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Old 03-09-2009, 03:27 PM   #1
blackheart
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Default DIY Temp controller for kegerators/fermenter freezers

Hello all. I have been hanging out here for awhile reading the forums and have alot of good ideas from many of the projects I have seen on these forums. I am ready to get serious about my brewing and move to a 10 gal all grain setup. Before I can do that I want to have somewhere to store my 10gal batches in a temp controlled environment. And before I can do that I need to be able to store and serve at least 20gal of beer.

I picked up a whirlpool 8.9cu/ft chest freezer from lowes, who apparently is the only person who sells this model. It holds 5 kegs perfectly. I have sense painted it black and I am ready to add the taps and all the fun parts to make it a kegerator. But first I need to regulate the temp so that the beer does not freeze.




I could buy a temp controller from Ronco or Love. But where is the fun in that? Plus they are 50-100$. Also they are a bit redundant because they simply cut the power to the whole freezer (ie pulling the plug)

I came up with a super simple design using analog circuits. This means that there is no programing (to fail) and it can be built with a trip to radio shack. Currently it is in a prototype stage but it is working great.

In its current configuration you adjust two variable resistors to set the high and low temp values. The circuit triggers a relay which turns on the compressor when the temp is too high and turns it off when it is too low. In the mean time the compressor is off until it warms up to the hight point again.

I am looking for your input on this as I would like to make a printed circuit board. again this isnt trying to be a Love or ronco digital controller, at its current design it would cost less than $20 to build. Also it plugs into where the existing thermostat is and requires no real modification to your chest freezer (at least my model).

Some ideas I had for the circuit....

- Integrate an ac/dc converter so that a separate converter is not necessary.
- Replace the variable resistors with permanent ones and a switch to switch between "serving temp" and "fermenting temp"
- Put the LED's on extended wires so that you can mount them in the side of the kegerator to indicate the circuit is on and its current state (blue-cold, red-warm, green-just right)

What other features do you think people might like in a basic temp controller? The focus here would be on working well for the cost, not advanced features and it may require some adjusting or tweeking to get the best results.

Here is a picture of the current circuit, the final design will be much smaller when printed. Currently it still fits in the existing plastic housing where the stock thermostat was. (blurry from my camera phone)

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Old 03-09-2009, 04:32 PM   #2
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Hmm I see a reed relay on there is I have used those in the past pretty cool. How are y ou measuring the temperature? I was actually thinking of something similar. I was a computer engineering major and one of my first labs we played around with circuits using thermisters.

I could see a possibily for building an very simple circuit using a thermister and a reed relay.

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Old 03-09-2009, 06:22 PM   #3
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Quote:
Replace the variable resistors with permanent ones and a switch to switch between "serving temp" and "fermenting temp"
When you switch to fermenting temp how many options do I have?
Bare minimum, we need a Lager & Ale setting.
Not all yeast strains have the identical optimum fermentation temp.
With two setting I am forced to select yeast strains with similar fermentation temps.
How can I ferment an Altbier or a Weizen?
Is this design only for aging, conditioning?

Quote:
What other features do you think people might like in a basic temp controller?
Has to have a dial with temp markings.
Unit must be able to control cooling and heating automatically.
No external load relays.

Cheers,
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Old 03-09-2009, 07:16 PM   #4
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I used a comparator (op-amp) to compare the voltage seen coming back from the temp sensor (johnson replacement probe from morebeer) and compare it to voltages set by the two (blue) pot's. Using the spec sheet for the temp probe I calculated what resistance values should be for 42 and 38F then set the 25 turn precise pot's to be those values.

If the voltage on the temp probe is lower than the voltage on the 42F high setting then the op-amp outputs 5v. Otherwise it outputs 0v. The low temp does the opposite. Both inputs are feed into a SR-Latch made from a quad-nand gate chip. Rising above the high temp sets the latch turning on 5v to the reed relay which then triggers the 12v power supply powering the circuit to trip a 12v relay which switches on the compressor. When the temp gets too cold the SR-Latch resets and the compressor turns off.


Quote:
Originally Posted by ClaudiusB View Post

When you switch to fermenting temp how many options do I have?
Bare minimum, we need a Lager & Ale setting.
Not all yeast strains have the identical optimum fermentation temp.
With two setting I am forced to select yeast strains with similar fermentation temps.
How can I ferment an Altbier or a Weizen?
Is this design only for aging, conditioning?
Currently temp is set by adjusting a 25 turn variable resistor, checking the resistor value against a chart, and then testing it to see if it works. This method makes the most amount of sense for testing purposes. This is NOT a digital controller that I can program to do amazing things. This is an analog circuit which relies solely on voltages and basic logic to operate.

