What is the purpose of resistor to suppress EMI? Couldn't I just use a suppression capacitor alone between the coil of the relay or contactor? I have tried to use capacitor alone and it did reduce EMI in my project, but I'm just curious of the effect of adding resistor in series with it.
Resistor in RC snubber
snubber
Related Solutions
Metal Oxide Varistors (MOVs) are cheap but will wear out and fail shorted. Properly rated capacitors as part ofa snubber will last indefinitely. Both will allow a significant voltage spike. See, for example, Electromagnetic Compatibility in Medical Equipment: A Guide for Designers ... By William D. Kimmel, Daryl D. Gerke
MOVs are more appropriate to deal with occasional spikes rather than continuous clamping applications, where they are appropriate at all.
The edited question is clear, now. The capacitor is correct WIMA MKP 250VAC is the correct choice. The resistor could be under rated, also it seems a little bit too low 360 ohm to me.
Have a look here: RC snubber circuit design for TRIACs - STMicroelectronics , there is a calculation for 26W pump and the calculated sbubber is 10nF and minimum resistance of 620 ohm. I wouldn't change the capacitor you've got, it's really high quality and for this specific task.
Choose a capacitor for higher voltage, like WIMA MKP 630V
Also, BTA-16 is somehow too big for the required load, if you can change it use a smaller one like BTA-06.
Best Answer
Snubbers are energy-absorbing circuits used to suppress the voltage spikes caused by the circuit's inductance when a switch,electrical or mechanical, opens. and may also cause false triggering of the device (relay or thyristor)
The snubber capacitance has to meet two requirements. First, the energy stored in the snubber capacitor must be greater than the energy in the circuit's inductance.
Secondly, the time constant of the snubber circuit should be small compared to the shortest on time expected, usually 10% of the on time.
consider the case When the transistor switch opens, the snubber capacitor looks like a short to the voltage change, and only the snubber resistor is in the circuit. Choose a resistor value no larger than the characteristic impedance of the circuit so that the inductive current to be snubbed can continue unchanged without a voltage transient when the switch opens. and R is also helps in power dissipation when the switch is open as C alone cannot do it.
hope this helps