$60 DYI Deadly Accurate Digital Cave Controller! (Photos)

[iratherfly]

So I was smart enough to purchase a GE wine refrigerator as a cave a couple of years ago. You know, a real one, with compressor. Not one of those thermo-electric ones that look stunning but boasts the reliability of a 1976 Fiat...  It's a simple refrigerator that locks moisture in and has insulated glass door, a 40°F-60°F thermostat and flat wooden shelves. Perfect.

Sadly it's a manual twist button thermometer like a toaster. Worst, it is un-stratigecly located externally at the back of the fridge (who is the genius that thought this one through???). Initially it was cooler than indicated, but as time went by it lost that lovin' feelin' and my 54°F point was giving me 60°F. I kept turning it down to get my 54°F and within a few month it was giving me that when I turned it down to "40°F".  A couple of weeks ago I noticed that this setting now giving me 57°F and as it was heading towards the 60's within a few days I freaked out and decided to fix it immediately  (3:00am of course).  I opened up the thermostat only to discover it was some cheapo Chinese hunk-of-junk of the highest order. For the life of me, I cannot fathom how/why this part was installed on a GE brand appliance. It was quickly apparent that it cannot be fixed because the material was too worn and I wish it was as simple as a toaster thermometer. It was going to be hell to replace (and costs $45). I quickly bypassed it with a wire to get the unit working again. Great.  Within 30 minutes my cheese was heading to 44°F and ice was covering the back of the thing.  STOP THE MADNESS!!!!

Luckily, I had extra parts left over from one of my Digital Sous-Vide / Cheese Vats (remember that post from January?) I went to work and built an incredible controller in about 45 minutes that would put to shame any professional Johnson brand controller. It's been connected to my cave for two weeks now and oh boy it is DEADLY ACCURATE. I thought I should share:

THE CONCEPT
The idea is to make a unit that connects to the wall on one end and the constantly-on fridge (or any fridge on lowest temperature setting) is plugged to it on the other. Between the input plug and the output outlet there is a PID controller that tells a solid state relay when to turn the fridge on/off based on temperature reading it gathers from a thermocouple that is hidden in the fridge. It may sound complicated but it's really simple and has 4 parts only: A PID controller, a solid state relay switch, a thermocouple and an extension cable.

THE PARTS

• 6ft PT-100 PID Precise 0.1 degree Thermocouple ($16.50)
• 25A Solid State Relay SSR DC In AC Out ($7.95)
• JLD612 Dual Display PID Temperature Controller ($33.50)
• Heavy duty grounded extension cable ($0.00 -Don't you have a box full of cables you're not using in the garage? What kind of person are you?)
• A Tupperware box ($0.00 -your spouse won't notice its gone)
• A few cable shoes and heat shrink insulation ($0.26)
• Optional: A glass vial ($0.00 -I used one that was used previously to store Vanilla beans)
• Optional: 16A 125V Illuminated Round Rocker Switch with Red LED ($3.99)

THE STEPS

• Cut a hole in the Tupperware to fit the PID in. Drill 3 holes in it. One for the input plug of the extension cable, another for the output socket and another to pass the thermocouple cable from. Cut a hole for a switch if you intend on using one.
• Cut the extension cable in half. Re-connect the ground. If you are using a conductive housing such as a steel box for this instead of the Tupperware I suggested, you may want to ground the box and the body of the SSR too (especially if you intend on screwing it onto such steel box).  Using a steel box may be more important if you are going to use it to power a heating unit such as Sous Vide or cheese vat, but in this case the amperage is so low that it keeps rather cool so Tupperware does the trick. Drip the PID into place, expose wires, put shoes on wires and screw all of them them into place according to the diagram (see last photo below). You will need to prepare a couple of wires with shoes on them too to connect the SSR to the PID.
• Close the unit and turn it on. If everything looks right, program the PID for the job and save it. (The program will tell it whether it is a cooling or heating device, type of thermocouple, required accuracy resolution, minimal/maximal time interval between switching it on/off, and whether to display temp in °F or °C). I will write down the programming instructions and add them here soon.
• Now test it (you can test it with a lamp). Set up a temperature, go above and below it and give the machine a bit of time to start responding.

This basically completes the whole thing. All you have to do it plug in the wine fridge to the unit and hang the thermocouple inside, at the very center of the fridge. (the thermocouple cable is very thin, you can close the door on it, that's fine).

