Friday, 31 August 2012

STC 1000

I posted this on the AHB forums a while ago, but forgot to put the details here.

A STC-1000 is a single set point digital temperature controller, it's cheap, easy to use, relatively easy to setup and a very useful bit of gear for a range of home brewing and other uses where precise temperature control is needed.  The controller has outputs for both heating and cooling (and will automatically switch between them as required) while cheaper but similar models are available that manually switch and control only the heating or cooling circuit.

A STC-1000 combined with a refrigerator/freezer and heating device (like a heating mat or even a light globe) can be used to control the temperature inside a fridge or freezer at temperature ranges outside what is provided by the internal thermostat.  This makes it ideal for fermenting beer or cheese maturing.  In electric powered breweries it can be used to control the temperature of the hot liquor or boil and even in a HERMS/RIMS system (but a PID is more accurate).  It can also be used with a hot water urn or similar water-heater to make yoghurt or cheese as well as a cheap and easy (but still very accurate) cooker for the increasingly popular sous-vide method of cooking.

There are various ways to setup and install a STC-1000, but the easiest way I have found is to use the plugs from an extension cord and then it's just a matter of housing it in an enclosure.  Obviously when dealing with mains electricity there are logical and legal reasons why this is not a good idea to do yourself.

This is what was used on the most recent (of 4) STC-1000's that I setup:
STC 1000 ($20 Ebay)
3 point terminal block ($1 for 12 point Ebay)
3x PG11 cable glands ($6 for 20 Ebay)
2x 3m extension cords ($3 ea Kmart)
Enclosure (click-storage container $2.50 Coles) - a black jiffy/hobby box is most often used, especially if there are children around that might want to 'investigate' what essentially looks like a 'lunch box'.

A step-bit is useful to drill holes in enclosure for cable glands, and a drill bit for the temperature probe hole:
Cable glands are not essential, but they do look neater and are a little better than knotting the cable or using cable-ties.

The cut-out for mounting the STC 1000 is a little rough but it does not have to be perfect since it won't be seen:

Power cables are cut to length (don't make them too long or they get in the way) and wires are stripped:
The wire colours seen here correspond to the Australian standard for internal household devices.

Fit the cable glands, push the cables through, and attach the wires to the terminal block (the terminal block is not essential but it makes it quicker, neater and safer to setup), the earth and neutral pass through the terminal block and to the output cables:

When in operation the STC-1000 acts as a relay to switch on/off either the hot or cold side of the controller as required, so the active wire is switched via the controller's hot and cold termials:

Once that is done, ensure there is no tension on internal wires (and that they are securely attached) and mak things look neat before tightening the cable glands.  Cable-ties for are useful for tension-relief on temperature probe:

Then it's just a matter of attaching the lid (use tape or screws so it cannot come undone) and labeling the hot/cold cables:

The fridge or cooling device is plugged into the 'cooling' control, and the heat-mat, urn, HLT or other heating device  is plugged into the 'heating' control.  Once it's plugged in and turned on, the temperature can be set via the digital controller, and when the set point temperature is reached, the controller will turn on/off the heating or cooling controls as required in order to maintain the system at the set temperature.

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