Low Voltage Living

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WIRING

As we've already suggested, there are certain technical limits to the size of appliances or generators in a low-voltage electrical system. Because wattage is a function of both voltage and amperage, when one goes down the other must rise. Unfortunately, amperage determines the carrying capacity of wire. Therefore, proper wiring and switching are particularly important in a low-voltage electrical setup. In general, No. 10 copper wire will serve any load of less than 150 watts in a normal-size home. There will, however, have to be some appliances that draw more than 150 watts.

To give you an example of what this can mean, let's suppose that you have an appliance that needs 480 watts to run-a vacuum cleaner, for example. At a normal utility household voltage of 120, you could use a 740-foot extension cord of No. 10 wire if you wanted to; but at 12 volts, you would be limited to 7.4 feet of wire from the battery to the vacuum. If you used a No. 8 wire, you could stretch out 12 feet into the room; No. 6 would give you a range of 18 feet; and No. 2 (which is heavy and costs upwards of $1.00 per foot) would let you swing around for 46 feet.

Obviously, all of these situations are pretty much intolerable. The solution is to run large appliances on 110-volt alternating current (VAC). One way to get 110 VAC at a remote site is to use a motor-driven generator. If used infrequently, one of these fossil-fuel burners can be really handy to have around. A more sophisticated alternative, however, is to use a solid-state inverter of about 1,000 watts capacity. This device transforms 12 volts to 120, for efficient transmission, and makes alternating current---the sort of power that utilities supply. An inverter will allow you to use appliances that run on normal household current and may be the ideal solu tion for operating large devices such as vacuum cleaners or for supplying appliances that require alternating current. You can refer to TJ Byers' two-part article on inverters in MOTHER NOS. 80 and 81 for the lowdown on such devices.

Just as independent power systems require special wiring, they also need switches that are up to the task of handling heavy direct currents. There are devices designed especially for this sort of use, but it's possible to get by with a standard snap (not silent) switch equipped with a 50-volt, 47-microfarad capacitor in parallel, to tame arcing. An accompanying photo shows you how this is done. Normal outlets are capable of handling DC loads, but it's a good idea to use a style different from normal 120-VAC receptacles, so that no one can plug a 120-VAC device into your 12- VDC system. Some people prefer automotive cigarette lighter-type receptacles, while others use outlets designed for 220 VAC.

You'll also need a control panel, which you can either buy or fabricate yourself. We've built several of these at Eco-Village-they're shown in the photos-and they're really not difficult to put together. At the minimum, a control panel will need an ammeter to show the rate at which you're using electricity, a voltmeter to indicate battery voltage, and fuses to protect against shorts. Circuit breakers can be used instead of fuses, but they must be designed for 12 FDIC.

Unless your system sizing turns out to be so accurate that power production exactly matches what you use, you'll also need a battery charge controller. These devices reduce charging current as the batteries become "full," and there are essentially three types. The reduction controller reduces the current going to the battery bank as its voltage rises, wasting the excess. The diversion controller shunts excess current (that which the batteries don't need) to a resistance heating load, such as a water heater. The balance of systems controller, a relatively new development, allows a wind or PV generator to produce at maximum useful voltage (and thereby also at maximum amperage) and then reduces that level to whatever the batteries happen to need.

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