Tobins Thermostat - Can Go In Any Old Fridge?

[Jez]

Hi all,

Long time lurker, first time poster. I've just finished reading the great discussion - espec Justins terrific circuit diagram - about creating an external thermostat using Tobin's part TS-040S. I'm fairly new to brewing and am looking to convert & use a modified fridge so I can get more consistent fermenting temps.

Today I found myself in Strathfield, dropped in to Tobins & picked up one of these thermostats (after the salesman tried to sell me an external model - they now manufacture them - for $130+GST).

I have a few quick questions:

1. is it better for the longevity of the fridge for me (or a suitably qualified person) to simply swap the current thermostat already in the fridge for the Tobins model rather build & use an external thermostat.

2. Is it possible to replace the existing thermostat in a fridge with the Tobins model?

3. Are fridge thermostats fairly standard - ie can I put the Tobins model in any old fridge?

These questions may be old hat to most of you so sorry in advance. Any & all help greatly appreciated.

Jez

 

[Justin]

Nice work, and what's going on with the $130 one? Are they trying to sell a premade model of this thermostat to homebrewers now after all the sales and interest in them?

Anyway, answers.

1. You can install the thermostat in the fridge if you want, depends how crafty and capable you are and if you can work out the wiring (it's pretty easy, just rewired another fridge on the weekend, most only have two wires and an earth going to the thermostat), pretty much a straight swap over in most cases). It wont effect the longevity of the fridge though, unless you stuff up -having it internal or external wont make a difference. The ease pf making an external one is you don't have to play with the fridges wiring, but that's a call you'll have to make.
One bonus of wiring it internally is you dont need other parts like a box and you wont have cables hanging out of your fridge.

2.Yes you can replace the fridges thermostat with this one (as I just answered above).

3. Yes the thermostat will go in any old fridge, just as long as the wiring doesn't get too complicated you should be right.

Cheers, Justin

 

[Jez]

Thanks for the advice Justin.

When the Tobins guy showed me their pre-made external thermo he said they are listed on the website for $169 + GST!!

He then said he could do me a deal and offered it to me for $130 + GST. I thanked him for his kind offer and just bought the thermostat.

When I told the Tobins guy I wanted to put this thermo in a fridge to run it at anywhere up to 18 degrees C he said he wasn't sure the compressor could handle running the fridge that hot. Is this a concern at all?

I have probably put the cart before the horse in that I now have the thermo but still am looking for a fridge to put it in.

When I get my fridge I will see how easy it looks to replace the thermo - otherwise I'll follow your great instructions and build myself an external model.

Someone else told me that the external thermo turning the fridge on & off all the time could stuff the compressor - since so many of you brewers out there swear by this method I assume this is not the case?

Thanks for all the help

Jez

 

[Justin]

Unfortunately, the fridge will turn on and off whenever it needs to to maintain the temp that is set, independent of whether the thermostat is internal or external. The only thing is that if the thermostat is internal then the effect of external temp working on the thermostat is minimised. For the most part your fridge will be actually running far less often than it would if it was being used as a proper fridge.

FWIW I think I will be moving mine internally, however I still have another thermostat out of another fridge to try in it first (I have two fridges, my keg fridge runs off my tobins thermostat because it's thermostat is stuffed-it runs all the time).

As for the fridge handling running at 18C, well it won't be running much at all at those temps. Only every now and then. I guess it could be hard on the fridge but I think most people get by just fine, and anyway if you look around hard enough you should find a fridge for next to nothing so it really wont matter much if it does die. My recommendation is to let everyone you know that you are after a second fridge for beer (you don't have to mention brewing) but I have no doubts you'll find one, and probably for nothing. I think people have trouble getting rid of them because they are big and hard to dispose of.

Good luck. She'll be right.

Justin

 

[Jez]

If there's no real diff between internal & external thermo's I think I'll build the external thermo using your plans & see how that goes.

Looks like even somone with my limited electronic expertise should get it right

Thanks again Justin for the info.

Jez

 

[user 384]

When I told the Tobins guy I wanted to put this thermo in a fridge to run it at anywhere up to 18 degrees C he said he wasn't sure the compressor could handle running the fridge that hot.

Jez

The guy is talking bollocks!

A quick think through the logic shows this. The Tobins external thermostat has a dial from 0-30C to set the temp, and a 2C differential either side of the setpoint. Say you set it at 18C, the compressor will come on when its 20C and turn off when it hits 16C. So the compressor will work to cool the inside of the fridge by 4C.

The original thermostat also has a setpoint and differential. The setpoint is usually selected on a scale (eg 1-7 or cool-coldest) rather than a specific temperature and the differential is most probably 4C. If the fridge is set to coldest and this equals 4C, the compressor will turn on when its 6C and turn off when its 2C. So the compressor will also work to cool the inside of the fridge by 4C.

It makes no difference what the setpoint temp is, the compressor will always be working to cool the inside by Xdegrees, which equals the differential.

Now there are a few other factors. 1) you're likely to open and close the beer fridge door less, thus requiring less cooling, 2) it's easier to cool from 20C-16C, than 6C-2C, particularly when the outside temp is 30C. So in actual fact the compressor will turn on and off less often, and therefore should last longer.

Cheers
Mark

 

[Jez]

Mark,

Yeah, even to somone who knows bugger all about fridges I had the same basic logic that you've outlined.

That the fridge would be on less therefore, if anything, the compressor would cop less wear & tear.

But he was supposed to be the expert so I left him to it.

Jez

 

[Thunderlips]

As for the fridge handling running at 18C, well it won't be running much at all at those temps. Only every now and then.

I use an external thermostat, a Gro-warm, and with the fridge set to 20c it's hardly ever on. I beleive the Gro-warm works in a way that it wont turn on unless the temp range is about 2c over or under what's been selected. It can take some time for that to happen.
I used the thermostat for the first time very recently and checking the thermometer that I stuck in there it was sitting right on 20c

 

[Hoops]

I believe someone posted something on AHB about this earlier . It was stated that as the compressor was running at higher temps the refrigerant was at a higher temp and therefore at a higher pressure so the compressor was starting against higher pressures and running hotter? :mellow:

Anyway I have a ferementing fridge and have been using it for ales and lagers for about 5 years now and it hasn't skipped a beat. It has been doing this for longer than 5 years though as I bought it second hand from another brewer who was expanding to a bigger and better setup. So I wouldn't worry too much about running in at higher temps. At the end of the day at 18C it is running for bugger-all so I believe it is getting less wear and tear than normal. My advice is to go for it. My fermenting fridge is by far my best investment for my brewhaus.

Hoops

 

[user 384]

I believe someone posted something on AHB about this earlier . It was stated that as the compressor was running at higher temps the refrigerant was at a higher temp and therefore at a higher pressure so the compressor was starting against higher pressures and running hotter?

Hoops, I reckon whoever posted that is talking bollocks.

The fridge isn't actually working warmer, it's still doing the exact same task of cooling the fridge by X degrees around the setpoint. The cooling cycle is done at the exact same temp every time. The only thing that varies is the amount of time the compressor is on and the frequency it comes on.

It doesn't matter if the setpoint is 2 or 20 the fridge will still cool the inside by usually 4-6 degrees and when the compressor is on it always cools at the same temp. There might be some very small difference in the amount of time it takes to cool, but this is cycle time and has nothing to do with what temp or pressure the fridge gas is at.

Also fridge compressors are very basic they turn on and turn off. They don' have complex varibale settings to adjust the pressure they compress the refrigerant. They simply vary temperature by varying the duration and frequency they are on.

Cheers
MAH