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How to use the classic STC-1000 clone thermostats, and a look at the circuitry inside them.
I think the original version of these units may be Elitech.
These modules are shockingly cheap for what is effectively an industrial control module. It's almost as if the software got out into the wild and everyone started cloning them in a common style of case.
As with all generic grey-import products you should only consider them for personal projects and prototypes. For professional or critical applications it's probably better to go with a higher profile unit for better construction standards and higher operational stability. That especially applies to where higher current loads are being switched. Although these claim to be able to switch compressors and heaters I would only recommend doing so via an external rugged high current relay. I'd also suggest a 12V DC system as the 12V relay coils are more rugged.
If you search on eBay for STC-1000 you'll find a lot of these at wildly different prices. Cost is not an indication of quality and what you get will be completely random - even when two are ordered from the same seller.
Here's a super compact guide to programming them.
The two main settings are temperature and differential (hysteresis), where the differential is the difference from the set temperature and is where the heating or cooling will kick in.
The compressor delay setting is to avoid rapid cycling of the compressor to prevent it stalling by starting under pressure.
The calibration function lets you tune the accuracy of the thermistor.
Press the up arrow briefly to check the main temperature setting.
Press the down arrow briefly to check the differential setting.
To change a setting press the "S" button for a few seconds to enter setting mode, and use the arrows to step up and down through functions F1 to F4.
To adjust the chosen setting press the "S" button briefly to display its current setting, and press and hold "S" while using the arrow keys to change the setting. If no button is pressed for a very ungenerous four seconds the unit will exit setting mode.
On some units the settings may not be stored unless the power button is pressed briefly while in setting mode.
F1 sets the required temperature. These units only operate in Celsius.
F2 sets the differential in degrees where the relays activate either side of the main setting.
F3 sets the compressor delay to between 0 and 10 minutes.
F4 lets you nudge the calibration of the thermistor to match a more accurate thermometer.
The temperature sensor is a very common 10K NTC thermistor. (10K ohms at 25C)
If the sensor is open or short circuit the unit displays EE.
Try to keep the sensor cable away from mains voltage wiring to avoid display instability.
To turn the unit on and off you can press and hold the power button, but this is NOT safe isolation/disconnection for working on wiring. It will self-reset to on with a power cycle.
To reset to factory default settings press and hold both arrow buttons simultaneously.
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Let's take a look at one of the most popular heating controllers or well heating and cooling controllers on ebay. It's a module called the stc 1000 and it's notable for having two relays one for the heater and one for either a fan or a compressor for cooling. The power supplies that can operate from our 12 volt, 24 volt or 110 to 220 volt, presumably encompassing 240 volt as well. I actually recommend not going for the mains voltage ones.

The circuitry inside is not usually that great. So i think it's going to be more reliable if you used an external power supply with it, although having said that they're so cheap, maybe just treat it as a disposable item. I also note that the relays in them they say 10 amp at 220, volts ac. I'm not sure i'd really trust me at that, because these are using these pokey little relays.

They tend to use i'd, only trust them for maybe about one or two amps at with a resistive load. I wouldn't trust them with an inductive load because it can cause contact, working and uh if you use a 12 volt one and then bring it out to 12 volt relays that is going to make things much more reliable. It depends how much money you want to spend depend depends how professional you want to be. Let's zoom down on this and i'll show you how to set various parameters in it.

So at the moment i wish i'd let this cool down a bit more to the point. It was it's on the borderline of actually bringing in the heating, because at the moment, if i press the up arrow, it shows the temperature it's set to. And if i press the down arrow, it shows the differential and i'll show you what those mean in a moment. At the moment, it's displaying 17.

The heater heating is not on, even though it's below 20 degrees celsius, because it's not reached that differential of 3 degrees. But as soon as this gets down to 17 degrees, then it will bring in the heater it's not going to do that soon. Is it i'm going to try i'm just going to hold the this in a pair of pliers to try and cool it down, because the pliers are fairly cool? I think this is going to be like watching paint dry. Oh there, it goes.

