Inexpensive Home Building

Cut through the jargon and nonsense of home building and house construction by starting from zero dollars and trying to figure best-value bang-for-your-buck when choosing construction methods or construction materials. My research might answer some of your questions and at other times perhaps you have the knowledge or experience to post the answers to my questions and thereby help others too. The goal is an affordable and sustainable home for all.

Friday, June 22, 2007

How To Make a 12V DC Power System Easy as 1-2-3

Get cheap energy, energy independence, and energy security by generating your own power at home. To do so, 12-volt Direct Current (12V DC) is a good choice for local power, which is why it is used in small, self-contained systems such as cars and boats. Alternating Current (AC) is better for transmission over long distances (which is why it is used) but most consumer products “rectify” the power to DC current at point of use anyway. Therefore, for short runs of wire, a 100% DC system is simple (of course, simplicity still requires caution).
  • Rectifiers change AC power current to DC power current.
  • Inverters change DC to AC (get AC from your car’s lighter plug).
  • Transformers change voltage.
Large Price Range in Cost of Alternative Power / Renewable Energy Systems
What To Expect? Some Possibilities:
  • $40,000-$80,000 for North American McMansion.
  • $4,000 with conservation and do-it-yourself (DIY).
  • $400 for beginners' starter system.

How To Make a 12V DC Power System Easy as 1-2-3

Start small. Think of it as a 7th-grade science-class project (useful if your 7th-grader has a science-class project due).

Stage 1: The DC Appliance

First, you need appliances that you can feed DC electrical current.

Battery-powered devices use DC current (batteries are DC).

Camping, marine/boating, and RV/motorhome suppliers are good sources.

Automotive DC-to-DC adapters are good sources, such as the “cigarette lighter” plugs.

12-volt DC 15-watt portable work light with car-lighter plug and battery-terminal clamps

12-volt DC 24-LED portable work light with both DC and AC plugs and rechargeable/replaceable battery pack

Universal laptop computer DC-to-DC adapter with adjustable voltage and jack assortment

Cigarette Lighter Socket with Internal 15A ATC Fuse and Powerpole Ends

Note: I have heard that lighter plugs do not meet building codes but I have no confirmation on the accuracy of that rumor.

With properly regulated voltages, amps, and fuses, you can power a device directly with DC power, and the electricity-generating source does not matter—wind, water, solar, heat, bicycle-pedal, hand crank, springs, gravity, potato.

Stage 2: Add the Battery

A battery is not necessary and actually causes a "system loss" inefficiency of maybe 20%. However, a typical self-reliant system will have a battery as:

  • A reserve of energy.
  • A buffer to moderate peaks and valleys in supply and demand.

Often, the battery loss is cheaper than increasing the size of your generator to handle infrequent peaks and then having wasted capacity most of the time and nowhere to store it for later.

You could use a car battery as a demonstration but not for long-term use. Use a “true” “deep cycle” battery that advertises “amp-hours” (ah) rather than “cold cranking amps” (CCA). In increasing order of suitability and cost, look for marine batteries from a boat shop, golf-cart batteries from Sam’s Club, or off-grid batteries such as Trojan from a specialty supplier. You can use standard lead acid with proper venting of the area but you can use the pricier "Absorbent Glass Mat" (AGM) lead acid without the venting issue.

Since most people currently live in an AC household, you probably can “learn the ropes” with your small battery system by using an AC-to-DC charger to simulate the input from your future “solar panel” or “wind turbine.” You can check to see if a common automotive charger will work or you can get a more efficient “smart charger.”

Black & Decker VEC1093DBD 40/20/10/4 AMP smart charger with 3-step battery charging, trickle, and float charge

Stage 3: Add the Self-Reliant Power Source with Charge Controller

You have many free or renewable power-source choices from high-tech solar photovoltaics to a donkey chasing a carrot.

Off-Grid Vs. Grid-Tied Systems and Net Metering

This article covers a self-contained system that is not connected to "the grid" (power company's distribution network). A "grid-tied" home generator might let you sell power back to the power company (net metering) and it could be small and battery-less because the grid handles the power spikes and the reserve power in normal conditions. However, a grid-tie adds cost and regulation to your home-generator installation (understandably, so your generator does not electrocute a line repairer down the road) and a grid blackout would leave you without a spike-handler or power reserve.

It is often difficult to beat the short-term price of grid power but you can choose to be off-grid anywhere--even in a city apartment.

I periodically will update this post with details about generators, wiring, fuses, regulators, etc.

See also:
The Difference between Energy and Power: Do Not Confuse
Real Power Usage of Appliances (Wattage)
DayLighting; Sun Tubes, Solar, PV, CFL
Candles Beat High-Tech Solar Photovoltaic?