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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?

JRE
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Jurgen
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  • Since I'm new to this, I also prefer ready made circuits, but I only found this online. – Jurgen Feb 04 '18 at 20:58
  • why not use a bidirectional tvs diode , this is a solution. if you donot want to get into the RC snubber calculations – ElectronS Feb 05 '18 at 01:25
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    A 40 mm MOV with a voltage rating the same as the coil will also dampen kick-back. –  Feb 05 '18 at 03:13
  • @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? – Jurgen Feb 05 '18 at 07:18
  • @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. – ElectronS Feb 05 '18 at 17:27
  • also google this :How To Select Transient Voltage Suppressors - Microsemi , also : Transient Overvoltage Protection - ON Semiconductor – ElectronS Feb 05 '18 at 17:27
  • @ElectronS thank you ever so much. Will a P6KE300CA do the trick then? I'm trying my best to comprehend, but I must admit I'm still way in over my head here – I'm pretty much an amateur trying to put an electromechanical relay to use without damaging the rest of the control circuit. – Jurgen Feb 05 '18 at 21:20
  • @jurgen , yes this will be my choice also , put this tvs across the coil. you could use an oscilloscope in single trigger mode to check the signal on each side of the coil with respect to system ground . try it with and without tvs to see the difference , this way you see the effect and hopefully will help you understand better such device. glad i could help :) – ElectronS Feb 06 '18 at 19:21
  • Does this answer your question? Sizing a RC Snubber - microcontroller restarting when switching off an inductive load – Tim Williams Jul 17 '23 at 00:26
  • @TimWilliams I agree, that the reference you mentioned covers this question very good, but this one is much older and therefore cannot be a duplicate of the reference. I am not sure how we handle this. – Jens Jul 17 '23 at 19:27
  • @Jens As far as I know, priority doesn't matter, just that the better question/answer(s) are chosen. Well, at the very least, readers can follow the link, not that doing so through comments is a great method. Closing would stop the bump spam. – Tim Williams Jul 17 '23 at 19:32

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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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