TETB kegerator build

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The-Engineer-That-Brews

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Hot-wiring the thermostat

This really was the easy bit.

First of all I fixed the fridge light to the roof. Double-sided foam tape is perfect for the job but make sure you get the right place because once it's stuck you won't get it off again in a hurry.

IMG_6261.jpeg


Next (after having checked the power was disconnected) I shortened and soldered together the mains-in, compressor and lighting cables and insulated with heat shrink. Make sure you understand the circuit before doing this because your wires may be different colours to mine. I spent a while tracing the circuit before I noticed it was actually printed on the label... :doh:

Notice how the three connections from the thermostat (that we disconnected) work: "B" is the mains input, "C" switches the compressor on above the set temp, and "L" is the power to the light (via the door switch) which is permanently on except when the thermostat knob is turned all the way to the OFF position.

IMG_6262.jpeg
IMG_6187.jpeg
 
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The-Engineer-That-Brews

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The beer was at 14°c when it went into a 12°c fridge yesterday; and this morning I turned the fridge down to 11°c.
It was measuring 12.2°c at 6pm but I see it’s now risen slightly to 12.4°c so I guess there’s some metabolic activity kicking off in there even there’s no Krausen yet. As the recommended top end for the yeast is 13°c I think I’d better turn the fridge down to 10°c.

Edit: I just checked and there are a few spots of krausen beginning to form so it definitely looks like there’s a bit of metabolic heat involved. I’ll have to keep an eye on it.

CE9DB591-48C9-4FD1-836D-0930B84667FE.jpeg
 
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The-Engineer-That-Brews

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Tomorrow I will adjust the code on the controller slightly so that I can tell it to target a particular beer temperature, but without running the fridge itself below zero.
 

Perrin_Abara

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Hot-wiring the thermostat

This really was the easy bit.

First of all I fixed the fridge light to the roof. Double-sided foam tape is perfect for the job but make sure you get the right place because once it's stuck you won't get it off again in a hurry.

View attachment 55120

Next (after having checked the power was disconnected) I shortened and soldered together the mains-in, compressor and lighting cables and insulated with heat shrink. Make sure you understand the circuit before doing this because your wires may be different colours to mine. I spent a while tracing the circuit before I noticed it was actually printed on the label... :doh:

Notice how the three connections from the thermostat (that we disconnected) work: "B" is the mains input, "C" switches the compressor on above the set temp, and "L" is the power to the light (via the door switch) which is permanently on except when the thermostat knob is turned all the way to the OFF position.

View attachment 55122 View attachment 55125
if I wanted to, could I just remove the housing and leave everything connected if it was just for the sake of fitting another corny in?
 

The-Engineer-That-Brews

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if I wanted to, could I just remove the housing and leave everything connected if it was just for the sake of fitting another corny in?
Hmmm.. if you just unscrewed the housing but left everything connected, then you could probably rest it on top of the second corny: in the photo you can see that the top of the corny only covers up about half of the alcove.
I think I’d want to add some more insulation around the connections though…
So would your idea be to control the temp using the existing thermostat?
 

Perrin_Abara

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Hmmm.. if you just unscrewed the housing but left everything connected, then you could probably rest it on top of the second corny: in the photo you can see that the top of the corny only covers up about half of the alcove.
I think I’d want to add some more insulation around the connections though…
So would your idea be to control the temp using the existing thermostat?
Yes but after further thought correct me if I’m wrong, I could just connect the light,compressor, mains in and then buy another inkbird.
 

The-Engineer-That-Brews

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Yes but after further thought correct me if I’m wrong, I could just connect the light,compressor, mains in and then buy another inkbird.
Correct, and that's what most people do. You'll need an Inkbird (or similar) with a 'cooling' output though.

Re-wiring the Compressor
This step is not at all compulsory: you can just follow the traditional route of hot-wiring the thermostat and plugging the whole fridge into your Inkbird or whatever. However that means that the light wouldn't go on unless the fridge was running.
 

The-Engineer-That-Brews

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Spent today converting the second fridge.
It's simply a carbon copy of the first one but as usual with these things doing the job the second time around is about three times faster.
The mounting bar in the top was about 1cm further back than in the first one, so there's obviously some variability in how they're made.

IMG_6287.jpeg
 

The-Engineer-That-Brews

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Slightly embarrassingly yesterday I had a problem with the circuit I used to control the fridge relays.
It really had me scratching my head: everything worked fine with either one fridge connected or the other, but bad things happened when I connected both at the same time.

Here's the circuit; nothing too unusual:
What I'm doing here is wiring one side of the relay to +12v, and using the transistor as a switch to turn the earth path on and off.

Screenshot 2021-10-13 at 10.39.17.png


Now... here's what I eventually identified as the source of the problem:

Screenshot 2021-10-14 at 20.52.25.png


This is the DC 5.5mm 'barrel' connector that I used to connect the controller to the fridge relay. There's an identical one on the other fridge.
Can you see the problem...? Well it took me a while.

The problem has three components: (1) the outer side of the connector also forms the metal casing. (2) I've mounted the connector on an aluminium plate that is screwed to the chassis of the fridge. And (3) the chassis of the fridge is connected to earth via the mains cable.
None of these things causes a problem when I'm only controlling a single fridge because the controller uses a 'floating' power supply. But when two fridges are connected then their chassis are joined via the mains leads. Again this wouldn't cause a great problem as such (except that both fridges would turn on and off together), were it not for the FOURTH component of the problem: I'd inadvertently wired one of the connectors up the other way round at the controller. The consequence of this was that the B/C junction of one of the transistors became forward biased with predictably fatal consequences for the device concerned.

Oooops.

The solution
I decided the best approach was to re-design the circuit so that I'm switching the 12v supply on and off, rather than the earth. Like I should have done in the first place... :rolleyes:

IMG_6290.jpeg
 
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The-Engineer-That-Brews

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Really enjoying following this, despite only understanding half of it athumb..
Thanks! It's curiously satisfying to have brews now fermenting in both fridges at different temperatures.

IMG_6297.jpeg


Now I've got the temperature control working I need to get cracking on fitting the font and the taps...
 

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