Shelly I4 gen3 disconnects upon relais input

[Stijn Schildermans]

I am building my dream smart home and decided to use Shellies all over the place. I use a TP Link deco mesh wifi set so that my signal quality is excellent. Generally everything works fine, but I ran into a rather strange problem when trying to use a Shelly i4 gen3 AC to read the input from a motion sensor. The setup is as follows:

-Motion sensor (Luxomat PD3-1C) set to pulse mode picks up motion. 
-Output of the motion sensor is used as a control signal for a relais (Finder 55.34.8.230.0054). Common contact of relais is connected to phase.
-Normal open contact of relais is connected to input of Shelly i4 gen3 AC. 

With this setup, the plan was to create a potential-free contact to drive the shelly. I.e. when the sensor senses motion, phase is connected directly to the switch contact of the shelly.

However for some reason, when the sensor detects motion and the relais closes the contact, there is about a 1/5 chance the shelly instantly disconnects from the network and only reconnects a minute or 2 later. I ruled out a defective shelly by replacing it with another one, electromagnetic interference from the sensor and/or relais by moving the shelly more than a meter away from the rest of the setup (another shelly is actually closer to the relais/sensor setup now and keeps working smoothly) and connection issues by moving one of the mesh routers to litterally next to the shelly. I tried reading debug logs but nothing gets printed at all. When taking the sensor/relais setup out of the mix and just manually holding the SW1 input agains the phase the Shelly behaves perfectly as expected.

All of this leads me to be almost certain the problem is caused by the signal coming out of the relais. However, I have no clue why. Can anyone help me with this?

Attached you can find some pictures of the setup for completeness. All blue wires are connected directly to neutral, brown ones directly to phase. The grey ones carry the signal from sensor to relais and from relais to shelly.

Thanks for any help!

 

Edited November 6 by Stijn Schildermans

[thgoebel]

Please connect a snubber (RC combination) in parallel to the relay coil. With a certain likelihood the Shelly is affected by transient voltage spikes.

[Stijn Schildermans]

Aha. The idea is that because the coils of the relais and sensor are in parallel with the shelly, the voltage spike induced by activating the sensor/relais also causes a voltage spike at the shelly, which forces the shelly to reboot, correct?

What dimensions would you recommend for the RC combination?

[Stijn Schildermans]

18 minutes ago, thgoebel said:

Please connect a snubber (RC combination) in parallel to the relay coil. With a certain likelihood the Shelly is affected by transient voltage spikes.

Also, does this issue also occur with motion sensors with built-in potential-free contacts? Is there a particular type you would recommend?

[thgoebel]

https://www.shelly.com/de/products/rc-snubber?_pos=1&_sid=88c78e939&_ss=r&_gl=1*85c0wr*_up*MQ..&gclid=EAIaIQobChMItI_Q5-DIiQMVcoCDBx0FDCC1EAAYASAAEgK7mvD_BwE&gbraid=0AAAAAoaU-9iH-H-5sh95NrgLf2qtZrovg
 

[Stijn Schildermans]

On 11/6/2024 at 11:30 PM, thgoebel said:

https://www.shelly.com/de/products/rc-snubber?_pos=1&_sid=88c78e939&_ss=r&_gl=1*85c0wr*_up*MQ..&gclid=EAIaIQobChMItI_Q5-DIiQMVcoCDBx0FDCC1EAAYASAAEgK7mvD_BwE&gbraid=0AAAAAoaU-9iH-H-5sh95NrgLf2qtZrovg
 

I tried both the Snubber and a 330 nF capacitor. The snubber is totally ineffective and the capacitor seems to work most of the time, but still I get disconnects every 1 in 10 times or so the motion sensor triggers. Any further ideas? I am totally at a loss..

[thgoebel]

Did you connect the snubber in parallel to the relay coil? 

[Stijn Schildermans]

2 hours ago, thgoebel said:

Did you connect the snubber in parallel to the relay coil? 

I was about to reply 'yes of course' because I connected the snubber to the same wagos I connected the relais, Shelly and motion sensor to. Then I thought of trying one last thing, namely directly connecting the snubber over the relais coil. This finally worked. I have no idea why though. I guess it must have something to do with the signal coming from the motion sensor not being the pure phase signal (why I had to put in the relais in the first place). 

Anayway thanks a lot for the help! As a final note, can you maybe refer me (and future readers of this thread) to some good information on how this snubbing stuff works? I have been trying to read up online but have a hard time finding a good source.

[thgoebel]

Your welcome:

https://en.wikipedia.org/wiki/Snubber