It's gone down below 17. That's the three degree differential between your base, temperature of 20 degrees celsius. Oh, it is just celsius. By the way i took a look through a display.

I couldn't see an f, so it is just celsius. Likewise, when you get up to the temperature that you're aiming at and i'll just heat this, which is in this degree in this case, it's 20 degrees as soon as you get there, it will cut out. But if it goes beyond that, if it gets too hot, it adds that three degree differential again in the positive direction, the higher direction and when it gets there, the cool led has started flashing. But there really hasn't come in.

That's because it's designed for driving compressors and you don't want to cycle compressors on and off too much so it started a time delay which i've set for one minute after one minute. The relay will click in. Let me show you how you set this, so i've already shown that you've got the up button to check the temperature you've got it set to you've, got the down button to check your differential above and below that temperature that the relays will kick in. If you press and hold s, it goes into the setting mode and there are only four settings.

This is good, so if we go to f1 and we display it by pressing s, we can then adjust it by holding the s down and using the up down buttons to adjust that temperature. So that's how you set the temperature that you're aiming for so let's set it to twenty one. I don't know why they give it in tenths. It just seems a waste of time really um the timer's timed out the uh.

The compressor started so going back into setting mode again because it comes out setting very quickly. If we then go into f2 f2 is the differential press, it it's displaying it's a three degrees differential and then you can adjust that up and down as desired by tenths of a degree again that that is the above the position above and below your base temperature. That stuff will kick in the next two settings: uh f, three and four. If i hold this to go into setting again and we go up to f3 and set it it's displaying one all you've got here are uh.

Well, i was going to say all you've got 10 options. This is the time that the compressor will hold off. So that's 10 minutes uh and it goes down to theoretically one minute, but some that's not documented. If you go down lower, if you go to zero, it just means there's no time delay.

The compressor would start immediately. The other setting is for compensating the thermistor because there's a bit of variation between thermistors. What you do is you put this unit into your uh application with the thermistor in a sensible position to get a good ambient temperature in there you put in a proper calibrated, therm, thermostat or temperature display, and you compare the two readings and if this is say A couple of degrees lower what you can do with this is you can go into the setting mode again, you can go into f4, which is currently displaying zero and then, by holding that down, you can then compensate for the accuracy of the thermistor. So, by leaving it at zero, it's just basically as it comes, but you can nudge it in either direction other functions that might be useful.

If you press and hold the power button, it turns the unit off, including all the relays, press and hold it again. It comes back on again it's useful to know that if you do press and hold it and turn it off, and then you kill power to the unit which i've done right now and then you power it back up again. It will turn back on by default, which is quite useful, so, let's take it apart now things worth noting because it uses pokey little relays in here as you'll see in a moment. Let me zoom out for this because i don't want to get too close.

I actually recommend backing it up if you've got a critical application, say: you're, heating, water or something like that, and if this crashed or if the relay welded shut, uh or if you're, using a solid state, relay to actually drive the final load and it failed short Circuit as they often do, it's really important to have an extra thermal cutout. This is a standard. Bimetallic switch readily available online and it's just simply it's at below the rated temperature it's uh closed, but when it gets above the rate temperature, it opens. If you want an extra safety feature, put a neon indicator with a built-in resistor across this and uh put it in the panel with little warning light again next to if it ever lights.

It means this is actually cut in it's unlikely in many instances unless you're using high loads, but it can happen um. But what happens when this opens and goes open circuits some of the current flows through the name and makes it light, and you could put a message on saying call the engineer now: let's open this so to mount into position in the panel you've got these little Grips aside and when you push them down it unlocks them, you take them off. You slide it through from the front of the panel, and then you slide these back on and uh when you actually slide them up. It kind of clicks into position and locks into position.

