Can I control a contactor with a thermostat?

[hammlm]

Question for you guys regarding a thermostat and a 240V relay / contactor. I'm not sure whether to go here or into the Heating and A/C subforum.

Background:
I have a shed where I do woodworking. This winter I installed one of those little 5000W electric heaters with an integrated fan. It's hung on the ceiling. It has an integrated thermostatic control (a black knob/dial) and it does a great job warming up the space and keeping it a temperature where I can work, the glues can be effective, etc. I determined that the heater (size, output, placement, etc) works well in the shop. Presently, I turn it off at the breaker when I'm not using it.

The problem is that many times I want to work in the shop in the evenings, but I'd like to get right to work so if I could start the heat in the late afternoon remotely, then when I get home, I can get started. Additionally, being able to monitor the temperature in the shop would be a "bonus"


Approach:
Install a basic (non learning) wifi thermostat, connect that to a relay/contactor to switch the heater on/off, set heater on max heat (so that there are not two thermostatic controls in play simultaneously) and let the thermostat turn the entire unit on/off to control the temp.

Is there a fundamental problem with this approach?


Specifics:
My thought would be to install a transformer to provide 24VAC to the thermostat ( I think I'd use "C" and "R" on the stat), and then use the basic "heat" relay connection (I think this is generally "W") to control the relay which would be installed in-line on the supply wiring for the heater.

I'd like to keep the thermostat power separate from the AC power supply for the heater so that if I have the breaker for the Heater switched off, the thermostat continues to read the ambient temperature, and I can see the temp on my remote devices (via wifi, etc)


This seems too easy?

Anything in particular I should consider when selecting the relay (other than it's rating?). Any suggestions or examples?


Thank you in advance!

 

[n20junkie]

Yes, I have done that exact thing more than once. Even used that setup to open a hydronic zone and turn on the 110v fan on a modine unit. Make sure you get AC relays or they will buzz something aweful.

On electric heating element units, I switch the element line, and let the thermostatic fan switch stay active to post cool the element.

 

[Falcon67]

Or just buy a 240V 25A thermostat and control the line -

https://www.platt.com/platt-electri...imetal/Cadet/C612-25/product.aspx?zpid=326151

I'd be more likely to use the cheap t-stat and a relay.

 

[hammlm]

Thanks! Good thought on the element line comment. I'll have to check that out.

 

[Git]

Here is another option. This device plugs into a wall outlet and will turn whatever you have plugged into it off or on depending on the temps. You could then 'plug in' the control circuit for your contactor into it

https://www.amazon.com/gp/product/B000E7NYY8/?tag=atomicindus08-20

 

[Fixin'Stuff]

That's exactly how thermostats control 240 volt a/c compressors. The contactor that can switch both legs is less than $10: https://www.amazon.com/dp/B06X8Z255M/?tag=atomicindus08-20 Add your 24-volt transformer and wire up the contactor inside a box for safety and you should be good to go.

 

[Bert_]

I've used these before,Electric heat relay

One part and done, 22A relay good for 5KW. And connections for a 24v thermostat.

 

[jhelrey]

How about just a commercial timer? Assuming you never run late, etc. from work.

 

[Brian_WK]

I've used these before,Electric heat relay

One part and done, 22A relay good for 5KW. And connections for a 24v thermostat.

That will I'll power to the thermostat when the breaker is off.

OP - Your original plan is spot on. Now get to it winter is almost over.

Brian

 

[hammlm]

That will I'll power to the thermostat when the breaker is off.

OP - Your original plan is spot on. Now get to it winter is almost over.

Brian

Brian --- you are spot on. I figured the way I work, I might just actually be ready for the cool season in the Fall.

Thanks to all for the responses. Even though some of the suggestions don't take into account some of the constraints and things I want to do, they are a perfect example of why I love this place. Tons of information, always learning.

Thanks

 

[tapered-pin]

do you have an existing X10 controller in your house (for any home automation) ?

HERE is a remote (X10) control outlet rated for 20A @240v

X10 Basics (explained)

X10 WiFi Hub

it's not difficult to set up and i believe it will give you exactly what you are looking for.
you can even set up keychain remotes (like a garage door opener) in your shop to open/close the outlet on a whim.

you could turn it on with your phone when you leave the office and by the time you get home, the shop is at a comfortable temperature.


(how big is your shop? I've been looking at these heaters as well for my garage shop, but I think they might be overkill)

 

[matt_i]

I think your plan makes sense. I just put into google "definite purpose contactor 24vac coil 30A"

And came up with this

https://www.amazon.com/dp/B01HF9YKWM/?tag=atomicindus08-20

I have a similar heater and as I recall it draws 20A at full load (240vac). The 30A is slight overkill but its going to see a good bit of use so some extra ampacity on the contacts is a good idea.

 

[dwasifar]

At first glance I misread this as, "Can I control a contractor with a thermostat?"

 

[TheEquineFencer]

At first glance I misread this as, "Can I control a contractor with a thermostat?"

