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This is better! There's a reason traditional core 'n' coil transformers are used in stuff like this. Using an old fashioned transformer gives better electrical separation and gets rid of the stressed out low-ESR capacitors.
I didn't originally intent to go quite so deep with the schematic in this, but it turned out to be quite interesting inside. Note the custom badged relays, which I would guess are of a better quality than the Chongle clone ones. The thermistor is the classic 10K type (10,000 ohms at 25C), but injection moulded in a plastic case like some of the industrial ones I recall from my Hussmann days.
This unit is notable for offering a choice of celcius or farenheit display, but changing that option will reset all the existing settings.
The allowance of circuitry positions for an RS485 network is intriguing. Especially as the address setting facility is already in the programming menu. I'll guess it's for remote monitoring of multiple cases. There are three pads for a connector, but only the RS485 data lines are connected. For the screen/reference the thermistors 0V connection would have to be used. So this may be a work in progress.
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I've already taken a look at some of the cheap generic thermostats on ebay. I thought i'd find one that i think may be the one that many of these were cloned off, because certainly it used to have the same sort of button there. I don't know if i don't know what the original one is, but this does seem to be a more up-market one and just taking a look in the back does suggest it really is a bit up market. So it's made by elitech leader of asia, market stc-1000x and it more or less has the same function.

So, let's zoom up in this and then i'll brighten the display up a bit like this. So we can see it better things notable about this one. You can use the up arrow to see the set temperature and the downward to see the differential temperature and i'll explain those in a moment, but before you can use any of these buttons, including the power button. If i press the power button down, you'll see a little uh, the little padlock symbol, flashes uh, you have to unlock things by holding this button until that little padlock disappears.

Then, when you press things like the power button uh after a time delay, it will turn the power off, but it will also display the little power symbol to show isn't a standby mode. You can either press and hold the power button again to turn on again. This is just so, you can turn a case off electronically, not actually completely, but if you kill the power as i'm doing at the moment, it does just like the other ones. It does reset does a redisplay test first and then it displays.

Presumably that's version. 1.2. I'm not sure why it's like an upside down a so i'll show you how to set this. So at the moment, as it's powered up, the padlock mode is off for some reason.

Oh it's just going on right hold on. I shall press the padlock and show you the functionality if you press the up button, there's a set temperature if you press the down button, but you have to wait for it to revert back down button. There's a differential temperature i'll explain that in a moment, if you want to change any settings, you have to press and hold the lock button again. It goes to f1 and then you can step up between f1 to f6 so f1.

If i press this is the temperature you want to set, if i press the power button to get back from that, and then i go up to f2 and press the maintenance button, the adjustment button, it displays the differential temperature. What this means is around that 20 degrees celsius. If you set the differential to three, it means that the thermostat won't kick the heater unless until it drops three degrees below at your set temperature of 20 degree in this case and uh in the case of the refrigeration mode, it won't actually activate the refrigeration. Until it's three degrees above that it's called the hysteresis, it just gives an allowance, it stops its cycling too much.

The next mode, f3 is the. Let me just think is the time delay for the compressor. Is it? Let me just grab the instructions here and give myself a quick refresher compressor start delay, so you can set that between uh zero minutes and uh 10 minutes. Typically, it would be set to say three so i'll store that what that means is that, when the compressor, when it's calling for the compressor, it won't start immediately, it starts little timer and the refrigeration symbol of flash for that time before it starts this stops uh.

The compressor, if it's cycled too frequently starting under load and tripping out the next mode f4, is the temperature calibration. You can nudge it up and down uh to supposing the uh you put a accurate calibrated, thermo thermostat in with the uh, the probe. That's in the unit, and you find a slight variation - you can fine tune it so that this display will be accurate just by nudging, the difference on, because it will vary between different thermistors 10k thermistors. Instead, that means around about 25 degrees celsius.

They'll have a resistance of 10 000 ohms. Uh f5 is uh unusual for this one. You can toggle it between one and zero if you toggle it to one, it's fahrenheit. If you talk toggle it to zero, it's celsius, that's quite a nice feature.

