How to know if a relay is open or closed

[RikH]

Hi there,

I am building a DIY solar system including a 60 kWh battery. The battery is monitored by a Victron BMV-702. The BMV can be programmed to switch a relay at a certain state of charge (SoC). I want the Hubitat to now what the state of that relay is so I can switch things on or off. Now my question is, how do I get the state from the ralay to the Hubitat?

[andy-e]

My favourite way is to wire a leak sensor to the relay contacts. When the relay closes, leak detector says it’s very wet!

[Madcodger]

Is the controller activating a dry contact closure that does not have voltage? If so, then some window-door sensors can be used to sense that dry contact closure. Another option is a MIMO Lite device, which I use to detect dry contacts opening or closing, which then produces a z-wave alert. Very reliable device.

Depending on the voltage, I've also used a RIB (Relay-In-A-Box) device to detect an electric circuit opening or closing, with the RIB then turning that into a dry contact closure. I think there might be other solutions, but that's all I've personally tried. Good luck with the system!

[RikH]

Thanks Andy, I'll keep that as an option but since I don't have leak sensors laying around I'll give it a try with a contact sensor as @Madcodger suggests (thanks).

@Madcodger

If so, then some window-door sensors can be used to sense that dry contact closure.

No the relay doesn't have voltage. It's only switching. Now I have Aqara (zigbee) and Neocoolcam (z-wave) contactsensors that I can use. Has anyone done this before?

[SmartHomePrimer]

MANY times. No voltage is perfect. The Xiaomi Aqara and Mijia contact sensors work well. Neocoolcam are garbage in my personal opinion (queue the Z-Wave fans to attack my personal opinion). Xiaomi are fine if you are careful about the repeaters you use. Not all work with them and range isn't great unless it's a Xiaomi hub you attach them to and then sync back to HE via HomeKit/Homebridge automation (this is what I do).

If there is voltage on one of these project for the contacts or power you need to monitor, you simply put a regular relay on that device you're monitoring so that the voltage turning ON at the device engages the coil of the relay, thus closing the relay's dry (no-voltage) contacts, to where you have connected the door/motion sensor (at the reed switch).