Looking for a voltage sensor

I have recently bought a Gardena Irrigation Controller, model 4030. In addition to controlling the water valves, it can also turn on a compatible water pump (by sending 24Vac on 2 terminals.) I don’t have a compatible water pump, but it is connected to a Homematic switch. What I am looking for, and so far haven’t found, is a sensor that can detect when the voltage on the pump terminals go high - 24v, and turn on a switch.

I’ve found a lot of switch sensors, but they are meant for potential free switches, not something for 24vac. Has anyone come across a device that could handle this scenario?

I suppose you want just a potential free input for something so search for a 24vac relay.

Shelly em?

One of the channels is voltage measurement and you can use those brackets to put around and outside of the cable, if I’m not mistaken.

I came across a homematic 3 channel switch interface, HM-SwI-3-FM, but it says its for potential free switches. I must admit that this statement left me a bit confused and I’m not sure if it is appropriate for my use case. Is this the kind of thing you meant with a 24vac relay?

Thanks for the tip, I will also check the Shelly line out as well.

My background is electrician. So basically your Gardena controller is using 24ac that is fine but you have a pomp that is using 230vac now you also have a homematic controlled actuator that turn on that pump right? What you want now is another homematic input module that you can use to turn on that actuator for the pump ? Now because gardena give you 24ac but the input module from homatic only accepts potential free inputs let’s say a basic wall switch then what you need is a 24ac relay or contactor. If you are not comfortable with electrics I suggest pay an electrician locally to do it for you probably it will come cheaper and more stable than ordering random stuff of the internet.

But anyways a relay will have A1 A2 label where your 24vac comes in from Gardena (make sure the coils is rated at 24vac) and also terminals label 11 and 14 and 11 where one is GND labeled on the homematic input module and 14 would be the IN1 till IN6 on the homematic module.

The relay should be something like this one

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Quick edit the homematic module you mentioned is labeled com and e1 till e3 so take instead of IN1 etc

basically, What you are looking for is something like this.

Thanks, but that won’t work. My pump is already plugged into a smart outlet that is controlled by Openhab. I am looking for a way to integrate the pump controller from the Gardena device into Openhab. The relay and the Shelly options looks like the right way to go.


Shelly em won’t work that for energy monitoring.

For my own personal education - why not?

Because it just a relay/mosfet output with some inputs for toroids to measure the magnetic field. What op said he has is an 24vac output from a garden controller to start the pump and an pump connected to a different actuator based on homematic. But that specific Shelly is not meant for voltage measurement and also it’s rated starting voltage is 110vac Wich will never work no matter what. The thing that most people forget in computer science is that electricians worked with binary long time ago :slight_smile: and also they programmers work at such a higher abstraction level they don’t understand the basic working principal of voltage current and how that is used to create all this logic gates you guys are playing around here.
Ask me more question if you have.

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Ha ah!! Then he should measure the different actuator which actually runs the pump - and assuming the pump runs on 110/220 volts it would work? Did I understand that correctly?
Cheers for taking the time to explain, super helpful!

Op doesn’t need to know if the pump is running or not he want that the Gardena controller starts the pump when irrigation is running probably to keep the pressure high or use a rain water tank to pump.
But if he wanted to control the pump with that Shelly and get a real status of running based on consumption then your proposition would make sense like say for example the pump was a vital part of the house to pump a basement if get flooded or gather water on below street level.

Does it make any sense for you now ?

Yep it’s clear now, thank you :pray:

Not sure why it or something like it would not work for you but ok.
A relay is a relay is a relay is a relay. application defines what type you choose i.e. number of poles ?P (SP,DP)(contacts) and number of positions ?T(ST,DT) then you have the NO (normally open versus NC normally closed (at rest and disengaged versus at rest engaged)
As long as the coil voltage is correct and the current rating for the coil is within the devices (Gardena controllers) coil driver rating then the relay will turn on and off what every is connected to the contacts. as long as the contacts are rated for a high enough current draw that can handle whatever device (water pump in this case) it is switching on and off then you are fine.
As for adding something to OpenHab to control I guess I am unclear on that part. Openhab will control the Gardena and manage the zone and watering times already. The Gardena need to be able to turn on and off the pump when those times are valid. A pump relay allows the Gardena to control the pump and Openhab controls the Gardena. Now if you have a alternate need to control the pump for a different application you could put the pump relay in Parrell with your smart outlet. but not if you are using your smart outlet to measure power consumption., Otherwise then it will still do same if outlet is on the pump runs or if relay is closed pump runs just fine. Or if smart outlet is on, and the Gardena controlled relay is open(disengaged) then the power from smart outlet’s internal relay will run the pump.
edit: There is one last thing that should be mentioned here the horsepower rating of the pump must also be considered. Relays have current ratings and motors have a horsepower rating that converts to a current draw. If the relay you use is not rated for the horsepower of the pump motor it will either fail and weld contacts together (underrated) or even possibly melt the relay housing and create a fire hazard so be sure what relay you use is sufficient for the horsepower of the pump motor.
This again is something if you are not familiar with you should consult an electrician as well.
Anyway, perhaps I am not fully understanding your requirements so I will leave it at that.

Thank you sir, I understand exactly what you mean and am confident I can do this. I’ve had some training in basic house/building electricity 25 years ago, but it has become quite rusty in the intervening years. Thanks for explaining the procedure.

From my understanding, the Gardena 4030 part owned by the OP does not have the Gardena Smart interface and thus can’t be controlled by OH, so the OP essentially looks for a different way of making it ‘smart’.

Aaww ok. I did not look the OP’s Gardena model up and just assumed he added an automation friendly sprinkler controller. Now I understand what he is back dooring a work around and trying to create a smart interface to let Openhab know the Gardena sprinkler is on and then turn on the pump using his existing smart outlet. Still a concern for the rating of whatever relay he actually uses for the pump motor must be considered. Everything else I guess is semi-automated kinda sorta… :upside_down_face:

if that is the case then he could also just get a standard doorbell transformer to power the sprinkler valves low voltage and this
https://www.amazon.com/Newgoal-Channel-Control-Compatible-Requires/dp/B0B978T5FT/ref=sr_1_9?crid=20BT3G7CTZTWZ&keywords=zigbee%2Brelay&qid=1694371750&sprefix=zigbee%2Brelay%2Caps%2C116&sr=8-9&th=1 to switch the valves off and on .via Openhab and a rule for his smart outlet and completely eliminate the Gardena and do it all through Openhab. and to go one step further use something like one of these to read rain delay sensor by using the switch part as on his rain sensor and have the added bonus of a repeater for his zigbee out in the garage or where every he has his rain delay.
I mean if you are going to create a homemade OpenHab controlled sprinkler system why not go for full Openhab control approach?
Oh, and BTW because the relay board I listed has SPDT NC relays on it you could still leave Gardena in place and have Gardena water or Openhab water the yard. :wink: