EJK's Desktop :: Voltage Multipliers

One of the cool yet elegantly simple gadgets you can build is a Cockroft-Walton Voltage Multiplier. You will need capacitors, diodes, and an AC power source of some kind. The diodes need to be rated for the peak AC voltage, the capacitors for twice it.

I currently have two such devices. One of them is a cute little thing attached to a perf board that will turn 25 volts into 600 with just enough current to (barely) run a 4-watt fluorescent. Good for waking yourself up if your fingers brush the discharge end (quite a jolt actually) . It's good if you need a semi-high voltage. The problem is that it takes 5 minutes under no load to approach peak voltage, having something like 20 or 30 stages. It uses 10uF/250V caps that I found a big bag of and just about every diode I've been able to scrounge up; Plug it into any source of up to 37VAC.

The other one [insert maniacal grin here] uses a 12000 volt / 30ma NST, eight 12000 volt diodes, and four 40Kv, 2nF capacitors. As Maddox would put it, "It kicks ass." This thing is just too cool to believe. Among it's awesome properties are:

  1. Generation of double- or triple-digit kilovolts at amps per discharge
  2. Sounding like a machine gun every time it discharges
  3. Being able to discharge a hundred times per second
  4. Throwing off such a damn huge electric field that it gives you a charge of 5000 volts when you sit 2 feet from it

3/16/05:

After getting my new NST (12000/30) and finding a power cord for it, I immediately threw a Cockroft-Walton multiplier together. This device was assembled in 15 minutes, the connections aren't work jack, and I think there are some burnt out diodes. But none the less, it generates a respectable discharge, somewhere in the hundreds of kilowatts. Having been deprived of any high-voltage for months, I was glad to hear the crash of artificial thunder again.

The marx generator. All the components are clearly visible: NST, caps, recifiers.
Ah, the acrid smell and sharp report of success! The power level in each discharge is somewhere in the hundreds of kilowatts (50 KV times at least 10 amps). Nothing like pulling that current through diodes rated for 1A! Gap was set to 1.5 inches before firing.

As suspected, there were faulty diodes present. To achieve the 1.5 inch arc required 80 Vin - not very good performance. After replacing the defective diodes and replacing gravity with solder to hold the connections together, system now achieves 1 inch spark on ~25Vin and 2 inch spark on ~70Vin. The connections are still downright bad, including exposed sharp edges which contribute to major corona loss at higher voltages.

At this point, everything is temporary - I only have 4 of these caps, and they will all have to pull duty in two different voltage multipliers, and a tesla coil.

3/22/05: Just a small addendum to the above, 25Vin is ~ 3.5KV peak input to the multiplier. If you assume that there are no major corona losses at that voltage, then securing the connections and dipping the assembly in oil to keep the corona down at higher voltages implies that an ~5 inch spark is possible if the Variac is turned up to 120Vin. At that point, it'd probably be a very good idea to make a salt water resistor to reduce the current.

EJK may be reached at his E-Mail address. That is all.