mini fridge issues

[fleabagmatt]

I picked up a mini fridge yesterday from Craigslist with the intention of using it as a fermentation chamber. I plugged it in last night and let it run on its lowest setting to see how it performed and this morning it's sitting at a balmy 15 degrees inside. I plan on building an STC-1000 temp controller to handle temperature regulation, so if the fridge's thermostat or controller has gone bad (I don't know for sure if it has or not yet) does it matter? Am I correct in assuming that those controls are bypassed by the STC-1000 anyway?

 

[jddevinn]

You are correct. The temperature controller will turn the fridge on and off by passing its thermostat.

 

[WrQth]

Depends on how you wired in the fridge to the controller. If the fridge power cord is just plugged into the STC-1000 then thermostat of the fridge controls the temp based on where the the control is set and the STC-1000 simply supplies power to the it until the temperature the STC-1000 probe readings matches the temperature set in the STC-1000.

Edit: For example if the temp dial in the fridge is set to is highest setting which will maintain a temp of 40 F and you have the STC-1000 temp set to 35 F, the STC-1000 would trigger the relay to supply power but the fridge thermostat sees that it has reached its temp of 40 F it will not cycle the compressor to make it colder to meet the 35 F the STC-1000 is set to, the STC-1000 will continue to supply power because it wants the fridge at 35 F and the only way it can do that is to supply power.

If however you wired the STC-1000 to the compressor then that'd be a different story.

 

[kombat]

Aren't you supposed to wait 24 hours after moving it before plugging in a fridge? Or is that just freezers? Something about letting the oil/refrigerant settle back down in the reservoir?

 

[balrog]

Aren't you supposed to wait 24 hours after moving it before plugging in a fridge? Or is that just freezers? Something about letting the oil/refrigerant settle back down in the reservoir?

I think that's only if you carry upside down on the back of a Vespa going through the streets of San Fransisco. At night.

 

[WrQth]

Aren't you supposed to wait 24 hours after moving it before plugging in a fridge? Or is that just freezers? Something about letting the oil/refrigerant settle back down in the reservoir?

I've heard that but think only if it was tipped over on a side or at a significant angle for an extended period of time such as transportation.

 

[WrQth]

I picked up a mini fridge yesterday from Craigslist with the intention of using it as a fermentation chamber. I plugged it in last night and let it run on its lowest setting to see how it performed and this morning it's sitting at a balmy 15 degrees inside. I plan on building an STC-1000 temp controller to handle temperature regulation, so if the fridge's thermostat or controller has gone bad (I don't know for sure if it has or not yet) does it matter? Am I correct in assuming that those controls are bypassed by the STC-1000 anyway?

If the fridge is set to is lowest settings and only came down to 15 degrees, I assume Celsius, and it is just plugged into a wall outlet then something must be wrong with the fridge, anything from a bad thermostat to loss of refrigerant.

 

[fleabagmatt]

15 degrees Fahrenheit.

Edit: I should also say, the fridge was never put on its side or anything, it remained upright in transportation.

 

[WrQth]

15 degrees Fahrenheit.

Edit: I should also say, the fridge was never put on its side or anything, it remained upright in transportation.

I have a wine fridge that goes as low as 40 F (fridge temp dial is always set to lowest), I have an STC-1000 that the power connects to. If I set the STC-1000 20 C (68 F) it will turn the power on and the fridge will run until the the STC-1000 probe detects 20 C then it turns the power off until it rises by more than .5 C then it will apply power again until the STC-1000 probe reads 20 C then it turns the power off, so on and so forth.

20 C (68 F) is higher than 4.4 C (40 F) so the STC-1000 probe controls when cooling is stopped but if I set STC-1000 to anything below 4.4 C then the STC-1000 will continue to apply power but the thermostat in the fridge will tell the compressor to stop running when the minimum temp the fridge has been designed to go down to is reached (40 F in the case of my fridge), so the fridge will never go below the fridge minimum temp.

 

[kombat]

15 degrees Fahrenheit.

If you bought a fridge that goes down to 15° F, I've got some bad news for you. You don't have a fridge. They sold you a freezer.

OT, funny side note: A few years ago, my wife bought a countertop wine fridge. It only holds about 6 bottles or so, on their sides. We found the bottles weren't very cold, even with the knob cranked all the way to the "Low" end of the dial.

