Monitor a motorized damper being open or closed?

Hi everyone - I’d like to know what device I can add to SmartThings that will tell me when my dehumidifier opens or closes a motorized damper.

Quick background: When it wants fresh air it opens a motorized damper on a duct line, and then after a certain period of time closes the damper. There are two low voltage wires coming from the dehumidifier control board that connect to two wires on the motorized damper. I don’t know how it works, but I assume it puts voltage on the line or takes voltage off the line accordingly.

I would like to wire a smart device into these wires so that I can get notified (using IFTTT) whenever the the damper is opened and to alert me to things such as being opened too long, or too much time having passed without the dehumidifier opening the damper.

Two questions please:

  1. What smart device or devices would you recommend I use to be able to monitor this open/closed state. Note that I cannot do this with vibration or moving parts like the multi sensor since nothing is moving externally (the damper is inside the duct work).

  2. How would the smart device be wired in? Just leave the existing two wires connected as is, but also connect these wires to the smart device?

Thank you!

I would recommend using one of the contact sensors with external contact capabilities, such as Ecolink.

Here’s a thread on using them for creative uses:

You could find a way to set it up so that the wires are brought together to close the circuit when the damper moves one way, and separates to set it open when it moves the other.

Thanks Brian! I’ll reach out to them. Any other contact sensors with external contact capabilities besides the Ecolink - just so I have some different options to look at?

There are a few others: Schlage, Monoprice, Linear, GoControl (can be bought at Home Depot fairly cheap, especially if your local one has the GoControl kits on clearance for 50% off)

Thanks, I’ll check these out! Any thoughts on how the dehumidifier is signaling the motorized damper to open and close? Maybe something like sending 12v down the wire when the damper is open and then changing it to no voltage when the damper should be closed? And if that’s the case, then you are thinking I can just connect these two wires in series with the existing two wires from the dehumidifier (and the two wires they are connected to on the damper) to the external screws on the contacts - and the contact will consider the unit closed/opened as the voltage it gets changes?

I’m probably not the best person to ask for that type of thing, but that does sound like a solid way of maintaining it.

I can only think of one potential problem, but it’s unlikely to happen. If for some reason, the damper actually fails to open, but the circuit isn’t broken, the contact would report incorrectly.
Again, I don’t see it being something that is likely to happen as there would need to be something holding the damper closed to cause this.

The first thing you need to do is determine the exact strength and type of voltage on the device wires in all states.

You can’t just use contact sensors for any possible electrical connection. In the pressure mat example, the mat itself has no independent electrical power. It’s simply physically closing the circuit. In other community examples, the contact sensor is wired to another battery powered device of similar strength. In a few examples involving mains power, a transformer may be used, but it’s more common to use a networked relay designed for mains power instead of the battery-powered contact sensor.

(Note also that in most US jurisdictions it may be against code to put a battery operated device inside a wall or a switch box unless specifically rated for that purpose (which most are not). This again has to do with fire safety. This is another reason for using a relay if you’re just trying to add a radio for notification. )

The motorized damper is drawing its own power, presumably from the mains. Before you start connecting a battery-operated sensor to it, you need to be sure you’re not creating a fire hazard.

@Navat604 or one of the other electrical experts could probably say more.

I’m not an HVAC guy, but I’m willing to bet that damper is controlled by 24v. Only way I see is a relay inline with the damper and using the relays NO outputs for a contact sensor as above.

There might be ez off the shelf options, but not that I’m aware of.

Thank you Paul. You are 100% correct. I verified today that indeed that’s how it works. Specifically the motorized damper is normally closed. When it is sent 24V AC (over two wires from the power supply) the damper opens, and when power is removed the damper closes.

Originally I was just trying to detect when the damper was opened or not. However now the requirements have changed… Before I just wanted to monitor if it was open or closed. Now what I want to do is use a Z-Wave device that I can send a command to that will actually open the damper and keep it open, until it receives another command that tells it to close the damper. So essentially I need something to act as a switch for 24V AC is I guess what it comes down to?

Can you or someone please point me to a Z-Wave device that will do this? I was looking at MIMOlite but I couldn’t tell if that would work (not sure if that’s something it can even do, and their product info mentions something about max 16V). Even if so I’d like to consider some other devices as well. If there are not any devices that can do this, is there some way to do it in combination with a few devices like one to handle the Z-Wave signal and use a standard relay with it, or something like that?


Would this work for you?

