HLT Upgrade – Digital Thermostat Control

Due to the coarse nature of the dial control on my HLT (which was originally a boiling urn for a conference room), I have had to hover around the tank with a glass thermometer held in the top waiting for the right strike/sparge temperature.  Miss it and it’s another wait with the lid open.

Clearly this instrument was never designed to be particularly accurate and there’s a ridiculous impediment to watching it – often perched on a milk crate to get up there.  What I really need is a large, easy to read display that is always reporting the temperature and ideally some electrical control to get me the right temps.

Solution is another STC-1000 aquarium thermostat, just like I used in the fermentation fridge.  I fitted the HLT with a thermowell to accept the NTC probe using the same silicone muffin tray gasket technique I used on the keggle.  Then I set it up for a trial run with a second digital thermometer dangled in the top to see how accurately it would heat to temp (although in the picture it looks like 7 and 17C, it’s actually my camera catching the scan-rate of the LED displays!). All went well, it would heat to temp and then overshoot by 2C – not a problem, factor that into the process and write it on the side of the HLT 🙂

With the proof of concept passed, it was time to commit it permanently to the HLT.  I cut the end of the NTC probe off and connected it to a gold, insulated RCA socket mounted in a 15mm brass pipe plug.  I then filled the plug with epoxy so that I would then be able to pump the thermowell full of thermally conductive grease without any risk of it being electrically conductive.  Seeing as NTC uses resistance to measure temperature I figured that even a small level of conductivity of the thermal compound would throw my temps off – and, lets face it, it was cheap and easy to do and made all my connections far more hard-wearing.

Lastly I soldered an RCA plug to the thermostat end of my cut wire and bingo: digitally controlled, set-and-forget HLT!


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