I have designed yet another custom PCB with an ESP32 and some relays that I will use for some IoT projects.
I am using one of these relays to switch a 230 V AC contactor which then switches a 230V AC pump.
I am using the COM-NO contacts of the relay to switch the 230 V AC phase to the contactor. For transient protection, I have added an RC snubber across the relay COM-NO contacts (on the 230 V AC side) and a diode (on the 5 V DC side). Please find a simplified schematic below:
Here's the thing: the relay switches fine, but the contactor remains powered ON even when I turn OFF the relay. I have measured the voltage across the A1 and A2 contacts of the contactor: when the relay is ON, I measure 230 V AC, which is correct. When the relay is OFF, I measure around 168 V AC, which makes no sense to me.
I have tried to switch the NO contact with the NC contact on the relay (that is: I switch the contactor using the COM-NC contacts of the relay): in this case, the circuit works fine and the contactor is switched ON or OFF according to the relay status. The only difference is that the COM-NC circuit doesn't have an RC snubber on the 230 V AC side, the rest is exactly the same.
I am puzzled... is it the RC snubber that is causing this "parasitic voltage" which keeps the contactor ON even when the relay is OFF? Or do you have another opinion?
These are the components I have used, for your reference:
- Relay: OMRON G5LE-1 DC5 - SPDT relay - datasheet here
- RC Snubber: ROXBURGH RE1202 0.2 µF, ± 20%, 120 ohm, ± 30%, 500 mW, 275 V - datasheet here
Regarding the RC snubber selection: I am an amateur, I haven't even tried to size the snubber - I wouldn't even know where to start. I know this is "bad", but I have selected this specific snubber primarily because I have seen it used in other projects similar to mine.
For reference, please find below the schematic of the relay switching circuit.
Thanks in advance!