Relay Shields: Audible switching but not releasing!? (... you read correct)

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Wookbert
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Relay Shields: Audible switching but not releasing!? (... you read correct)

#1 Post by Wookbert » 20 Nov 2021, 00:49

I have experiencing something I can't explain to myself: I've bought a couple of those Wemos D1 mini compatible Relay shields on AliExpress, which sometimes have problems „to let go“. When turning off via http request, they click audible and ESPEasy displays the state correctly as being [0], yet the relay doesn't open, so the attached electric appliance doesn't turn off.

I've replaced the relay shield twice, but both replacements show the same behavior. They work for a while, but occasionally they get stuck. I'm switching less than 300W @ 230V, not much. Definitely not burn-in. The D1 pin measure 3V high, 0.0V when low. The 5V pin sees 4.7V.

Any idea what’s going on here?

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ThomasB
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Re: Relay Shields: Audible switching but not releasing!? (... you read correct)

#2 Post by ThomasB » 20 Nov 2021, 02:08

They work for a while, but occasionally they get stuck. I'm switching less than 300W @ 230V, not much.
The shield probably has a SRD-5V-SL-C relay or similar China flavored part.

The important question: Inductive or resistive load?

Some warnings: The ratings printed on them are for resistive loads, such as traditional incandescent lighting. Relay life will be short if you use it on a 230V inductive load due to contact welding. Also, some appliances have huge inrush, which can be problematic for these small relays.

Some related information:
https://www.omron.com.au/service_suppor ... /index.asp
... they click audible and ESPEasy displays the state correctly as being [0], yet the relay doesn't open, so the attached electric appliance doesn't turn off
If you can hear the relay drop out then maybe the relay is not welded closed. For example, if the problems occurs and the appliance turns off when you reset the ESPEasy device then the relay contacts have not welded. If this is what you find then do more investigation.

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Re: Relay Shields: Audible switching but not releasing!? (... you read correct)

#3 Post by TD-er » 20 Nov 2021, 10:48

Maybe you can also consider replacing the relay with some solid state relay.
The sending end is just a LED, so should not be that hard to operate :) and the switching side is switching at the 0 Volt crossing.
This also means you cannot use (most) solid state relays to switch DC, but switching AC should not be a problem.

By switching at a 0-crossing you also make it easier to handle for the connected appliance as the inrush current will be smaller.

If you plan on buying a solid state relay from the "far east", make sure to overdimmension the relay as they tend to exagerate the specs quite a bit.
And those can get warm, so keep an eye on the thermals.

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