Help to reduce Inductive Kick

Discussion in 'The Projects Forum' started by saikat36, Apr 30, 2011.

  1. saikat36

    Thread Starter Member

    Jan 28, 2009
    16
    0
    Hello,
    I have a PSU having

    i/p--- 230V AC & 2A
    o/p-- 20V AC & 4A
    whenever I going to switch off the PSU from AC outlet it creates large spark due to inductive kick. Anyone can suggest me a good schematic to reduce such inductive kick.

    Thanks.
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    Is there a ground pin on the power supply plug?
     
  3. saikat36

    Thread Starter Member

    Jan 28, 2009
    16
    0
    No, no ground pin. Only Line & Neutral pin.
     
  4. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Perhaps a MOV across the primary? If so, it should be preceded by a fuse.
     
  5. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Second thoughts:
    Perhaps an RC snubber across the primary would be helpful? A 1000pF to .1uF will present a fairly hi Z to 60Hz but will present a much lower Z to a fast rising spike. I would start with a 1000PF in series with a 1/2W - 100Ω resistor. If you need more suppression you can work your way up to .1uF.

    If this is a class assignment I will leave the circuit TPD @ 60Hz or 50Hz (depending where you are) to you.

    BTW, others may have their own opinions regarding the value of R. I chose 100Ω but that's not cast in stone.
     
    Last edited: May 6, 2011
  6. saikat36

    Thread Starter Member

    Jan 28, 2009
    16
    0
    Ok 'CDRIVE' thank you very much to you.
    I have one query about Cap. What type of cap. should be used Tantalum or Ceramic & What wiil be the voltage rating for cap.?

    Thank you again.
     
  7. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    Ceramic Disk caps. 1KV would be nice but they're not that easy to find. 500V should suffice though. I would also fuse the input.
     
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  8. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Actually if it's going across the AC mains you need one of those caps that are designed for doing that. They're called suppression caps and are designed to have mains voltage at 50 or 60 Hz across them constantly. Most anything else could be a danger.

    I'd use a 0.047 and you won't need a resistor.

    Mouser, DigiKey, Farnell etc.
     
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  9. saikat36

    Thread Starter Member

    Jan 28, 2009
    16
    0
    Thank you 'CDRIVE' to clear my doubts.
     
  10. saikat36

    Thread Starter Member

    Jan 28, 2009
    16
    0
    Welcome & thank you 'marsh' for your suggestion.
     
  11. CDRIVE

    Senior Member

    Jul 1, 2008
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    Marshall, thank you for correcting me. When I first read your post my impulse was to Pooh Pooh the statement. However, I then remembered that I had a bag of Digikey caps that I had ordered some years ago for a centrifuge repair that I did. I managed to dig them out and sure enough these caps are rated @ 250VAC! These particular caps are "film", not ceramic as I stated.

    http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&KeyWords=p4633-nd

    The odd thing is, and I'm going to have to dig though 40's and 50's vintage schematics to confirm it, but I could swear that back in the day the industry used plain old HV ceramics or those old tubular waxy models for this. If not, it won't be the first senior moment I've had! :rolleyes:
     
    Last edited: May 1, 2011
  12. marshallf3

    Well-Known Member

    Jul 26, 2010
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    No problem, I use suppression caps quite often and always get the ones designed for that function, anything else tends to overheat and blow up after time.
     
  13. marshallf3

    Well-Known Member

    Jul 26, 2010
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    You're correct, in the old days I also remember the waxed paper caps used in AC situations, usually one leg to the chassis so in essence there would be very little if any current passing through them. Often there was a very high ohmage resistor in parallel with them. They were there to help reduce AC hum in the audio of radios and early TVs. You will also see them in early model guitar amps with a switch that chose which one of the AC main lines was going to the cap that went to the chassis. you put the switch in the position that had the least hum. The switching arrangement was probably due to there not being polarized plugs in those days so you had to switch to find the neutral.
     
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