Which Transformer for 220v to 24VAC for Heating Smart Thermostat


I have a 220V electric baseboard heating system which is controlled by a 24 VAC 2 wire thermostat (RH, W). There is a 220V to 24VAC relay in the circuit from the thermostat to the heating system.

I plan to replace the thermostat with a WiFi enabled smart thermostat so I can control it remotely. The Smart thermostat (Emerson Sensi) needs a C wire (return ?) so the thermostat can be powered.

My choices are 1. Use an external 110V to 24VAC adapter from an outlet to power the thermostat (connect to C and R terminals on the thermostat) 2. Replace the existing relay with a transformer that has a common wire and pull a 3 wire thermostat cable through the floor & wall.

I plan to do option 1 now as it's zero risk in the middle of winter and follow up with Option 2 in the summer. I'm not sure which transformer I need to get for the 3 wire (RH, W, C) application. Any ideas ?

Also, the current thermostat has a backlight feature operated by a button to light up the...

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Recently, I needed to create a mock HVAC system so that I could have a portable smart thermostat for various demos. I searched around but couldn't find any such thing. So, with some sleuthing and the help of my friend Bruce Eckel, I was able to build a simple system that powers a smart thermostat and simulates a heating system. This post will document how to do this in case anyone else ever needs such a thing.

Modern HVAC systems typically provide 24-volt AC power to thermostats, so the first thing you will need is a 120-VAC-(wall power)-to-24-VAC transformer. I used this one.

Then, you'll need something that can simulate a single-stage heating system. A smart thermostat uses 24-volt AC to flip on and off a relay (the electronic component that uses one power current to toggle another, usually stronger, current). I could have used an actual relay for this, but decided to go with something easier, a red LED light that runs on 24-volt AC.

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Back in the olden days, thermostats were simple on/off devices that didn’t need their own continuous power supply. Modern thermostats with Wi-Fi and backlit display, by contrast, need a steady supply of juice.

The C wire, or “common wire” enables the continuous flow of 24 VAC power to the thermostat.

Technically speaking, power flows from the R (red) wire, but not continuously (not on its own, anyway). To make it continuous requires a common wire to complete the circuit. When the circuit is complete, 24V energy will flow continuously.

If you’re considering purchasing a smart thermostat, you’re probably thinking of doing the installation yourself. After all, if you’re able to change a light switch or receptacle, you’re skilled enough to install a smart thermostat – assuming your system already has a C wire.

If your system has a C-wire, it might be in use or just tucked away behind your current thermostat.

If your system doesn’t have a C-wire,...

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Ok, I got some follow up questions for someone that knows about thermostats and ac systems.

I have a heat pump unit in my house. So I apparently have a reversing valve. On the current thermostat, there is an orange wire going into the "O" terminal. From what I can determine, this needs to be "energized" to activate the reversing valve for cooling mode. If it were connected to the "B" terminal that would mean it would have to be energized for heat mode.

Is this accurate?

I'm assuming by "energized" that means, I just need to activate a relay to pass the 24v red power line into the O terminal / orange wire, right?

Same for cooling yellow, heating white, and fan green? So, when the temperature gets high enough to need the AC, I would have to activate 3 relays and pass the 24v red lines power to the reversing valve, compressor, and fan at the same time. Is there any reason not to just have the reversing valve and compressor work off the same relay? I'm not...

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which can be determined by turning the equipment off and on, the

user is encouraged to try to correct the interference by one of more of

the following measures:

Reorient or relocate the receiving antenna

Increase the separation between the equipment and receiver

Connect the equipment into an outlet on a circuit different from

that to which the receiver is connected.

Consult the dealer or an experienced radio/TV contractor for help.

Warning: Changes or modifications not expressly approved

by ecobee Inc. could void the user's authority to operate

the equipment.

To satisfy FCC/IC RF exposure safety requirements, a separation

distance of 20 cm or more should be maintained between this

device and persons. To ensure compliance, operations at closer

than this distance are not allowed.





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In your browser go to http://mobicle.io/

Sign in using your Particle account credentials.

Once loaded you should see a list of your Particle Devices.

Select the module installed in your I2C shield connected to the temperature sensor mini module.

Here you will see two functions setTemp and setSwing. Set temperature allows you to enter the temperature you would like the room to be set at. Go ahead click on setTemp and enter the temperature you would like to room set to.

Click on setSwing and enter the degrees of variance you would like to allow in the room. Most thermostats set this to 1 degree so if your thermostat is set to 75 degrees on heat the thermostat will not click on until the temperature gets down to 74. Using setSwing you can set that variance to anything you would like. Enter your value and send that.

On this screen you can view the current room temperature, the HVAC set temperature, the swing variance, and the HVAC Mode(AC or...

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With the holiday season in full swing, I'm certain many of our readers will be receiving some awesome tech gifts from loved ones. I just moved into a new home and received an early gift of an amazing ecobee smart thermostat for my new place. Although in my last home the installation was as easy as swapping some wires from the old system to the new ecobee, my new home wasn't as kind to us. But with a bout of googling and posting to HVAC support forums, we persevered and are enjoying the features of a connected thermostat!

Here's how you can set up your ecobee thermostat if installation isn't exactly going smoothly.

How to install your ecobee thermostat

We've briefly detailed how to go about the installation before. If everything goes as expected, here are the steps in short form:

Power off the breakers for the HVAC system (heating, ventilation, and air conditioning).

Remove the cover of the old thermostat.

Prior to unscrewing anything,...
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Nortek Security & Control LLC | Smart Thermostat - Wireless Thermostat

Model GC-TBZ48 is a battery powered Z-wave thermostat that connects to all Z-Wave hubs, including the 2GIG GC2 panel giving you control over your home’s comfort wherever you are. This model is designed to be incredibly easy to install and includes a front loading battery compartment to hold 4 "AA" batteries to power the thermostat for two full years, or it can be powered by the HVAC systems 24 VAC "C" wire. The 7 character scrolling display makes programming simple.
The GC-TBZ48 works with most contemporary Central HVAC systems, whether standard or heat pump, which makes this thermostat a great solution for all retrofit or new construction needs.
• Battery powered design runs on 4 "AA" batteries
• Extremely long 2 year battery life
• Can be powered by 24 VAC "C" wire from HVAC system
• Z-Wave compatible - Ver. 4.5.5
• Supports Z-Wave FLiRS...

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