All you need is a compact fluorescent light (CFL) and a flyback transformer.
Flyback transformers are found in TVs and CRT monitors. They make the high voltage, high frequency current necessary to trace the electron beam across the screen. They are small and compact, and you can take them out from an old computer monitor or TV.
CFLs are very popular high efficiency fluorescent lights. They are similar to their ancestor the fluorescent light tubes but use electronic ballasts instead of the big and heavy ballasts in the old technology.
The electronic ballast works by generating high frequency currents that are fed to a tiny high frequency transformer that boost the voltage and run the fluorescent tube. It is the high frequency that makes the assembly compact.
The electronic ballast generates less than 1000 volts. But by replacing the fluorescent bulb of the CFL with a flyback transformer, spectacular voltages can be achieved.
Step 1: Some Info on CFLs
Most CFLs have a similar circuit topology. All of them have 4 wires coming out of them. The wires are in pairs, and each pair connects to a filament inside the light bulb.
The CFLs I came across have the high voltage on the outer wires. You only need to connect the outer wires to the primary coil of the flyback transformer.
You will find a comprehensive description of CFL circuits on this page
Step 2: Some Info About Flyback Transformers
The challenge with the flyback transformer is to find 3 pins out of 10 to 20 pins. One pin will be the high voltage ground the other two pins will be that of the primary coil that will connect to the CFL's electronic board.
If you can get the schematic of the flyback transformer that will save you time. However you can figure out the pins by following the instructions here.
Danger - if you are going to get the flyback from a TV or CRT you need to discharge it. It can hold a dangerous charge even days after the TV or CRT is turned off (see picture for details).
Step 3: The Finished Setup
Remember, this is a DC supply. The output from the thick wire is positive. In TVs and CRTs this high voltage output drives the negative electrons from the filament to the screen.
If you need AC high voltage, you have to remove the built-in diode or find an old flyback transformer that does not have a built-in diode.
Step 4: Troubleshooting
Then I decided to get a bigger CFL and I build it exactly like the first circuit. It didn't work. I was disappointed. I thought that the CFL electronics were shot.
But when I reconnected the fluorescent tube to the four wires, the CFL worked again. I realized that this type of CFL circuit needed to "sense" the filaments in order to operate. Remember, I was only using the outer wires and leaving the two inner wires alone.
So I put a resistor across the outer wire and the inner wire. The circuit worked! But within seconds the resistor was in flames.
So I decided to use a capacitor in place of resistor. The capacitor allows AC currents but blocks DC while a resistor allow both AC and DC currents to flow through it. Also a capacitor does not heat up because it provides a low resistance path for AC currents.
The capacitor worked great! The arcs produced were very big and thick.
So in summary there two things that can go wrong:
1. You wired it wrong, either on the CFL side or the flyback side.
2. The CFL electronics needs to sense the filament and you can use a capacitor as a substitute.
Use a high voltage rated capacitor. Mine was 400V and I got it from another CFL circuit.
While troubleshooting, be very careful, you are dealing with very high voltages and high currents.
When soldering, disconnect the circuit from the power outlet.
Step 5: Disclaimer
These currents and voltages are deadly! You can easily hurt yourself, as well. Build this circuit at your own risk.
This type of high frequency high voltage current is used in surgical cauterizers. So if you get shocked you will burn yourself and cut your flesh. There is also a considerable fire hazard from the circuit.
Use the Nikolai Tesla's safety techniques when working with high voltages:
1. Only use one hand (put your other hand on your lap or pocket)
2. Wear insulating shoes
3. Use a dead man stick or insulated pliers when touching or manipulating the circuit.
4. Use a power bar with a thermal fuse rather than sticking the circuit directly in the socket. This will limit the current that will go through your body.
5. When soldering, disconnect the circuit from the power outlet.
Generally, in electricity it is the the current that kills. if the currents are low there is little danger even if the voltages are very high (think of Tesla holding the his Tesla coil).
This circuit has high currents which makes it considerably dangerous.
a 65W CFL can deliver 65mA easily (65W/1000v).
And if you look at the picture below, at greater than 50mA the little guy is dead.