honeywell termostato This is a topic that many people are looking for. bluevelvetrestaurant.com is a channel providing useful information about learning, life, digital marketing and online courses …. it will help you have an overview and solid multi-faceted knowledge . Today, bluevelvetrestaurant.com would like to introduce to you #022 Classic Honeywell Round Thermostat Teardown. Following along are instructions in the video below:
“I got my new thermostats yen. But i wanted to take a look at these these old honeywell round thermostats that they replaced because they re really really kind of these were introduced in 1953. They ve been around just forever. You can still buy them at home depot for twenty six twenty seven dollars.
The basic heat. Only model is i think a twenty seven f. The original was a the t or s. Rt t.
Eighty seven f. I think. The original was the t 87. So they ve been slight changes in the technology.
And there are now fancier ones that do heating and cooling and and so on. But this is the basic heat. Only model that s probably very close to the original one that was introduced visibly as well the design. Just really hasn t changed in you know sixty years more than sixty years and i can t think of many pieces of sort of home electronics.
If you consider this that that have been around for you know significant fractions of a century both technically and visually want changed so a really bit really successful bit of technology and also one that you know. It s iconic. This is the design that the nest thermostat is basically kind of alluding to this this classic round design. So i wanted to take a look at how it works so a diagram so a slightly simpler version and then we ll look at how the how this one works.
So imagine we have the two terminals here they re the red and the white and what we have across them is this component whoops. My pen is dying all right as we have this component and all this is only driver okay imagine this is all heavy this is the entire electrical circuit of the thermostat this component here is a mercury switch and it s actually a really good the schematic symbol for it is really good at explaining what it does because it s basically a glass capsule. The two leads poked into it and there s a ball of mercury here. And more recently this have been you know with environmental and health concerns about mercury this has been replaced.
I m sure with some other kind of liquid metal. But basically the same idea and all that happens is when you tilt this this way the ball of mercury runs down to this end and shorts out these two contacts. So the switch is closed. You rotate.
The other way the ball of mercury rolls away opens. The contacts and the switch is off so. That s basically how it works so this is essentially an on or off it s an angle sensing device. But it s only on or off it doesn t give you sort of proportional.
A feedback is just on or off based on the angle. So how do you convert a temperature..
Which is what we really want to measure temperature to an angle. Well that uses another interesting bit of technology called a bimetallic strip. And it s why it sounds like bimetallic to metals in the strip. And they re sort of laminated together welded were riveted or however it s done and as we know materials expanding interact as temperature changes but different materials do that at different rates so they have chosen two different metals with with as different rates.
You know reasonably different rates. And what happens in is one expands faster than the other let s say this one expands faster than this one in order to be longer than the other one has to curve the things around you know it wants to be longer than the other one so it causes a bend. It s a very slight effect. So to really have a good a good range of that in a very very very long strip well what they do instead is it created the wind this very very long strip in a spiral like this okay.
And this end is fixed and as it heats up this part wants the outside of this of the spiral wants to get longer so it it kind of unwinds and this end. Here the very far end of it will tilt away like this and as it cools down it ll tail back like this so. You might your mercury switch on here. And see which way you have to do it.
If you do it as it winds up right. So you want your your control. Like this. I guess so as it heats up this tilt away.
The mercury runs off of the contact and the heat shuts off as it cools down it lines back up this tilt. The mercury hits this turn the heat back on and there you go so that s sort of what s going on on here. And i ve got one of these already taken apart. Here you can actually see this there s two two bimetallic strips in this there s one that s here.
This is a springy looking thing with a mercury switch on it actually if you look the mercury switch. See if i can get that we can see it you see the blob metal in there. And it s a bit dull looking metal. I don t think.
It is real mercury would be shinier. I think so it probably is some other replacement metal. Now. But you see it runs back and forth.
So this is bimetallic strip and then there s a little teeny tiny one here that s that reads your current temperature. Actually if i see is you know kind of 65 ish. There if i just breathe in this gently alright see. It s gone up to almost 80 and it s coming back down as it contracts.
See that so that s all that s happening you can bring a temperature into an angle. And then so there will be some sort of balance point here..
Where you know some specific temperature. Where it has kind of the balance work between on and off. And there will be a little bit of hysteresis in there. Where you know the weight of this of the mercury ball went to this way the way to the of the mercury will be holding.
It kind of holding. It off a little bit longer. So you ll have to go extra far for it to the ball to roll and turn it on and then when the ball is weighting it this way it ll have to take a little you have to heat up more for the ball to finally tilt so it you know it s not an exact temperature sort of a there s a lower temperature where it ll turn on at a higher temperature. Where it will turn off.
But there s sort of some kind of balance temperature in the middle of that so that would give you a fixed. You know a fixed temperature thermostat. So to make it adjustable. All you sort of need to do is rotate this one way or another to bias.
It all right and that s a gear temperature adjustment and you might think that that turn that you would just have this attached to this dial directly and as you rotate the dial. It would rotate this mechanism. But actually if you look at here as i d rotate the dial clockwise. You see it s going the other direction so what they ve actually done there s a gear here so.
