Vera - Smarter Home Control Forum

General => Temperature Monitoring & HVAC Control => Topic started by: mikoz on May 08, 2018, 09:30:19 pm

Title: detect 24VAC with zwave
Post by: mikoz on May 08, 2018, 09:30:19 pm
Hi all,

I want to detect the presence of a 24VAC signal and trigger a zwave sensor.  In other words, when a 24VAC signal is present, I want to trip a zwave sensor. 
is such a thing available? 


My alternate plan is to just use a relay. 

thanks.
Title: Re: detect 24VAC with zwave
Post by: zedrally on May 08, 2018, 09:55:48 pm
Not directly to my knowledge.
A couple of work arounds.
Title: Re: detect 24VAC with zwave
Post by: mikoz on May 08, 2018, 10:02:39 pm
What about the fabrio universal sensor?
Title: Re: detect 24VAC with zwave
Post by: zedrally on May 08, 2018, 10:25:58 pm
Sorry about the sizing.
Never used a Universal sensor so I can't comment.
Title: Re: detect 24VAC with zwave
Post by: HSD99 on May 10, 2018, 10:02:22 am
The Nexia Doorbell Sensor would do this, but as I recall, no one has been able to set it up with Vera. I used a relay with a 24VAC coil and wired the relay contacts to the external contacts on an Ecolink door and window sensor.  The only issue with this method is the coil current of the relay. If your 24VAC source has limited current drive, the relay might load it down.

You could also use the http://www.onsemi.com/PowerSolutions/product.do?id=HCPL3700 if you don't mind doing a little soldering. The HCPL3700 was designed for sensing AC voltages in industrial systems.

Title: Re: detect 24VAC with zwave
Post by: Tillsy on May 10, 2018, 07:26:08 pm
The Aeotec Dry Contact Sensor (Gen5) would be your best bet I recon - it's specifically intended for exactly what you are doing.
Title: Re: detect 24VAC with zwave
Post by: HSD99 on May 10, 2018, 09:20:13 pm
The Aeotec Dry Contact Sensor (Gen5) would be your best bet I recon - it's specifically intended for exactly what you are doing.
Just to be clear, the Aeotec Dry Contact Sensor (Gen5) is not intended to have 24VAC connected to it's input terminals. It's a door and window sensor without the reed relay and magnet.
Title: Re: detect 24VAC with zwave
Post by: Tillsy on May 10, 2018, 10:29:36 pm
Yes sorry, just like a fridge isn't intended to have milk poured straight into it ;D

24V > RELAY > DRY CONTACT SENSOR > Z-WAVE PLUS > VERA > Sensor trigger

I'd be doing stuff like this, but as I already used a Z-Uno to control other devices I have lots of spare ports and thus hooked relays to that for my various inputs.
Title: Re: detect 24VAC with zwave
Post by: HSD99 on May 11, 2018, 12:00:47 am
I wanted to log doorbell presses. Ten minutes digging through the lab parts stock got me a 24VAC coil relay and a spare Ecolink door and window sensor. There was enough room in the doorbell enclosure to mount everything, and I had my doorbell integrated in less than an hour. Sometimes things work out!

