cheap temp control electrical questions

mummasan · 12-24-2008, 12:06 AM

I have a son of fermentation chiller and I want to upgrade so I bought a used Kenmore mini fridge to use as a fermentation chamber. The warmest setting is 50 degrees - too warm to ferment ales. I can buy a Loves controller but it will end up costing $70 ($20 to ship to HI) and I want to try to do something cheaper.

I saw a guy made a remote sensing DIY temp controller Wort-O-Matic: Remote Sensing DIY Controller for Less Than $25 and I thought I could try to control my mini fridge temp with this idea.

Could someone look at this page and let me know if I can do this with what I currently have? I'm interested in the second diagram towards the bottom of the page.

I have a 12VDC power supply that I am using for my old son of fermentation chiller -can I use that for the power supply in this configuration? In the diagram there are instructions that say 'Make sure the coil voltage is the same as the power supply. If you have a 24 volt DC power supply make sure to use a 24 volt DC coil relay.' What does that mean?

Also, next to the diagram on the web page it says 'Make sure the relay contacts are rated for 120 volts AC and are rated to handle the load amps.' What does that mean for me and my mini fridge? Can I buy a 12VDC relay that has relay contacts rated for 120 volts AC?

Any help is appreciated.

Durangstang · 12-25-2008, 11:04 AM

A relay is basically a switch that needs its coil energized to open or close its contacts. The coil can be rated to accept various voltages so if you are going to use the 12 volt dc power supply make sure that the coil of the relay is the same. Also the contacts on a relay are rated up to a certain amperage. Look for the nameplate on the fridge and try to find where it says what the full load amps are. This is the total amperage draw of the fridge and you have to make sure the contacts on the relay are higher than that number. I'm not too familiar with dc relays so I don't know how easy it will be to find one with a dc coil and ac contacts but I'm sure they're out there.

In the end you are going to end up spending between $25-$30 between the thermostat and the relay. There is going to be a bunch of wiring involved and you risk screwing up the thermostat when removing the thermistor.

Why don't you look into something like this HVACR > Controls > Line Voltage Thermostats > Line Voltage T-Stat,-30 to 90 F,SPDT : Grainger Industrial Supply

Grainger can be expensive but they have a branch in Honolulu. I don't know if you were looking to spend that much but you may be able to find something similar for less locally. Maybe try at a refrigeration supply shop. Something like that will be a lot easier. All you need to do is wire the fridge to it.

missing link · 12-25-2008, 04:30 PM

Grainger sells the johnson controls fridge controller and they usually have them in stock. I tihnk I paid $60 for mine at grainger.

If you can walk in and get one, that will save you some cash. Though the Love at $49 + Shipping ends up being almost the same.

mummasan · 12-26-2008, 04:38 AM

thanks for the info - you're right - I'll probably spend $25-$30 on the thermostat, relay, and wires - if I can spend $50-$60 on a device I can just plug in then it may be worth the extra money