Temp controlled fridge

[Stefan Wiswedel]

So I finally finished my temp controller (with SD card data logger) for my fermentation fridge. Tested it out overnight with a half-filled carboy of warm water. Set the temp to 16 degrees and let it do its thing (graph attached).

Logged the data every second, which is probably way more than I need (2.5mb for 12 hours). Even every minute would probably be fine.

I set it to turn on the fridge at set point + 0.5C and turn off at setpoint -1C. I think I might make it +- 0.5C to make the swings a little less drastic. I suppose it's a fine line between stability and not cycling the fridge on and off too often. 

Anyone else done something like this? It's  a fridge very much like this one. How often is 'too often' in terms of cycling the fridge on and off?

Pretty excited it works so well :)

Stefan

[Daniel DeGagne]

Interesting to see your results. Question which chip are you using? and whats the voltage and amps your running at. I have an idea of my own that I'd like to work on with a peltier so any experiance other have to share would hopefully make my idea easier.

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[Stefan Wiswedel]

This is being controlled with an Arduino. Using an LCD shield and Data Logger shield from Adafruit. In terms of the relay, I am using the beefcake relay from Sparkfun. 

I also played with the idea of using a peltier with a water pump and a water-block (for cpu cooling) to cool a water bath that I was going to sit my fermenter in. I never got around to finishing it (was having issues powering the whole thing) before my wife said I could put a mini-fridge in the living room :)

What are you planning?

[Ninety Nein]

Be careful with that beefcake relay!  I was looking at picking one up a while ago, but decided against it after reading the comments section.

[David Lowy]

Hey Stefan,

Out of curiosity, have you graphed the performance of the thermostat that came with the fridge?

Dave

<graph.jpg>

[Stefan Wiswedel]

Ninety Nein: I will double check the relay but I think I am well below the threshold for it, so hopefully it will be fine. Also, they did a recent re-design to take care of some of the issues that others reported and I got one of the newer ones. What specifically should I look out for?

David: Nope, I didn't but that's not a bad idea. I will do that overnight and see what it does :)

I also want to record when the relay is on or off so I can graph that as well if needed.

[Ninety Nein]

Seems like it could short due to the close proximity of the mounting points to the copper pour.  The suggestion is to not use metal screws to mount it.  Also, the high and low voltage traces are too close, apparently.

Check out the comments.  Like I say, I didn't look into it too closely, and I didn't have time to look for a replacement.  I just shelved the project for now.

https://www.sparkfun.com/products/10733

As mentioned, DO NOT use the mouting hole in the corner by the “normally open” label. There is no clearance between the screw head or thread and the copper pour. At best, you will blow your fuse if your case is grounded. At worst, it could cause a fire or shock.

I would not use this above 52v until the spacing issues are fixed.

[Stefan Wiswedel]

Hmmm. That is a bit worrying. I am not using the mounting holes so that should be OK but I guess it's still not good running at 110v :(

[Stefan Wiswedel]

OK. So the fridge is rates 115V at 1.5 amps ... a bit nervous leaving it to run now.

To see how it cycles by itself (and not run the relay until I decide if I want to), I am running the fridge on it's 'warmest' setting. Seems to be holding at about 11C. Will keep it there over night and look at the graph in the morning.

Another option (if I don't want to use the relay) is to see how 'warm' I can get the fridge using the built in controller. I opened it up when I got it to take a look and there are two screws that look like 'calibration' type screws. I could play with those and maybe get it to keep a good ale temp by itself and then just monitor with arduino and data logger and control manually ...

Lets see what happens :)

[Dallas Luther]

Yeah, I'd be concerned due to the spikey nature of a fridge compressor, and cycling it so frequently.  Most full size fridges sit on dedicated 20-amp breakers due to their start-up draw and voltage spikes. Maybe not the best for a shoddy relay board with known issues. 

[Stephen Young]

Stefan, look up "SSR", Solid State Relay.  There are some at the club.  If not of the proper rating, I surely have one to spare.  You drive them with 5Vdc (Arduino!) and can easily switch 20+ amps at 120VAC.  Piece of cake.  And you get great isolation.  You "might" need a heatsink, but that is a small price to pay for peace of mind.

SDY

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From: Dallas Luther <dallas...@gmail.com>
To: "vhs-g...@lists.hackspace.ca" <vhs-g...@lists.hackspace.ca>
Sent: Monday, November 19, 2012 9:57:56 PM
Subject: Re: Temp controlled fridge

[Stefan Wiswedel]

Hey Stephen,

Thanks for the info. I might have to take you up on that. Think you'll be at the space next Tuesday? I can't make it this Tuesday ...

Because apart from the relay concerns, my system works really well :)

Stefan