This is a radio frequency (RF) and high voltage spike and kickback protection circuit. It protects your power control cabinet, and the low voltage 60 cycle house wiring. This circuit is recommended for the low voltage side of all types of step up transformers, regardless of taps, grounds, etc. on the windings. X1 is the step up transformer. The center core is grounded to the dedicated RF ground that also grounds the safety gap and the base wire of the Tesla secondary. RFC 1A and RFC 1B are about 5-10 turns of heavy insulated wire (sufficient to carry the current requirments of X1) on a large iron powder or wire ring toroid core. I use 4-6 diameter iron powder toroids and heavy cable to wind these chokes. "Protective Capacitors PC1 and PC2 are not critical and can be rated in the vicinity of .5 to 2 microfarads. Use a voltage rating as high as possible. The usual 400-600 volt capacitors will not withstand kickbacks for very long. 1 KV rating or more should work fine." In place of this circuit, a large heavy duty commercial EMI/RFI line filter may be placed here. These filters offer the convienience of good efficiency in a compact unit. Where current throughputs are high I use several in parallel. Quality commercial line filters employ iron powder chokes, as well as the "PC" capacitors of the circuit at the top of this post. The Line Filters I use also have RF choke coils in the ground path; the ground wire can be run reversed (it is neutral) and can be used to trap stray RF, preventing ground path contamination to the 60 cycle breaker box. I use a minimum of two independent grounds. ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Date: 08-08-94 15:25 From: Terry Smith To: Richard Quick Subj: Tesla Coils ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ PC1 X1 RFC 1A RFC 2A ÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄ¿ºÚÄÄÄÄÄÄïïïïïÄÄÄÂÄÄÄÄïïïïïÄÄÄ> TO TESLA TANK ÄÁÄ )º( ³ ÄÂÄ )º( ³ ³ )º( O grnðÇÄÄÄ´ )º( grndðÇÄÄÄÄo SAFETY GAP ³ )º( O ÄÁÄ )º( ³ ÄÂÄ )º( ³ ÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÙºÀÄÄÄÄÄÄUUUUUÄÄÄÁÄÄÄÄÄUUUUUÄÄÄ> TO TESLA TANK PC2 RFC 1B RFC 2B RQ> "Protective Capacitors PC1 and PC2 are not critical and can RQ> be rated in the vicinity of .5 to 2 microfarads. One little point of safety, which should be pointed out to the folks with limited electronics safety knowledge, is that PC1 and PC2 would have to be NO HIGHER than 0.1 uFd, in order to meet a 5mA ground current leakage standard. The circuit and values of PC1 & PC2 shown above could be lethal if the building ground connection were marginal or missing. Obviously that would decrease filtering effectiveness. A 120 V isolation xfmr, or additional stages to add both filtering and safety related line isolation, as you later described, would be possible solutions ot that problem. BTW, I have seen foolish and inattentive engineering of power supplies for broadcast equipment from one reputable and fairly quality oriented manufacter, which caused 6 and 12 mA of ground leakage with power on and off, due to similar low cost but irresponsible RF filter cap size choices. RQ> rating as high as possible. The usual 400-600 volt RQ> capacitors will not withstand kickbacks for very long. I RQ> prefer capacitors with ratings of from 2500 to 5000 (or RQ> higher) volts" What are "the usual"? Orange drop or block type small leaded film or mica caps? I would think that current ratings (which would be related to ESR, and filter effectiveness) might be more important than voltage rating, so long as no less than 400-600 volt rated caps were used. At 450 kHz, the Xc of the range of caps we're discussing would be 0.1 to 3 ohms, which makes me wonder if "voltage rating" isn't being substituted for physically larger cap with higher thermal and current limits? Such overall higher rated caps should be more effective as RF filters due to the same lowered ESR which results from other design parameters being increased. Do you know if smaller cap failures are from voltage punch through, or if it's really from cooking due to a 3-5 amp repetitive surge