Where to put the snubber in attached schematic

Hello All,

I just started using Arduino and was able to program and test (without Ac Motor) my setup see attached. I found that when I connect the AC motor my arduino hangs, after searching in forums, I found that it is due to back EMF, and we need to connect snubber to suppress this EMF, but am not sure how and where exactly i need to connect it.

This is my first post, so sorry for this bad English and schematic and may be this question might have answered somewhere in the forum which i could not find .

Edit:
More information: Hanging only happens when relay input is set HIGH to turn off the motor. If I remove motor from the setup then all is well

Thanks in Advance.

I think this is a good question :slight_smile:

Across the relay contacts will obviously work to snub spikes when the contacts open, but leaves an
RC path connecting live mains to the motor even when it is off, with both safety and power-consumption
implications.

Across the motor means that the spike can still be dissipated, but is likely to push more interference
along the wires (the live wire coming in may have its own inductance due to transformers for instance).
Across the motor means the live is isolated from the motor when the relay is open-circuit, a safety
feature.

Probably the best way for suppressing interference and isolating the load is to snub across the motor
and across the incoming mains (say with a MOV which is useful protection anyway).

But I'm not sure whats normally done, and it probably depends on regional regulatations too.

BTW make sure your relay module itself is properly mains rated and preferably opto-isolated.

I don't think back EMF if hanging your Arduino since the Arduino is completely isolated from the motor via optocouplers (if your diagram is accurate). How do you know the code is hanging vs just a bug?

Power_Broker:
I don't think back EMF if hanging your Arduino since the Arduino is completely isolated from the motor via optocouplers (if your diagram is accurate). How do you know the code is hanging vs just a bug?

Disconnecting an inductive load can cause sparks across the relay contacts, which are basically like a klaxon horn of EM noise.

I saw one thread on here where physical proximity to his running motorcycle engine was a factor in causing malfunctions, most likely caused by radiated noise from the spark plugs.

I would put an MOV across the motor and add a capacitor on the arduino 5v. I would also look at the distance from the Arduino to the relay board.

The MOV will likely protect the contacts somewhat but I doubt it will reduce the EMI very much. If the contacts open mid way between the 230V peak ( some where around 325V) the resulting di/dt will still be significant before the MOV starts conducting.

I don't know if there is any other circuitry, but from what I see I would connect the AC adapter to the arduino and then the relay.

Good luck

Jon