Temp control limits

[chunk1227]

I scored a chest freezer off of craigslist to turn into my fermentation chamber. I like tinkering with electronics, so I built my own controller using an Arduino http://www.arduino.cc/. I wrote the code to turn the freezer on or off if the temp gets higher or lower than 1 degree F of the setpoint. I am curious if this is tight enough control or if I would benefit by reducing this to say .5 degree difference? For reference, I tape and insulate my temp probe to the side of the fermentation vessel. What's everyone think? Should I go tighter or RDWHAHB?
Prost!
Chunk

 

[WatereeBrew]

you may burn up the compressor clicking on and off so frequently

 

[chunk1227]

I have thought of that also, but it seems that there is enough thermal mass that it flucuates pretty slowly. I also have a safety coded in the firmware that doesn't allow the compressor to cycle back on unless it has been off for at least 20 minutes.

 

[wizardofza]

On my johnson controller, I have the differential set to 2 degrees. The freezer rarely goes on. Just make sure you have a nice tight seal where the lid closes, and I don't think you'll have much of an issue.

 

[bmckee56]

I checked out the site listed in the OP and am interested in this inexpensive controller. What type of input are you using? Do you intend to do any control using the PWM feature and if so, what type of controller would you employ in that case.

I may be wrong, but it looks like you need to purchase amplifiers in order to use Type "K" thermocouples. Is this true of all I/O points attached to the motherboard?

Hope your controller works out well for you.

Salute!

 

[david_42]

I use a delta of 1C. Can't imagine needed tighter control.

 

[chunk1227]

@david This is what I figured, I was just looking for some input to back me up, thanks.

@bmckee The Arduino is a opensource microcontroller project. It is really flexible and can be used with a ton of different inputs and outputs. It is programmed in a mix of C and processing. I am not good with writing code whatsoever, but by reading through the help guides and examples I was able to pik up how to write arduino code fairly easily. I have never used a type k thermocoupler with it, but I don't think it would be much of an issue. There are several variations of the board, but the standard has 14 pins that can be either an input or an output, 6 of which can output PWM. The board also has 6 analog input pins. For the most part this thing is like a PLC except you instruct it how to behave with code rather than ladder logic. If you like hobby electronic stuff I really recommended getting one to play around with. As far as it being cheaper, not so much. I probably spent a little less building my own controller, but if you figure in time, it would have been cheaper to buy a prebuilt model. The same can be said for homebrewing though. If you have any questions let me know.