It turned out to be a semantic mix-up. "Low" in the context of the fridge meant the compressor was on it's "lowest" setting (i.e., not working very hard), whereas we were interpreting "low" in the sense of the desired temperature. Once we cranked the dial to "high," the thing really kicked in and got the wine nice and chilled. It was counterintuitive, but funny.

 

[jddevinn]

Depends on how you wired in the fridge to the controller. If the fridge power cord is just plugged into the STC-1000 then thermostat of the fridge controls the temp based on where the the control is set and the STC-1000 simply supplies power to the it until the temperature the STC-1000 probe readings matches the temperature set in the STC-1000.

Edit: For example if the temp dial in the fridge is set to is highest setting which will maintain a temp of 40 F and you have the STC-1000 temp set to 35 F, the STC-1000 would trigger the relay to supply power but the fridge thermostat sees that it has reached its temp of 40 F it will not cycle the compressor to make it colder to meet the 35 F the STC-1000 is set to, the STC-1000 will continue to supply power because it wants the fridge at 35 F and the only way it can do that is to supply power.

If however you wired the STC-1000 to the compressor then that'd be a different story.

15 degrees Fahrenheit.

I'm assuming his thermostat is broken causing the compressor never to turn off. If this is the case it doesn't matter as the temp controller will turn the entire fridge (compressor included) on and off. If the thermostat was broken the other way, where it never turned the compressor on, it would need to be wired around.

 

[fleabagmatt]

I'm assuming his thermostat is broken causing the compressor never to turn off. If this is the case it doesn't matter as the temp controller will turn the entire fridge (compressor included) on and off. If the thermostat was broken the other way, where it never turned the compressor on, it would need to be wired around.

I suspect you're correct and the compressor isn't shutting off. I figured using the external controller would take care of that issue, just wanted a bit of reassurance.

Thanks.

 

[DurtyChemist]

Depends on how you wired in the fridge to the controller. If the fridge power cord is just plugged into the STC-1000 then thermostat of the fridge controls the temp based on where the the control is set and the STC-1000 simply supplies power to the it until the temperature the STC-1000 probe readings matches the temperature set in the STC-1000.

Edit: For example if the temp dial in the fridge is set to is highest setting which will maintain a temp of 40 F and you have the STC-1000 temp set to 35 F, the STC-1000 would trigger the relay to supply power but the fridge thermostat sees that it has reached its temp of 40 F it will not cycle the compressor to make it colder to meet the 35 F the STC-1000 is set to, the STC-1000 will continue to supply power because it wants the fridge at 35 F and the only way it can do that is to supply power.

If however you wired the STC-1000 to the compressor then that'd be a different story.

I don't think this is true. I'm pretty sure the STC will power the refrigerator until the STC senses the temperature is whatever the set point is. I could be wrong as I have mine cranked pretty low but only run it around 50-55 so I will have to test this tonight and report back.

 

[kombat]

I don't think this is true. I'm pretty sure the STC will power the refrigerator until the STC senses the temperature is whatever the set point is.

Right, that's what he's saying. However, if the fridge is set to 40° F, and the STC-1000 is set to 35° F, then the fridge will stop running its compressor once it detects that it's gotten things cooled down to 40° F. The STC-1000 will keep providing power to the fridge, but the fridge will simply do nothing. The light inside will work, but the compressor won't run, because as far as its concerned, its job is done (i.e., it's reached its target temperature of 40° F). The STC-1000 would never cut power to the fridge, because the fridge will never cool down to the 35° F setting in the STC-1000.

 

[fleabagmatt]

So if your fridge is working properly, you ideally want it set as cold as it will get so that the STC handles all the on/off duties, right?

 

[kombat]

Yes, exactly. Or even better, use a freezer.

 

[Spartan1979]

So if your fridge is working properly, you ideally want it set as cold as it will get so that the STC handles all the on/off duties, right?

I would say that depends on if you are measuring the air temperature or the liquid temperature. If you are measuring the liquid temperature (through a thermowell) and the fridge temperature is set as low as possible the air in the fridge will be much colder when it shuts off and the temp of the fermenter will continue to drop. I try to adjust the fridge so it's just a little colder than the temp I want my beer at.

 

[kombat]

If you are measuring the liquid temperature (through a thermowell) and the fridge temperature is set as low as possible the air in the fridge will be much colder when it shuts off and the temp of the fermenter will continue to drop.

Not by much, as it turns out.

 

[jddevinn]

Not by much, as it turns out.

Yep, specific heat of air is 1.01 J/gºC and specific heat of water is 4.179J/g°C. ie much more energy to change the temp of water (or beer) than air.