Smart thermostat for two wire Websto heater?

[Hydraulicjump]

There is a lot on this general issue embedded in earlier posts, but I thought I would reach out to see who might have the latest solution.

We have a Webasto Evo 55. It is controlled by a standard programmable 2-wire thermostat (basically on and off) powered by two AA batteries. Now that we have reliable wifi on the boat I would like to put in a smart thermostat, like a Nest, Ecobee, etc. But all of them require a C wire or something to power them. Some have the ability to wire in power to them from a 120v socket, but I am trying to avoid that.

Wondering if anyone has or has tried a fully self-contained, battery operated smart thermostat. Or is the power demand just too great to pull this off? And I am not interested in installing one of the boat monitoring systems. At least not at this point.

Thanks.

 

[Pete Meisinger]

I wouldn't worry about the power drain, it has to be minimal. I would be concerned about losing your information (pre sets, codes, etc) when you lose power. If the thing operates off a 110 outlet power will be interrupted often.

pete

 

[Hydraulicjump]

Thanks Pete. What I am searching for is a way to avoid wiring the thermostat into power and just rely on battery within the thermostat. The heater runs off the 12v system so that is not a concern. So far I haven't found the workaround I am looking for.



Jeff

 

[PennBruce]

The older Ecobee models will run on 12 volts. I have two of them installed in my motorhome. You can find them on eBay.

The model number is EBSMARTSI01. Here's a pic:



Here's a link to the owner's manual:

https://www.ecobee.com/wp-content/uploads/2014/05/EB-SmartSiUM-01-rev1_april3_general.pdf

Bruce

 

[Hydraulicjump]

Thanks Bruce. I called up the installation manual for this unit and it looks like it runs off of the power from the heat/ac unit. What I am looking for may not exist, actually. That is, a thermostat that does not rely on a connection to the equipment to power it, but instead relies on internal batteries to power it (much as my current thermostat on the boat does...it gets nothing from the Webasto). Am I missing something?

 

[PennBruce]

I assume you have a 12 volt house bank. If so, you don't need a thermostat that runs on internal batteries.

On the Ecobee:

The Y terminal is 12+ and would be connected with a fuse in the circuit to your 12 volt positive distribution buss. The C terminal is 12 - and would be wired to the battery ground buss.

I believe the W terminal is the heat control and would be wired to the corresponding wire on your Webasto. The other Webasto wire is probably a ground wire.

Thermostats are not powered by the equipment. Thermostats are wired to an external power source usually an AC transformer.

Bruce

 

[Hydraulicjump]

Thanks Bruce. That really helps. So at this point, it would make sense to fish two wires up to the controller. One from the house bank with a fuse (3 amp?) and the other back to the ground buss bar that has the house bank on it. Yes, the Webasto only has a power and ground wire.


Much appreciated!


Jeff

 

[PennBruce]

You will also need a wire from the thermostat to the Webasto.

Is a 3 amp fuse sufficient for the Webasto? If not, you will need a relay to switch the power on for the Webasto.

Something like this:



The thermostat would trigger the relay and the relay would turn on the power to the Webasto.

Bruce

.... bank with a fuse (3 amp?)Jeff

 

[Bmarler]

I haven’t found any of the Wi-Fi thermostats that keep the radio working when on battery power alone. I guess the logic being that your router will be down in a power outage, so why power the radio.
The 12 volt one is probably the best choice, especially if it has battery backup so it doesn’t lose your settings.

 

[marcs]

I haven't found anything I'm happy with (Ecobee may work fine, but not interested), so I'm about to try rigging something up myself:

https://www.shelly.cloud/en-us/products/product-overview/shelly-plus-1-ul
https://www.shelly.cloud/en-us/products/product-overview/1xadd-us

More details on the hardware:

https://kb.shelly.cloud/knowledge-base/shelly-plus-1

They can be powered off 12v and have a dry contact. The claimed specs are 12 VDC ±10% and Max switching current DC 10A, I'm not sure if they'll run into issues running off the house bank directly when charging as 12v + 10% is only 13.2 volts but I'm going to try it unless someone changes my mind. You may want an extra relay for reliability depending on your heater's load, I wouldn't trust the Shelly's at 10 amps, but my existing thermostat (Aube #TH135-01 on a Webasto 2010) is rated at 5 amps so I'll probably try it directly. Switching DC is notably harder than AC.

This is not a straightforward project and I don't expect it to be super reliable, I haven't done more than play with a Shelly device but reviews online are definition mixed. Regardless, these little devices are quite fun to play with if you are into that sort of thing. They are cheap enough to play with, run a webserver, support bluetooth, and have all sorts of interesting APIs and integration possibilities including Google Home, etc. This should all be configurable in the app without programming but I haven't gotten to that step yet.

My plan is to leave the existing thermostat in parallel as a backup / low temperature failsafe. Alternatively, you could use the existing one as an input on the Shelly for fancier control but I don't trust it enough for that.

 

[jgwinks]

The thermostat I had in the house ran on AA batteries and only two wires to the furnace. No AC or ability to run the fan without heat, the t-stat would do that but we didn't have those features. I don't remember the brand but I got it at Ace Hardware, about $30. If the two wires to the Webasto just turn it on and off, I bet one like that would work.

 

[Hydraulicjump]

Thanks. That is precisely the configuration that I have now and it works great. But my goal is to set up a smart thermostat I can control remotely so the cabin is nice and warm when she-who-must-be-kept-warm (“thermal princess”) arrives. We have been together for 46 years and I have lost count of the number of times I have heard some variant of “nothing in life is worth being cold for, and that includes you, dear”.

 

[Jeff F]

Do you leave heat on when away? A simple remote on/off seems trivial.