breakers, each DC circuit can be added as need arises. If just one or two circuits are needed, your existing DC power center usually has enough extra positions to install DC load circuit breakers. If a large number of low voltage circuits will be used, a separate breaker box for DC is best, like the Square D brand breaker box with "QO" series AC/DC rated breakers. Remember that circuit breakers or fuses on each wire are just as important for low voltage DC as for AC circuits.
DC outlets should be distinctly different from your AC outlets to meet building code as well as to prevent damage to equipment accidentally plugged into the
A notebook computer usually kept at the desk doesn't need to constantly cycle or overcharge its internal battery. Notebook computers come with a cord containing an external converter to power them from 120 volts AC. You can order a DC power supply from most computer makers to operate the notebook computer from a 12 volt battery or a car's lighter outlet, even with the computer's rechargeable battery removed to avoid shortening its life. These cost US$70 to US$100, because notebooks usually require a boost to 16 volts to charge the internal battery (this may vary with brand).
Beware of computer catalogs that sell a cheap AC inverter to connect a 12 volt source to the notebook's 120 volt AC power supply cord. This cheap fix uses much more energy, because it converts 12 volt DC to 120 volts AC, and then the computer AC cord converts it back to 16 volts DC. The give-away is that these "12 volt computer power cords" connect to the computer's AC power cord. A real DC-to-DC converter cord uses far less energy by converting 12 volts directly to the computer's required voltage. It is identified by having the exact plug to match the DC connector on your notebook, never connecting to the computer's AC adapter cord.
wrong outlet. A good choice is the 240 volt AC duplex outlet, either 15 or 20 amp, which fits conventional AC outlet boxes and cover plates. They look like the standard 120 volt outlets except one or both prongs are turned 90 degrees, so AC appliances cannot be plugged into DC by mistake, or vice versa.
For easier identification, select a different color for the DC outlet and its cover plate. The 240 volt AC outlets are legal to use for DC circuits if you have no actual 240 volt outlet circuits in the house. Don't use the junky cigarette lighter plugs and sockets, which are poor quality and do not meet building codes.
AC/DC—Making Smart Decisions
In the end, I defend the modern inverter as the easiest way to run nearly any AC appliance. No longer would I change the motor on a washing machine to a DC substitute, as we did 30 years ago when good inverters did not exist. Nor would I want to see several and various DC voltage circuits running throughout the whole house for a mix of random appliances of various voltages.
But when confronted with operating an important electronic device that should be on duty full-time, DC connection has the advantage if the device needs very little electricity, and actually uses low voltage DC internally, with an easy way to input the DC.
A 240 VAC outlet (left) for DC circuits meets code and prevents damaging appliances with the wrong voltage and current.
For alarms, message machines, doorbells, cell phone chargers, and other applications discussed here, it is easy to wire a DC circuit. This offers simplicity and efficiency rather than sending your prized solar electricity on a roller coaster ride, converting up to 120 volts AC, and then taking it right back down to DC again for those appliances. Low voltage DC is always waiting right there in your battery bank, ready to use in the right application.
Steve Willey, Backwoods Solar Electric Systems, 1395 Rolling Thunder Ridge Rd., Sandpoint, ID 83864 • 208-263-4290 • Fax: 208-265-4788 •
Solar Converters Inc., C1-199 Victoria Road S., Guelph, Ontario N1E 6T9, Canada • 519-824-5272 • Fax: 519-823-0325 • [email protected] • www.solarconverters.com • DC voltage converters and motor speed controls.
Lind Electronics, 6414 Cambridge St., Minneapolis, MN 55426 • 800-697-3702 or 952-927-6303 • Fax: 952-927-7740 • [email protected] • www.lindelectronics.com • Custom and computer power supplies; Ask for unit with wider low voltage input tolerance, so it will not shut off due to low voltage line drop as if it were protecting a car's battery from discharge. ^nfc hupsolarone.com
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