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mojo2008 12-17-2013 07:53 AM

STC-1000 Too Accurate?
 
Using a STC-1000 I set up a side by side fridge as a fermenter. I wired it so that when the temp was above the setpoint, the compressor would kick on and a computer fan would draw air in from the freezer side. Below the setpoint, a ceramic heater and a circulating fan would kick on.

I was able to lager one batch of beer, but afterwards, the fridge stopped working completely. I'm pretty sure this setup burned out the compressor. because the controller only has one setpoint, the heating and cooling temp swings overshot the setpoint frequently resulting in the compressor running a lot.

Has anybody had any issues like this? Any suggestions to fix it? I'm considering a second STC-1000 in order to introduce a second setpoint. Alternately, a better temp controller that has two setpoints.

Thanks for any feedback!
Andy

FatDragon 12-17-2013 08:06 AM

You can set a deviation on the STC-1000 so the heating/cooling functions don't turn on within a certain range of your set temperature. By default I believe mine was set to 0.5C, so if I'm set to 17.5 the heater turns on at 17 and the cooler at 18. I don't recall offhand which of the functions controls this, but you can set it way wider than mine is set.

Another option would be removing the heater from your setup - that way your temps won't swing as much, meaning less compressor time.

mojo2008 12-17-2013 08:19 AM

Thanks for the information. I didn't realize you could adjust the setpoint accuracy on the controller.

As for the heater, I probably could remove it from the system during most of the year. The fridge is in the garage and it typically doesn't get much cooler than 50 degrees or so in the winter.

smertz001 12-17-2013 12:20 PM

Before blaming the compressor I would check the relay connected to it. I thought my compressor went, and it turned out to be a $30 relay instead after checking closer and testing.
A video on testing compressor and relay.

IslandLizard 12-17-2013 12:29 PM

+1^

Did you set the cooling delay at 10 minutes (the max)? That curbs excessive wear on the compressor and relay.

raouliii 12-17-2013 01:20 PM

In the Setup menu, F1 represents the set temperature; F2 represents the difference value. When the measured temperature is equal to the set temp + the diff temp, the cooling relay closes. When the measured temp drops to the set temp, the cooling relay opens. Vice versa for heating.

In every system there will be undershoot of cooling and overshoot of heating. IMO, it is best to determine what these values are for your system, operating in steady state, and establish an F2 value that is greater than both the undershoot and overshoot values. This will keep the cooling and heating functions from constantly fighting one another. If undershoot or overshoot are unacceptably large values, redesign may be necessary. A simple change in probe placement may help.

acidrain 12-18-2013 12:24 AM

Did you have the temp probe taped and insulated on the fermentation vessel? A thermowell into the beer would be even better. If you just had the temp probe in the air, it will way overshoot.

cgrivois 12-18-2013 01:13 AM

The first heater i had was causing my system to overshoot on the heating side, causing the compressor to run more. I replace the heater with one of my wifes scented wax deals that only has a 40 watt bulb and I vary rarely overshoot on the heat now. In fact the compressor rarely comes on especialy since its in the garage and it has been cold lately. The first one heated the air inside of the fridge too fast causing it to over shoot. Long story short, go with the lowest power heat source that you can.

FuzzeWuzze 12-18-2013 01:15 AM

Quote:

Originally Posted by acidrain (Post 5749889)
Did you have the temp probe taped and insulated on the fermentation vessel? A thermowell into the beer would be even better. If you just had the temp probe in the air, it will way overshoot.

You have that backwards, in the thermowell the freezer will kick on for a long time because it will take it a long time to move the beer even half a degree...by then your freezer is at 0F.

If your using a STC-1000 and not something like BrewPi with a PID controller your best bet is to measure the AIR temperature inside of your chamber and set it a few degree's below your expected fermentation temperature.

You should only really use a thermowell if you have a PID mechanism that will compensate for overshoot and shut the freezer off early so that your freezer coasts in to the set temperature.

For example this is what my BrewPi setup results in using nothing but a Lasko personal ceramic heater and a thermowell in my 8 gallon bucket, its about 30-45 in the garage where the freezer is. The worst temperature swings were after fermentation ended on the 15th and it was still overcompensating only about .5F as it figured out the new settings it needed.
https://dl.dropboxusercontent.com/u/2798684/hgipa.jpg

Your beer will always be pulled towards ambient, if you set your chamber to 62, the beer will get to 62, start fermenting and be around 64-65 most likely, this can be monitored with a separate probe or just one of those thermometer stickers you stick to the side of carboy/buckets. It should only take a few brews to figure out what this delta is and set your chamber accordingly.

To keep your freezer at 62 it should only have to turn on every once in a while...honestly i wouldnt use both a heater and a cooler. If its too cold(which it likely is by now in VA) just use the heater instead of having them combat eachother. Save the cooling for spring/summer.

cgrivois 12-18-2013 01:23 AM

My probe is in a thermawell and I my temp doesnt coast more than the .3C the controller is set too. As mentioned above I used the smallest heat source I could. I also placed an aditional 5 gal bucket of water in the fridge for some thermal mass.


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