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Surge current?

  1. Dec 2, 2009 #1
    Dear Gurus,

    I have a doubt about switches.
    I have a proximity magnetic switch i used to switch on and off a circuit.
    I wonder would there be arching or spikes or current surges when the switch is switched on and off repeatedly ? My circuit has resistors to limit the current. Will switching on and off cause current surges that can damage the low current circuit components? Or is it that the resistors is sufficient to protect the circuit?

    Seeking your advice.

  2. jcsd
  3. Dec 2, 2009 #2
    If your switch is on the primary of a transformer or other inductive device, you can get voltage spikes and sometimes arcs. If the switch is directly coupled to a capacitor without a series current-limiting resistor, you can get current surges. If the switch is in series with an incandescent lamp, you can still get a surge due to the low resistance of a cold filament. A pure resistive load is ok as long as it is within the switch's voltage and current rating.
    Bob S
  4. Dec 2, 2009 #3


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    Gold Member

    It really doesn't have anything to do with surge but "switch bounce" can be a problem with analog and digital circuits that are fast enough to see the bounce. When you close a switch, the momentum of the contact coming closed can cause it to reopen/bounce. I've seen switch that will bounce open and closed several times before finally settling down.
  5. Dec 4, 2009 #4
    Dear Bob and Don , thank you so much for giving me advice.

    The device to blink is a 10Watts filament bulb.
    So, I gather from the forum is that for such a mechanical switch, arcs can occur.
    I assume that by arcs (like lightning) implies more current than necessary will flow through the circuit requiring a resistor to protect the circuit.

    Should I be using a greater than 10 watts resistor, of say 1 ohm, or just a 10watts or lower resistor, of say 1 ohm to handle the arcing/surge?

    If LEDs were used, would using flashing circuits that uses a combination of 555 timers, capacitor ad resistors be able to avoid current surges that could damage the LEDs?

    Last edited: Dec 4, 2009
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