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

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.

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.

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.

+1^

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

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.

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.

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.

acidrain said:

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.

Click to expand...

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.


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.

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.

FuzzeWuzze said:

....If your using a STC-1000... 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......

Click to expand...

Why measure and control the AIR temperature, which we are NOT trying to control, when we CAN measure and control the wort temperature by attaching the probe to the outside of the carboy or bucket?

Attaching the probe to the outside of the fermenter, under a layer of insulation, has performed flawlessly for my brews.

+1 to raouliii

FuzzeWuzze said:

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.

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.

Click to expand...

Ha, nice chart and all, but the point is to control the beer, not the air. I use a thermowell and ferment in Sanke kegs with an ST1000... works perfectly.

On the other hand, If I forget to put the probe into the thermowell, it cycles constantly with wild temp swings.

Why would you control the air and guess at what is actually happening?

acidrain said:

Ha, nice chart and all, but the point is to control the beer, not the air. I use a thermowell and ferment in Sanke kegs with an ST1000... works perfectly.

On the other hand, If I forget to put the probe into the thermowell, it cycles constantly with wild temp swings.

Why would you control the air and guess at what is actually happening?

Click to expand...

I guess it depends how bad your overshooting...if by measuring the side your wort is overshooting +-2F then you'd have better precision measuring the air because the beer will naturally gravitate towards that temperature.

Even if the wort starts fermenting, your chamber is going to be at a set temperature and resisting your wort from warming up.

It also likely depends on how powerful your heater and or freezer are. My chest freezer goes to -20F when its on. If its even on for 15-20 minutes the entire thing is super cold..sure my beer may be 70F to start moving towards my set point of 62, but because its so ridiculously cold in the freezer and it holds temp so well its going to take hours for it to warm up to even freezing inside even when its turned off..and as a result the beer goes way below the set point.

If your using a fridge it might not be as much of a big deal than if your using a modern chest freezer. Those damn things get super cold super fast.

Actually, if you look at the graph, you'll see a lot of fluctuation in the air temp. In fact there's so much that it ends up pulling the fermenter temps wild toward the end.

The graph is a perfect piece of evidence that the probe needs to be insulated and measuring the wort, not the air.

FuzzeWuzze said:

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.

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.

Click to expand...

I've tried several methods, and found that the greatest overshoot was when measuring the air temp. Not only that, but measuring the air temp can often cause excessive cycling, which is hard on the compressor. This is pretty obvious when looking at Dec 12-13th on your graph. People on this forum have killed brand new freezers within days because they were measuring the air and didn't have enough thermal mass in there. I agree that using a thermowell can cause some overshoot issues, but dangling the probe can be even worse, and can be damaging to your fridge or freezer. IME the best results ore obtained by taping the probe to the exterior of the fermenter.

acidrain said:

Ha, nice chart and all, but the point is to control the beer, not the air. I use a thermowell and ferment in Sanke kegs with an ST1000... works perfectly.

On the other hand, If I forget to put the probe into the thermowell, it cycles constantly with wild temp swings.

Why would you control the air and guess at what is actually happening?

Click to expand...

FWIW I also ferment in sankey kegs and use an STC-1000 to control temps. I've tried using a thermowell for the probe, but found that it had significant overshoot when there was much differential between the beer temp and set temp. It worked fine when it finally settled, but there was a definite yo-yo effect when bringing it down to pitching temp, or cold crashing, or ramping temps up near the end of fermentation. I've since switched to taping the probe to the outside of the keg, and find that the exposure to the ambient shuts the fridge or heater off a little earlier, which prevents the overshoot, and the temps are significantly more stable. A thermowell is better than measuring the air temp IMO, but still not as stable as taping to the exterior of the fermenter. As always, YMMV.

Let's say your basement held a steady temp of 62°. You pitch your yeast at 68° and place your fermentor in the 62° basement. We know that the temperature of the fermentor will want to adjust to ambient, but yeast activity will raise the temp around 6° so with the basement at 62°, and the heat from active fermentation raising the wort temp it will ferment at 68°. If my basement gets cold in the winter and drops to 59° the 6° increase in the fermenting wort would mean I would be fermenting at 65° That's not to bad right?

like many have said you can set the margin of error. I think 0.3 is as low as it gets. you can also set the compressor delay, the max is 10 thats where I have mine set. I also unplug which ever device I wont need so that they arent constantly fighting each other. like I'm making lagers right now and they probably wont need to be heated. if the freezer chills too far past the margin of error I have set the heater wont get turned on because I have it unplugged.

iaefebs said:

Let's say your basement held a steady temp of 62°. You pitch your yeast at 68° and place your fermentor in the 62° basement. We know that the temperature of the fermentor will want to adjust to ambient, but yeast activity will raise the temp around 6° so with the basement at 62°, and the heat from active fermentation raising the wort temp it will ferment at 68°. If my basement gets cold in the winter and drops to 59° the 6° increase in the fermenting wort would mean I would be fermenting at 65° That's not to bad right?

