High Voltage Pulse Device
Here is a fun little circuit that makes a nice long spark from a normal car ignition coil. The output is in the form of short high voltage pulses. Here is the general idea of the circuit:
Simply charge up a capacitor to several hundred volts and discharge it through a pulse transformer... very much like a tesla coil, though we aren't particularly careful of the resonant frequencies involved as the transformer has enough voltage gain as is.
For the high voltage power supply I used the classic 2n3055 flyback driver powered from a simple 9V battery. The flyback transformer's output is rectified with 2 series 1n4007's, while not the best choice at this frequency, they seem to work fine. C1 is 4 parallel .22uf 600VDC polypropylene GE capacitors for a total of .88uf, this was later replaced with a single .68uf 1200V capacitor. I don't recommend more than 1uf capacitance for the sidacs to handle the peak currents. The Sidac is actually made up of 8 series 120V sidacs sampled from On semiconductor. They are part number MKP1V120RL. The pulse transformer is just a simple car ignition coil. The sparks so far are 3" easily. When I separate the electrodes further, I get insulation breakdowns elsewhere in the circuit. The 3 inch spark:
I eventually achieved 4.75" sparks from a single coil, but more interesting is the 6+" sparks achieved from 2 ignition coils wired in anti-parallel (the primaries are in parallel, but one of them is reversed). I'm now using 1.1uf of capacitors. Also, since I run this from a 9v battery, I put a much smaller heatsink on the 2n3055 that drives the flyback. Here is a picture:
Also, I must warn that the pulse capacitors, when charged, go give a nasty shock (I found out the hard way).
UPDATE: I have since destroyed one of my ignition coils from pushing it to about a 5" spark. Eventually something has got to give and the top of the ignition coils body broke down internally limiting the coil to about a 1/2" spark. Also, I should give some credit to Jim Mitchell that originally planted this idea on me when he was doing the same thing with some small pulse transformers. Since I didn't have pulse transformers I decided to try ignition coils.
Hope somebody gets some use out of this. Its a really cool (and easy!) device!