RC Snubber Values

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

  1. Tyler54

    Thread Starter New Member

    Aug 26, 2012
    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 = ??


    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


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

    Senior Member

    Apr 23, 2009
    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

    Active Member

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

    Thread Starter New Member

    Aug 26, 2012
    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.

    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