RC Snubber Values

Discussion in 'General Electronics Chat' started by Tyler54, Dec 23, 2012.

  1. Tyler54

    Thread Starter New Member

    Aug 26, 2012
    15
    0
    Hi, I have been fighting with a noisy pump that is switched by a relay. I have decided to give a RC snubber across the pump a try to see if it will quite it down. I'm however having some difficulties calculating the Capacitor and Resistor values.

    Here is what I have:
    I = 2 Amps
    V = 120V
    R = V / I = 60 Ohms ??
    C = ??

    [​IMG]

    I tried to follow this pdf but it was a little over my head http://www.cde.com/tech/design.pdf. I also tried the ehow article http://www.ehow.com/how_12030206_design-rc-snubber.html but it seemed like they dummied it down to much plus their math doesn't seem to work.
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,973
    3,219
    What type of noise?
     
  3. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    Instead, put the RC snubber across the relay contacts. Typical snubber values are 0.1mf. & 100 ohms in series.

    Cheers, DPW [Everything has limitations...and I hate limitations.]
     
  4. ramancini8

    Member

    Jul 18, 2012
    442
    118
    Use a capacitor rated for full ac line voltage.
     
  5. Tyler54

    Thread Starter New Member

    Aug 26, 2012
    15
    0
    Thanks for the responses. I believe it to be EMI as it's radiating over all the lines and jumping opto-couplers on the other side of the relay.

    I came across this document and Excel file that seems very helpful.
    http://www.hiquel.com/fileadmin/userfiles/AppNotes/Englisch/HIQUEL_Snubber_AppNote_EN_0100.pdf
    http://www.hiquel.com/fileadmin/userfiles/AppNotes/Englisch/HIQUEL_SnubberCalculator_AppNote_EN_0100.xls


    I put in all the numbers in and it's recommending:
    C: .1 uf
    R: 600 Ohms

    I have a 600V .1uf Capacitor on hand so I'm good there.

    It's also suggesting a 2.5 Watt resistor, with a Max peak voltage of 1716V. I can't seem to find a Carbon Composite resistor beyond 1 watt though. There seems to be some wirewound ones though. I'm a little lost on which type I should be picking for this purpose?
     
    Last edited: Dec 24, 2012
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