Fridge Fermentation Chamber Conversion

[thekraken]

Beginner here, got some conversion questions. I've been researching fermentation chamber options and come to realize I may have everything I need already on hand.

1. I have an arduino, raspberry pi, and multiple jeenode microcontrollers laying around.
2. I have a few thermistors and a DS18B20 temperature sensor.
3. I have a ready made relay switch, the power switch tail ii. http://www.adafruit.com/products/268
4. An in-law is supposed to be giving me a full sized fridge sometime soon (or I may buy a mini fridge and go that route)

The Power Switch Tail II is rated 15 amps, mechanical relay. Can I just plug a fridge into this thing, and use it to turn the fridge on/off with out modifying the fridge? OR are there precautions I have to take, or fridge hardware that I will need to bypass/disable.

 

[byrone]

Using that relay module from adafruit you can just plug in the fridge and go. You won't have to modify the fridge, but just make sure its thermostat is set to the coldest setting as the arduino will control the temperature. Getting the temp sensor inside the fridge may be the only troublesome portion of the build(because of the seal), unless you're willing to drill a hole. With my setup i used ribbon cable and it doesn't interfere with the seal at all. I just started using brewpi and it works amazingly well so I highly recommend it as your control strategy.

 

[thekraken]

Using that relay module from adafruit you can just plug in the fridge and go. You won't have to modify the fridge, but just make sure its thermostat is set to the coldest setting as the arduino will control the temperature. Getting the temp sensor inside the fridge may be the only troublesome portion of the build(because of the seal), unless you're willing to drill a hole. With my setup i used ribbon cable and it doesn't interfere with the seal at all. I just started using brewpi and it works amazingly well so I highly recommend it as your control strategy.

Thank you! Yes, I was just stumbled across the BrewPi project, it looks right up my alley.

For any one in the future with the same/similar questions check this article on options to convert a fridge: http://www.brewpi.com/fridge-hacking-guide/

 

[FuzzeWuzze]

Yup you have everything you need really. You dont need to hack your fridge apart.

It will work just fine with the Powerswitch tail II, wire it as you would for other projects(may have to google i cant remember which pins go where) and just make sure the control/data line goes to A4 on the BrewPi setup.

I used a PSTII for my first build and it worked fine, i just moved to the smaller relay board for the initial BrewPi build because the PSTII is just a bit clunky and i hated having long wires to it, and you obviously only have control over hot or cold not both at the same time.

Most of us just stick the BrewPi box outside the fridge/freezer and run the probes through the door seal and close the door. Only using 3 wires the cables can be incredibly small and you'll have no issues with cold air getting out. The best place to bring the cable i've found is between the hinges on that side of the fridge. That way when you close the door the seal is forced tight and held by those hinges. If you do it at the other side its possible the cable will create a "weak" spot in your seal and the door will pop open, especially if your fridge already has a weak seal .

 

[thekraken]

The best place to bring the cable i've found is between the hinges on that side of the fridge. That way when you close the door the seal is forced tight and held by those hinges.

That's a good idea, thanks for the tip.

How do most place the temp probe in the fridge? Top, middle, bottom, in the back away from door, taped against a bucket/carboy, doesn't really matter?

 

[FuzzeWuzze]

That's a good idea, thanks for the tip.

How do most place the temp probe in the fridge? Top, middle, bottom, in the back away from door, taped against a bucket/carboy, doesn't really matter?

There are two probes required for a brewpi setup, so you need to have two DS18B20's.

One is for the fridge, and one is for the beer.

Preferably as the main BrewPi topic states you can get a thermowell down into your beer, its actually pretty easy unless your using a stainless conical or something but even those usually are sometimes formed with thermowells.

The other fridge temp just kind of goes anywhere in your fridge, i usually just set mine on top of my bucket dangling off the side, you just dont want it touching any of the walls where the condenser coils are or it will give wrong readings.

The beer temp is obviously your set point, and it uses some math and PID to use the fridge temp to calculate how cold it needs to get your fridge to get your beer to its set point. So say you set it to 65F and its currently at 67F. BrewPi may for example get your fridge down to 55F because it knows(learns) that the ambient temp inside at 55F will get it close to 65F beer temp in the end...its not always perfect so having a heater to counter balance this can help but its not required.

 

[thekraken]

I installed the BrewPi software last night and got a chance to play around with the software, it's pretty cool I can't wait to get a fridge to put it to use! I got the impression from playing with it that you could use it's PID to control either the beer temp OR the fridge temp, if you are required to run two temp probes I guess I'll have to write my own sketch for the time being.

How does the temp probe go into the carboy/bucket exactly? Do you need a special airlock or blow-off tube? Also what about food safety with the probes in the beer? I know the BrewPi store's probe specifically says it's not food safe.

EDIT:

I just saw your HOWTO post from your sig. Good write up! I'm guessing you solved the food safety issue with a giant thermowell? A quick google search shows thermowell and thermwell stoppers ie:http://morebeer.com/products/stopper-thermowell.html. I'm guessing you use a stopper something like that one?

Also, I'm wondering, for most accurate readings do you need to fill the tube with any thing other than your probe? Maybe some thermal paste or something?

EDIT EDIT:

Just noticed where you said you drilled a whole in your bucket lid for a rubber stopper with another drilled whole in it. Simple enough, may just drill a hole in my lid and stick a snug rubber grommet in there.

Still wondering about the thermal paste though.