So I wanted to use my RANCO ETC controller to control my electric HLT, but I realized that the probe that came with the unit was coated with a crappy plastic. I thought about housing the probe in a thermowell, but the stock probe is essentially already a thermowell for a 30 kohm thermistor. The response of this probe didn’t seem all that good and so I set out to make some custom probes to use with this controller. I thought I would chronicle the process here for the benefit of other homebrewers who may be using this common controller.
I ordered the following components from Digi-Key.ca (all costs are in $CDN):
Part Part # Unit Cost
30 kohm thermistor, 30mm NTC CP3-1004-ND $0.887 ea
Male phone plug, 2.5 mm 490-4655-ND $0.507 ea
Right Angle Panel Jack, 2.5 mm CP-2502-ND $1.34 ea
They have flat rate shipping ($8.00) which makes things relatively easy. I believe the US site for Digi-Key also offers the same deal. I also purchased some ¼” brass tubing from Metal Supermarkets to make the probes. I chose brass over stainless to get quicker response.
First, I cut the tubing to the lengths that I wanted for my probes. I then crimped one end of the tube using a pair of vise grips:
I then used a stationary belt sander to round off the crimped ends:
Once all of the probes were roughly rounded off as above, I proceeded to solder the ends closed. I used some very fine grit sandpaper to smooth out the probe tips and the probe:
Once the probes were done, I proceeded to solder the thermistors. I decided to use cat5 cable that I had lying around. These types of thermistors only require 2 wires, so I only needed 2 of the 4 twisted pairs in the cat5 cable. I twisted the pairs together and soldered them to the end of the thermistors:
I then covered the thermistor connections with shrink wrap tubing:
I pushed the thermistor into the brass tubing until it hit the end. I then filled the open end of the sensor tubing with JBWeld using a disposable syringe:
Once the ends of the probe were filled, I put some shrink wrap and electrical tape over the end to seal it all up. On the other end of the wires, I soldered a male 2.5mm plug for making the connection to the RANCO or to a DMM:
The last step was to add a female plug connector to the RANCO control unit so that I could use different probes for different applications. The internals of the RANCO controller before I made any modifications looked as follows:
The stock probe has two wires coming in from the thermistor sensor. Thermistors are not a directional device and therefore it doesn’t matter which wire is connected to which side of the thermistor. I cut the existing 2 wires to make the connections for a plug:
I drilled a hole in the case to house the female panel mount jack. I soldered the 2 wires to the jack and mounted it to the case:
I also added a similar female plug to my digital multimeter (DMM) so that I could also take temperature readings without the RANCO unit:
All in all, this setup has worked excellent for me. I have calibrated all of my probes using 2 accurate thermometers from my lab, and the factory curves were very accurate. I have made a 16” probe to reach into my HLT thru the lid rather than make a hole in the side of the vessel. I have also made 2 probes to reach thru the lid of my MLT so that I can measure the temperature of my mash without lifting the lid. I hope this info helps. Any questions, post away.