Having hacked away with high voltage for many years I’ve ended up using a large number of very different high voltage sources. I say sources and not power supplies because I’ve even powered a corona motor by rubbing a PVC pipe with a cotton cloth, making use of the triboelectric effect. But while the voltage from that is high, the current is too low for producing the necessary ion wind to make a lifter fly up off a tabletop. For that I use a flyback transformer and Cockcroft-Walton voltage multiplier power supply that’s plugged into a wall socket.
So yes, I have an unorthodox skillset when it comes to sourcing high voltage. It’s time I sat down and listed most of the power sources I’ve used over the years, including a bit about how they work, what their output is like and what they can be used for, as well as some idea of cost or ease of making. The order is from least powerful to most powerful so keep reading for the ones that really bite.
You’ve no doubt encountered this effect. It’s how your body is charged when you rub your feet on carpet and then get a shock from touching a door knob. When you rub two specific materials together there’s a transfer of electrons from one to the other. Not just any two materials will work. To find out which materials are good to use, have a look at a triboelectric series table.
Materials that are on the positive end of the table will become positively charged when rubbed against materials on the negative end of the table. Those materials will become negatively charged. The further apart they are in the table, the stronger the charging.
An example of where I’ve used this is to power the corona motor shown here. I vigorously rub a PVC pipe with a cotton cloth, and as the pipe emerges from the cloth, a sharp wire a few millimeters away takes the charge from the pipe. You can see this corona motor being powered by other power sources in the video here.
This would be considered an electrostatic power source because charge is accumulated on surfaces. Being insulating materials, that charge can’t move around.
The amount of charge transferred between the materials per unit of time is small meaning that the current available is small. You won’t be powering any heavy loads with this, but the corona motor powered this way turns at around one revolution every 5 seconds and can be stopped with the light touch of a finger. You already have a feel for the power from getting mild shocks from touching doorknobs. This is of course an easy power source to make.
A Wimshurst machine is also a high voltage/low current power source. It consists of two counter-rotating disks, usually rotated with a hand crank. The disks have metal sectors on them that are spaced apart. The charging occurs where the neutralizer brushes contact the sectors as they pass by. That charge is then removed at collectors on the left and right edges of the disks and is usually accumulated in Leyden jars (capacitors) and across a spark gap where a spark occurs when the voltage is sufficient to break down the air in the gap.
But if you’re making use of the Wimshurst machine then you’re usually not producing sparks. In the photo you see wires going from the Wimshurst machine to a ball cyclotron, making the balls in it rotate around inside the bowl.
The voltage with this one is limited by your losses in the Leyden jars and spark gap and your load. That’s why efforts are made to have everything be well rounded. The spark gap also limits the voltage and with this one I’ve produced sparks around 3 inches/7 centimeters long.
The current is indirectly determined by the disks’ diameter. That’s because larger selectors will produce more charge than smaller sectors. Also, the faster the disk turns, the more sectors will pass by the collectors per second and so more charge will be available.
A Wimshurst machine can’t provide enough current to make a lifter fly. However, it does provide enough current to power a smoke precipitator.
They aren’t too hard to make. I find that the trickiest parts are to find or make the pulleys needed for transferring the hand crank rotation to the disks. The disks can be acrylic which you can cut with a scroll saw or laser cutter, and often small Wimshurst machines are made using CDs.
Van de Graaff Generator
From the outside, a Van de Graaff generator looks like a big ball, or dome, on top of a vertical tube and more stuff at the base of the tube. While that dome is hollow, inside the tube is a belt on rollers. The stuff at the base of the tube includes a motor to turn the rollers and belt. The outer surface of the belt is charged by a combination of the same triboelectric effect we spoke of above, and some nearby sharp pointed brushes. That charge is transferred to the outer surface of the dome.
The amount of charge that can accumulate on the dome is limited only by its diameter. A smaller diameter dome can be thought of as a sharper object than a larger diameter dome. Sharper objects have stronger electric fields surrounding them, which break down the air more easily, taking charge from the object. The big Van de Graaff pictured is rated at around 400kV and the small one is around 80kV.
They’re still a low current source, as the current is produced by the triboelectric effect at the belt and rollers and mechanically transported by the movement of the belt. Wider belt and rollers and a faster rotation gives higher current.
They’re medium hard to make. Since the triboelectric effect is involved, the rollers and belt have to be the right combination of materials. For a small one the dome is often a soda can and for a large one it’s often made using metal salad bowls or a large garden ball.
Moving on to the higher current power sources, an often used type is a circuit using a flyback transformer and one or more transistors. As expected, the flyback transformer has a primary winding which induces a current in the secondary winding. However, there’s also a feedback winding which at the same time shuts down the transistor which stops the current going to the primary. This causes the magnetic field to collapse and a large high voltage spike to appear at the secondary. Since there’s now no more current on the feedback coil, the transistor turns on again and the cycle repeats.
A similar circuit using MOSFETs exists called the ZVS flyback driver but as I haven’t made one I’ll refer you to this one put to use making smores.
Flyback transformers can be bought online but can also be salvaged from old CRT TVs and CRT PC monitors. They’ll most often have high voltage diodes built-in after the output of the secondary winding, which means the output is DC.
I built mine into the small cube shown above. You can see the nice continuous arcs you can get from it. I’ve also powered a Jacob’s ladder. Mine produced around 20kV output with a high current.
Flyback transformer plus Cockcroft-Walton voltage multiplier
If you’re lucky enough to find a flyback transformer with no built in diodes like the one shown here, then at the output you can add a Cockcroft-Walton voltage multiplier circuit. This multiplier consists of capacitors and diodes that take the flyback’s alternating output and smooth it out to flat DC but while multiplying the voltage over some number of stages. The number of stages simply depends on the number of sets of capacitors and diodes you add on. Each added stage increases the output voltage.
The voltage will have been stepped up, but the current will be lower than without the multiplier. It will still be high though, high enough to provide sufficient ionization to make a lifter fly.
You can make your own multiplier boards or you can buy multipliers. The ones you can buy are usually called triplers since they have three stages. They’ll raise a 20kV input to 30kV, also sufficient for flying a lifter.
An almost out-of-the-box source of these types of power supplies is to use an old CRT PC monitor. Simply remove the high voltage wire going into the cathode ray tube and use that wire. I do find that long sparks will damage these monitors easily so be sure to include around 240 kilohms of at least 2 watt rated resistance in series with the output.
These are the interesting high voltage sources with which I have experience. But I’d love to hear about your own high voltage hacks in the comments below. I’d also enjoy hearing questions or ideas on using or building high voltage supplies so don’t be shy.