In one of the answered questions at the bottom I see this:

Question: Does it work with the US frequency and 220 volts input and output? Thanks.
Answer: YES, it works with the US frequency 908.42MHZ and 220 v input and output.
No load standby power : 0.48W (230V) & 0.35W (120V)
90 ~240VAC
Input voltage : 24-60V DC ±10% (working in this voltage range will have no meter function)

There is a community device type for it over here:

Use a 110 - 24V transformer and any Zwave 110 receptacle to power it. That’s an EZ , seat of the pants idea.

Something like this:

Thanks. So if I’m following you - the idea here is to get a smart AC plug, and plug this transformer into it. The transformer puts out 24V AC and I’d connect that to my motorized damper. Then just by controlling AC power to the plug I am turning the voltage on/off. Got it. Yes that seems like it would work, tho that is a fairly “crude” solution.

Not that its a big deal, but there is already 24V AC available to feed the damper (tapped of the 24V AC output on the HVAC system. Plus ideally I’d like a little more “smarts” in the solution. Such as a switch that I could set a maximum “on” time, in case it never received an off signal - stuff like that.

I found this device GoControl Z-Wave Isolated Contact Fixture Module - FS20Z-1 . Spec sheet is here: . If I understand this correctly, it requires 120V AC (wired from wall) to run, but it interfaces with my existing 24 V AC feed. So although the input is 120v, it still only passes the 24V source on and off to the damper - by setting this up in the “dry” wiring shown in that PDF. Is my understanding correct?

Are there any other such dry contact relays that are like the GoControl, but offer a bit more smarts (like the auto-off feature I mentioned)? Thanks!

Thanks. If I’m understanding this, the PHILIO PAN04 would only work to pass 120V on to the thing being hooked up. In the case of a light that can work nicely. But in my case it needs to only pass 24V AC.

Sure- if you already have 24v available use any dry contact , there is the one mentioned and a few others out there. I know of none with smarts, that’s where the programming would need to come in to play.

In essence you are doing the same as one of those smart registers,

As far as smarts - you mean like a IFTTT rule that says if the switch has been in the closed state (or whatever state equals having power supplied to the damper) then close it? Easy enough.

As far as “if you alrady have 24v available use any dry contact” - can I use ANY dry contact? According to the wiring diagrams I was looking at for some of them they only showed a connection where the thing being controlled was expecting to get 110VAC and share the same power source as the smart switch/contact itself.

By definition a dry contact is just an open/closed switch - I’d carefully read the specs. or a wiring schismatic before I purchased any.

  • used a lot for garage door - Might look at some of them for ideas.

IFTTT or rule machine, you could probably add a tilt sensor as well to show position, you would need to mount it external to the duct, maybe on the arm if possible. If internal - changing the battery would be a PITA.

Thanks. Unfortunately there’s no way to put a tilt sensor on the damper. Its embedded in the duct line. There’s an electronic box that sits on the outside where the wires connect to to give it 24VAC but other than that everything else is internal. The place where I’d have to put the Z-Wave device is easy access to no problem getting to for battery changes.

Yes I noticed a LOT of these dry contacts are being talked about all over the net for garage doors (seemingly the most popular use case). But what I don’t get is this - what power is it relaying to the garage door? So the sensor is getting 120VAC in, but when it sends power to the garage system, what voltage is that? If its 24VAC also then indeed those would be good for my use case too.

A dry contact relay gets 120V power to power the z-wave radio and actuate the relay, but it controls whatever sort of power you wire into it.

120V Hot---------|Relay|
120V Neutral-----|Relay|
+12VDC-----------|Relay|------Switched +12V-----|Damper|

Thanks Paul! Is it the case that all dry contacts work like that - where you connect it to 120VAC and then there’s a place to insert the power supply of the equipment that your trying to control into it some how? I only saw the GoControl diagram which seemed to show this. All others I looked at made it look more like the equipment you are trying to control needs to share its same power feed (120VAC).

What are some of the most popular and we’ll behaved (in terms of working with SmartThings and IFTTT apps and community support/drivers) dry contacts that I should look at? The GoControl seems like it would work but there were complaints in the reviews about it not behaving well or not being recognized by the app etc, and also complaints about its wiring diagrams not being accurate. So I’d rather go with something well known to be the best and well behaved. Thanks!

I use this one on my hot water recirculating pump. It has never failed me.

A MIMOLite has dry contact relay on it as well, but it’s much more expensive.

Sharing or not sharing the 120V supply is the difference between a “relay” and a “dry-contact relay”. You need a dry-contact relay. If you use anything else, you’ll end up frying the damper’s motor.

Edit: One more thing… none of these relays will be able to monitor the true status of your damper. They can only tell you if the relay is energized or not (meaning, they can tell you if the damper has power… not if the damper has actually moved).

The installation manual is here:

The wiring diagram you want is the one for “dry contact wiring” (in the center of the first page at the top).