How to wire an STC-1000 temperature controller

There are many questions that come up regularly in brewing groups and forums, “how do I wire up this STC-1000?” has to be right up there in terms of how often we see it, and this is despite, or perhaps because of, the vast number of posts or videos out there purporting to show you how to do this. I believe part of the problem is not that people find the instructions difficult, but rather that they just need a light bulb moment to understand how the electrics of these controllers work, and then the wiring process makes much more sense. If you understand electronics, then the chances are that the circuit diagram on the controller makes sense to you straight away, however if you have not needed to understand these diagrams before, it is easy to see why people can have trouble wiring them up properly.

Before we go any further, remember that we are dealing with electricity here, so if you have the slightest doubt that you can do this safely, then make sure you get an electrician or a competent friend to do this for you as you do not want to be playing with unsafe electrical equipment. All stages of the assembly and wiring of the controller is done without connecting it to the wall socket and it is only once all connections have been made, tested and the controller and wires are all safely sealed in a case that you should connect it to the mains.

 

STC-1000 wiring digram
STC-1000 wiring digram.

The model shown here is one suitable for the UK. The diagram shows a 220 volt alternating current supply (220VAC) which is fine for 240 volts according to the manufacturers specifications, but they do several other models including ones for 110 volt AC and 12 volt DC, and both 10 AMP and 30 AMP versions, so make sure you get the right one. Don’t try to use a 220VAC 10AMP model to switch more than 2400 watts, (2.4KW) or you are going to have issues, including the possibility of it not switching off, or catching fire. If in doubt, get the 30 AMP model, where the fuse in your plug will blow before you overload the relay inside the controller.

This symbol is just a switch
This symbol is just a switch

Before I show you the wiring process, it is important that you understand exactly what happens with these controllers. Both the heating and cooling circuits in this controller are just switches. There is no link between the switch and the power, it is just like the light switch on your wall. If you connect a bulb to the two sides of the switch without any other wiring, it will not work. You take your power from the wall, battery or whatever source you are using to light your bulb, run it through the switch, out of the switch to the bulb, then from the bulb to the other connection on the wall, battery or where-ever you are getting your power from. It is exactly the same with these controllers.

 

How to wire up a light bulb with a switch
How to wire up a light bulb with a switch

Lets look at how we would wire up a light and light switch and then we can apply this to how we wire up a socket.

 

How to wire up a socket with the STC
How to wire up a socket with the STC1000 temperature controller

 

I am sure that now looks pretty simple to understand, and whilst this would work, we need to supply power to the STC itself and possibly to a cooling circuit, as well in which case, it would be a bit of a pain having to use 3 plugs for your controller, one to power the controller, one for heating and one for cooling, so we try to do everything with just one plug, and it is at this point the wiring seems to get very complex, but if you take it one step at a time, it is still very simple.

 

Terminal strips or connector blocks
Terminal strips or connector blocks

We are going to need to join several wires together if we want to power the finished controller from a single plug, and terminal strips, which are also known as connector blocks, are going to be your friend for doing that. Make sure you get a terminal block that is correctly rated for the system you are building. If you have a 10 amp STC you need to make sure you have at least 10 amp blocks, but 15 amp terminal strips are the most common so just go with those. Not all wires are created equal, so you will also need to ensure whatever cable you are using to wire the system up will handle the current you are going to be using. If you are going to run a heating circuit, you cannot just use the thin wire that you see on a desk lamp, you need the type of cable used on kettles and other high power devices, so when you are getting your cable, check it is rated to handle whatever wattage you intend to use on your element, or fridge if it is just used for cooling.

 

Before you run any wires, make sure to run them through a hole in whatever case you are going to use for your controller, or you will be rewiring it all over again in order to get it into a case. First step is to wire your connector block up. If we run some wire between terminals like this, it gets much easier to wire it to the STC and your heating / cooling circuits later. You need the wire coming from your plug into the terminal strip. Then a little loop of wire coming out of the block your plug is connected to and going into the next block. The aim is to have three blocks all connected with live wires, three with neutral and two with earth.

Connect your plug to a terminal strip and loop wires between terminals
Connect your plug to a terminal strip and loop wire between terminals

 

At this point you now have to connect 4 wires to the STC. Three live wires to the power supply (1), heating (5) and cooling (7) connectors and one neutral to the other power supply terminal (2) on the STC. Please double check the diagram on your controller to make sure the terminal numbers are the same, as it has been known for some cheaper copies of the genuine STC controller to use different terminal numbering..

Connect the terminal block to the STC
Connect the terminal block to the controller

 

Next we connect the heating circuit to your heater. It doesn’t matter if this is a little tube heater, a heat mat, pad, belt, lamp for a fermenting chamber, or an element for a HLT, the method is exactly the same. Just remember if you are using a powerful element, all the cable used in the system right from the wall plug to the element and back must be capable of handling the current for your element. There are 3 wires to connect here. The live goes to the empty heating terminal (6) on the controller. The neutral goes to one of the empty blue terminals on the terminal block and the earth, if your heating device has one, goes to the earth section on your terminal block.

 

Connect up your heating device
Connect up your heating device

Connecting up your cooling device is just a repeat of the last step, using the remaining empty connectors. Live goes to the empty cooling terminal (8), neutral to the remaining empty neutral block on your terminal strip and earth to the empty earth connector on the strip.

Connect the cooling circuit
Connect the cooling circuit

That is the wiring completed. The same technique can be used for most controllers. If they show you the same symbol for the heating or cooling connections, then what you are looking at is just a switch, so you need to supply it with power for it to do anything.

A completed STC controller
A completed STC controller

Your completed controller should end up looking something like this once it is mounted. In this case you are looking at the bottom of the controller instead of the top, so the wires appear to be the other way round from the diagram. .

 

Hope you found this step by step guide useful.

Sarah Written by:

Sarah is an experienced home brewer, a qualified BJCP beer judge, organiser of the Welsh National Homebrew Competition and sometimes Brewtuber under her home brewery name, Daft Cat Brewing

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