I shall save that and the final one is reserved. It says this is interesting. It lets you choose an address as if these are possibly on an address network default is one that says it's reserved, but it lets you choose one of 127 addresses, presumably a networking system, which should be quite useful. Let's store that, it's interesting to note that it does say to store the setting once you've adjusted it.

You have to press the power button to actually do that. So, let's go back out of this now and i shall show you it kind of operating. Let's see if i can go out of it, i've not tried this bit yet or i could just leave it for a long enough time that it will actually back out itself right. Tell you what i'll pause while it does that one moment please, the lock has kicked back in so to demonstrate this.

It's currently showing the little heat symbol like a little sunburst um, because it's below the 20 degrees celsius. If i heat the thermistor up, the temperature will rise until it cuts the heater off at 20.. So it's approaching that now it's cut it off, but as it goes beyond that, if it gets too high when it gets to 23 you'll see well, in this case the uh the heater came on, the compressor came on immediately. It didn't use that time delay.

That's odd did i set that to zero or something or was it just because that time has already expired, but likewise now, once it comes on at that 23 degrees degrees celsius, that's your set temperature plus the differential. Once it comes down below that, it will then sort of cut back off okay. So let's take it to bits, so i shall zoom back out again. I shall adjust the exposure, so it's non glary and i shall turn the power off.

This is a 204 volt one. Well, it's a 220 volt one. It's not getting smoking hot on 240.. First thing i know, is that there's no cover over the back, like some other ones, do uh it's direct connection to terminals.

You can put the screwdriver through these plastic holes here into the terminals um. I don't need to take the wires out of this. I will take the wires out. It's rising clamp terminals.

That instantly wins it points. That means it's a better quality terminal that is better suited to technical use, because the cheap nasty terminals that just crush a little metal leaf down under the screw are not very good these ones, as you actually undo the screw. The cage physically opens up that grips. The wires nice and tight the other terminals uh one niggle i've got here.

Actually this is live, this is neutral and then there's the thermistor right next to them, see what the spacing's like in the back. But at least they've put it next to the neutral connection, which should be at roughly earth potential. These other two are just the relay contacts for the um. This one is for the heating, and this one is for the cooling, so this could possibly be heater, and this one could either be a fan or it could be a compressor, okay, usual approach here.

I think that if you have these little side catches that when you actually put it into a panel uh, you slide these up and they lock it into place, but you press this and slide off to get it open. I wonder how easy this is going to be to get open. I shall find out in a moment i've not had it open. Yet i'm going to have to slit the label here, because uh, it's got one of those little sort of warranty-ish labels.

That just basically goes across here, presumably just stop you opening it easily. I think i'm gon na have to peel that off completely because there's little clips under there, the bastards, really they don't want us in here. Do they let's try leaving this off? Is it going to be one of those ones that, as soon as you leave her one off the other one pops back in it is that's extra annoying oh dude they're all clipping back in yeah? I think i prefer the other one for opening, but we'll see how we go on if it takes too long. I shall just uh pause momentarily while i try and get it off.

This is uh working out. Okay, so far, it's off these felt. Strangely, oh, it's big! Oh, it's a squishy rubber membrane behind the buttons the display is much more complex than this one. Oh look at that.

Oh things that it doesn't show, it's got a fan display. It's got the freezing. It's got. What looks like defrost.

It's got. The heating but actually looks more like a lighting symbol, it's got the lock. It's got a warning signal. It's got oggs auxiliary here.

It's got a network symbol, it's got a power symbol, it's got a little leaf. That's the eco symbol, probably spanner to show when it's uh in program mode. It's got the relative humidity display as well here option for uh humidistat and degrees celsius and fahrenheit. Okay, let's slide this out.

It's going to come out i'll push it from the back. It's coming out so first thing i notice here and it's a big thing is that the transformer is a split core transformer. Let's take a look at those terminals, they have anti-tracking slots and they have got a relative amount of space. There is that one of my beard hairs or is that someone else's beard, hair uh but they've - got that into tracking slots fairly narrow things.

So it's not a huge issue having the live and neutral. Next to this, the liver neutral are going directly to the transformer. It's probably got thermal fuse in it unless it's just got such a high impedance. It uh has that protection internal impedance protection against a short circuit in the secondary side.

