Tesla Three

Time for a lashup!

Once the varnish had dried I was desperate to try my new secondary out. I had the OLTC circuitry working on the bench, but not very well since it had the wrong IGBT with no co-pack diode. I got round this by bodging in a couple of fast-recovery diodes from an old switching power supply. They looked like 1 or 2 amp diodes.

The primary circuit

Here you can see the primary which is 2 turns of 20-amp zip cord with both cores connected in parallel. In the final version, each of the two cores will be driven by its own IGBT. You can see the two kludged-in diodes (the small grey balls directly in front of the IGBT) and also the "mmc" tank cap which is three 0.47uF 500V caps in parallel. Yes, a 1.4uF tank cap and a 2-turn primary with inductance of 0.8uH. If you do the math you can see that, when the circuit is running at full voltage, it'll hit 900 amps at the peak of the first cycle. I wonder how those 2-amp diodes will like that?

The complete lashup

My topload here is a "Balti Dish" which is a bowl that Indians (and Brits) serve curry in. I bought a couple out my local supermarket. Eventually I'll saw the handles off and fix the two bowls together but for now I used one as it was. The breadboard at the bottom contains a 555 Timer driving the gate on the IGBT with 20 volts at 400bps. The rig is powered by my tube regulated 0-300v power pack, which looks like something out Dr. Frankenstein's lab.

Too bad it only gives 150 mA

Strewth! It works

With the power pack up at about 100 volts and the circuit drawing 150mA I was getting a 0.75" spark. I couldn't up it much more because the power pack only gives 150mA. To overcome this, I reduced the break rate to about 110bps. I whacked it up to 300 volts, it gave 1.5" for a few seconds (drawing 100mA) and then those diodes blew out with a loud bang. The IGBT was unharmed.

Return to TC Page