The back for wiring has these horrible little clips that you squeeze in and they come out to say horrible, because these little grips when you squeeze it, it cantilevers them and they only open a tiny little bit. It's actually you're not pushing the clip in as such you're actually leaving it, so it twists uh. I actually recommend just getting a file and just taking the edge off those a little bit it'll make them much easier to get off later on. There is also the option uh in some of these to put a screw in to actually lock it into position.

You'd have to be careful about that because uh, it doesn't seem drilled or anything for it, but the functionality has been put in there. This label is actually presumably doubling up as a warranty label we're going to have to break the warranty label. I'm going to slit this, i have slit it and then to get it off. We pop a screwdriver in here and we just lift this little flap at the side and the other side and then the whole lot just slides out.

What do we have? We've got a bridge right for some wire links. Oh, this is designed to take the if we take a closer look at this. It's designed to take the full main circuitry, including the switchboard power supply and the little switching chip um, but in this case they've just jumpered across that from the primary side to the secondary side. Um and they've got uh, probably the first level of smoothing capacitors.

That second and they've got a little regulator here, probably a 78l05, i'm going to guess: 78m05 medium sized one uh other things - i'm noticing here i'll take a picture of this later on just for a general reference. But i see a couple of transistors pull down resistors or series resistors, and then i see the protection data there's really not much to it. The thermistor, which comes in right in the middle of all that means circuitry. I wonder if that's going to be like another one uh, it seems to go up to this unit and if you look at this display, you can see the circuitry tucked underneath it it's very, very basic.

It's like one little microcontroller doing everything, including driving the display. Let's peel that display cover off, i just don't like those being left on, but they usually do that plastic film is put on during manufacture to stop all the resin flowing out the bottom. But it's you left on as a protective layer. It can look a bit shiny and glarish uh, oh, and this one actually has this.

One actually has a little microcontroller on the bottom and i'm going to guess that it also uses that, for a serial display driver for the um for the driving led display. There's not really much in them is there the relays have beefed up soda beefed up tracks. It's actually got the position for a changeover contact, but only in one of them. That's a bit strange um.

It also has other contact positions, maybe for two sensors, i'm not really sure it'll be a fairly universal design. Right. Tell you what let's take the mains voltage one apart so once again, we've got i'll try and keep these bits separate, just in case they're, not that standard. So once again, click down on this click down this uh.

We don't really need to take the back off. This one will just uh pop the little catch up like that pop the little catch up like that, and it should slide out how does it compare very similar, but with that, the transformer in that there's a little switch mode chip um? Some of these pads are populated and the switch mode circuitry is all around that temperature sensor with the pads in very close vicinity. That's a bit creepy! That's not good design. Another thing worth noting that when you root the thermistor cables, keep them away from mains cables.

They can pick up interference in the means and it causes instability of the display. So this one is not coming out easily. It's got little clips at the side that i shall poke in. There is once again it's got that film that i just like rip it off.

Don't think it really matters that much, but i'm going to do it anyway, because uh yeah, it's just got this c here. So it's not designed to have the option of firing out at all, and this one i don't know if this one is the same brand or not we'll find out. It looks very similar, but it came from a different supplier and it came in different packaging once again, i'm going to have to slit the label here, oh very badly, slit no blending. I really didn't slip that well not to worry.

It went all over the place. Clumsy i should just use brute force, then different er, but not that different. Is it a standard circuit board? Is it different companies at one capacitor missing the cheap, skates um, but more or less the same, although they've got more components down here and the circuit board, this one is the chips in the back. This one does not this one will have that thing.

The chips are just tucked under the display um. Let me shine a light down the side of this. Can i see anything yeah? I can just see one chip uh, the fact it's got. One chip suggest it's this little microcontroller, it's just in there um the other one probably doubles up with the microcontroller and display driver, but this one is just being cheap, which suggests it might run.

The display dimmer is the display going to look any worse for that hold on. Let me just uh slap the power supply onto these connections. Here, willy nilly display looks okay. I don't know what it's set for, because it's gone into.

