How to configure temperature controller for brew fridge?

[timcunnell]

Hello chaps,

I know a few guys on here have setup brew fridges, and I was just after some advice on how to configure my temperature controller.

I have modified a fridge to include a small tubular heater and wired up the heater and fridge to an STC-1000 heating and cooling controller. I've just mounted the temp probe inside the fridge - taped to the back wall.

It certainly looks like I've got it working okay at least (which I am quite pleased about as wasn't 100% what I was doing!!). Admittedly I have still got to mount the controller and wiring in a proper sealed box - it has only been wired up for test purposes for now.

I just reckon I could do with some advice on how best to configure the controller to maintain a stable temperature. I've experimented by setting the controller to cool when temp exceeds 20c, and heat when temp falls below 18.5c. This definitely works - BUT what I am finding is that while the cooling mode clicks off at 20, the temperature continues to fall. Typically it'll fall a degree or 2 below 18.5 (when heating kicks in). Similarly, when heating kicks in with the temp below 18.5 it eventually starts warming up in the fridge temperature after a couple of minutes and the temperature rises. Heating mode clicks off at 18.5, but obviously the heater is still warm and the temp continues climbing well past 20. At this point the cooling starts again! It seems like an endless cycle of over-cooling, and over-heating.

So I am really interested to know how others have configured their controllers. Is there a good way of maintaining a fairly constant temperature without what seems like a fairly inefficient amount of heating and cooling?

Thanks very much for any advice!

 

[ghb]

Even when the heater is switched off it will still be radiating heat. If you want a more precise control you'd have to go with a PID controller
which senses when the set temp is approached and alters it's output accordingly. I think it switches on and off frequently as it's nears the set temp and thus avoids overrun.
I'm sure there's other members that can offer a better description of how it actually works.

here's a more detailed bit of splurge


A PID controller (proportional integral derivative controller) is a control loop feedback device that is used to continually calculate the difference between the target temperature and the measured temperature and takes the appropriate action to make up for any difference.

A PID controller is an intelligent device that learns and trains itself to the behavior of a system so as to not overshoot or undershoot the target temperature. It is more advanced than most simple temperature controllers that only look at the temperature. A PID controller also considers the rate of change of temperature. This means that as a PID controller sees the target temperature approaching, it knows to "slow down" so that it doesn't overshoot the temperature. A PID controller uses calculus to measure this rate of change instead of simply looking at "am I too high or too low?".

The end result is a more consistent temperature, one that doesn't continually oscillate over and under the target temperature. The good news is that the PID controller does it all automatically for us. We don't have to have any understanding of how this all works (no need to remember your high school calculus).

 

[timcunnell]

Thanks GHB very interesting, and I shall definitely look into getting a PID controller then. In fairness I need a bigger fridge ideally, as I only got an under the counter one because we were throwing it out at work. So I reckon I will use this as a prototype and get a bigger fridge and PID controller!

One thing that did occur to me as I have been researching this is that in most cases you probably aren't going to want heating and cooling mode. In summer you may only want cooling mode, and only heating mode for winter. So as it is getting cooler now and I have the brew fridge in my garage, I reckon I can probably unplug the compressor (fridge/cooling) anyway, as the temp in my garage is going to be below 19 pretty much all the time anyway. So in theory the ambient temperature in my fridge, and more importantly the temp of the liquid in my fermenter should be much more stable as I will lose the over-cooling that cuts in after the over-heating phase.

Can't wait to get it working properly really and see what happens!

Even when the heater is switched off it will still be radiating heat. If you want a more precise control you'd have to go with a PID controller
which senses when the set temp is approached and alters it's output accordingly. I think it switches on and off frequently as it's nears the set temp and thus avoids overrun.
I'm sure there's other members that can offer a better description of how it actually works.

here's a more detailed bit of splurge


A PID controller (proportional integral derivative controller) is a control loop feedback device that is used to continually calculate the difference between the target temperature and the measured temperature and takes the appropriate action to make up for any difference.

A PID controller is an intelligent device that learns and trains itself to the behavior of a system so as to not overshoot or undershoot the target temperature. It is more advanced than most simple temperature controllers that only look at the temperature. A PID controller also considers the rate of change of temperature. This means that as a PID controller sees the target temperature approaching, it knows to "slow down" so that it doesn't overshoot the temperature. A PID controller uses calculus to measure this rate of change instead of simply looking at "am I too high or too low?".

The end result is a more consistent temperature, one that doesn't continually oscillate over and under the target temperature. The good news is that the PID controller does it all automatically for us. We don't have to have any understanding of how this all works (no need to remember your high school calculus).