I tell you what i showed it's quite cramped here, but i shall try and take a picture of what's down here and then we can explore it one moment please. I wasn't going to go too deep in this, but i did so. I've reverse engineered most of the circuitry and let's explore it. So we've got the transformer here, just a traditional uh transformer split, bobbin transformer, where we've got the mains voltage side on this side and it is completely isolated.

I wish modern transformers. I wish the switchboard once did this, but they always wind the windings top each other for greater efficiency or better magnetic coupling. But in the old days with these transformers, which are super reliable, we've got the primary side and we've got the secondary side and there is physical plastic between them so safe. That goes to redirect far big fat, smoothing capacitor.

The capacitor has to be quite high value. One thousand microfarad in this instance because uh it's dealing instead of dealing with like 20 or 30 000 hertz from a little switching supply. In this case it's just dealing with 100 or 120 hertz. So it needs to be a bit of a higher value for that ripple.

The upside of that is it's a bigger capacitor. It's much less stressed. This capacitor is probably not going to fail anytime soon: decoupling capacitor, another decoupling, capacitor a 5 volt regulator down here and then another 100 microfarad capacitor. Just for that 5 volt supply one two, three transistors one for the relays, one for each relay and one for this sounder and then this little thing looks like a transistor.

Here is a double diode package. It's the snubber network across these diodes to shunt that back emf spike on the back circuit board itself, which is just skewed up an angle. Here there is the processor in there four transistors. These are display driver transistors, which are used in conjunction with these resistors here, which are driving the segments and these switch the individual digits.

This circuitry over here is not implemented, but i know what it is. I reverse engineered it and it's. The serial network is in place in this, but they've not actually put it in this resistor down here 1k, and this capacitor down here are part of the divider network for the thermistor input the 10k thermistor. Let me bring in the schematic.

I shall tame this down. A little bit before i bring this in because otherwise it's going to be quite ferocious. I don't know if that came down much, i don't think it came down. No, it didn't really tame down much.

This is the wrong page. One moment pays: that's what i get for making a last-minute addition. Max 485 is the last minute edition. So here is your well 220 volt.

It says about 220 to 240 volt. There is a traditional transformer. The secondary, which is about 12 volts, is going into the direct fire and coming out and being smooth by that big fat. Uh 1000 mega fart capacitor 25 volt, the relay coils uh.

They might be 15 volts. Certainly, when they're powered the voltage, whatever it floats up to here, it drops down to 14 volts, and one of these is powered, which is the bit that matters uh. If it floats up too high, it puts a little bit of strain on the voltage regulator, but the main thing is the relay coils. I suppose the relay coils have the little back emf diode, which are both in a single three pin package.

There are transistors to switch those really coils, then there's the voltage regulator, with its decoupling capacitors puts out the five volts uh. There's the hundred microfarad smoothing capacitor there's the sounder, which is in the five volt rail and then a transistor to switch that, and then we go over to the next page, i've abbreviated this because it would be a very, very busy drawing. Otherwise, there are the display itself: it's not getting any soda pins on it, because it's just heat staked directly onto the circuit board, because this panel in the front is just a light guide. There are leds on the circuit board, which could either be basically a bare chip mounted in the board with a pad next to it like that with rebound wire across or is more likely in these cases, uh to be just a little surface.

Mount chip solder to both ends, but a really tiny one for each segment here the segments will probably be tapered in there coming up to us of narrower thing. Just so you know it's a light guide, basically, and it just has to cup over that led, but the led displays each of the four displays has its own pnp transistor, pulling up to the positive rail and then the microcontroller is driving via resistors. The negatives of the leds directly but they're actually about 12, because it's not just the digits, it's driving. It's also driving clusters of about four of these uh symbols.

Um, the relays they'll just be resistors, going out to the relays for the uh, the transistors for the relays. The buttons are all come to the positive rails, so just feeding straight down to the microcontroller. As far as i can see - and i expected the thermistor just to have a divider there's a 1k resistor and then going to out to the thermistor, i would i thought that was going to be from the 5 volt supply. But it looks as though it might be from the microcontroller.

