R&D Corner

What's Tesla Three going to be?

I have my eye on a mini version of the OLTC (Off-Line Tesla Coil) invented by Terry Fritz: A conventional Tesla coil with the spark gap replaced by IGBT transistors. The improved switching action of the transistors should allow good performance with only a few hundred volts supply, which comes from rectifying the AC line voltage directly (hence off-line). OLTC design is similar to ordinary TC design but the aim is to keep the peak current in the tank circuit down. In practice this means that the operating frequency must be low: Terry's prototype ran at 36kHz (IIRC)

My proposed mini OLTC is a conventional DC resonant charger running off 340V, so charging tank cap to 680V. It runs 100W at 400bps. I designed a short, fat secondary coil (14cm dia x 20cm tall) with very many turns of thin wire (2000 of British 40 SWG=0.125mm) and a large flat topload. Analysis with the FANTC program shows that it resonates at 85kHz. Note the secondary circuit values in schemo below are WRONG. Also I found a better IGBT, International Rectifier part# IRG4PF50WD. Terry Fritz tested it up to 750 amps pulsed current (!)

schemo of the proposed mini OLTC

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