Background info: I'm trying to create a spark gap tesla coil that uses a ZVS / flyback combo, and so far, given the initial tests with a 12 volt 20 amp power supply, I managed to get it to work, but when I increase the gap between the spark gap, the sparks went through the secondary coil, which could signify that the primary/secondary is too coupled. Note that the primary coil design I used before I took it down is a vertical type.

So I thought after looking at the designs, I should either go with a flat or pancake coil design for the primary, but which one of the 2 suits them best or should I go back to using the vertical type again? I hope I get much powerful sparks for such a small-medium sized coil!

Here is what my tesla coil looks like, note the stick is supposed to be where the primary coil is supposed to be: enter image description here

  • \$\begingroup\$ There are few Coilers on this site, you won't get knowledgable replies. You'll do better looking for a specialist TC forum like pupman, or High Voltage forum with a specialist TC section like 4HV. \$\endgroup\$
    – Neil_UK
    Aug 4, 2021 at 4:51

1 Answer 1


I believe what you are seeing is the phenomena that the larger the spark gap, the more voltage is needed to jump the gap and or maintain the ARC. They make a crona paint that if you paint the windings with should solve your problem. It has been a long time since I worked with spark gaps and jacob ladders.

  • \$\begingroup\$ Oh, I also lacquered the secondary coil, it's a must when making a spark gap tesla coil. \$\endgroup\$ Aug 4, 2021 at 1:05
  • \$\begingroup\$ From what I gather sparks are going through the lacquer. Just a note your assembly looks very nice. \$\endgroup\$
    – Gil
    Aug 4, 2021 at 1:10
  • \$\begingroup\$ Yeah, It seems to be the case, but it also looks like it's jumping to the primary (it's honestly too quick as I need to unplug it to avoid the damage.) So that's why I wonder if it's the cause of high coupling, so either use the cone or flat coil for primary? PS, thanks for my design! I honestly want to make it more presentable, compact, and easier to fix. \$\endgroup\$ Aug 4, 2021 at 1:14
  • \$\begingroup\$ There was an insulation material we called "fish tape (a yellow insulating tape)" which I believe was actually varnished cambric, a good HV insulation. That was a way long time ago, I am not sure if the terms are correct anymore. \$\endgroup\$
    – Gil
    Aug 4, 2021 at 2:04

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