Maybe it's got a regulated output there, but that has a decoupling capacitor across it to remove any transients just to give a stable feedback from the thermistor and then a resistor going back up to the microcontroller. To actually read it, that's the circuitry, i think, is in there it's all a bit cramped uh. I didn't want to start stripping this thing to bits because it would break it, and i quite like it the bit that's missing over this side. Uh is the network and we've got the two lines of the rs-485 network.

I presume some transients presses going down to the zero volt rail to protect the circuitry. A couple of resistors are going up to what looks like an max 485 rs485 receiver, uh, possibly bi-directional. So you can send a signal and it'll send the temperature back. That would kind of make sense, and that is then well.

The circuitry is not there. It will be heading over to the microcontroller. It's all fairly. It's all fairly logical, as these things are.

Ah damn. I wish it took as little time to explain the circuitry as it did to reverse engineer it, but it doesn't. But the upshot is it's uh very neat. I like this custom display with all its little graphics.

It is the even the seven segments they're curved. It's very stylish, it really is completely custom, as is the front panel, is looking a lot more stylish than the traditional ones, with its smoked bezel for a good contrast and these uh stylish chevron buttons very neat - so don't know the history of these. I don't know if the other one, if others are cloned off this or if this is just an upmarket version of a standard style of unit but uh. It definitely seems quite good.

I like that transformer that is a significant factor in reliability, but that's about it. So uh, yes, the ella tech stc 1000 x, it looks quite a smart unit. It looks nicely made inside electrical separation is good uh, there's proper they've beefed up the tracks and the circuit boards. It looks like the the relays are kind of custom made for for them for this application, and it's got loads of anti-track slots between these for electrical separation from all the circuitry, even uh, where, like when the oddity of the temperature sensor going in next to the Uh next to the mains, but it does of that separation and they have chosen the neutral to be there, which is more or less ground potential.

Normally but yeah. It looks a sensible design. Quite a smart, thermostat.

14 thoughts on “Inside a better quality elitech thermostat with schematic”
  1. Avataaar/Circle Created with python_avatars Keri Szafir says:

    Elitech-not-Keritech, haha 🙂
    Nicely designed electronics inside, and it's interesting to see their brand on relays as well.

    Personally I wouldn't waste GPIO lines on MCUs for segment on 7seg display, unless the controller had a whole whopping damn lot of them. When running out of lines, I'd go for a MCP23017 or similar GPIO expander.

  2. Avataaar/Circle Created with python_avatars Rayote says:

    Can anyone help me with a strange issue, I need to find one of these with a higher range, say from 60F-220F, and I didn't have, nore couldn't find any with a range above 99F. I can't just use an adjusted thermistor to trick it, because the Individual/friend/customer needs the display to be accurate. I had installed one of these as I had it on hand, after the thermal overload exploded due to poor maintenance in a big wood planer. and honestly we all agreed that it was janky at the time, and I could do this for free to get them by. but as the OEM part is non-available. a new one can only be bought if you replace the entire driveline, they are fine with just waiting for everything to cool off every 20 minutes rather than buying a whole new unit, I just wish I could get them going properly soon.

  3. Avataaar/Circle Created with python_avatars getyerspn says:

    I've used these in mimic panel's for external chillers in a factory and for mould coolers inside the factory…and they're good but the relays do fail ..I've modified quite a few of them to use external din rail mounted to relays so less technically aware techs can swap out the relays with no soldering.
    All that said they're really good value and they offer quite a range with many functions.
    The relays failing is the most common failure point on most makes not just elitech as they're often used to switch 24vdc to control external contactors in industrial settings .

  4. Avataaar/Circle Created with python_avatars Ted McFadden says:

    I would love an RS-485 version of this. I've been thinking about building a smarter climate control system, without resorting to the off-the-shelf "smart" devices. RS-485 means I can tie it into a sensor network, and make decisions based on the state of the whole house (as opposed to just where the thermostat is). It also means no Ethernet or Wifi networking overhead. Very nice. 👍️

  5. Avataaar/Circle Created with python_avatars OV3K1LL says:

    Hi BigClive, I’ve been watching your vids for a while and also watching a few paranormal programs like ghost adventures and paranormal lockdown and many others on YouTube. I always wondered what’s inside some of the tech they use like the Melmetre and rempod etc and what if anything they actually is measuring or detecting. This would could be a debunking paranormal devices playlist. Is that something that would interest a electrician or a magician? Any thought everyone?