current demand, which small inexpensive caps can't handle? BTW, I'll be Freq'ing your archive tonight. I'm curious about what resonant circuits you might have brewed. Thanks for making it available! Terry (203)732-0575 BBS (1:141/1275) ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Date: 11 Aug 94 17:01:49 From: Richard Quick To: Terry Smith Subj: Tesla Coils ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ PC1 X1 RFC 1A RFC 2A ÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄ¿ºÚÄÄÄÄÄÄïïïïïÄÄÄÂÄÄÄÄïïïïïÄÄÄ> TO TESLA TANK ÄÁÄ )º( ³ ÄÂÄ )º( ³ ³ )º( O grnðÇÄÄÄ´ )º( grndðÇÄÄÄÄo SAFETY GAP ³ )º( O ÄÁÄ )º( ³ ÄÂÄ )º( ³ ÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÙºÀÄÄÄÄÄÄUUUUUÄÄÄÁÄÄÄÄÄUUUUUÄÄÄ> TO TESLA TANK PC2 RFC 1B RFC 2B RQ> "Protective Capacitors PC1 and PC2 are not critical and can RQ> be rated in the vicinity of .5 to 2 microfarads." TS> ...PC1 and PC2 would have to be NO HIGHER than 0.1 uFd, in TS> order to meet a 5mA ground current leakage standard. The TS> circuit and values of PC1 & PC2 shown above could be lethal TS> if the building ground connection were marginal or missing. Good point, though yours is a worse case scenario. There were already several reasons why I did not like the circuit above, you just added another reason to the list. TS> Obviously that would decrease filtering effectiveness. A TS> 120 V isolation xfmr, or additional stages to add both TS> filtering and safety related line isolation, as you later TS> described, would be possible solutions ot that problem. My improvements on Harry's circuit above work pretty well, and I have always loved isolation xfrmrs as an additional safety/RF/ spike/surge measure. I am considering the addition of a pair of back to back pole pigs in my low voltage feed lines for just this purpose. RQ> "Use a voltage rating as high as possible. The usual RQ> 400-600 volt capacitors will not withstand kickbacks for RQ> very long. I prefer capacitors with ratings of from 2500 to RQ> 5000 (or higher) volts" TS> What are "the usual"? Orange drop or block type small TS> leaded film or mica caps? Again, I am quoting Harry Goldman above, but generally speaking the "PC" caps used in Harry's circuit are the typical "can" type caps used in capacitive start motors. I have seen a lot of these used (and NO they are not filter caps) simply because they are cheap; surplus caps with a rating of .1 uf @ 400 vac are locally available for around $0.25... TS> I would think that current ratings (which would be related TS> to ESR, and filter effectiveness) might be more important TS> than voltage rating, so long as no less than 400-600 volt TS> rated caps were used. At 450 kHz, the Xc of the range of TS> caps we're discussing would be 0.1 to 3 ohms, which makes me TS> wonder if "voltage rating" isn't being substituted for TS> physically larger cap with higher thermal and current TS> limits? Very possible. TS> Such overall higher rated caps should be more effective as TS> RF filters due to the same lowered ESR which results from TS> other design parameters being increased. Good point. TS> Do you know if smaller cap failures are from voltage punch TS> through, or if it's really from cooking due to a 3-5 amp TS> repetitive surge current demand, which small inexpensive TS> caps can't handle? I don't know. You could ask Harry Goldman (I have posted his SNAIL address should you choose to correspond), as he recommended the above circuit (recently too); I have never used it. But in my experience voltage punch through has only occurred as a result of a typical coiling type "incident" where there was no doubt as to the cause (run away oscillator, direct strike to low voltage feed lines, xfrmr breakdown, etc..). Perhaps this is what he was referring to when he said the lower voltage caps don't last very long. On the other hand a repeated 3-5 amp surge current demand on the filter implies something else is wrong... perhaps he is not properly grounded or choke/filtered at the RF side of the xfmr??? Like I said... I don't know, but I would not recommend the above circuit.