Hoping to control heat tape using a 240V smart switch (Enbrighten zwave, 40-amp) using timer control combined with a temperature sensor to turn on heat tape say between 15F and 35F. Most temperature sensors are only rated to 14F. The Zooz ZSE44 temperature sensor is rated down to 5F but not sure how well batteries will last throughout the winter. Any suggestions for this application?
As you’ve noted, almost all batterypowered sensors in the price range That work with smartthings won’t work much below freezing. It’s just physics.
What most people do for similar projects is use the weather report. In particular, they’ll turn on the smart plug if it starts snowing.
There was just a discussion of this a few days ago:
I believe @Paul_Oliver is using a temperature sensor outdoors, but I don’t know what brand and model.
I used 2 Tuya, Zigbee, Model TS0201, temperature and humidity sensors that use 2 AAA alkaline batteries out at camp last winter. My camp is in the northern USA. One sensor was on a covered porch, and one was inside an unheated cabin. Battery like was acceptable, but the indoor sensor was better, probably because the temperature fluctuations were less severe, so it reported less.
Lithium batteries would work better.
You also buy AAA battery eliminators that are powered by USB plugs.
I would avoid sensors that use coin batteries outdoors because I have found battery life to be poor in many cases. An exception are the Ring, Z-wave, contact sensors.
Keep in mind the my heat tape is self regulating and I use the smart plug to shut it off in warm weather to minimize the leakage current. There are no safety concerns in my case if it fails, just higher electric bills.
EDIT: I forgot that I have 2 of the above sensors installed in freezers (+6 to -8°F) using alkaline batteries. They work fine and battery life is very good. Keep in mind that temperatures don’t change a lot, so there is not a lot of reporting
We should add that there are some lithium ion batteries specifically designed for use in colder weather, typically down to around 0°F, which are popular for trail cameras and outdoor sensor use. But using these gets a little tricky because it’s likely that the battery report that you get in the smartthings app will be off somewhat (and if they are rechargeable’s, it can be off by a lot. So a lot of people will recharge those as soon as they get a report of around 40%.)
The following site is discussing the best batteries for trail cameras, but it lists three specific AA models, which can give you a good cold-weather performance. So that’s another option.
Also note that lithium batteries have different operating temperature ranges for “Charging“ and “discharging.“ When the sensor is in normal use, the battery is discharging.
In all the cases I am aware of, even rechargeable batteries designed to operate effectively when discharging in temperatures well below freezing need to be above freezing when they are being charged. Again, physics. So don’t get a rechargeable lithium ion battery because it’s rated to work well when discharging at well below freezing and then put it in a charger at those temperatures. You need to bring it back inside in order to charge it up.
Also, with the specialty rechargeable models expect to have to recharge them much more frequently when the temperature is below freezing then when it’s above.
So I don’t know if those will meet your requirements or not, but it offer some additional possibilities. I have a friend who has trail cameras on a big rural property in Minnesota, and they go out every two weeks and swap the batteries for fully charged ones. And it runs fine in pretty brutal temperatures all winter long. But obviously that’s quite a short run time between charging.
One of the most popular single use specialty models is the Energizer L 91 ultimate, which I believe is also the model that blink recommends for its outdoor cameras.
You should be able to find this model at target, Best Buy, Home Depot, etc., again it’s a very popular specialty model.
I have been using a couple of Sonoff ZNZB-02 in my fridge and freezer (currently at 5.4 °C and -22.3 °C, respectively) for a few months without any problems so far. I haven’t had to change the (non-rechargeable) batteries yet.
Appreciate all the commentary, especially so quickly. It seems that the best go-forward plan will be to steer away from batteries due to shortened life with really cold temperatures.
Two follow-up questions:
- The Weather Underground IFTTT seems promising but not familiar with this. Can a SmartThings hub be used to pull in WU data to control a z-wave switch? Does this require a subscription to get the WU data or are there other sources for weather data that are free?
- As an alternative, are there non-battery z-wave temperature sensors that I could plug in the garage and run outside to mount on the exterior of the house. This would allow better location-specific temperature measurement.
If you just use the Ifttt service, it has a free tier that includes the weather underground information. You can only set up a couple of rules that way, but it may be enough. They also have a paid tier, which let you do more. There’s a cloud to cloud integration between Ifttt and Smartthings. So you use the Ifttt weather service as the “if“ and the Z wave switch as the “that“ in a rule that you create in the Ifttt service. Ifttt sends the request to smartthings to turn on the switch when needed.
I’m not familiar with what’s available through the weather feature in the smartthings app and it does vary by location.
As far as using a mains powered device in the garage and then running something outside, some people do that. There are some devices that can attach a temperature probe. Shelly is popular for this because it’s a Wi-Fi device, so you get really good range. But there are also some Z wave devices that accept a probe.
The following recent thread lists a couple of options that are known to work with the 2023 smartthings architecture. I’m sure there are more, I just don’t know which specific ones. Hopefully other people will post with more suggestions.
Using the Weather Underground makes alot of sense for our application so appreciate your explanation.
However, now I am concerned about using the Enbrighten 240V smart switch. This is probably not the right forum but maybe there is knowledge out there in controlling heat tape with a smart switch. This smart switch is rated to 40A and we have an EPD 30A breaker so that looks good. But the startup amperage perhaps could exceed the 40A for milliseconds and not sure what would happen to a smart switch in that scenario. Are there any users that have controlled heat tape with a 240V smart switch. And apologies if I should hop on a different forum. Thanks!