I thought that too...

 

[hammlm]

I do have some X10 Stuff. I was fully committed to x-10 in my last house (was a dealer for HAI in the 90's), and I got so frustrated with electronic ballasts sending stray signals all I really use it for any more is controlling window candles and interior christmas lights during the season. Even that is finicky.

So, I appreciate the insight and the x10 wifi controller is intriguing and interesting. But if this works, I'm thinking I'm going to put one of these same heaters in my garage using the same setup. With the honeywell wifi stats (which aren't the best by far), you can stack multiple stats up in the same app on your device, which seems convenient to me (already have honeywell stats in the house).

With regards to my shop, it is 12x20 and the little 5000 Watt heater does a good job, even down in single digits and teens. Of course it takes longer to get things warmed up (table saw, etc) at those low temps, but it does over the course of the day. It can take the early spring chill off the space in about 20 minutes and then runs infrequently. It's not insulated, but is pretty tight with the sheathing (has some reflective foil on it), plus siding, and I put plywood and caulked all seams on the inside after wiring, etc. So, not insulated but that (more or less) sealed airspace helps a great deal.

I only paid $80 for the heater, so I'm tickled with its performance thus far.

 

[hammlm]

If I could control a contractor with a thermostat, I wouldn't have to ever worry about working again!

 

[dwasifar]

If I could control a contractor with a thermostat, I wouldn't have to ever worry about working again!

That depends on how you read it. Are you using a thermostat to control a contractor, or are you controlling a contractor who has a thermostat?

On second thought, I guess it doesn't matter after all. Nevermind; carry on.

 

[mrVanagon]

I had the same idea a few months ago when I added a forced-air wall unit to my finished attic bedroom. I intended to use a belkin wemo light switch to control a relay to turn the heater on and off. Not as feature-rich as I'd like but seemed like it would work well but then I found this:

https://getmysa.com/

It's a new product but it's fairly cheap and does exactly what you discuss out of the box. I ordered one but it won't arrive till May. If it works as advertised, I'll get a second one for the garage. Plenty of time to get it set up before it's cold again.

 

[hammlm]

I had the same idea a few months ago when I added a forced-air wall unit to my finished attic bedroom. I intended to use a belkin wemo light switch to control a relay to turn the heater on and off. Not as feature-rich as I'd like but seemed like it would work well but then I found this:

https://getmysa.com/

It's a new product but it's fairly cheap and does exactly what you discuss out of the box. I ordered one but it won't arrive till May. If it works as advertised, I'll get a second one for the garage. Plenty of time to get it set up before it's cold again.

Very cool. The price is about the same, all-in. Thanks for sharing. Something to consider when I do the garage.

I like wiring stuff and making contraptions.

 

[tapered-pin]

With regards to my shop, it is 12x20 and the little 5000 Watt heater does a good job, even down in single digits and teens.
...
I only paid $80 for the heater, so I'm tickled with its performance thus far.

my shop is 11X24 so good to know it's working for you. I live near Atlanta, so I'm really only looking for something that will run about 2-3 mos a year..

 

[hammlm]

my shop is 11X24 so good to know it's working for you. I live near Atlanta, so I'm really only looking for something that will run about 2-3 mos a year..

I'd think it would be perfect. It doesn't throw a ton of heat, but our spaces area small and don't take much. And honestly, the thermostatic control on the unit (the black knob) works great. It's remote control and information / observation that is driving this project.

 

[hammlm]

Today I finally got around to doing this project. It was very easy, but since I struggled (a lot) to figure out what to do, and had little confidence, I thought I'd put this here so that hopefully I help someone else out in the future.

Links to what I used:

Heater $89 on sale
https://www.tractorsupply.com/tsc/product/comfort-zone-240v-ceiling-mount-heater

Transformer: Packard PF42440 $11.49 Prime
https://www.amazon.com/dp/B01HPJT7C0/ref=cm_sw_r_cp_ep_dp_nuDdCbP7XD3Y5

Contactor: Packard C240A $8.76 Prime
https://www.amazon.com/dp/B06X8Z255M/ref=cm_sw_r_cp_ep_dp_WvDdCb0F9SWK3

Enclosure: Hubbel Weigmann SC 060604RC ~$16
https://www.homedepot.com/p/WIEGMANN-NEMA-1-6X6X4-Screw-Cover-Wall-Mount-Carbon-Steel-SC060604RC/100584755
(I wouldn't use this box again. I'm not sure what I would use, but not this)

Stat: Honeywell wifi thermostat $69
https://www.amazon.com/dp/B00Y6M2OUC/?tag=atomicindus08-20
(you could use any thermostat you want)


So, I wired it up as shown in the diagram below. Sorry it's not the best schematic. I only used three stat wires. I did end up setting the thermostat to heat only mode, so it won't try to switch modes when it gets hot (if I had it on Auto).

I have the thermostatic knob on the heater set to the highest setting, so it won't be acting as a "dual" stat.

