Wednesday, July 18, 2012

Freezers, Refrigerators, Coolers & Chinese Thermometers

I've been doing some eutectic experimentation to see how long I can go by using a small chest freezer ($160 f/ Walmart) as a cooler. We often take the trailerable houseboat out for 2 to 5 days at a time. Ice not only can be expensive, but can also be a pain in the neck getting replentished. The idea was to plug in the small chest freezer installed on the back of the boat and freeze 5 gallons of water into a brick. Then when we head out, unplug the freezer and use it as a cooler.

Well, this endeavor proved totally successful. The frozen brick would keep things inside the chest cool for 6 days. The trouble is that while the brick is near 32°, the temps can vary inside the chest up to 40°.

I want the max temp in the chest/cooler to be no higher than 36°. This means I need to freeze a solution that has a lower freezing temp than 32. The idea is to introduce salt into the brick so the melting temperature is about 28° or so?

About this time in my experiment, my thermometers, both of them, failed. I ordered 4 new remote bulb thermometers on eBay. It took a couple weeks to get the shipment from China, but at $1.80 each including shipping I didn't mind the wait. Because these thermometers only read in Centigrade, I made up a little chart to show what the Fahrenheit reading would be. In the process of placing one of these thermometers in the freezer, it got away from me and ended up in a puddle of brine that had spilled from the brick.

I figured the thermometer was trashed, but rinsed it in the sink to see if there was any hope of revival. I'll be darned if the little thermometer didn't come back to life, and was now reading in Fahrenheit, complete with the proper temp and an 'F' on the display. The 'F' readings reverted back to 'C' when the unit dried out.

I eBayed a note to the seller with my findings and a request about how to make the 'F' readings permanent. They advised me that the unit would only read in 'C', but a previous buyer converted it to 'F' with the addition of 'an accessory'. They eMailed me a photo showing which traces on the circuit board needed to be connected in order to get an 'F' reading, but they insisted that the procedure had not been verified. Well, not surprisingly, it does work - a well placed drop of solder is all it takes.

Now on to see how much salt it takes in the 5 gallon container to keep the chest at 38° or lower without freezing my beer.

I also got a remote line thermostat on eBay. With this unit, I can set the freezer thermostat to max cool and put the remote thermostat bulb inside the freezer. Then I connect the freezer power cord to the remote line thermostat and can have the freezer chest maintain any refrigerator temp I desire. I've experimented enough to know that this works to maintain any chosen temp in the freezer but this requires constant 120vac power.

The final step is to determine how much generator run time is necessary to maintain a refrigerator temp (of about 38°) in the chest. I have found a 120vac hour meter on eBay that I can wire into the line thermostat circuit to the determine power/generator run time. Once this is determined, I will know how long I will need to run the generator to keep the freezer at refrigerator temps. Then we'll see what the effect of including the brine brick will have on the runtime.

Freezer/Refrigerator Findings

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