Teardown of three STC-1000 style thermostats

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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#ElectronicsCreators

[TotallyNormal-]

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!

[AtomicShrimp]

Must be something in the ether. Yesterday I dug out a single relay version of this style of device that has been lurking in my 'future projects' box for years, with the intention to make something with it, then that evening, I saw this video. Strange alignments!

[noahsheehan]

I've been using STC-1000's for temperature control for my aquariums for years, with the oldest one being 6 years old. Simple, accurate, and cheap. The heat and cooling control is amazing. I have both heaters and chillers on my tanks and by using one controller, it eliminates the risk of having both the heaters and chiller on at the same time. Highly recommend them.

[gali]

I live in an RV (caravan) in Mesa, AZ where it can get to 120F (50C) in the summer. The back of the refrigerator is exposed to the outside and has a problem operating above 85F (30C) so I bought one of these to switch on a small fan at that temperature so that it blows on the refrigerator coils. This works pretty well up to an outside temperature of 105F (40C); after that, nothing will help and the temperature inside the refrigerator will go up to around 50F (10C). The refrigerator operates on 12v so I hooked it up to the 12v line coming into the back, and the device will work even when I'm on a trip and not connected to shore power. My project for this summer is to add a second fan that will blow cold air from inside the trailer into the area behind the refrigerator to increase the efficiency of the refrigerator on very hot days.

[SovTekBestTek]

I LOVE THE STC-1000! I have one I installed to control a deep freezer, and it has reliably served for at least 5 years now. Never an issue, perfect absolutely perfect little device.

[PaulLemars]

I came across these PID controllers when I was upgrading/modding my Gaggia Classic Pro espresso machine. The normal bimetallic controller would control the boiler approximately within 10 degrees which if you're obsessed with espresso is no beuno. You can set the temp precisely on them and these little buggers will keep the boiler within a degree. I've also seen them being shoehorned into Rancillio Silvia machines.

[Weissenschenkel]

Seems about right for controlling a fridge full of Lager beer during fermentation! Also love the pro tip regarding relay failure that can be mitigated with a bimetallic switch and a neon bulb + resistor as failure indicator placed across the switch. Neat!

Thanks for sharing!

[phils]

I've been using one of these for ten years! We use it to drive a heating pad, so our parrots are nice and comfy during our chilly winter nights, and it's been absolutely reliable. Mind you the load switched is only 25W (so 100mA) resistive. Easy to set up, and easy to get parts for (important for when "they" chew through the NTC probe cable!)

[marcussoininen]

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.

[SaberTail]

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.

[christ]

I use one of these as a "freeze guard" on our central AC unit. I threw it in while I was waiting on some R22 a few years back but after I fixed the issue and recharged the system, I ended up leaving it on just as a failsafe. If my suction line gets below 5C, it cuts off the condenser and just lets the inside fan run by itself. Just set the cooling temp to 6C and a 1C swing. It's wired to always be on and only the condenser control line is switched thru it. I set the compressor delay to 10 minutes so if it *does* start to freeze, it'll kill the compressor for 10 minutes to let the evaporator thaw. I know 5C isn't freezing but if the suction is that low, icing has already started on the evaporator on the first few loops after the expansion point and once the first few turns start to freeze, the rest will ice pretty quick.

Great video as always Clive!

[piconano]

My experience has shown these relays to be incredibly dangerous.
They arc weld easily. I bought one with exposed PCB that runs on 12V and only one relay, but after a few months it wouldn't turn on the heater.
I found a relay like it on Digikey, and replaced it with a real Omron for about $10.
3 Years so far an no worries.

[ohyou_]

I've had a 110v one in operation since 2016, It is used as a low temp cutoff for an array of server fans propped up in a window to cool off my room.
it has switched up to 5 amps of 12v for years, but usually it's ran on a lower voltage unless its quite hot.
they are great units for the price. at just $15 I've ended up with more of them now to just use as thermometers for various things. the relays are an added bonus at that point

[CountDrunkula]

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.

[AvgDan]

I used one of these to convert my dad's old analog electric smoker for his birthday. It made the smoker maintain a much more precise temperature. I got one that had a 30A relay built in.

[connclissmann]

I used 3 of these (mains voltage type) to control three (Beko) domestic full-sized chest freezers, in order to maintain them in the range -25 to -18 degrees C. This was required to maintain chemical thermal blocks within a known temperature range prior to use in pharma shipping of cold chain products. They (and the freezers plugged into them) worked flawlessly over 3 years, at which time we left that business. Great to see the innards and learn of their circuitry, as always. Like you suggested, I always kept two units as spares (given the low cost) but they were never needed. I would happily use again, should the need arise.

[TheGhungFu]

Love these things. I used one to make a sous vide machine out of our slow cooker. Must be a manual (not electronic) slow cooker.

[iconoclad]

I have two similar 240v units mounted in a box by my bed. I have one temp sensor in the bed at foot level under the electric blanket. I set this at 30c. The other unit is wired in series, measuring the room temp, set at 24c. The electric blanket is set on #3 ( full heat). All this is powered by a clock timer to run between 10:30 pm and 7:30 am April to September. I was so sick of waking up shivering at 3am or covered in sweat if it was a warm night. So now I have the Goldilocks setting and it is just great. Its has been running for nearly ten years. Plugged in last week for the on coming winter.

[adrian_foden]

I think a return visit is required Clive, the relays and their real-life current switching capacity and the loads they're capable of dealing with are where the rubber hits the road. A brief run through the comments here says there is a story to be told.



Jumping into some of the datasheets for them is.... interesting!

[uSlackr]

I've been fermenting with two of these for 5-7 years. Using 120V power source and running a small refrigerators directly on the load side.