Homebrew Low Voltage DC Refrigeration Bob McCormick For years electrical refrigeration and freezing of perishable foods was the "Achilles Heel" of AE power systems. In the last few years, low voltage refrigeration appliances have become available. They have very low power consumption rates, but priced at figures few of us backwoods people can afford. I will explain here how the use of low voltage refrigerators and freezers can be more affordable to a larger portion of AE users. Especially if you don't mind doing a little work. Food Preservation Essentials The preserving of perishable foods by canning, drying or freezing has been a way of life for modern people. We no longer hunt for our food from day to day. Many of us who make our own electricity, live where it is not practical to buy our food each day at the supermarket. We need some way to keep our perishable foods from spoiling. This is true whether we grow our own food, or buy it at the store. Canning and drying foods is time consuming and we loose some of the nutrients, as well as flavor and appearance, during processes. Freezing is the preferred method of storing food for long periods. Freezing is quick, convenient, healthy, tasty, and more appealing. Freezing Before PV We have lived beyond the power lines for 22 years. We froze foods until 1985 with 3 old Servel propane refrigerators. We simply removed the temperature sensors from the main control units. The burners operated at high flame continually. This provided adequate freezing when they were placed in the coolest location available. This method was costly, but did the job. Our First 12 Volt Freezer We purchased our first 8 Kyocera PV modules in 1985. The system was sized for our short winter days. These 8 modules powering our energy conservative home meant we had a considerable amount of excess power available during long summer days. The logical choice was to use the excess power for refrigeration and freezing. 12 volt refrigerators and freezers are expensive. None are manufactured in Canada where we live. Importing to Canada would add 40% to their cost. To say nothing of the extra freight charges involved. Instead we bought a DANFOSS 12 volt DC refrigeration compressor with electronic control and a capillary type temperature control sensor. This is the same compressor used in many manufactured appliances, like the Sun Frost units. We replaced the 110 volt ac compressor with the DANFOSS in a conventional freezer box. The capillary temperature control sensor was needed, as the 12 volt compressor would not operate on the 110 volt controls in the box. We discussed the installation with our local refrigerator repair man. He said our idea would work. He also told us that if we installed an external condensing unit on the back of the freezer box we could super-insulate the box with styrofoam, urethane foam, or bat insulation. This would cut down the running time and power consumption dramatically. We found a used 7 cu. ft. deep freezer, with a good box, whose 110 volt compressor had given up the ghost. Our helpful refrigerator repair man replaced the 110 volt compressor with the 12 volt DANFOSS compressor, electronic control unit and capillary temperature sensor. He installed a properly sized external condensing coil on the back of the box. The completed unit was ready to charge with refrigerant. Our repair man evacuated the system of air, charged it with refrigerant, and the installation was complete. The tested unit maintained an internal temperature of 0¡F. The running time of the compressor to maintain 0¡F was 30 to 40 minutes per hour at an ambient temperature of 70¡F. The compressor consumes 4.1 Amps per hour. With a running time of 30-40 minutes per hour our "new" freezer would consume 60 amp hours per day. Three of our Kyocera modules output. This seemed excessive, so we went to work insulating the box. Super-Insulating the Box We purchased enough 2" thick styrofoam board insulation to completely cover the four sides and top of the box. We cut the styrofoam to overlap at the sides and edges for neat square edges. The styrofoam was applied to the box with PL 200 multi-purpose construction adhesive. If styrofoam is used, care must be taken in the choice of adhesives. Some compounds will melt styrofoam and it will not adhere properly to the box. We also purchased enough 1/8 inch thick acrylic bathroom or kitchen panel board to completely cover the styrofoam. This board makes the exterior easy to clean and gives a pleasing appearance. The acrylic paneling was applied to the styrofoam with the PL 200 adhesive. The corners and edges were finished with 3/4 inch 90¡ cabinet moulding, in a contrasting color. One word of caution for you do-it-yourselfers, DO NOT attempt to place any screw or nails into the sides of the freezer box. You could pierce the cooling coils, lose the refrigerant and make the freezer box useless with no hope of repair. Running Time Cut In Half After completing the super-insulating of the box, we plugged the unit into the 12 volt DC of our house. Of course the freezer was located in the coolest possible location. The average running time at approximately 65¡F was cut from 30-40 minutes per hour to 15-20 minutes. This was with the box empty. After filling it and the food were frozen, the running time was even less. The closer to full any freezer is, the less will be its running time. Now, on an average summer day it only takes one 1/2 of our Kyocera modules to run our freezer. We can live with this quite comfortable. After starting our AE business in 1986, we've sold a number of these units in various sizes ready made. Finally the lack of available, good freezer boxes has led us to marketing the DANFOSS compressor, electronic unit, and capillary temperature sensor as a package. The customer finds a local refrigerator repair person to do the installation in the box of their choice. Alot of money is saved in freight costs. The size of the external condensing unit will vary somewhat with the size of the box used. These will be available from your installer. Prices will vary slightly with size. These single compressor installations have been made in freezers and refrigerators from 5 cu. ft. up to 12 cu. ft. Only the amount of super-insulation will vary with box size, to keep running time to a minimum. These compressor units can be used in tandem in freezers from 15 to 20 cu. ft. with a corresponding increase in power consumption. Only one temperature sensor is required when a tandem configuration is used. Cost in CAnadian Dollars The following cost figures will generally be about 15% less in US dollars for components and materials. Installation costs may vary somewhat from place to place. INSERT TAble This is about 1/3 to 1/2 the price of 12 volt refrigerators and freezers that are manufactured today. Access Bob McCormick, Northern Alternate Power Systems, POB 14, Pink MOuntain, BC, Canada V0C 2B0.