I'm going to have a bit of a #tech#rant (less charitable people might say #whine) here. If you just want jokes and cute bunny pictures, feel free to skip this one.
Object of my #ire this week? #Furnaces. I'm not even going to rant about their main control boards; most of that's been said better than I could say it, by others with more knowledge than I.
How does it #sense the #speed the motor is turning at? The motor only has 3 terminals, and those go to the points between the three motor #windings. There isn't another #signal coming out of the motor to tell the #controller how fast it's actually turning.
Except...
Apparently, while driving those three motor windings, it is #simultaneously sensing the back-#EMF that the windings (which are essentially #electromagnetic#coils) produce from those same terminals.
The actual 3-phase motor is #simple - that's one of the reasons they're used in industry, simple means less to go #wrong. And it appears to be well-made, so there are #quality#bearings and #windings and everything in it. But the motor itself isn't expensive. Rheem probably doesn't pay more than USD 100 for that part of it, and maybe less.