Looking for Normally Closed ESPHome Smart Plug with Power Monitoring

Hardware
1

Hi all,

I have a lot of smart plugs at home, primarily from Athom, as I have had a great experience with how easy they were to set up since they are pre-flashed with ESPHome and come with power monitoring. Most of them I use them to measure energy consumption of individual devices and tell when they are operating, such as my washing machine so I can have alerts in Home Assistant when finished.

However, Athom now has a V2 of their plugs that has been my new go to, seemingly for good reason, as I have had 4 or 5 V1 plugs of theirs outright die on me. All these plugs were rated for 15A and never exceeded 7A, usually much less. The device they are connected to shuts off, I see them drop off the WiFi, and unplugging and re-plugging them has no effect, no light or power, and the button does nothing.

I programmed all these plugs that I strictly use for monitoring to default to have the Normally-Open (NO) relay closed so that power is available at all times. Perhaps they were never designed to run with power on at all times? I’m hoping this issue was resolved with their V2 plugs, but I haven’t had them long enough to tell and they did not respond to my email.

This leaves me with two main questions:

  1. Does leaving a NO relay Closed 24/7 have any additional wear on them that could cause these failures? Maybe in the transistors or whatever provides the relay the current to stay closed?
  2. Does anyone know of any suitable replacements for these smart plugs that come with a relay that is Normally-Closed (NC) and still has Power Monitoring? Like I don’t even need there to be a relay at all for this application. I guess effectively an ESPHome-enabled Kill A Watt is what I’m looking for.

The main reason for this ask is I like to have these plugs to monitor the power usage of devices that could have potentially catastrophic issues if left unpowered and it went unnoticed. Ie. Fridges, Freezers and Sump Pumps. The whole purpose of the power monitoring is to detect when the connected device has failed, but with NO relays I am actually introducing an additional point of failure that would at least mostly be mitigated in my eyes if they were NC.

CTs would not really be an option to my understanding without modifying the power cord of the given devices, so I’m trying to find as simple a solution as I have currently but with a fail safe so that should the smart plug be fried, power continues to flow and only monitoring data is lost.

2

:point_down:

1 Like
3

Great suggestion, thank you! It seems so obvious now, add ANOTHER power cord. :joy:
Having something more ready-made and discreet would of course be preferred, but if nothing else I can add this to the bottom of my project pile. :slight_smile:

4

Regarding your question about relays, the short answer is it won’t hurt them. They’re designed to do this, and may industrial relays are NO or NC and energized nearly 24x7 as a means of detecting something is wrong. For example a safety circuit may be Normally Open, and require the contacts to be closed to operate. So most of the time, they’re operating exactly as you are.

The concern I’d have is you’re not using hardwired circuitry, but rather logic. So instead of a clear when plugged in, relay is energized, instead you’re relying on code to determine this. So if the code ever went out to lunch. You lose your outlet. I’d imagine the ESPHome firmware had local storage and interprets / executes code locally, so you shouldn’t need a constant connection to Home Assistant. So it’s a fairly safe approach.

5

That’s correct. Still it doesn’t help against hardware failures. And you don’t want to loose the stuff in your fridge because a capacitor blow and turned it off. :boom:

Best is really to only use non-contact measurements for such a use case which can’t cut power to your load even when it fails :bulb:

6

Agreed. In an industrial environment, we use relays / contactors very often; but we typically know when they go bad and have spares on hand to address this. We also use high reliability parts, and would alarm on critical system failures / outages.

In residential, I’d expect smart components to start to fail after a period of time. Try to avoid running critical equipment off of smart devices unless they’re designed for integration (such as solenoid valves for your water system). But even then, having a manual failsafe is always a good idea such as a bypass.

The whole point of smart devices is to make your life easier, so it’s always a good idea to assume it will fail, and make sure you’re not sitting on a potential disaster.