Coil working
Posted: Thu Apr 10, 2014 2:00 pmMy coil is now working moderately well (about 18" arcs) and playing polyphonic music. See the movie at http://www.shustek.com/teslacoil/OneTesla_10Apr2014.wmv and the attached photo.
At first I had a wimpy arc and blew the IGBTs. My secondary is 240 ohms and resonates with a signal generator at 293 KHz. The primary was 6 turns and resonated at 254 KHz, which was too low. And at moderate power they seemed to be way too far apart: 312 KHz and 238 KHz, respectively. So I raised the primary resonant frequency by changing to 5 turns, and the result is what you see. I can run at max power with no ill effects. I suspect some fine-tuning (changing the primary capacitor or using partial turns on the coil) could make the arcs even better.
This is a nice and remarkably simple design! I'm working on a coil twice as large, using more more complicated circuitry and 75-amp IGBTs driving a primary made from 1/4" copper tubing. But I keep blowing the IGBTs there too. Now that I see how critical matching the primary and secondary resonance is, I might be able to get that one running.
-- Len
At first I had a wimpy arc and blew the IGBTs. My secondary is 240 ohms and resonates with a signal generator at 293 KHz. The primary was 6 turns and resonated at 254 KHz, which was too low. And at moderate power they seemed to be way too far apart: 312 KHz and 238 KHz, respectively. So I raised the primary resonant frequency by changing to 5 turns, and the result is what you see. I can run at max power with no ill effects. I suspect some fine-tuning (changing the primary capacitor or using partial turns on the coil) could make the arcs even better.
This is a nice and remarkably simple design! I'm working on a coil twice as large, using more more complicated circuitry and 75-amp IGBTs driving a primary made from 1/4" copper tubing. But I keep blowing the IGBTs there too. Now that I see how critical matching the primary and secondary resonance is, I might be able to get that one running.
-- Len
