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.
Modern "condensing" furnaces will commonly have a separate motor/blower for the exhaust flue, but I'm not talking about that one.
For decades, the furnace motor was a bog-standard #AC motor with two terminals. A #relay controlled by the furnace control system (in turn controlled by your thermostat) would turn the #power to the #motor off and on, and that was it.
Simple. Reliable. Simple AC motors can go for decades without a problem, especially if you oil them periodically.
Things didn't change much for a long time. They went from being driven by a #belt and #pulley to direct drive, because that's a little more #efficient, and there's no belt to have to inspect and replace (or worse, snap in the middle of winter).
But as houses became better-sealed and #insulated, a couple of things became issues.
(1) Because the furnace wasn't running as much - not as much cold #air#leaking in, and #heat leaking out through the walls - the air stratifies.
The #hot air rises to the ceiling, and the #cold air pools at floor level. Without all the drafts and leaks to stir the air up, this means that your #feet feel #freezing even if the room is nominally the right temperature.
(2) #Indoor#air#quality went down. No more fresh air coming in around every window and door and half a dozen other places in each room.
To help mitigate this, one solution is to keep the furnace fan #running all the time, not just when it's actually producing heat.
The trouble with this is that a traditional furnace AC motor uses quite a bit of #electricity. It's trying to push a large volume of air through a system of ducts and vents that are fairly restrictive, so it needs to be fairly #powerful.
So running it all the time uses a lot of #electricity.
The solution to that problem is to run the fan at a much lower speed when "off cycle" (not producing heat) - just enough to stir the air and keep it from stratifying.
Those simple, reliable AC motors generally only run at one speed. They have no easy way to run them "#high" and "#low" like this.
When I replaced the furnace in my previous house, the new one had what was fairly new furnace technology at the time - its blower motor was a #DC motor. I think it was a permanent-magnet brushless motor, though I can't swear to that.
Such #brushless motors are everywhere these days. Cheap computer fans use them; better cordless tools use them, etc.
The advantage is that they are easily speed-controlled. They have simple #electronics on board -- simple today, they would have been #miraculous in #1970 -- that allow you to run them at almost any speed between "stop" and "full speed". They also have an easy way to #sense how fast they're turning, so you can adjust the control signal until it matches the speed you want.
It worked great. #Motor runs at #low speed all the time, stirs the air, runs fast when delivering heat, saves money.
Of course, if my furnaces today used that design, I wouldn't be #ranting.
I have two #furnaces - at the time this home was built, it was the style here to put in two furnaces, one for the upstairs, and one for the main floor and basement. Kind of like a really #janky#zone system. I replaced both of them when I bought this #house.
Well, last #winter, the blower motor in one #died. It's kind of nice having two; the house was #chilly but #livable while I was getting it #fixed.
But that's when I learned about the new-new kind of motor that (at least my) furnaces use.
They call it an "#ECM" motor, but that is just an acronym for Electronically #Commutated Motor, which just means it doesn't have motor #brushes - just like a DC #brushless motor.
So what it actually is is two parts - the first is a very simple 3-phase AC motor. Which seemed bizarre when I figured it out, because #residential#electrical#service isn't 3-phase; only #industrial/#commercial customers need that. 3-phase motors are very common in industry.
The other part is, of course, the embedded electronics for the motor.
So the electronic module bolted to the back of this 3-phase motor contains what's called a "Variable Frequency Drive", or #VFD. That is a complicated setup with a bunch of very high-powered #transistors to turn 1-phase power into 3-phases for controlling and running the motor, along with a #CPU/#MPU to manage it, send different #waveforms to each of the 3 motor terminals to control its #speed, etc.
It also has to "talk" to the furnace control board. And there's another #puzzle.
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.
However, when you push a current through a conductor, it "pushes back" some, fighting the change to its magnetic state. This is normal; you sometimes have to account for it to prevent damage to the driving electronics. It's called "back-EMF".
From the timings of those back-EMF spikes, the #embedded#CPU can determine how fast the motor is turning. But even trickier is that by sensing the shape or magnitude of that back-EMF signal, it can determine how much #torque the motor is producing - and therefore how much air is actually moving.
This is useful; in an A/C setup, you want to know if air is actually moving past the #evaporator#coil, not just how fast the motor is turning, so you can detect the coil "#icing up".
I'm #impressed by what it accomplishes; it is quite the #feat, and not totally #obvious at first glance.
But it means that little control module is really quite #complicated, and is a dense little #blob of high-power circuitry. It would be expensive enough just for that.
Not by you or me, of course. Programmable by the furnace #manufacturer. They're actually made by a division of #GE, which brags in their sales literature aimed at industry that the customers only have to buy one #model of motor for a given power, and then they can #program it for all different kinds of applications. No need to stock thirty different 1/2 HP motors for different furnace types!
But the furnace companies take this #opportunity to basically #DRM the motor/furnace combo.
So of course each furnace line has a different (in my case) #Rheem#part#number for the motor, even though all of them are actually the same 1/2 HP GE motor and controller -- they've just had different #settings "blown" into them.
And if you try to use the "wrong" motor from another furnace, the control board says "no way!" and won't work.
So Rheem gets to keep #selling#parts that are #exclusive only to them, and only for one model of furnace, so they're stupidly #expensive.
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.
As you might have #guessed, the motor in my other furnace #failed last week.
I've removed it from the furnace and #tested it, and just like the first one, the motor itself checks out fine - no #electrical or #mechanical#problems at all.
The #electronics in it have failed. And only a few months after the other one. It's almost like they're #designed to #fail; otherwise, how could you make a ton of #money by #charging#monopoly prices for what is otherwise a #generic 1/2 HP motor?
My furnace guy had a hard time getting a #replacement from his #supplier last winter, so I cursed and paid a thousand bucks or so (plus labour) for the replacement.
I bought a replacement myself this time. I paid about $800 for it, but it's coming from the U.S., so FedEx will probably send me a bill for brokerage charges. But between the part price and doing the work myself, I should save about $500 this time.
But this "make a #generic#part#incompatible with all other similar parts by using #electronics that refuse to operate if the other end doesn't have the right matching settings blown into its software, so you can #charge ten times as much for it" should be #illegal.
#Apple is getting famous for this lately. You can replace parts in an Iphone or Ipad, but they won't work right because they're paired by serial numbers for no operational purpose whatsoever.
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