This is this is mounted on a funny looking sort of gear. Like this. This is mounted here and then the there s a smaller gear. Here that s that s turned by the dial and this just give you a wider range rather than having like a really narrow fiddly range.
It gives you this nice. It s about of a third of a rotation of the dial from one end to the other and that translates to you know a much smaller rotation of the of this component. So that s kind of the basic theory of it this design is actually a little bit more complicated because the problem with this if you just did it this way it would work. But the trouble is there would be so much an overshoot on this when you turn the heat on it s going to take quite a long time for the heat to make its way through the house and finally heat up the the coil to turn this off.
And then there would still be loads of hot water left in your radiators or whatever. And it would you would overshoot by quite a bit so they ve enhanced this with something called a heat anticipator and so what this is is let s see you ve got your switch. And these may be in a different order than i m drawing it but roughly the same idea and then this comes through a variable resistor through a heating element and i m sure how we draw the heating element. But and that goes to your terminal here so when this turns on it also is generating with me some heat here and this is heating this up the idea is that it s causing this to heat up anticipating the heat.
That s going to be coming from the furnace and turn itself off and you see here. There s this little adjustment. Thing here and this is adjusting the this is the the rheostat or variable resistor. That s here let me find a light okay so if you can see in there.
You see the green that s the winding of the rheostat around around so and then this this copper thing here. I believe is the heating element..
That s sitting on top of this this coil right here. So that is heating this up in advance of the heat coming from the furnace and sort of you know the longer it runs then the hotter it gets. But also it s sort of proportional to how long the furnace is running and so on and and then this back and forth lets you adjust for the how much of that effect you want you know if you really have it low resistance. Here.
Then there s going to be or as you just this. There s be more or less heat. So this would kick out you know faster or slower. And let s see right so.
And then you re supposed to adjust this based on a current measurement of the current that your furnace is sending through it you adjust this to the kind of match that and if you can see that there s a little label this as longer this way and so on. But so it s just slightly more complicated this sort of anticipation mechanism to make it anticipate and turn off turn itself off at the time when you know the residual heat in the system will continue to heat up the house and it will actually reach its desired temperature or keep it in that that range and then if you were to crank this entirely too far. The wrong way this heat up. Really fast.
Then your furnace would would shut off too early now this weak heat off heat up shut off the firmest furnace. Before really things had warmed up and then this would cool down. And it would have to take multiple steps to get up to the real temperature or perhaps. It wouldn t even get up there at all so that s the basic idea and i thought i ll show again.
So i got a lighter here. So i can show the turn all the way down. You can see the effect of heat on this bimetallic strip with it when i apply lighter to this bigger. One here that s going wrong right here see that rising up.
So that s the theory of operation for this thing really ingenious electromechanical is on very very simple very uh durable. These things will last last and last and last. I suppose eventually you may get arcing in here with the mercury switch that could over time. I mean that this would be the part.
I would expect would wear out or if you were constantly just think the temperature. I suppose you might wear out the gears or who knows. But really this just fundamentally not a lot to go wrong with us so. I m gonna keep at least one of these around as a backup for the eco b s you know there it s nice as they are they re extremely complicated devices.
They ve got wi fi and a microprocessor and display. And there s just so much more to go wrong. It d be good to have a backup. These mean.
There s a chance if you had one of the originals from 1953. There s a chance it still works i think there s almost no chance that might you ll be able to be working 60 years from now so that s the classic honeywell round thermostat..
Wonderful iconic design two of the things i wanted to add actually three the first being when you think of two other things to add to your video. It s nice and then the furnace comes on it s nice to be able to just turn it off from your phone. So that s a nice unanticipated feature of the ecobee. Although then the hot water was on as well so i still had to wait for it shut off.
But anyway. So the two things were first of all you may have noticed that when i was showing this they re actually three wires on the on the mercury switch here so that s i ve drawn it here as a as a single pole single throw switch. But actually it seems to be a. I m not exactly sure what the proper symbol for this is but hmm that s right let me try this again here.
I think. It s this. It s a single pole double throw switch in actuality. So i think.
It s something like this with the the idea being of this blob. You where it s out these two or these two. So. This is your common and this and one of them would be your heat.
And one of them you d be your your cool basically. And so it s only using these two the the third connection that would be you know so it s using the ones. That that clothe the clothes that could excuse me the contacts that close when it gets cold is what it s using this is this other pair that are common and the other one that clothes when it gets when it s heated up enough and the wire for that one just seems to go off to this here which matches up with this where there s no no contact or anything. So i think what they may be doing is they ve just they re able to use the same top unit with a different base that has a contact here for cooling.
And maybe the switches and so on so essentially what i ve drawn us is correct. Because they re not really using this the third contact at all the other thing. I wanted to mention is. I said in the one of the ecobee videos how nice it was that they gave you a little spirit level to help you a get it level on the wall.
Whether that was just for cosmetic purposes. Which is nice. But but as you can imagine with this arrangement. It s actually critical that you get it mounted level otherwise you are biasing your temperature.
And the temperature you set is going to be accurate for what it actually control so you do need to get it really level. So they don t give you a spirit level on this of course anyway. ” ..
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