Talking about temperatures. The first thing I did after building my own sauna and before mounting proper speakers inside, was checking the temperatures at the targeted locations. Even when having very long sauna sessions the temperature right at the floor (where I placed the lights and speakers) was 40-50°C depending on air circulation level. Would I mount a bare PCB that is specified to 85°C in this area? Yes. Would I put a plastic box with a battery and an epaper display at the same location? Hmmm, there are many people who just put their bluetooth-boombox/Alexa into their sauna and mount LED-strips that are specified for 50°C right at the ceiling where it can be >90°C an at least it lasts some months. So maybe I would try it of there is no other option available.
Reading Shelly Plus H&T it says
|Ambient temperature:|0 °C to 40 °C / 32 °F to 105 °F|
|Humidity|30 % to 70 % RH|
So it does not seem to be capable of the temperature I need.
I will be keeping an eye on this thread then. The shelly survived the first run last night. Would really be interested to know if somewhere in the world there is a wifi/zigbee or simliar unit that survives a sauna.
So answer back from Shelly support. The unit I have Shelly H&T is NOT suitable for a sauna. The epaper display is the apparent weak point. Now looking for another option.
A couple of brief tips for anybody who’s looking to instrument a sauna or pool-room using a thermostat or humidity sensor:
Firstly, you should purchase devices which have (removable) external probes with a number of meters of lose cable. Unless stated otherwise the electronics end of the sensor should typically be installed outside of the hot/humid room with the sensor cable routed into the room and away from the exhaust or points where warm/humid air could leak from the room and condense. Only devices which are specifically marked and manufactured to be installed in hot and humid environments should be installed in such a location, this typically requires that the device be capable of operating at up to 125 degrees C. This is because the electronic devices will suffer from condensation over the thermal cycling of the sauna/pool room and the internal components will pretty rapidly corrode. Additionally batteries will suffer from reduced life from operating at elevated temperatures.
Secondly, thermal or humidity measurement sensors should be routed from the electronic device into the sauna/pool room through a well sealed hole and then mounted off the wall and sufficiently away from it so that they are somewhat ‘thermally distant’ from the external wall. A distance of about 3cm / 1" is probably sufficient. This will allow the device to respond quickly to any change in the environmental cycle and ensure that it does not become a destination for condensation. Condensation on the sensor may corrode the sensor over time, but condensation will also slightly affect the accuracy of the readings due to small amounts of energy released due to evaporation or condensation.
Lastly, if the sensors are powered by mains, you should ideally have galvanically isolated sensors, such as the Shelly Plus add-on. This prevents a situation where mains electricity is present on the sensor becoming harmful if the sensor is touched by a person.
The temperature of the sauna can be measured with a misappropriated cheap grill sensor.
I use thew one from Inkbird with 2 sensors: “Bluetooth Grill Thermometer IBT-2X”). The measuring device is connected to Home Assistant via Bluetooth and with the INKBIRD integration (see INKBIRD - Home Assistant)
Entities: “sensor.xbbq_0a30_temperature_probe_1” and “sensor.xbbq_0a30_temperature_probe_2”. I use an avarage sensor, built up in “helpers”.
Eckart, That sounds really interesting. Might flash out and get one of those for a trial. Do you happen to know a reliable humidity sensor in similar format suitable for a sauna?
Pat