I am looking for a solution for a specific situation.
I have a sewage pump in the basement that provide a 24V signal when something is wrong. The general alarm is not always audible, so I want to make this smart (at least receive a notification on my phone).
The problem is that I can’t connect a device in the vicinity of the pumps, I’ve only the 24v signal to work with (via a 15m long signal cable). At the location where I can connect the smart-device, I only have Wi-Fi (not Zigbee or Z-wave)
I think, for example, a Shelly 1 won’t work in this case:
I don’t think the device is made to handle a signal on the SW-port from a different circuit. Powering the device with a (separate) 24v adapter doesn’t matter, I think.
I was thinking of something like that too, but it feels redundant to control a relay with a relay. If the ‘simple 24V relay’ were smart, it would be all done.
But I’m not very familiar with the world of relays (except the standard smart ones, like the Shelly), and there are many types. I don’t know what to look out for or which ones can handle the pump’s 24V signal.
No, figure 2 shows how to power from 24V and to switch 230V, which is not what you want.
If you’re going to use two 24VDC power sources (a separate power supply and the signal wire from the pump), you probably need to connect GND from both power sources to make it work.
One last try : you need a device that is able to detect whether a signal is zero or 24 Volt, so no switch involved.
When you lower the 24 V to lower then 10, using resistors, you can use the analogue input port of the Fibaro Smart Implant, however that one is Z-Wave.
The issue isn’t so much the voltage, it’s that both devices need a common ground, otherwise you might run into reliability issues (and possibly also safety issues).
A voltage is a potential difference between two points, not an absolute value. The 24V from the pump is only relative to the pump’s GND, not Shelly’s (or rather, its power supply) GND. So unless you connect those two GND’s, the 24V signal from the pump may be at (say) 100V potential difference with Shelly’s GND.
From the wiring diagrams you can see that the grounds are connected, that is the minus of the pump is connected to the minus of the 5 VDC power supply, the common ground.
The Shelly Plus Uni supports 0-15 or 0-30V, the Fibaro 0-10V only.
Yes, that’s what it should look like eventually, and that’s what I’ve been trying to say: you need to connect the (DC!) GND from the pump to the GND of the power supply somewhere.
Also, with this Shelly device you can only hook up a 24V signal wire to the analog in, which isn’t ideal. You’d rather want to use a switch input that can handle that voltage (and the diagram suggests the two IN’s only support 5V).
@robertklep This schematic might work, but I still have my doubts about whether this is actually intended; you still end up with two 24V sources with a shared ground that are never exactly identical.
I had hoped there would be a simple smart device (with its own isolated power source) that could simply detect if there is power on the 24V signal wire (just like a red light comes on now).
I also submitted the question to Shelly themselves, and they indicate that it is only reliable by placing a ‘dumb’ relay (24V optocoupler) in between (parallel to the current lamp) and then a Shelly smart relay (various types possible). (just like @Bubiai_2 indicated)
The signal cable has 4 wires, two of which are currently being used (+ and - of the light). Maybe I can see if I can put 24V permanently on the other two (from the same source); then I can probably connect the Shelly 1 directly, without a (extra) relay.
That’s the point: by combining the GND’s, they become identical (don’t confuse “GND” with “protective earth”, those are two very different things in this case).
The whole issue here is: 24V in reference to what? Voltage is a relative unit, not an absolute one.
That would probably be the best solution, yes (although I assume you mean you’d put 24V on one wire, then GND/- on the other one).
An extra relay or optocoupler is only required if you want galvanic separation of the systems. Such requirements are common for example in case systems are connected to the human body, i.e medical systems.
When you connect the two minus poles of two power sources, they are the same. So I don’t see your problem.
Thanks again; this information is definitely helpful. I’m going to try something out soon and also take a good look at how the current alarm light works with 24V.
: you need a device that is able to detect whether a signal is zero or 24 Volt, so no switch involved.
