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Thread: Conversion from contact to pilot arc ignition

  1. #1

    Conversion from contact to pilot arc ignition


    I'm looking for info about how to convert an older plasma cutter that has neither pilot arc nor HVHF ignition (contact ignition) to pilot arc using an S45 torch. I'm not new to electronics and electricity but I don't have an in-depth knowledge about plasma cutters yet, therefore I'm looking for hints. These are the first things I'm not sure about:

    1. Can I turn on the pilot arc, the main cutting power and the air all at the same time and then turn off the pilot arc after 1-2 secs or thereabouts or do I need to turn on the pilot arc first and then turn it off before turning on the main cutting power and the air?

    2. I understand that the current to the pilot arc needs to be limited to about 10 amps, right? The simplest way to do this would be a power resistor of about 10 ohms, however this one would have to sink a lot of power and I doubt that commercial units do it this way. Can someone tell what the commercial way is?

    3. I'd probably want to only use a S45 head and keep the existing hose, can someone tell what the connection to the hose inside the head is called and what thread it is?


  2. #2
    Senior Member
    Join Date
    Dec 2010
    Andover, Ohio
    Martin, welcome to the forum.

  3. #3
    Thanks M J!

    In the meantime I googled a lot more and finally found a source that describes such a pilot arc circuit in more depth, this is U.S. patent US7615720 by Hypertherm Inc. It works quite a bit different than I thought, instead of mechanical switching they use a RC circuit plus a discharge relay to make the pilot arc start, transit to the main arc and later discharge for a new ignition. Very clever.

    I would be very interested if anyone knows their systems and the actual circuit used because they might well have left out some minor parts and furthermore I'd like to know the actual values and specs of the components. The patent often says "in some embodiments" which is suspicious...

    Even though modern cutters seem to use again different IGBT pilot arc circuits I need this older, call it stone age method because it is simpler to realize in my opinion.


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