Oh, it's set for 10 degrees celsius with a differential of three that is the default setting. I think so that's going into compressor mode, so that kind of suggests these are originally come out kind of set for refrigerator type applications right. Tell you what i'm going to take a picture of one of the circuit boards um and do a little bit of exploration, and i will then let you know what i find one moment. Please: okay, let's explore.

Let's start with the mains voltage version, so the supply comes in here and it goes straight to the redirect farm. Then a smoothing capacitor rated about 4.7 microfarad 400 volts. I think it is which is uh chang's in capacitor yeah about that it's hidden. There are four points in mcfar, 450 volt extra 5g death beams of this one that supply the positive then goes to the uh coil of the uh transformer the primary and the negative gets switched with this uh switching chip there's a little snubber network across it.

Just the usual setup, there's an auxiliary winding used on the transformer, and this is how they've actually done a double jump across this in the level dispersion, there's an auxiliary winding, which feeds via this diode to this capacitor and uh. That is also trickle charged at the beginning, through these two 1.5 mega mega mega ohm uh resistors, so about three mega ohm, which slowly charges capacitor up until it's ready. Once this reaches a certain voltage threshold, it starts this chip running and then the circuit powers itself. So, there's that little initial time delay before it starts uh, it's also if the capacitors fail at loss by the bit.

That makes it pulse on and off the display will flash, probably uh other things that happen in this uh. The feedback winding that also powers that chip is also used for a sense via a couple of resistors here, there's a little capacitor, probably for internal reference, uh, there's a sense, resistor uh, three ohms, but they've got a position for two as usual. It's fundamentally the standard. Uh switch or power supply.

The output goes via a single shot, key diode over to charge this capacitor up to uh, probably about 12 volts um for the relays and it'll power them directly. Then there's a 5 volt voltage regulator and its little 5 volt smoothing capacitor. The relays are switched by these two transistors and there's a back emf: protection diode across the coil of each to protect the transistor from the spike caused by the collapsing magnetic field in the coil. These are longer it's like sango, but it's longer because it's longer as opposed to sungl, that's like a clone.

That's a clone of a fairly standard relay! I'm not confident about these um. The sensor over here with its connections directly in the vicinity of direct reference to the mains, basically speaking within millimeter or so of the uh rectified, means it goes over to this little cluster of resistors over here, and the arrangement is 5 volts goes through the 10k Negative temperature coefficient temperature sensor and then it forms a potential divider with another 10k resistor, with a capacitor across it for filtering and then via 1k up to the microcontroller itself. That's uh repeated another unit. There is another.

There are more pads here because it's designed for multiple functions, i'm wondering if the two sensors here are maybe for an alternative unit where it's got heating, defrost, heating and refrigeration, and it's maybe got like cavity temperature and evaporator temperature or ear on ear off, not really Sure it looks a very universal unit. I think this thing over here may have been a buzzer, because it does mention an alarm sounder. If you disconnect the probe or if it's short-circuited or open-circuited, it will uh display error on the display double e. I think it is, and potentially it would have sound alarm, but the alarm would also sound if the temperature exceeded a ridiculous level, that's more or less it for the mains voltage one.

Let's take a look at the lower voltage, one with what look like better quality relays, they're bigger, not sure about the brand, why you can see all the component layout as if it was the other one, but instead of actually having the mains voltage circuitry, it's got The main the low voltage coming in it's going through the spread rectifier, and then it goes the because that would normally go to positive and negative and because the primary winding would normally have the positive and the feed, the bootstrap line would normally have negative they've. Just taken a link from those over to the other side, one of those then provides a negative. The other one goes through this diode, which is the same diode used on the mains voltage version. It's a shortcut diode and there's probably the same capacitor used.

They have left off the five oak pasture because they decided to leave that off for some reason, i'm not really sure why they did that. It seems a bit of an odd thing to do. Oddly they've got the same arrangement with the 1k resistor and sears with the base of each of these two transistors. That's switching the relays and they've got the same diodes, but they've got two sets of thermistor uh components here and two links the links just go nowhere.

