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    RC snubber for 240v contactor coil

    Hello all!

    I have done a control circuit that needs to operate two contactors (with 240v ac coil). I'm experiencing interference on the circuit, the LCD goes mad when installed. And after some research I found that maybe, using an RC Snubber circuit on each coil would resolve the problem...

    If the RC Snubber is the way to go, now I need to select the components. Some people say that 220 Ohm resistor and a 0.5µF are good values for a 240v AC coil, what do you think? And since I can not measure the power consumption of the coil right now, what would be the power required for the resistor?

    Thank you!
    Last edited by Imperyal; 2nd January 2012 at 17:00. Reason: Spell check

    •   Alt2nd January 2012, 16:57

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    Re: RC snubber for 240v contactor coil

    Here are a few snubber circuit design notes:

    DESIGN OF SNUBBERS FOR POWER CIRCUITS

    Snubber Circuits

    Snubber Circuits: Theory , Design and Applications

    You should be able to determine the appropriate component values by following the guidelines of the above design notes.

    Here is an online snubber circuit calculator as well:

    Snubber Circuit Design Calculators

    Hope the info helps in your endeavors,

    BigDog



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    Re: RC snubber for 240v contactor coil

    Thanks bigdogguru!

    On my research I already saw all that links. But I never put a RC Snubber on any coil. And if someone on the forum already do that it would be much faster and easier for me. I think I have the values right, but the power for the resistor is the missing info. I have no idea how much a coil draw, and I don't have the contactor here to measure, only on the next weekend. And by that time I would like to have the values figured out so that I can install the thing. If someone knows or have a coil on hand to measure, it would be sufficient info for me.

    Thanks again!



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    Re: RC snubber for 240v contactor coil

    What is the part/model number of the "contactor"? Have you attempted to locate a datasheet for the device?

    Since the required calculations largely depend on the properties of the contactor/relays coil, any advise would be an educated guess at best.

    BigDog



    •   Alt2nd January 2012, 17:54

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    Re: RC snubber for 240v contactor coil

    Ok, I have some more info on the coil. It's the LXD1P7 coil for contactor. It's supposed to draw 500mA at 230V. I estimate I need a 55W resistor...? Is that right? Thank you!

    PS: 220 Ohm resistor
    Last edited by Imperyal; 2nd January 2012 at 20:56. Reason: Add resistor value



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    Re: RC snubber for 240v contactor coil

    @ bigdogguru:
    I go through the document links provided by you. But I could not able to extract my simple requirement of choosing the values for R and C of RC snubber. Suppose I want to use TRIAC to control a 100W induction motor (FAN) and another TRIAC for 1000W induction motor operated in 230V AC. So, how can I calculate the appropriate values of R & C?



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    Re: RC snubber for 240v contactor coil

    Its a practical logic, and works to dampen the high energy signal path. So during operation your operational frequency may be 1/T but transient time can be <<T/5. Snubber circuit should bypass or dampen this very small time transients (average out)(integrator at high frequency). at low frequency it works as simple voltage divider.

    You need to know your transient frequency. You define the RC snubber time constant to 5-10 times of transient time. There are various modified topologies also available to support even more functionality.



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    Re: RC snubber for 240v contactor coil

    Hello again!... Just to let you know that o solve my problem, not with a RC Snubber but instead with a software fix. Restart the LCD more often did the trick.
    Thank all of you for your help.
    Last edited by Imperyal; 20th January 2012 at 12:07. Reason: Spell check again!



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    Re: RC snubber for 240v contactor coil

    @varunkant2k:
    Could you please show the sample calculation for a simple RC snubbar circuit. Line voltage 230v, frequency 50Hz.



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    Re: RC snubber for 240v contactor coil

    Hi sam781, Snubber works for transient frequency not for line frequency.



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