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Switch Arc Suppresion

Discussion in 'General Electronics Discussion' started by roston.elwell, Aug 31, 2011.

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  1. roston.elwell

    roston.elwell

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    Aug 31, 2011
    I have a hair dryer with a switch that arcs when it is turned off and I would like to build a series RC circuit to suppress this arc but I am not sure on the sizing of the resistor and capacitor. Also, I am not sure of the placement. Can the circuit go across the the switch or will the capacitor allow current through since it is AC through the switch? The motor has a diode bridge to rectify the voltage to DC so can the RC circuit be placed across the load? Any thoughts/suggestions would be apreciated.
     
  2. davelectronic

    davelectronic

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    Dec 13, 2010
    RC circuit

    Hi there.
    This is a common occurrence on an inducted or resistive load at or in mains electricals, i doubt there is any need for a RC circuit, as there are a number of suppression capacitors that contain the RC circuit as a network all in one package, Google mains suppression, some units are low voltage dc motor, and mains on the elements, you need to determine the circuits power requirements. Dave. :) PS some units the spark is common to a lot of these type of consumer units, i would not worry to much about it.
     
  3. Resqueline

    Resqueline

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    Jul 31, 2009
    RC suppressors across switches are mainly used with inductive loads afaik. I'm not sure it would help here where the load is resisitive.
    I believe the main reason for the arcing is the high current and a slow switch action. Does the switch break both phases?
    You could try 100nF & 100 ohms. Some current will pass but not enough to make anything run or become hot.
     
  4. roston.elwell

    roston.elwell

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    Aug 31, 2011
    Isn't the inertia of the DC motor an inductive load? The switch only cuts the hot lead in a US 120V/60Hz circuit. Which is single phase right?
     
    Last edited: Sep 1, 2011
  5. Resqueline

    Resqueline

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    Jul 31, 2009
    Permanent magnet DC motors have a back-emf but are hardly inductive to speak of. In hair dryers they're also low-voltage and so contributes very little to any disturbance.
    The inertia represents just a small DC voltage, but it's not an inductive kickback voltage (that can reach hundreds of volts) as in a coil or a reactor.
     
  6. roston.elwell

    roston.elwell

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    Aug 31, 2011
    I just want to fix it for my own satifaction more then because it really bothers me. Do you have any suggestions on a good place to order stuff like this from?
     
  7. roston.elwell

    roston.elwell

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    Aug 31, 2011
    I guess I was confusing that back emf with being inductive. Will this RC circuit help with the back emf?
     
  8. Resqueline

    Resqueline

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    Jul 31, 2009
    No, I seriously doubt that. An arc will form on any (cheap) slow-opening mains switch, even with a purely resistive load.
    I think you'll have to seriously complicate the dryer switch circuit to get rid of that arcing.
     
  9. roston.elwell

    roston.elwell

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    Aug 31, 2011
    Thanks for the help. I guess my best option maybe to just close my eyes when I turn it off.
     
  10. daddles

    daddles

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    Jun 10, 2011
    Before undertaking any project, I like to ask "What problem is this solving?" and "Is this really worth doing?". The first one is very important: I spent many decades in industry and you'd be amazed how often individuals and groups don't carefully ask the first question and get meaningful answers to it. A corollary is "Make sure you're draining the right swamp". Now, only you can answer these questions for your situation, but they certainly popped into my mind when reading your question... :p
     
  11. duke37

    duke37

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    769
    Jan 9, 2011
    I suggest that no components are put across the switch. If they fail, power could stay on the dryer.
    You can get voltage dependant resistors which will clip the very high induced voltages if placed across the dryer supply after the switch. Some extension leads have these in as protection for items like computers. You could try plugging the dryer into one of these leads and then switching the lead on and off and see if things improve.
    A VDR could then be mounted in the dryer.
     
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