It's like a really: they don't really know what they're doing in this case uh or that or it's almost as if this um version with the links. If the links are in, they can leave these transistors off and it's switched from the unit itself. It's very odd. I'm not really sure i've not seen one like that.

The other thermistor these these two resistors in this capacitor go to that unpopulated position. I wonder if they just put them in because they didn't know any better. It's very odd, but that's the main differences they've just left off the power supply and put two links across. I wouldn't use an ac transformer for this.

I would use a 12 volt dc supply and because, if you do use a 12 volt ac, it will end up a quite high voltage. It will be well, let's work it out. 12 volt ac would uh peak at 12 times 1.41. It would peak around about 17 volts and minus the diodes here and the short key.

It's not going to drop it down much. So it's going to potentially overvolt the coils a wee bit, make them last last time get hot, so i'd recommend running at 12vdc supply. That would also let you connect. Let me just grab something here in the case of this much more opulent and more expensive temperature controller.

What brand? What brand is this In the case of this one, it does use a little external transformer, a traditional one, to power the module, but for switching loads. It actually has a external relay and all the wires are just sort of like blobbed. In with hot melt glue. You can't really change the thermistor in this one, which is a bit disappointing, bigger thermistor arrangement, thicker cable, but it has a couple of cables that go into the transformer.

And then it's got these two spade connectors going to the relay and i'd recommend using a 12 volt relay and a 12 volt dc supply. With these things and a 12 volt module 12 volt all the way, it's a little bit more complex, wiring up, but it's going to last a lot longer, and that is about it not really much else to say not happy at the separation on the mains to The thermistor - i don't know, if that's a huge problem or not. It means that the thermistor cable. I mean it's not directly connected to the mains, but the vicinity of that could cause problems with humidity and tracking and stuff like that, i suppose really, although nothing should really be referenced to ground what the display is like the same displays throughout the other one yeah.

Very cloney very strange: it's just like copies of copies of copies, so there we have it. That's uh, the classic gon na, have to look at the front of this stc 1000 temperature controller that can both cool and heat. I mean there's a lot you're, getting a lot for your money um but, as i say just, i prefer i'd recommend against the mains voltage one and i'd recommend against switching high loads through these relays. I'd recommend if you've got a serious application, 12 volt and using these release to then switch the coil of a beefier chunkier really, and that means all the wearers move to the outer relay, and it means that it's a cheaper, easier fix.

Although having said that these are about 10 pounds each, so it's not that dramatic! It also avoids any awkwardness of these things burning up inside, as can sometimes happen. So there we go interesting. It was certainly well worth exploring inside, i'm always tempted to see. If i can find some that don't look the same just to see what variations there are, but i'll also be getting some other temperature modules just to see how they sort of variant in quality and uh and if, if they're, just rip-offs again but interesting stuff, really Interesting to look at.

14 thoughts on “Teardown of three stc-1000 style thermostats”
  1. Avataaar/Circle Created with python_avatars Space Cadet says:

    I have taken apart many coffee makers, and they rely on a thermal cut out switch that cycles the appliance on and off to warm your coffee pot all morning. That is a part that if it fails,1500 watts of power to the heating coil could start a fire.

  2. Avataaar/Circle Created with python_avatars Francis George says:

    I had one of each, mains and 12V, to prepare for the pandemic when it looked like we were all going to die. My brother and I were going to ride the fever to blast the virus with temperature probes sealed in to our armpits wired to 120decibel alarms in case they went over 39C, and so pop a paracetamol as an anti-pyretic. haha! In the end, as data came through, especially the French nicotine patch study, we keto dieted and smoked instead, and were barely affected when we got it.

  3. Avataaar/Circle Created with python_avatars Count Drunkula says:

    I've been using these with my fermentation fridge for years with an incandescent light bulb, and for controlling a freezer as a keg fridge. I also use Inkbird 308s but the non. WiFi version has occasional temperature transients that cause the fridge to kick in for a brief time occasionally (it's a known bug they know about) and its cali bration can shift. I find cheap stcs more reliable than 308s.

