This is a recipe for how to make a yoghurt maker that you can make larger amounts of yoghurt in than you would be able to do with a standard commercial yoghurt maker. It also allows you to control how long you ferment for, so you are not bound by an pesky timers that a commercial yoghurt maker might come with.
MASSIVE DISCLAIMER: This involves electricity, which can kill you. Only try this if know what you are doing and feel confident. It is not without risk.
Step 1: Obtain Equipment and Strip Wires
1. A heating belt which is used typically for home brewing purposes.
2. ATC-800+ thermostat controller
3. An esky that you are prepared to cut a hole in
4. Some jars, preferably made of thick glass, such as fowlers vacola show in the second photo, in which to ferment your yoghurt.
5. A power cable which plugs into the wall, with no device attached. For example, you could cut one off an old lamp or hair dryer or whatever, as long as the cable is still good, that's all that counts.
Your heating belt will wrap around your glass jars to heat them up to the optimal temperature for fermentation, which is between 39 - 44 degrees celcius. That's it on the right in the first photo.
Cut the wall plug off and then strip the wires back so you can wire it into the ATC-800+ thermostat controller. The thermostat controller allows you to set a temperature and then plug in a heating and/or cooling device. It comes with a temperature probe, shown in the first photo on the left (you probably should really replace it with a food safe probe, I intend to do this). The ATC-800+ will then switch on the heating device (or the cooling device) so that the temperature that you set, is maintained.
You will also need an old cord with wall plug, which you will wire into the ATC-800+ to provide 240V electricity source. Strip the wires on that back so you can wire them in too.
The second photo shows how the heating belt will wrap around your jars to heat them up.
Step 2: Cut and Drill the Esky
Carefully mark a correctly sized hole on your esky just big enough for the back of ATC-800+ to fit through. Cut out the hole carefully, using a sharp stanley knife.
Drill a hole in the back of the esky just big enough to run your 240v power source cable through. Run the cable through and then bring it out through the hole which you cut for the ATC-800+.
Step 3: Wire Everything In
Wire everything into the ATC-800+. The ATC-800+ comes with a wiring diagram, which you can just follow. Just in case you can't be bothered or don't know how to follow the diagram, here are the instructions in words.... You want to connect the neutral of your 240v source into terminal 8, along with the neutral of your heating belt. Then connect the live wire of your 240v source to terminal 7 and bridge terminal 7 to terminal 4 with a jumper wire that you have prepared (the little red wire in the photo). Connect the live wire of your heating belt to terminal 3. When the ATC-800+ deems that heat is required, a relay will connect terminal 4 to terminal 3 to complete the circuit and provide power to your heating belt. Magic. The temperature probe connects to terminals 5 and 6.
Step 4: Mount the ATC-800+
Mount the ATC-800+ in the esky by pushing it through the hole you cut out. Now everything is in place, tidy up any excess cable with some cable ties.
Step 5: Plug It In, Set Temperature and Make Yoghurt
When you plug in your device, you can make use of a simple 240v timer unit like the one shown in the photo. This will allow you to set an on and off time and effectively control how long you ferment your yoghurt for. I am fermenting for 24 hours. Now you are ready to go, you can look up how to make yoghurt and then set the set temperature on the ATC-800+ to the desired temperature (39 degrees celcius works well for me). I put the temperature probe inside one of the jars, in the yoghurt (again, the reason why you should use a food safe probe), so that temperature is measured in the right place. Once you're set up, do some experiments and you should be making decent yoghurt pretty quickly...and plenty of it.