A few pics of the install. I still need to tidy up the thermostat cable.

One of the pics is proof of concept / testing, not the final install....

I hope this helps someone else.

It works great!!!! I can monitor the temp at any time, and turn the heat on and off remotely. I can start the heat up when I'm at work and have the shop toasty when I get home.....it's like nirvana.

 

[CoogarXR]

I don't know how I missed this thread, but I did something similar with my garage HVAC:

https://www.garagejournal.com/forum/showthread.php?t=372238

 

[hammlm]

I don't know how I missed this thread, but I did something similar with my garage HVAC:

https://www.garagejournal.com/forum/showthread.php?t=372238

Ok, so that’s the kind of enclosure I should have used!!! Maybe I’ll switch it up, because what I have now is kinda bad and definitely klunky. Thanks for sharing


Sent from my iPhone using The Garage Journal mobile app

 

[cadunkle]

Thanks for the posting this. I used your guide to put a wifi thermostat on my basement electric heat. I used Honeywell since I already have one in the house and garage.

I did not use a 120v circuit for the transformer, since it can be powered with the 240v circuit used to run the electric heat, no need for new wiring. The contactor I used had spade terminals so I just used those on the hot side of the contactor to power the transformer.

I used an 8"x8" Wiegmann box since you mentioned not being thrilled with the 6"x6" box. It's mounted high on a block wall in a basement closet and takes up about as much space as the previous two box setup which had a separate junction box and contactor enclosure. I attached the contactor and transformer to the backside of the box with self tappers, then cut the protruding tap portion off to allow flush mount to the wall. I mounted this high on the wall so actually gained useful space if I ever want to mount anything else there. In retrospect I could have used the same box you used, smaller working space for something I'll rarely touch is not a big deal.

I have a shed I plan to insulate and then heat with an electric heater when I'm working, and maintain temp above freezing when I'm not. I'll use a similar setup for that.

 

[nadogail]

IMHO, you can definitely control a contacter with a thermostat. I say this because a thermostat is a single pole switch that is in series with the coil winding of the contacter.

I have a similar heater that I am controlling with a spring wound timer. When heat is desired; turn the knob and the switch closes until the time runs out. If more heater run time is wanted, turn the knob again.

I used a 24 Volt wall wart, plug in power supply from a sprinkler timer and a definite purpose 40 Amp rated contacter I ordered from Automation Direct. The contacter is in a metal enclosure ordered from them also.

Dear wife does not have to remember to turn off the heat when she leaves the garage; the timer does it for her.

 

[dogdog]

Just go google up "isolation" relay or "echobee isolation relay" which is my fav article for reference. as far as 120/240... it doesn't matter... they sell 240 to 24Vac transformers as well as 240V rated relays/contractors with 24V working coil-... heck I even have a 3ph 200-480V configurable to 24Vac transformer somewhere from the ebay evil buys... means they exists...

https://support.ecobee.com/hc/en-us...ermostat-installation-with-an-isolation-relay

 

[Rp19]

I had the same idea a few months ago when I added a forced-air wall unit to my finished attic bedroom. I intended to use a belkin wemo light switch to control a relay to turn the heater on and off. Not as feature-rich as I'd like but seemed like it would work well but then I found this:

https://getmysa.com/

It's a new product but it's fairly cheap and does exactly what you discuss out of the box. I ordered one but it won't arrive till May. If it works as advertised, I'll get a second one for the garage. Plenty of time to get it set up before it's cold again.

I use Mysa for my baseboard heat. The ability to monitor usage and make simple changes is useful. It paid for itself within a few months. My energy usage dropped 60 percent in those heaters. It sounds like your pretty diligent about controlling things manually so you may not see the savings I did.

 

[alfredeneuman]

Some electric heaters run the fan after the thermostat is off to cool the case off enough to avoid overheating. Using a contactor to shut the power off would defeat this feature

 

[kylefitz]

Some electric heaters run the fan after the thermostat is off to cool the case off enough to avoid overheating. Using a contactor to shut the power off would defeat this feature

I have the same heater as the OP. The fan is controlled by a separate thermostat that’s non-adjustable. That allows the fan come on after the heating elements have warmed up and run while they’re cooling down.

From the factory, the knob thermostat on the side of the unit is wired in series with the heating elements, and independently from the fan. I plan on installing a contactor in place of that thermostat, in series with the heating elements, and using a wall-mounted thermostat to control the heater.

The wall-mounted thermostat can eventually be swapped out for a Smart thermostat in the future, and it actually has numbers so I can set the heat for a certain temperature versus trying to figure out what feels comfortable on the knob.

 

[nadogail]

I used a 24 volt "wall wart" supply that I " liberated" from a defunct irrigation controller and a mechanical 30 minute twist timer to warm the garage my wife putters in. In a worst case when she forgets to turn off the heat, it automatically shuts the heater down.

Transformer and timer were free from my junk box, the relay and enclosure came from Automation Direct.