350 V. It is very important that the polarity of the capacitors is correct, and it is very important that you use capacitors which are rated for a sufficiently high voltage. Otherwise, they WILL explode. I am not saying this because I read it on some other website, I am saying this because I have experienced it first hand.

Why my Villard voltage multiplier failed

My villard cascade voltage multiplier was successful in that it did multiply the voltage correctly. However, because it multiplied the voltage 4 times, theis circuit was simply not able to supply enough total power in order to charge my coilgun's capacitor banks. Perhaps it would have been better if I had a high power transformer, but alas, I could only afford a cheap transformer from Radioshack.

Before you decide to buile a voltage multiplier

The single most important thing you need to keep in mind when building any of these voltage multipliers is that AC voltage is not equal to DC voltage. 120 volts AC actually has a peak voltage of about 170 volts. Likewise, for any AC voltage, you need to multiply the AC voltage number by the square root of two, and this will give you the actual, peak DC voltage. If your capacitors aren't rated for such a voltage, they will explode. So be absolutely sure that your capacitors are of sufficient rating and quality to be used in a high voltage multiplier.

LEGAL DISCLAIMER
Coilgun projects can be extremely dangerous if you don't know what your doing. Capacitors can unleash massive amounts of electricity which can seriously injure or kill. Please use this information with caution, as I can not be held responsible for your actions.