  4. Avataaar/Circle Created with python_avatars Canyon Racer says:

    My Goto are the REX -C100 with 40A SSR and heat sink. We have 30 anodizing tanks running 24/365 for a few years, with only 4 failures…….So cheap I can stock a few dozen back-ups… just in case the supply chain really goes to hell for a decade….and Much cheaper than my annual Starbucks habit😎

  5. Avataaar/Circle Created with python_avatars Ken Bakker says:

    At work we use similar controllers of European manufacture to control large cold storage rooms at 2'C. Since it is critical that the product being stored must never freeze, pairs of thermostats are used with the outputs wired in series, providing redundancy. These thermostats are also programmed to fail to the open (off) state if there is a sensor failure. Calibration is performed by placing the sensors into an insulated container full of crushed ice and distilled water and tuning them to 0.0'C.

  6. Avataaar/Circle Created with python_avatars PepperTaco says:

    I'm using a mains powered one to control an old under-counter fridge repurposed as "climate controlled" cabinet in my shed to store paint etc. Put a small heater element in the fridge as well to heat it in winter. So far it has been running for about a year. Just to be safe I put it in one of those extruded aluminium cases, outside the fridge.

    Would be fun to actually try to switch 10A with those relays, I bet it will grenade within a few cycles.

  7. Avataaar/Circle Created with python_avatars random flake says:

    yaaaaas i love these cheap lil bastards there great i use them for my sneks and there perfect edit also if you power off the unit after setting it it resets but if you hit the power button before it returns to operation it saves it also im not the only one who has to peel those displays ps ooooof 10 quid they go for 5 usually just gotta poke about a bit

  8. Avataaar/Circle Created with python_avatars Phonotical says:

    I've only seen square types, how strange! Be I teresting if you could use it in an oven and make it a little more efficient

    Would a relay in a vacuum still weld shut? Or perhaps between the two contacts a conductive rubber?

  9. Avataaar/Circle Created with python_avatars Luminous Fractal says:

    Nice, I've had one sitting there waiting to become an egg incubator control, but didn't exactly trust the mains connections on it…will be watching this one closely 👍 much better than panty cleaners lol

  10. Avataaar/Circle Created with python_avatars Marcus Soininen says:

    I've used one to cool a fermenting beer, to 18°C in a 21°C room, it ran an aquarium pump that sat in a cooler filled with ice water, replaced ice as needed. It worked well for that at least, ran for about a week.

  11. Avataaar/Circle Created with python_avatars says:

    Iv'e been using a 110v version to turn a chest freezer to epoxy storage (keeps it at below 50f) for many years. They work great and my first one lasted about 5 years and the current one is on year 7 right now. I sell the epoxy and it has to be stored somewhat cool

  12. Avataaar/Circle Created with python_avatars DC Allan says:

    I notice only the 1st one has any sort of isolation gaps milled into the pcb. Not sure if the others are for lower voltage use But I dont think anyone should trust running anything expensive with these. Especially if it was a paid job. Interesting bit of kit. 2x👍

  13. Avataaar/Circle Created with python_avatars Totally Normal says:

    Ah ha! I was looking for a low voltage thermostat with an adjustable differential to use with my pellet stove! Using a standard thermostat with a pellet stove results in it cycling on and off constantly-the typical thermostats usually have a 1 degree differential. The stoves take about 20 min to shutdown completely, and about 5-10 min to power up and start producing heat. For me, an 8-10 degree (F) differential is perfect! (As well as time delays) thanks for the video!

  14. Avataaar/Circle Created with python_avatars Hola! TailSaber says:

    These aren't the same units, but I learned not to trust the relays in these types of things after a PID controller running some simple resistive heating tape managed to fail after only a few months. The relay got stuck in some halfway-closed state and emitted a bunch of smoke. After that, I switched to having the relays in these switch a solid-state relay that would switch the real load. More expensive and less efficient due to the drop in the SSR, but never had problems after that.

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