To get a spark plug to fire I read that it requires approximately 12,000 Volts. If I have an ac generator giving a RMS Voltage of about 10 Volts (pretty small) what do I need to do to get the spark plug to fire? I was thinking about possibly adding a step up transformer but unsure whether or not that would even be possible. So what is typically done with an ac circuit to get enough voltage to allow the spark plug to fire? I would like the spark plug be able to fire periodically like an engine.

  • \$\begingroup\$ What is the wattage capacity of your AC generator at 10 volts? \$\endgroup\$
    – Eric Urban
    Commented Jul 24, 2016 at 12:28
  • 1
    \$\begingroup\$ Will, give a bit more detail in your question (and not in the comments) about what you are trying to achieve. Is the end goal just improved understanding and the wild joy of creating a spark or are you trying to make something else that requires a spark. It may help if you research car ignition systems and magnetos. \$\endgroup\$
    – Transistor
    Commented Jul 24, 2016 at 12:46
  • \$\begingroup\$ What would you do if you knew the wattage? \$\endgroup\$
    – Will
    Commented Jul 24, 2016 at 13:12

1 Answer 1


The usual way that a spark plug is fired is to provide a low-voltage DC pulse to an ignition coil. An ignition coil is a pulse transformer that is specifically designed for that purpose. If you search "ignition coil spark circuit" or anything like that, you should be able to find lots of detailed information with diagrams. Very little power is required. Any simple AC to DC power supply will profide a good starting point if you must use AC. Here is the basic diagram:

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  • \$\begingroup\$ So if you have commutator and a voltage dc of 1 volt. All you need is an ignition coil? \$\endgroup\$
    – Will
    Commented Jul 24, 2016 at 13:09
  • \$\begingroup\$ Ignition coils that are easily available will work with 6 volts. One volt would probably produce a spark across a very small gap. \$\endgroup\$
    – user80875
    Commented Jul 24, 2016 at 13:14
  • \$\begingroup\$ So if I get it cranking up to 6 volts what should I be looking for in an ignition coil? \$\endgroup\$
    – Will
    Commented Jul 24, 2016 at 13:19
  • \$\begingroup\$ In ignition coil for a motorcycle, tractor or car can be found in a junkyard. \$\endgroup\$
    – user80875
    Commented Jul 24, 2016 at 13:29
  • \$\begingroup\$ You may find an ignition coil from a magneto motor (old lawnmower etc) will also work, in parallel with its capacitor. Close the magnetic circuit with an iron bar across the pole pieces, spaced from them with a couple of sheets of paper. They would have been about 0.5mm from a permanent magnet in the flywheel. Connect a few volts across the primary. Wait a few milliseconds until the current builds up (one coil I have here measures 0.7 ohms, so about 4A from 3V). Disconnect the voltage and the inductive kick should give a nice high voltage pulse from the secondary. \$\endgroup\$
    – user16324
    Commented Jul 24, 2016 at 15:56

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