Living Offgrid Affordably - Power Usage Patterns

| 1/4/2013 3:01:52 PM

After electrifying the building with D/C last time in blog post number 16, “The Power Inside,” we are ready to try one of my famous experiments. (I love working in the laboratory!) Higher efficiency will be realized by using D/C for long run-time loads, but we also want to use some A/C appliances as well. The solution?

Power was drawn from the battery bank and ran to a Xantrex 175 amp D/C main disconnect, then to an inverter. Since I wanted to power small battery chargers, cell phone charger, home office equipment, and various other electronics, I chose a true sine-wave inverter, the Xantrex xw1800. A modified wave inverter is less expensive, but can exhibit problems running some electronics, electric motors, and cordless tool or cell phone chargers. A true sine-wave inverter will avoid these problems. A capacity of 1800 watts should provide plenty of A/C power for this small building, and we can add another inverter when we transition to the main house.

The inverter fed a second Square D 100 amp breaker box, from which all A/C circuits emitted. I wanted A/C power in the kitchen to power a blender, crock pot, and various other kitchen aids. We wanted A/C in the entertainment corner to power stereo and TV hardware, although I retained the D/C components to use during the lean power winter months. The entertainment corner, along with the home office circuit, was fitted with a surge protector strip for protection, as well as adding the ability to switch off all of the phantom loads, devices that use power even when turned off. The inverter draws about 2 amps when running, and this doesn’t seem like much, but adds up quickly in winter when generation is low. Doing without is not the objective!

We now have a building wired in duplicate, one breaker box each for A/C and D/C circuits. Direct current powers all interior and exterior lighting, a ceiling fan, small refrigerator, stereo and TV, small fans for HVAC and the composting toilet, and numerous receptacles throughout the building. Alternating current powers a window air-conditioning unit, stereo and TV, the home office, and numerous receptacles.

This arrangement could be very dangerous. What if we plug an A/C load into a D/C receptacle, or vice-versa? Something just blew up! The simple solution is to use keyed plugs and receptacles. Most standard 110 A/C plugs use two vertical spades, but plugs and receptacles are available with one vertical and one horizontal spade, which were used for D/C circuits. This must be done to adhere to code, but more importantly, is a no-brainer. We can’t mix up A/C and D/C circuits and appliances and have things blowing up!

I began the lighting experiment by using recreational vehicle 12 inch florescent fixtures with F8T5 bulbs. They emit lots of light, but consume 1 amp when on and are not environmentally friendly. The high power consumption is not a problem during ten months of the year, but is too high for the period from Jan. 1st thru the middle of February. I began the process of converting to led fixtures and bulbs.

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