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snubber capacitor help - halogen lights

Discussion in 'Electronic Components' started by Eric, Aug 16, 2004.

  1. Eric

    Eric Guest

    I just bought 3 low voltage halogen pendant lights. Inside the canopy, each
    light has a small transformer with 120VAC primary and a 12VAC secondary. The
    lights cause a tremendous amount of interference on AM radio in the kitchen
    and makes it so you can hardly listen to anything except the strongest
    stations. I am no electronics expert, but I have some RIFA PMR 210 snubber
    capacitors I was thinking of trying across the primary, secondary or both.
    My knowledge is very limited and I have only used these capacitors in my job
    to solve some problems across relay coils.
    From looking around, this seems to be a "X" capacitor (line to line).
    However, I noticed that the interference gets worse when the ground touches
    the shield of the light cable which is connected to one side of the
    secondary. So I am concerned I need a "Y" type (line to ground). Anyway, I
    plan to try the capacitors that I have. Does anyone have experience with
    this problem? Any suggestions on the type / value of capacitors I should be
    using? Is there another way to solve the problem?
    Thank you.
     
  2. Any time one connects a capacitor from hot to ground, etc., the current
    is supposed to be limited to a few mA, and the "y" cap size is usually
    4.7 nF or less. This is for safety reasons.
     
  3. What you have is not only a capacitor but a RC-unit with a resistance in
    series with the capacitor, see
    http://www.evox-rifa.com/n_america/film_capacitor_catalog.htm . The
    resistance will of course increase the impedance so the attenuation at radio
    frequencies will be less.

    If you want just the capacitance a PME 271 from Evox-Rifa would be better.
    An X-capacitor is ok as long as you do not connect it to earth, for that you
    will need a Y-capacitor.

    For technical information see this page:
    http://www.evox-rifa.com/n_america/technotes_filmcaps.htm

    Regards
    Stig Carlsson
     
  4. Eric

    Eric Guest

    Thanks. It looks like I should use .47uf capacitors because they seem to
    attenuate the AM radio frequency range the best according to the Rifa
    charts. Do you agree?
    Any idea where to buy them retail? The local electronics shops in NJ never
    heard of X and Y capacitors and Rifa's distributors only sell wholesale.
    Please let me know if you have any ideas.
    Thanks.
     
  5. Graham W

    Graham W Guest

    Eric,

    It occurs to me that the PSU you have there is not a simple transformer
    but a switched mode power supply (SMPS). Therefore radio
    interference from it may well indicate a faulty unit and in any case,
    in these days is most likely to be outside of legislated emission limits.

    You could perhaps use a real copper/iron transformer to eliminate
    the problem.
     
  6. Sorry, I live in Sweden so I can not help you where to get the capacitors.
    Anyway the brand of capacitor is not important, any X-capacitor with enough
    voltage rating will be ok to try. If the shop staff do not know X- and
    Y-capacitors maybe they are more familiar with the term interference
    suppressors. A local tv repair shop (if they exist anymore) should be able
    to supply you with some, new or used.

    Stig Carlsson
     
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