High Voltage Forum

Tesla coils => Spark gap Tesla coils => Topic started by: thedoc298 on October 12, 2019, 12:26:44 AM

Title: First revision
Post by: thedoc298 on October 12, 2019, 12:26:44 AM
https://drive.google.com/open?id=1sL2R1a7om4OT4U0Gt8UwrXXuiRFYxg8b

After some tips, made a change for the better. The cap cage is easy to pop apart and now can watch the caps.  Thanks for the help.
Title: Re: so far video
Post by: MRMILSTAR on October 12, 2019, 02:38:43 AM
It looks like things are progressing nicely. With 7200 volts from your pole transformer you will have to run some tight gap spacing on your RSG, probably no more than about 1 mm per gap but it is doable.

You may regret putting the capacitors inside that tube. Even though they do fit nicely, you can't see what's going on. You can't see if there is excessive corona, flash-over, blown capacitors, etc. I like to be able to observe everything in operation so that I can anticipate problems and to make everything easily serviceable.

Looking forward to see it in operation.
Title: Re: so far video
Post by: thedoc298 on October 12, 2019, 02:56:17 AM
It looks like things are progressing nicely. With 7200 volts from your pole transformer you will have to run some tight gap spacing on your RSG, probably no more than about 1 mm per gap but it is doable.

You may regret putting the capacitors inside that tube. Even though they do fit nicely, you can't see what's going on. You can't see if there is excessive corona, flash-over, blown capacitors, etc. I like to be able to observe everything in operation so that I can anticipate problems and to make everything easily serviceable.

Looking forward to see it in operation.


Well now is the time for making the change, I have been thinking about a different setup for the cap anyway, something will pop up. The spark gap will be close because of the low voltage of 7200 is that correct...? Maybe just ought to junk it.  Got one more question what is you no load current draw on your transformer.
Title: Re: so far video
Post by: thedoc298 on October 12, 2019, 02:58:19 AM
It looks like things are progressing nicely. With 7200 volts from your pole transformer you will have to run some tight gap spacing on your RSG, probably no more than about 1 mm per gap but it is doable.

You may regret putting the capacitors inside that tube. Even though they do fit nicely, you can't see what's going on. You can't see if there is excessive corona, flash-over, blown capacitors, etc. I like to be able to observe everything in operation so that I can anticipate problems and to make everything easily serviceable.

Looking forward to see it in operation.


Got a idea to remove the center tub and repace with 4 pvc poles around the cap.

Well now is the time for making the change, I have been thinking about a different setup for the cap anyway, something will pop up. The spark gap will be close because of the low voltage of 7200 is that correct...? Maybe just ought to junk it.  Got one more question what is you no load current draw on your transformer.

The pig going to the back corner of the basment till a later time. Going to start the mod for the center support tomorrow, thanks much for the heads up.
Title: Re: so far video
Post by: MRMILSTAR on October 12, 2019, 05:13:28 AM
I think that you can make 7.2 KV work, its just that your gap spacing will have to be about 1 mm using 3 KV/mm as a rule of thumb. Remember that 7.2 KV RMS is 10.18 KV peak so your gap spacing is not quite as critical as first appears. Each of my gaps is about 1 mm even though I could get away with more since I am operating with 14.4 KV RMS. Its best to get the gaps as close as you can for the most reliable firing anyway. Some people have made 4 MOTs in series work and that is only about 8 KV RMS. I would try the 7.2 KV pole pig. No harm in trying.  If you find another 7.2 KV pig, you can put them in series.  :D I have seen that done.

One more thing to mention is that a higher voltage transformer is also better because of

E=0.5*C*(V**2)

where the capacitor energy, which also determines spark length, is proportional to the square of the voltage. The more charge you can put on that capacitor, within its safety limits, the better for discharge length.

I've never checked the no-load current on my pole transformer. There is usually a spec on this if you can find it or probably easier just to measure it yourself.

You may want to look at lots of pictures of how others have implemented their coils. It may give you some ideas. I looked at lots of pictures of coils before I built mine.
Title: Re: so far video
Post by: thedoc298 on October 12, 2019, 05:28:01 PM
I think that you can make 7.2 KV work, its just that your gap spacing will have to be about 1 mm using 3 KV/mm as a rule of thumb. Remember that 7.2 KV RMS is 10.18 KV peak so your gap spacing is not quite as critical as first appears. Each of my gaps is about 1 mm even though I could get away with more since I am operating with 14.4 KV RMS. Its best to get the gaps as close as you can for the most reliable firing anyway. Some people have made 4 MOTs in series work and that is only about 8 KV RMS. I would try the 7.2 KV pole pig. No harm in trying.  If you find another 7.2 KV pig, you can put them in series.  :D I have seen that done.

One more thing to mention is that a higher voltage transformer is also better because of

E=0.5*C*(V**2)

where the capacitor energy, which also determines spark length, is proportional to the square of the voltage. The more charge you can put on that capacitor, within its safety limits, the better for discharge length.

I've never checked the no-load current on my pole transformer. There is usually a spec on this if you can find it or probably easier just to measure it yourself.

You may want to look at lots of pictures of how others have implemented their coils. It may give you some ideas. I looked at lots of pictures of coils before I built mine.


Thanks, working on something different today.
Title: Re: so far video
Post by: davekni on October 14, 2019, 05:40:27 AM
I'll second that 7.2kV RMS should be plenty.  My RSG coil uses two MOTs in series with resonant charging, so gets to about 9kV peak, which works well (with close gap spacing).

Did you say 27nF primary capacitance at 32kV?  I have no familiarity with pole-pig transformers.  Is there some resonant-charging effect that will get you much above 10kV?  If not, 27nF will be rather low energy per spark.  For my two-MOT coil, I used 680nF with a 3-turn primary coil to get reasonable energy per spark.
Title: Re: so far video
Post by: thedoc298 on October 18, 2019, 04:42:52 AM
I'll second that 7.2kV RMS should be plenty.  My RSG coil uses two MOTs in series with resonant charging, so gets to about 9kV peak, which works well (with close gap spacing).
Thanks, the 27nf is for the 60ma nst. The pig is 7200 rms and for a later build. Glad to know it will work.
Did you say 27nF primary capacitance at 32kV?  I have no familiarity with pole-pig transformers.  Is there some resonant-charging effect that will get you much above 10kV?  If not, 27nF will be rather low energy per spark.  For my two-MOT coil, I used 680nF with a 3-turn primary coil to get reasonable energy per spark.