Fridge built in thermostat logic

[jwhazel]

Couldn't find this answer while googling so hoping someone has some insight. I know that most mini-fridges/freezers are extremely simple devices at least electrically. But do thermostats have some built in logic that keeps the compressor from running constantly outside of the temperature threshold that it normally controls? Or is this logic somewhere upstream closer to the compressor?

I currently have a wine cooler I use as a ferm chamber. I set the internal thermostat to "max cool" and run the whole thing off an ITC-308. I know wine fridges aren't the best but it will get 5gals down to ~40F which is all I need. But on that way down from ambient I notice the compressor will still cut out occasionally (~10 mins?) even when the inkbird cooling relay is open. I'm fairly sure it's not a faulty compressor either. So this tells me that for some reason they designed it to keep from running non-stop. But there's nothing on the elementary schematic I can see that would indicate this.

And that is the root of my question: if I convert this to an ITC-1000 and cut out the internal thermostat am I asking for trouble? Is there normally some logic that should keep compressors from running constantly while they are on their way to a target temp?

 

[grampamark]

That sounds like the compressor delay function of your temp controller doing its job. Scroll through the functions until you get to “Pt”. It’s probably set to 10 minutes.

 

[day_trippr]

Making the assumption that "open" would more correctly be replaced with "closed" in this statement: on that way down from ambient I notice the compressor will still cut out occasionally (~10 mins?) even when the inkbird cooling relay is open. I suspect the compressor is experiencing thermal shutdowns...

Cheers!

 

[Deadalus]

Couldn't find this answer while googling so hoping someone has some insight. I know that most mini-fridges/freezers are extremely simple devices at least electrically. But do thermostats have some built in logic that keeps the compressor from running constantly outside of the temperature threshold that it normally controls? Or is this logic somewhere upstream closer to the compressor?

I currently have a wine cooler I use as a ferm chamber. I set the internal thermostat to "max cool" and run the whole thing off an ITC-308. I know wine fridges aren't the best but it will get 5gals down to ~40F which is all I need. But on that way down from ambient I notice the compressor will still cut out occasionally (~10 mins?) even when the inkbird cooling relay is open. I'm fairly sure it's not a faulty compressor either. So this tells me that for some reason they designed it to keep from running non-stop. But there's nothing on the elementary schematic I can see that would indicate this.

And that is the root of my question: if I convert this to an ITC-1000 and cut out the internal thermostat am I asking for trouble? Is there normally some logic that should keep compressors from running constantly while they are on their way to a target temp?

What temperature does the wine fridge internal think is "max cool"? Mine has white and red settings but it's digital. However, I think the lowest is 44F. Try looking in the product manual or attempting to find the manual online (and be careful where you download from!) You can find old manuals online. I wonder if max cool perhaps is what is shutting it off. Then it comes back on and then shuts off. I was also thinking of that setting that Grampamark mentions as a possibility, see what it says it will be set to a default or could have been set otherwise in the past, purposefully or not.

 

[jwhazel]

That sounds like the compressor delay function of your temp controller doing its job. Scroll through the functions until you get to “Pt”. It’s probably set to 10 minutes.

Happy to be wrong here but I think Pt is used to keep the compressor from quick cycling due to a rapid change in temp above the cooling differential CD. I.e. the cooling relay has to actually open first before it starts the countdown for this. I don't think this is happening here.

Making the assumption that "open" would more correctly be replaced with "closed" in this statement: on that way down from ambient I notice the compressor will still cut out occasionally (~10 mins?) even when the inkbird cooling relay is open. I suspect the compressor is experiencing thermal shutdowns...

Cheers!

You are correct, meant to use "close". So you are confirming fridge/freezer compressors normally don't do this? Assuming no thermal shutdown, they will run till they hit target temp? I realize I could test this with my kitchen fridge, but don't want to loose a whole bunch of food

Also do you happen to know what triggers thermal protection? As in is it the compressor itself or the lines that radiate through the surface?

What temperature does the wine fridge internal think is "max cool"? Mine has white and red settings but it's digital. However, I think the lowest is 44F. Try looking in the product manual or attempting to find the manual online (and be careful where you download from!) You can find old manuals online. I wonder if max cool perhaps is what is shutting it off. Then it comes back on and then shuts off. I was also thinking of that setting that Grampamark mentions as a possibility, see what it says it will be set to a default or could have been set otherwise in the past, purposefully or not.

Owners manual says 43F. I can believe that once it hits 43, it cycles off. But I wouldn't think it would cut off before that. Unless the post above is correct about hitting thermal load and shutting down?

 

[Deadalus]

ITC 308 Manual says

When the controller is working normally, the LED displays current measured temperature, and automatically identify and switch refrigeration and heating working modes. When the measured temperature PV ≥ TS(temperature set value) + CD (cooling differential value), system enters refrigeration status, the cool indicator lamp will on, and refrigeration relay starts to work; when the cool indicator lamp is flickering, it means the refrigeration equipment is under compressor delay protection status.

Does that last part happen? The quote is from Section 5.1. Compressor delay protection (PT) is further discussed in 5.3.

I find their manuals can be a little difficult to follow, partly due to translation and partly because I don't routinely use this type of equipment. If you were able to catch when this occurs and time it, if the time value equalled your PT value that would seem to indicate the culprit. Or look for the light to be flickering.

 

[jwhazel]

I realize I may have muddied this. If I plug the fridge into the wall (no Inkbird). The compressor will cycle on its way to the lowest possible temp. It's not the Inkbird doing it.

Edit: I'm starting to really wonder if the answer is simply that no one uses a wine fridge for sub 50F temps so mfg's put tiny compressors in and at that point during operation it's simply a race to which opens first - the thermostat or the thermal protection switch.

 

[Deadalus]

Maybe this will help diagnose Open Thermal Overload on Compressors