This means in order to set the temp to x degrees I need to convert x degrees to a resistance value then set the resistor appropriately. I have not thought of another way to do this other than having multiple sets of resistors and switching between them.

This is only accurate to within a few degrees. It works great for serving beer. I set the high temp to 42 and the low to 38 and the beer is always at about 40 degrees. In reality it may be constantly cycling up and down through those temps (its too cold out now to know for sure but thats the logic behind it)

This is meant to be a simple and a bit more diy solution to more costly temp controllers. Above all it is meant to be much less expensive than any of them which start at $60.

Maybe it will not be the best solution for fermenting but for a kegerator it should work great. I plan on testing it out for fermenting soon.


Quote:
Originally Posted by ClaudiusB View Post

Has to have a dial with temp markings.
Unit must be able to control cooling and heating automatically.
No external load relays.


I could have a selector switch or something like that which switches between common temps like, 38-42, ferment range 1, ferment range 2 etc.... and cover 2-3 ferment temps. If you want exact control you will want to go with a Love controller etc. If you picked up a chest freezer or have an old one and want to turn it into a kegerator or temp controlled fermentor this could be a simple and cost effective solution.

It can control cooling at the moment. I am sure I could redesign it so that it could heat and cool.... in most situations I would assume you would want to do one or the other. In that case a simple toggle switch could flip the inputs so it worked in reverse, heating when it was too cold.

What do you mean by no external load relays? Right now the logic chips are switching on a 5v reed relay which is switching 12v to a 12v auto relay which is turning on the compressor. Is there something wrong with this configuration? is there a better way to make 5v switch 120v outlet?

I appreciate your feedback so far and I have some good ideas I will be testing out. Let me know if you have any more questions or ideas!
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Old 03-09-2009, 07:52 PM   #5
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Quote:
What do you mean by no external load relays?
Only one relay on the board to turn the compressor on directly.
You could replace the 5V & the 12 V relay with an inline solid state relay as long the compressor or heater does not exceed 6 A.

Sample part Kyoto KB20C06A
https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&productId=176698&catalogId=10001&storeId=10001&k rypto=CMF4gzkADQxxj3r9%2BdbaPdGAfPQ%2F9w5ynOW8ICGi 3NLWFBd5dWAZMO73iVXvSI4qlDUPNF%2BktSo%3D&ddkey=htt ps:StoreCatalogDrillDownView

Don't give up

Cheers,
ClaudiusB
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Old 03-09-2009, 08:07 PM   #6
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Most people don't want to worry with two pots. I would figure out what good high/low values are, and use a single pot with an additional resistor to get your two values. Two pots is good for testing, but just means one more thing to adjust and worry about when it's actually in use.

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Old 03-09-2009, 09:23 PM   #7
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Quote:
Originally Posted by Hopaholic View Post
Most people don't want to worry with two pots. I would figure out what good high/low values are, and use a single pot with an additional resistor to get your two values. Two pots is good for testing, but just means one more thing to adjust and worry about when it's actually in use.
I see what your saying. Thats a great idea... I could control the High temp point with a large knob connected to a pot. A resistor could add x resistance to the output of the pot making it, lets say 2-4 deg less than whatever the pot is set to. I am sure I could roughly calibrate the pot so that at x degrees the temperature should be y, close enough to fine tune your self.

Thanks for the link to the SSR. I will check that out. See, thats why I posted my project. You guys are a huge help!
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Old 03-09-2009, 09:28 PM   #8
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Quote:
Originally Posted by blackheart View Post
I see what your saying. Thats a great idea... I could control the High temp point with a large knob connected to a pot. A resistor could add x resistance to the output of the pot making it, lets say 2-4 deg less than whatever the pot is set to. I am sure I could roughly calibrate the pot so that at x degrees the temperature should be y, close enough to fine tune your self.

Thanks for the link to the SSR. I will check that out. See, thats why I posted my project. You guys are a huge help!
Another idea I just had- If you really want to get fancy, just use a surface mount small pot for that differential resistance. Still gives tuning ability for your high-low values, should there be a need to change duty cycles.
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