I am baffled as to why nobody offers a  sensor for AC or DC from, for example, 9 to 40 volts. It's trivial to build an opto-isolated sensing circuit that can drive the input on the Z-Wave micro.
Title: Re: detect 24VAC with zwave
Post by: MarcusB on May 11, 2018, 03:19:19 am
The Fibaro rgbw controller does this. It has 4 12/24v outputs and four inputs. From memory the inputs are only 0-10v but thats easily fixed with two resistors acting as a voltage divider.
Vera can?t detect the inputs, but an input can be set at the unit to control one of the four outputs, so very can detect when an output goes high.
That way you can have four inputs.
Title: Re: detect 24VAC with zwave
Post by: HSD99 on May 11, 2018, 10:49:07 am
The Fibaro rgbw controller does this. It has 4 12/24v outputs and four inputs. From memory the inputs are only 0-10v but thats easily fixed with two resistors acting as a voltage divider.
Vera can?t detect the inputs, but an input can be set at the unit to control one of the four outputs, so very can detect when an output goes high.
That way you can have four inputs.
I would suggest some cautions with this approach. The Fibaro unit is designed for DC operation. An AC signal applied to the analog inputs will need to be rectified and clamped to insure that the voltage seen by the inputs is never more than the 10 VDC limit, and never goes negative with respect to the Fibaro device circuit common. Capacitive  filtering should also be used to smooth out the AC waveform in order to get a reliable ON or OFF indication. For sensing an external AC voltage, I would rather use a relay or opto-coupler to maintain isolation between the AC source (whatever it may be) and the Z-Wave sensor.
Title: Re: detect 24VAC with zwave
Post by: Tillsy on May 11, 2018, 08:31:01 pm
Totally agree - you're mixing AC and DC so I'd be completely isolating that.
Title: Re: detect 24VAC with zwave
Post by: zedrally on May 11, 2018, 09:15:54 pm
The OptoIsolator and a Door/Window sensor hack is probably more sensible.
Title: Re: detect 24VAC with zwave
Post by: kwieto on May 12, 2018, 04:27:56 pm
Yes sorry, just like a fridge isn't intended to have milk poured straight into it ;D
24V > RELAY > DRY CONTACT SENSOR > Z-WAVE PLUS > VERA > Sensor trigger

That might work but it might be also the case when the contact is so called "potential free" which in fact mean that you shouldn't apply any external voltage for the contact, just close/open the circuit.

This is the case for example for Fibaro binary sensor (FGBS). Its contacts are potential free and if you apply any external current to the sensor you may broke it. I don't know the specification of Aeotec Dry sensor, but here you may appear similar case. AC/DC problem, as mentioned above is another thing to take care.

I would use 24V relay or optoisolator in the installation, to separate sensor contacts from the current coming from measured device.
Title: Re: detect 24VAC with zwave
Post by: mikoz on May 14, 2018, 03:54:15 pm
Hi all,

I basically gave up and took another route.  I want to trigger an evaporative cooling pump for HVAC when certain conditions are met: the AC is running the compressor, the humidity is below a certain amount, temp above a certain amount, wind speed below a certain amount.  Originally I tried to use the Honeywell plugin to check the HVAC status, but this has proven to be completely unreliable,  it simply does not update properly and the API's means to determine if the compressor call is on is is simply if the set point is lower than actual temp. 

So what I did was use a Zwave switch that gets triggered by the environmental conditions and then I just used a 24VAC low-coil current relay fed by  themrostat wires that drive the contactor outside  to switch the output of the switch into the pump.  So, for the evaporative cooling pump to be on, it gets the environmental info from zwave which then issues an on/off to the Zwave switch and then the 120VAC from there goes into a relay triggered by the 24VAC from the outside unit. 

I actually like this better because it's a fail-safe... the pump won't go on if the compressor is off, and if Zwave gets messed up somehow, the pump will be gated by the compressor being on. 


Title: Re: detect 24VAC with zwave
Post by: MarcusB on May 15, 2018, 12:52:16 am
The Fibaro rgbw controller does this. It has 4 12/24v outputs and four inputs. From memory the inputs are only 0-10v but thats easily fixed with two resistors acting as a voltage divider.
Vera can?t detect the inputs, but an input can be set at the unit to control one of the four outputs, so very can detect when an output goes high.
That way you can have four inputs.
I would suggest some cautions with this approach. The Fibaro unit is designed for DC operation. An AC signal applied to the analog inputs will need to be rectified and clamped to insure that the voltage seen by the inputs is never more than the 10 VDC limit, and never goes negative with respect to the Fibaro device circuit common. Capacitive  filtering should also be used to smooth out the AC waveform in order to get a reliable ON or OFF indication. For sensing an external AC voltage, I would rather use a relay or opto-coupler to maintain isolation between the AC source (whatever it may be) and the Z-Wave sensor.

You're right and it's good that you pointed it out.  I kind of figured if someone knew how to make a resistive voltage divider then they would know that AC needs to be rectified before being fed into a DC sensor.  It's similar to people saying to use a relay to trigger a sensor, but not warning about supressing back EMF on electronic circuits.
Title: Re: detect 24VAC with zwave
Post by: HSD99 on May 15, 2018, 08:19:57 am
It's not always easy to determine the level of someone's expertise on a forum (this or others). I tend towards the cautious side.  :)