MAKE IT EVEN BETTER
In the beginning I was experiencing too much sensitivity. This thermocouple is very accurate and captures 0.1 of 1°F in temperature changes, which naturally occur in the air every few seconds. It was turning the unit on and off like crazy and the compressor began to rattle and complain... I then adopted an idea from commercial wine cellars. They put the thermocouple inside of an old sealed wine bottle full of water so that it captures the PRODUCT temperature instead of the Ambiant air temperature. I obviously don't have a space for a whole wine bottle, so instead I used a glass vial that used to store Vanilla beans. It's perfect. It has a sealed cap that I could drill a hole in for the thermocouple and I can seal it with the thermocouple in it, full of liquid and hang it out of the way inside the fridge!  Initially I filled it with water. It was an improvement but was still too fast. I then replaced the liquid with Olive Oil which is extremely dense st low temperature. PERFECT!

RESULTS
Temperature surfing on this unit are now from 53.7°F to 54.3° with a little recovery time after I open and close the fridge. I am so impressed with it. I like it better than the Johnson controllers because it shows you the real temperature on one LCD and the target temperature on the other. It also indicates to you with lights when it had turned the fridge on or off.

[zenith1]

I love tinkerers! Great work,thanks for posting the details of your efforts.

[Boofer]

Great article! Excellent instructions for other folks wanting to tweak their cooling controls.

I bought one of those JLD612 devices a while ago. I grew disenchanted when it looked to be too sensitive. I didn't realize that it needed something like the "thermocouple-in-a-bottle" to tame it.

I sought another solution and found it in a RANCO ETC-111000 Digital Cold Temperature Control. Although it doesn't offer a dual display or show when it is activated, it does offer:

• LCD display
• Easy control push button adjustment
• Self-contained relay for digitally turning on the refrigerator voltage
• Set for Cooling or Heating
• Set for temperature in Fahrenheit or Celsius
• Set target temperature
• Set temperature variance (the allowable swing before the unit activates) up to 5 degrees

The Ranco offers a control solution for those not overly electrically-inclined. 

-Boofer-

[iratherfly]

Thanks, zenith1
Thanks Boofer, my inclination too was naturally to purchase a Ranco or Johnson unit. They are very good and not expensive, solid, well contracted and certified safe.  However, by the time I would have gotten it shipped to me my entire cheese collection would have either been frozen or rotten... I was lucky enough to have the parts to build a unit on my own.  This was an emergency hack. (I should have added the word 'emergency' to this thread's title, it's part of the story really).

Little known fact; you can actually change the sensitivity of the JLD612.  I made it cool without the blinking effect and I set it so that it must wait at least few minutes (I think 3) between turning on and off so that it ignores overly sensitive data and doesn't kill the compressor.

The thermocouple in a bottle is a neat little trick but I didn't come up with it (though in a vanilla bean glass vial, that's all me!) It's a rather standard practice with wine cellars, like here and here. There are even companies like CellarPod that makes wireless thermocouple to put in wine bottles.

The benefits for my unit are:
- Far more accurate
- I can re-program it to control a cheese vat or sous vide cooker or a smoker with a few touches of a button
- Would work comfortably with 125V / 16A and up to 25A even (I would add a fuse and SSR heatsink for that though)
- I can see the target temperature and the ambient product temperature on the same split-screen LCD.
- LCD and SSR both turn on LED signals to show me when it is auto-adjusting or when sending power to the unit (active-on, see last photo before the diagram)
- 24/7 illuminated LCD
- 24-7 customer support onsite (heck, that support guy is so good, he will even turn and wash my cheeses and cook my wife dinner)

[Boofer]

This was an emergency hack. (I should have added the word 'emergency' to this thread's title, it's part of the story really).

I think the 3:00AM action told me it was an off the rails hack. Understand totally.

- 24-7 customer support onsite (heck, that support guy is so good, he will even turn and wash my cheeses and cook my wife dinner)

Oh boy, you've got a winner there!

I do happen to have a few of those SSRs sitting in my toolbin...and I have several boxes of cables, ICs, and other discrete parts out in my garage. The wife keeps trying to get me to throw them out...eh?!

Bottomline: excellent (& elegant) emergency fix. I tip my hat (if I was wearing one). 

-Boofer-

[iratherfly]

Awesome.

A good trick to get her off your back is use it to build such interesting devices -even if they have no function and not even working. As long as there is some blinking light in it she will think you are indeed making good use of your stuff and really need it: "Honey, I built a cheese lactomator with flex capacitor. Very sensitive, do not touch!". The next thing you know she is proudly showing it off to her guests, not knowing it's just an artistic version of parts storage for you