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STC1000 & Maxi Cooler Project

STC1000 Build

The basic version of an STC1000 temperature controller build can be seen on the Equipment page but this project takes the concept a stage further, to provide complete heating and cooling control. The basic component still uses the STC1000 as a temperature switching device but adds some additional support for heating a HLT.

Project Objectives

1. Add a Relay to boost to 15A

Although the STC1000 is a great bit of kit, considering it's price, the built in switching relay can only support a 10A load. If you want to be able to use your temperature controller with an HLT kettle element, it will be on/exceed this limit. A 2400W element at 240V will draw 10A and may overheat the relay in the STC1000. This is easily rectified by adding a separate relay to the circuit, which will take the load away from the STC1000. There are two types of relay, SSR's and the good old mechanical ones. Using an SSR is only really necessary if you are using a PID Temperature Controller as this switches on/off very rapidly, which would burn out a mechanical relay. SSR's also get very hot and need ventilation / cooling via heat sinks & fans. The STC1000 is a simple switch, so we are safe to use the mechanical relays, which are cheap and easier to use.

Wiring a relay can be a bit confusing to start with, so the best way to get this clear in your head is to read up on how a relay actually works. The basic components within a mechanical relay are, an electro magnet and a high amp switch. From your existing switch you control the Electro Magnet, which just pulls the the high amp switch into the on position. On the magnet side, we need a Live and Neutral connection to activate the magnet and you connect this to the STC1000 switching. On the high amp switched side, we are just switching a Live connection.


I will be using a 15A miniature relay that I bought from Maplins, this will suit my purposes. If you read the forums you will see that some people have used 40A relays as they control multiple kettle elements. Remember that a standard UK mains socket / plug can only support a maximum of 13A, so going beyond this requires specific wiring. It is possible to use two mains sources but these cannot be on the same socket and should be on different circuits to avoid overload. If you are lucky enough to be able to tap into a 30A circuit or get an electrician to install one, then this problem can be overcome but will still require specific plugs (commando plugs / sockets are rated at 32A).


2. Support Heating & Cooling

The STC1000 has two separate circuits, one for heating and one for cooling. You cannot use a standard double socket in your build as these are usually wired as one and therefore cannot be controlled independently. To achieve separate control, we will need to use 2 single sockets so that we can wire them independently. I have chosen to use sockets without switches, as I want the STC1000 to decide when they are live and not have an opportunity for error by having a switch accidentally turned off.

3. Lights

This is complete overkill but looks great and is actually quite useful. Originally, I was going to label my power sockets as "Heat" and "Cool" but I also wanted to have a neon light, which indicated the socket was live. After lots of searching on the internet, I realised that sockets with a neon light built in but without a switch, were near impossible to find. After deciding to find some mains driven neon indicator/pilot lights, I also found that they do these in Red and Blue. This kills 2 birds with one stone as I will not need labels if I put the red neon above the heat socket and the blue neon above the cooling socket.


4. Connections

In order to pack the controller away after each use, I wanted to be able to detach all external cables. This is not an essential feature and does add quite a of bit extra cost but if you do not do this you will have cables wrapped around the controller box, which can become damaged. To achieve this I have decide to use Neutrik connectors as these are easy to use, lock in place and have no external connections exposed when disconnected.

For the Power in connection, I will be using a PowerCON Socket and Plug. These are rated at 20A, which is way above the 13A max that I need but the plugs are much better than standard kettle leads and also lock in place.

For the Temperature Probe most, people seem to use the XLR plugs as these come in 3 pin versions. However, these have exposed pins and are not as tidy as the PowerCON type connectors that I am using for the Power in. Neutrik also sell a range of plugs called SpeakOn, which as the name suggests are designed for speaker connections. As the STC1000 NTC probe only has a two wire connection, the 2 pole SpeakON connectors are perfect.


5. Upgrade NTC Probe

The standard probe that comes with the STC1000 works well but is not ideal for brewing. I have used Southern Temperature Controllers Ltd. to make me a 200mm stainless steel probe that will work with the STC1000. They have also completely sealed the wiring to the probe so that it can be immersed without leaking. This made the probe quite expensive but gives me peace of mind. Submerging the probe is not necessary or advised but it happens occasionally, when things are not going completely to plan (most brews).

Complete Parts List

Wiring

Before we get started, I need to add a disclaimer. I am not an electrician and we are messing around with mains electricity. As this piece of kit will be used for brewing, it will also be working in close proximity to water / wort. If you are unsure about any of the wiring diagrams then you should ask an electrician to check your work for you. The wiring diagram shown below is a representation of how I have wired my STC1000 project.

Build

The first step will be cutting the various holes in the project box. Before cutting any holes, plan the layout of your main components. You should consider how the cables will connect to the box when it is to ensure that you have sockets facing in the correct direction. Whether you are going to fix your box to a wall or lie it flat on a bench may change the layout.