    Thanks for the informative vids mate 🇬🇧✌🏻

  6. Avataaar/Circle Created with python_avatars Barry Davies says:

    Technical people? Clive seems to think He and the "Technical People" are something special… Define "Technical People" ?… I would advise Clive to not alienate the non Tech bods who make up the vast audience to this channel … Besides, History tells us that Techies usually go to the wall first in a conflict as too much knowledge is frowned upon …. Right Off You Go

  7. Avataaar/Circle Created with python_avatars tubastuff says:

    Clive, I'd like to see you do a teardown on one of the higher-end heat/cool thermostats made for home use. When the new heat pump was installed in my home, the installers looked at the old thermostat wiring and noted that the bundle had only 7 wires, where 8 were called for. "No problem" said they–and came up with a thermostat (color touchscreen LCD Honeywell) that needed a connection with only 2 wires. The base unit has lots of options, including net connectivity, and remote outdoor sensors. I imagine that the whole setup is rather complex, but it's done well for several years here.

  8. Avataaar/Circle Created with python_avatars Garage42 says:

    Most of these industrial type devices will have modbus and it uses rs485 which all have addressable functions which allow you to remotely monitor the operation. It doesn’t look this particular model has that installed though – probably why its marked as reserved under f6

  9. Avataaar/Circle Created with python_avatars dafeichu says:

    I got an Elitech STC-1000 Pro in 2020. It has two heat inputs instead of one heat and one cooling. I used it to heat up and spin two fans in a cabinet in my shop where I keep my glues and finishes and such. It worked for about 1.5 seasons but one of the inputs failed. I couldn't figure out what the problem was so I went to buy another one but the price had went up significantly so I got another brand. The new one wouldn't turn on but I was able to find the fault, B/O solder joint on the input.

  10. Avataaar/Circle Created with python_avatars Glenn Maughan says:

    Does anyone know of a temperature control that can compare two temperatures and do basic logic? Ie turn on an air transfer fan when the internal temp of a room is greater than say 23 degrees and switch it off when the inside temp and outside temp are equal rather than trying to run the fan forever if the outside temp is above 23 degrees.

  11. Avataaar/Circle Created with python_avatars RLFWE1 says:

    I've got an Elitech ATC1550 temperature controller that I have been using as a fermentation temp controller and to keep a freezer at fridge temperatures when I'm not fermenting. It's a similar controller form factor mounted in a nice plastic enclosure with a 13A plug socket on each side one for heating and one for cooling. Sadly the controller failed open and froze my stash of Italian prosciutto. I'd love to swap in a new elitech controller and squeeze in an SSR. I just don't think 10A onboard relays last long driving inductive stop-start freezer compressors. Anyone have a good non-fake seller recommendation for a 25A SSR?

  12. Avataaar/Circle Created with python_avatars Sparky Projects says:

    We used Elliwell controllers where i worked, this must have been about 20 years ago when we started.
    I notice RS are doing some similar controllers to yours with their branding
    It's nice to have the fancy corners, but you'd have to be accurate with cutting the hole

  13. Avataaar/Circle Created with python_avatars ElmerFuddGun says:

    It originally looked like it was a red back lit LCD (segmented) because of the lower contrast where you can actually see the unlit segments and because it has those custom symbols. You can also see fading at the ends of the segments that aren't getting as much light from the LEDs. Using a red diffuser (instead of grey) would have helped.

  14. Avataaar/Circle Created with python_avatars Peter Walker says:

    The compressor delay will start at the time of the last stop, not from when it commands a start. It;s meant for then something might want to cycle off then on again in short time.
    You could have a look at the Inkbird ITC-308-WIFI unit. It is designed for things like reptile enclosures, where you need to maintain a close temp tolerance, as it can control heating and cooling all in the one unit. There are 2 versions, one with WiFi and the other without. With the wifi version you do all the programing via an app on your smart phone.

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