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Old 01-26-2012, 03:38 AM   #1
centex99
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Default Thermostat complete bypass?

So... trying to adjust the thermostat on my keezer/freezer build... the screw came out... so I took it apart and in the process, destroyed the thermostat... (I popped the pressure in the copper tube/thermometer)...
So I have a temp controller on order and my question is... should I just use that and wire that up as the thermostat... or replace the thermostat and try to adjust again/hook up temp controller with thermostat in line...



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Old 01-26-2012, 03:44 AM   #2
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I have done it both ways.
I prefer using my controller in place of the cold control thermostat on the freezer.
This way none of the other functions are interrupted.
For example, the light will still work properly this way and the fans will remain on after the compressor kicks off. (timers still work properly)



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Old 01-26-2012, 04:00 AM   #3
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$7.66 to replace + $6 shipping... :-/ Plus it further delays my kegerator getting up and running....

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Old 01-26-2012, 07:19 AM   #4
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Definitely hard wire the controller in place of the thermostat. Like mredge73 says, you'll be guaranteed to get the temps you want regardless of what the original thermostat says, and since you're not disconnecting power to the entire fridge, running lights and fans (if you have them) will remain powered even when the box is within temp range and the compressor is off. I did my chest freezer/kegerator/keezer this way and I'm super happy with the control I get.

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Old 01-26-2012, 11:48 AM   #5
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Its a chest freezer.... so just hardwire in to where the hot in/out was on the thermostat...
Will the cheap eBay one work Ok for this?
I have one on order... also ordered the replacement thermostat...
My only concern was thermostat going crazy and keeping it on 100% and burning up compressor...

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Old 01-26-2012, 01:30 PM   #6
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I have a cheap PID on mine in place of the cold control thermostat; works perfect.
(SESTOS PID http://stores.ebay.ca/MixTea)
I set the cycle time to 2 minutes as to keep from rapidly cycling the compressor and my sensor is placed in a gel pack. This is much better than the factory mechanical thermostat with a air sensor; so I should actually get more life out of it.
I went with the SSR version since the internal contacts max out at 3A. (my fridge runs at 3.5-4A) If your chest freezer is below 3A then you can save some money by getting the the one with contacts.
Small deep freezers can run as low as 2A.

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Old 01-26-2012, 01:59 PM   #7
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I already have an ST-1000 on its way... only question I have would be where and how to install the temp sensor that comes with it... in the side panel (in place of factory thermostat that is shoved through the hole into the side wall) or in the freezer... and if in the freezer, I'd guess towards the bottom... but loose or in some liquid....

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Old 01-26-2012, 02:37 PM   #8
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I have mine installed in a cold gel pack in my kegerator.
The gel pack and the liquid in the beer stay within 1C of each other.

My fermentation chamber sensor is currently taped to my fermentor; but I plan to add a thermowell soon to the fermentor for better temperature control.

Point is that air temp is not what you are looking for.

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Old 01-26-2012, 03:14 PM   #9
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Where do I get a gel pack that I can insert a probe into? Or could I just use a mason jar of water?

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Old 01-26-2012, 06:12 PM   #10
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It's a little off-topic for this thread maybe, but since you asked, and since I've been thinking about it...

I know a lot of people put their temperature sensors in gel packs, water, or other buffers, but I actually think this is unnecessary and causes the temperature of the liquid to vary more than if you leave it in the air.

My logic is as follows:

There is a lag time between a temperature change in the air and the corresponding temp change in the liquid, since it takes time for heat to transfer into or out of the liquid. If you raise the temp of the air in the chamber, say 10 degrees, the temp of the fluid will gradually start to rise until it's sitting at the same temp. Because of this, the air temp can fluctuate relatively rapidly up and down while the temp of the liquid changes only very slightly. There are some threads on this board where people have measured air temps varying in the 5-10 degree range, and the liquid in the carboy varying less than a degree.

Let's use a cooling-only case as an example. When the compressor is off, the air temp in the chamber is gradually rising. If you leave the temp probe exposed to the air, the compressor kicks in pretty much immediately as soon as the air temp hits the set point and works to bring the air temp back down to below the threshold. As such, the max temp of the air in the chamber using this system is very close to the "compressor on" set point.

Now consider the case where you buffer the temp probe. The compressor is off. Remember the air temp in the chamber is gradually rising. It hits the "compressor on" set point, but because the temp probe is buffered, it keeps rising until the heat can work its way through the buffering solution and eventually to the probe itself. By the time the compressor kicks on, the temp in the chamber may be much higher than the set point. The temp of the liquid in the chamber (both the carboy and your temp probe buffer) has actually moved enough to trigger the compressor.

The only reason I could see to buffer a thermostat temp probe is if you want to slow down the response time of the system. It's bad for compressors to cycle too quickly, but most temp controllers allow you to explicitly set a minimum cycle time (2-3 minutes is fine, but you can do more if you want) to avoid this. This is actually more reliable, since it guarantees that the compressor won't cycle more frequently, where the buffered temp probe system still could if the temp differentials were high enough.

The other reason I could see to put a thermometer in a gel pack is to act as a proxy for the actual liquid temp if you don't have a thermowell for your carboy. But note that this is not to act as a temp sensor to control the system, it would just be to give a better estimate of liquid temp than you'd get by measuring the air.

Sorry that was long. Hope it's helpful.



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