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disconnect switches

Discussion in 'General Electronics Discussion' started by swagguy8, May 5, 2015.

  1. swagguy8

    swagguy8

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    Dec 10, 2014
    hey guys, do you know if a disconnect switch will isolate electricity enough that the two contact points are far enough away so that a 16000 volt spark won't jump across it? will a knife switch work?
     
  2. Kiwi

    Kiwi

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    Jan 28, 2013
    From memory I believe a spark will jump 1cm in dry air at sea level for every 30kv. So 16kv would be about 5mm.

    What are you trying to do?
     
  3. swagguy8

    swagguy8

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    Dec 10, 2014
    kill switch.
     
  4. Kiwi

    Kiwi

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    Jan 28, 2013
    "kill switch" ???
     
  5. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    If by "kill switch" you mean to interrupt a 16 kV circuit with current flowing through the switch, there are people and companies who know how to safely do this, and switches are made for just this purpose. If you need to ask the question here, you are unqualified to work on this type of equipment. The problem is air ionization creating a sustained arc as the switch is opened. This arc can extend for many inches because a low-impedance ionized air path is already present as the switch contacts open. The arc is extinguished by special switch designs, usually employing a strong permanent magnet to deflect and "blow out" the arc as the switch opens. And, yes, knife-blade switch designs are quite common for this application, as are vacuum relays.
     
    Harald Kapp likes this.
  6. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
  7. swagguy8

    swagguy8

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    Dec 10, 2014
    Its a kill switch for an engine so it doesn't start up for any reason, not really to stop the engine except in emergency situations. basically what i'm doing is grounding the spark plug signal using a switch and a resistor.
     
  8. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Oh. Well, a knife switch will do just fine for that. Or maybe an automotive fuse block you can mount near the spark plug and insert a fuse (just about any size will do) into when you want to "ground out" the spark plug. I am thinking of the newer type fuses that have a little plastic handle and spade terminals. I think the spade terminals are spaced far enough apart to hold off the ignition spark (allowing it to arc in the spark plug) when the fuse is removed. Knife switches are kinda hard to find nowadays, at least little ones.
     
  9. Kiwi

    Kiwi

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    Jan 28, 2013
    Thought that might be what you were trying to do. Never seen it done in the high tension side to the spark plugs.

    Engine kill switches are usually connected to the low tension side of the ignition system, or to cut fuel to the fuel injection system.

    Is this a "cheap DIY" alternative to fitting a burglar alarm?
     
  10. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Best way to make sure the engine "doesn't start up for any reason" is to remove the spark plug, maybe lock it away in a tool box or bank safety deposit box.:D
     
  11. swagguy8

    swagguy8

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    Dec 10, 2014
    In a way :). its just to make sure the engine doesn't start. I cannot open the flywheel to access the primary coil, so unfortunately, i have to ground out the secondary. i'm thinking of a large resistor or something similar should work. The tool rent at home depot uses my method to ground out their engines.
     
  12. cl10Greg

    cl10Greg

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    Mar 20, 2014
    In higher voltage applications, like electric vehicles, they use contactors that are filled with nitrogen. That way when the circuit is broken it can suppress the arcing that is trying to retain the connection.
     
  13. Kiwi

    Kiwi

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    Jan 28, 2013
    Is this a small engine with a magneto type system?
     
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