Now we are ready to start marking up the box and the cutting holes. It is usually advisable to measure your openings as accurately as possible, which may mean they are on the tight side when you first offer them up. It is better to be a little tight and have to widen the openings than it is to have them too big as there is nothing you can do about it at this stage. How you cut the holes in your box depends on type of material it is made from but in most cases you will need a drill, coping saw (or similar), sharp knife (if working with plastic), hole cutters and possible a file. Drill some holes in each corner of your marked up opening, which will allow you to get a coping saw in. Saw around the edges until you have your hole and then offer up your component. At this stage it is probably a little tight, so you can now use a knife or a file to tidy up the hole and widen it accordingly. There is no real easy way of cutting the holes so just take your time, go slowly and be patient.

For the mains power and sensor cables you can just drill cable sized holes in your box, which is easy and will probably utilise tools you already have. If you are using Neutrik connectors like me, you will need to cut a 24mm hole for the sockets. The only way to do this neatly is to use a 24mm hole saw (drill) but this is not a standard size, so you may need to buy one.

The Cavity Wall Pattress boxes are designed to grip to the thickness of a cavity wall (plasterboard thickness). As the box that I am using is only a few millimeters thick I have had to pad the yellow feet with some strips of the plastic waste plastic cut from the holes. You may just be able to spot this in the picture below if you look closely at the yellow clamps on the pattress boxes.

Once you have all your components fitted into the box you can start wiring it all together. Make sure that you use the correct colour wires for Live, Earth and Neutral as this will make it easier to follow and you are less likely to make mistakes. The STC1000 requires a Live and Neutral connection on points 1 & 2, which provides the power to the unit itself. The heating and cooling points 5&6 and 7&8 are a simple switch for the live connections. This is wired in a similar way to a standard light switch, which also just switches the Live wire. The Neutral and earth connections can be wired directly from your mains supply, leaving the Live wire for the sockets to be switched on and off via the STC1000. Where a Relay is being used this is slightly more complicated but if you understand how the Cooling socket is wired in the diagram above then all we are doing on the Heating side is switching on a Relay, which in turn switches the live for our socket. If you are only using the temperature controller to switch a heating belt or tray, this will be under 10A and you will not need a relay. If you want the additional flexibilty to control a kettle element in your HLT, a relay will be required.

Plan the routing of the wiring and ensure you have wires of the correct length, which are stripped correctly to make connections. If you strip off too much sheath you may find that you have bare live wire that could connect with something you do not want it to. I use a combination of screw terminal blocks and the connection points on the 13A Socket, which have large screw terminals, which you can use to connect wiring together.

The wiring diagram does not show the Pilot light connections as it is important to ensure that the main wiring principles are understood. If you want to use Pilot lights, they are not essential, ensure that you wire them directly into the sockets. This way, whatever happens, the pilot light will indicate when a socket is actually live, either through design or incorrect wiring. I have just wired the Pilot lights directly to the Live and Neutral terminals of each socket.


Further Upgrade

After years of manually moving wort between mash tun, boil kettle and fermenters, using buckets, I have finally invested in a pump. In order to control my pump I have added a control panel switch, a green indicator light and a grey powercon power out socket. The pump has a powercon plug rather than a standard 13amp UK plug as these are much neater and lock in place.



Maxi Cooler Used as Fermentation Cooler

With smaller batches (23L) you will normally find that a little heat is required to keep fermentation at the optimal temperature. Since moving to larger batches (50L), I have found that the heat generated during fermentation is more of a problem. Most people seem to use an old fridge to cool fermentation but this does not work too well with larger pots.

To solve this problem I have decided to take advantage of the recirculation loop on a Maxi Beer Cooler. You can usually find second hand Maxi Coolers on ebay for between £40-£100 but price depends on model and condition. Once you have a working Cooler you can then hook this up to your fermentation vessel. There are many ways to do this but the 2 common ways that I have come across are:

For my project I have decided to use the external method as this means that there is no risk of contaminating the beer. I am using a stainless steel pot as a fermenter so this will conduct the heat well, as opposed to a plastic fermenter where this method may not work so well. The 10mm copper pipe, which is available in most plumbers merchants and DIY stores is ideal for this and can easily be shaped by hand. You can secure the coil in place using cable ties to the pot handles or bend the copper in a way where it can be hung over the handles. Connecting the 10mm copper to beer line was not possible using John Guest fittings. The easiest way is to use some flexible PVC tube to stretch over the 10mm copper and then stretch this onto the standard beer line, which in turn is connected to the recirculation loop of the maxi cooler. I will also wrap insulation around the outside of the pot/coil to ensure efficient cooling.

The most difficult part of this project was to get the 10mm copper tightly would around the pot. You do not want it to be loose as it needs to be in contact with the pot to allow heat/cool transfer. After a few attempts, I worked out that the best way to do this was to wrap the copper tightly around something slightly smaller than the pot first. I then removed the tap and bulkhead/tank connector so that there was nothing in the way and turned the pot upside down. Sitting the coiled copper on the pot base I gently stretched it, coil by coil, over the pot. This ensures that the natural spring effect is pulling the copper tight against the pot.

The maxi cooler is hooked up to the temperature controller for cooling during fermentation. This seems to work well and is capable of reducing the temperature of 40l of wort by about 0.5C in 10 minutes.