Click to expand...

that's not bad IF those are the correct figures and the temps ramped up at the end of yeast activity preventing them from going dormant too early. but in all honesty that's fine.

The first time I used the STC-1000 controller, was the first batch in my freezer. Initially the heater and the freezer were cycling on/off, about every ten minutes. The wort was still higher temped than I wanted, so I cut off the heater, set the temperature I wanted, and by the next morning the bucket was where I wanted it to be. At that point, I turned the heater back on, and all was well.

ianw58 said:

Actually, if you look at the graph, you'll see a lot of fluctuation in the air temp. In fact there's so much that it ends up pulling the fermenter temps wild toward the end.

The graph is a perfect piece of evidence that the probe needs to be insulated and measuring the wort, not the air.

Click to expand...

Im willing to conceed on the air argument at this point

FWIW, the wild fluctuations you see at the end I found out is actually due to the fact i'm an idiot and didn't fully close my stand up freezer door all the way while i was gone on vacation for the weekend...so it was just blowing hot air right out of the freezer all weekend.

Good to see it will still able to keep it within .5F of my set point though...Not bad considering it was like 40F in the garage all weekend.
Normally my heater only turns on for 5-10 minutes every 3-4 hours or so to maintain mid 60's when the ambient outside is in the 30-40's...

I still dont quite understand why people setup hot and cold to fight each other, just seems like a waste of energy.

I <3 BrewPi, helps me document my stupidity in graph form.

FuzzeWuzze said:

...I still dont quite understand why people setup hot and cold to fight each other, just seems like a waste of energy....

Click to expand...

I certainly agree with you on that. IMO, undershoot and overshoot should be accounted for and F2 set outside of those values, and modify the system to reduce them, if F2 becomes unacceptably large. Besides being a waste of energy, having the heater and compressor cycle back and forth in a constant battle, will prematurely wear the components.

Thanks everybody for the information. I wasn't expecting to start a debate, but it certainly provides me a lot of food for thought!

I was originally of the mindset that having the temperature probe insulated against the liquid will cause larger temp swings as the sensor won't feel the new temperature as quick. Ultimately though I thing I understand that it makes sense to control the until based on the temperature of the liquid since that's the ultimate goal.

Here's my question though, and I hope I didn't miss this in the above discussion: Because the entire unit is insulated from the environment, wouldn't it make more sense to have the temp sensor uninsulated against the liquid chamber? This would theoretically allow the liquid to reach the desired temperature more quickly.

Thanks again!
Andy

mojo2008 said:

Thanks everybody for the information. I wasn't expecting to start a debate, but it certainly provides me a lot of food for thought!

I was originally of the mindset that having the temperature probe insulated against the liquid will cause larger temp swings as the sensor won't feel the new temperature as quick. Ultimately though I thing I understand that it makes sense to control the until based on the temperature of the liquid since that's the ultimate goal.

Here's my question though, and I hope I didn't miss this in the above discussion: Because the entire unit is insulated from the environment, wouldn't it make more sense to have the temp sensor uninsulated against the liquid chamber? This would theoretically allow the liquid to reach the desired temperature more quickly.

Thanks again!
Andy

Click to expand...

No, if I am reading you right.
Insulate the sensor, against the liquid containing vessel.
A piece of foam insulation, and an "Ace" bandage are all that's needed.
With this configuration, you'll have maybe a 2-3 inch width of the vessel covered with the bandage, and maybe a 2 inch sq. area insulated.

As I said, don't know if I read you right, but don't insulate the whole vessel.

Stealthcruiser said:

As I said, don't know if I read you right, but don't insulate the whole vessel.

Click to expand...

You're right, I hadn't read it correctly and it makes much more sense now. THanks!

Haven't had a chance until now to really dig in to the issue with my fridge. After using the video above (thanks Smetz001) as a starting point, I discovered the compressor is OK. So is the relay though. Turns out the ADC (Automatic Defrost Control) board is bad, so it's not sending 115/120 VAC to the compressor. Depending on what I can find, I may replace the board, but I think I am going to try to bypass it. After all, my end goal is to maintain the freezer side at just above freezing for cold storage, so no defrost control would be needed.

I may consider wiring direct to the compressor assembly from the controller if this doesn't work. I would essentially pull the relay and inject the voltage at that point directly from the STC-1000.

Once I get the fridge working THEN I'll wade through the rest of the info in this thread!