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In a project I use several 12VDC coil electromechanical relays. I use diodes in parallel to the coil protect them from flyback.

I also have one relay with a 240VAC coil. I have learned that I should use an RC snubber in parallel to the coil instead of a diode (I'm new to electronics.) I have researched a lot, but I feel unable to transpose most calculations or answers I found on here or the internet to my project (again, I'm a novice.) Can anyone help me calculate which type of RC snubber (or which values) I need for my relay?

These are the numbers from the datasheet (marked in yellow):

enter image description here

Is an RC snubber enough for protection?

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  • \$\begingroup\$ Since I'm new to this, I also prefer ready made circuits, but I only found this online. \$\endgroup\$
    – Jurgen
    Feb 4, 2018 at 20:58
  • \$\begingroup\$ why not use a bidirectional tvs diode , this is a solution. if you donot want to get into the RC snubber calculations \$\endgroup\$
    – ElectronS
    Feb 5, 2018 at 1:25
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    \$\begingroup\$ A 40 mm MOV with a voltage rating the same as the coil will also dampen kick-back. \$\endgroup\$
    – user105652
    Feb 5, 2018 at 3:13
  • \$\begingroup\$ @ElectronS I came across this suggestion as well, but found even less info on how to calculate or select the right type and value for my specific use case. Would you mind helping me? \$\endgroup\$
    – Jurgen
    Feb 5, 2018 at 7:18
  • \$\begingroup\$ @jurgen , the calculation of the TVS is easy if you know the amount of energy , or power over time . but a quick look at the relay coil , shows that the relay is rated 5mA at 220v , which is very low power and is very easy to suppress , 400w bidirectional TVS and up is more than enough . and regarding the voltage rating (Reverse Standoff voltage ) should be greater than peak AC voltage by a little. check littlefuse website for appnotes on selecting tvs diodes , it doesnot matter the application. \$\endgroup\$
    – ElectronS
    Feb 5, 2018 at 17:27

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I think it is better to use an RC circuit rather than a varistor that is mentioned above. The disadvantage with the varistor is that it wears out more quickly than the RC snubber. Two things to keep in mind is that the Cap should be for AC use and the resistor to not be low watt rated.

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