# How to connect snubber across the relay?

How can a snubber circuit be connected across a relay? Because when we connect a snubber across the relay then the capacitor always allows the current to flow through it.

The relay I am using is 12V DC powered which controls 220V AC Voltage.

In figure 3 below

• You are confusing people by taking an Application Note that's talking about snubber networks for AC circuits while you ask about a snubber network for a (low power, DC powered) relay. Also it is unclear where you want the snubber network: across the DC powered coil of the relay or across the relay's contacts? – Bimpelrekkie Jan 8 at 13:40
• @Bimpelrekkie I want to place snubber accross the relay contacts. I have placed a diode across the coil of the relay. – user193395 Jan 8 at 13:46

Yes, there will be some "leakage" current through the capacitor when the switch is open. This is normally not a problem with the kinds of heavy reactive loads that need a snubber. If you need complete isolation, then you can't use this approach.

Usually, there are multiple sets of contacts controlling such a load anyway. The normal switch to control the load would have the snubber across it, but when you need total isolation (for servicing, etc.), you open the circuit breaker as well.

• It reduces efficiency a bit due to the charge/discharge power every cycle, but the cap is very small so is pretty high impedance for 50Hz/60Hz. – DKNguyen Jun 19 at 14:12

then the capacitor always allows the current to flow through it.

No, that's not how capacitors work.

You're unclear if you want to add the snubber network across the coil of the relay or across the (AC) contacts of the relay.

I'm assuming that you want the snubber network across the coil:

A capacitor will only allow current to flow when the voltage across the capacitor changes. In this application the voltage across the capacitor only changes when the switch opens or closes.

When the switch is open or closed, the voltage across the capacitor is either 0 (zero) or Vs. So it is constant and no current flows through the capacitor.

A snubber network is intended to short circuit any rapid changes in voltage as these rapid changes can disturb other circuits nearby (EMI). The capacitor sorts these rapid changes and forces these currents to flow in a short loop through the capacitor and series resistor. That resistor dissipates the harmful signals and EMI is reduced.

• but the input is AC voltage right. So I think the voltage accross the capacitor will be alternating. – user193395 Jan 8 at 11:23
• Most relays cannot work with AC so unless it is specifically mentioned that AC is used, we can assume the relay coil is powered by DC. But even if AC is used, the frequency of AC (50 or 60 Hz) is much lower than the frequencies that the capacitor needs to short (like 100 kHz and higher). So even with AC, the current through the capacitor will be quite small as the impedance of the capacitor will be very high at low frequencies. – Bimpelrekkie Jan 8 at 11:26
• the relay I am using is to control AC voltage with a DC signal.(electro mechanichal relay). – user193395 Jan 8 at 11:30
• [electronics.stackexchange.com/questions/344574/… I am using an interrupt for button press detection. But the problem is when the relay is switched of then the interrupt is also triggered. – user193395 Jan 8 at 11:39
• The coil in the picture is not the coil of the relay that the OP is talking about. The picture is only showing the relay contacts. – Dave Tweed Jan 8 at 13:33