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Registered Member #1180
Joined: Mon Dec 17 2007, 12:26AM
Location: Nope
Posts: 28
I am designing a spark gap Tesla coil for the college I work at and I want it to be around long after I'm gone, so naturally I want to take every measure to prolong the coils life.
This coil is being powered by a 10 kV, 23 mA, oil burner ignition transformer which I want to protect with an RF filter.
As there are many means to create a low-pass filter I was wondering if anyone here could help sort out which work best for TC's and how one goes about designing them so they will take a a beating.
Registered Member #1180
Joined: Mon Dec 17 2007, 12:26AM
Location: Nope
Posts: 28
The answer, it would seem, is an RC filter as inductors one would use in an RF filter would be prohibitively large and lossy. Ceramic capacitors and wire resistors is is.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
For a small 6kV 30mA NST I use 4x 100W 300 Ohm wirewound ceramic resistors with a 1nF 80kV filter capacitor. Two resistors in series on each leg, with the capacitor in parallel with the NST in the middle of the resistor network (resistors before and after the cap connection). I've used this filter reliably with a 12kV 60mA NST.
For my larger 8.2kV transformer ballasted to 350mA, the 100W resistors got far too hot, so I had to switch to 225W 200 Ohm resistors which were almost twice as expensive as the 100W resistors, but still far more compact and practical than a pair of inductors.
IIRC, the most effective components in a protection filter for Tesla Coil use, like the Terry Filter or Information Unlimited's circuit, is the resistors and capacitors. I think I've read that the resistors and caps (and any safety spark gaps) take the brunt of the HF HV, and any extra inductors or MOVs are just there for extra support. I'm not entirely sure on this however, and would really appreciate if someone more experienced could clarify this.
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Optimum RF Filter for SGTC
