$5 MICRO TESLA COIL
5,000V, 50KHz
From Electronic Goldmine, others

Several surplus electronics companies sell very small hi-volt power supplies called "fluorescent lamp inverters." In fact, these devices are solid-state CW Tesla Coils: they produce one or two thousand volts at high frequency.

The device sold by Electronic Goldmine is particularly interesting because of it's low cost: $5 normally, less during sales. The low cost means that anyone can afford to buy one of these to play with.

• Power Osc. theory
• Elect. Goldmine, 30KHz 1KV $4.95
• Coolerguys (inverter w/fluroscent tubes, $5.95)
• All Electronics INV-4 $6.80
• Elect. Goldmine G9614 $1.89 (overheats)
• Excess Solutions, TDK 4watt inverter $5.00
• Alltronics FLPS $5.99
• Marlin P. Jones 14840LA (w/fluor. tube) $7.95
• CCFL inverters, TDK App Note (PDF)
• Elec. Goldmine G12866 $1.19 (currently sold out)
• All Electronics INV-7 $2.50 (currently sold out)
• All Electronics INV-9 $8.95 (currently sold out)
• ALSO: High Voltage (Instructables)

I've messed around with the one from Electronic Goldmine. Although it's designed for 5VDC input (at up to 200mA or so,) actually it works down to around 0.5V. Most of them can tolerate a 9V battery just fine, and a few can make it all the way to +15V before running into problems. To smoothly alter the high voltage output, just change the voltage of the DC input.

Fixing the arcing problem

If you crank the input higher than 5Vdc, the high voltage coil will become warm. If you go much above 8V, an internal arc will develop within the coil and burn it out. However, this problem can be cured. Inside the xformer, the ground wire for the secondary coil runs across that coil. Perhaps this is an intentionally bad design to keep the HV below a certain voltage (where any accidental overload will trigger an arc and shut down the output.) To fix it, carefully remove the white tape from the bottom of the xformer. Go slowly, since the hair-thin ground wire runs across this tape. With the ground wire exposed, slather it with RTV silicone caulk or with epoxy. Or perhaps remove that wire so it no longer extends across the coil, then strip the varnish from the end of the wire and solder it to a different ground location. Put a bit of silicone goo on the thin wire to keep it from breaking by accident.

WARNING: CAUSES BURNS! NOT FOR CHILDREN!
While these devices cannot cause electrocution, they can easily burn holes in your skin because they can supply several watts into a continuous electric arc. The danger is similar to that with a candle or a match. In other words, if you "zap" yourself on the high-voltage electrode, you'll end up with a tiny black-charred hole in your finger, a cloud of burning-hair scent, and a small painful burn. See: "electrocautery"

USES

Carefully use the 1/8" arc from the HV terminal to cut things. You can slice through thin solder or through #30 wire. Perform "Electric Discharge Machining" on various kinds of fruit or possibly meat.

Sandwich a piece of foil (or PCB) between two sheets of plastic insulation. Connect the foil to the HV terminal, then cover all the slots with silicone caulk or epoxy. Power it up. Any neon or fluroescent tubes placed on the insulated plate will light up. The plastic keeps you from getting zapped-burned accidentally.

Hook the HV terminal to one end of a fluorescent tube. Glue a thin strip of metal foil along the length of the fluorescent tube, and attach the foil to the ground terminal. Now vary the +5V power supply. A glowing "plasma finger" advances and retreats within the tube. Looks like a Light Sabre from Star Wars. (A hundred of these can be computer-driven as a large electronic sculpture.