Comment by cyberax
2 days ago
Yet, it's common. They typically are drop-in replacements for classic mercury switch thermostats. Mercury is not available anymore (for a good reason), and gallium alloys wet almost everything.
Bare bi-metallic strips don't work as well because contacts tend to get oxidized and/or stuck. They are also a pain to calibrate.
A small microcontroller with a relay tends to be more reliable.
> A small microcontroller with a relay tends to be more reliable.
Until some bug surfaces that requires a reboot to -fix- work around, but since the device is powered by a battery (EDIT: still puzzling through what might happen when this battery runs out..) which isn't user serviceable and has no reset switch... The device I tore down this morning fits that description. I'll take my chances with a bit of calibration and some yearly maintenance. My vehicles all have grease points and maintenance schedules, I can handle also greasing my thermostat contacts ;)
That said, the regulators taking away the mercury switch isn't an excuse for the user hostility. They could have made a device that is less sketchy. Even if they actually did a great job and it's in fact much safer and more reliable than the analog device (in which case they should show data), I know I can open up the analog one and make it work. I can figure out how to keep it working. I can look at it and evaluate whether I trust it. I cannot do that with some proprietary blob on an MCU.
They are typically not powered by batteries. These thermostats either use the common wire or utilize the fan circuit to periodically charge a capacitor powering the MCU.
> I can look at it and evaluate whether I trust it. I cannot do that with some proprietary blob on an MCU.
Your air conditioner/heater likely has a controller. Probably several, at least for thermal protection and overcurrent.