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I am trying to couple a high voltage transformer (automobile coil) 220 V to 10 kV, with a low voltage home made transformer 220 V to 6, 12 V (think MOT but bigger).

I have tested/used the LV transformer for spot welding so I know that it outputs a lot of current, upwards of 1000 A. The HV transformer (auto coil) is being driven by a fan regulator (Triac) so it outputs somewhere around 10 kV that run through my homemade 15k capacitor. I can see the high voltage output jump the spark gap1 (3–4 mm wide).

I have coupled these in series via a 27:30 turn coupling coil wound around ferrite rod as shown in the image below, one side of LV runs through the coil and the other side makes ground. There is a small gap (spark gap2) where they meet and I can see the spark in this gap also when I turn on the HV circuit.

I was expecting to see a large increase in current through this gap (gap2) when I turn on the LV transformer, as spark through the gap will produce plasma which will make the gap behave like a short, so high current from LV transformer will get added in series and spark will be much bigger, just like a welding machine. But I do not see any increase in current when I turn on the LV transformer while HV is sparking through gap2.

I have tried to turn on both together with same switch, still size of spark is small, as if only HV transformer is running. Turing on LV transformer has no effect at all. My LV transformer is center tapped and I have tried with both 6 and 12 V tap, still I see not effect. What am I missing here?

enter image description here

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  • \$\begingroup\$ Why do you expect to see a large increase in current by increasing the voltage a small amount? \$\endgroup\$
    – Hearth
    Commented Sep 3, 2023 at 15:55
  • \$\begingroup\$ I was expecting to see a large increase in current through this gap (gap2) when I turn on the LV transformer, as spark through the gap will produce plasma which will make the gap behave like a short, so high current from LV transformer will get added in series and spark will be much bigger, just like a welding machine. \$\endgroup\$ Commented Sep 4, 2023 at 3:21
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    \$\begingroup\$ I don't understand what you're trying to do. You get a certain current with 10 kV, you're not going to suddenly see a drastically increased current with 10.012 kV. \$\endgroup\$
    – Hearth
    Commented Sep 4, 2023 at 3:36
  • \$\begingroup\$ Sounds like a TIG welder, or spark EDM - a high voltage pulse is used to start an arc that a low voltage can then sustain, though the low voltages I’ve used previously are DC and closer to 20V \$\endgroup\$
    – Bryan
    Commented Sep 4, 2023 at 5:30
  • \$\begingroup\$ @Bryan you are right... I'm trying to make a high voltage arc starter... kinda like they have on TIG... it can also be done for transformer type stick welding (which is what I have) to stabilize the arc... through the coupling coil the HV (low current) output added in series to the LV (high current) so arc can be started and stabilized during welding. \$\endgroup\$ Commented Sep 4, 2023 at 6:10

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