Most people don't know it, but there are usually over a dozen, battery backup systems in your home already. The average American around 18 battery backed up devices in their home. These battery backup systems backup the crucial, expensive, or mobile electronics, right under your nose. Examples of battery backed up consumer electronics including the SMOKE ALARMS that beep in the night. Other examples include: wireless or satellite phones, laptop computers, MP3 players, tablet computers, and a variety of GPS devices all qualify. The battery on board design allows consumers to plug their appliances and electronics directly into any power grid without worry.
Other devices just run on Direct Power rather than the Alternating power that comes from the wall. Many consumer plugs change this power to Direct Current, the same type of power that comes from a battery inside the plug. A battery discharges and is charged with DC power or Direct Current, so by switching the current, inside the power plug, the accessory can be smaller and lighter. The photo at right shows a number of different types of AC-DC wall plugs that actually charge the batteries, or circuits of your electronics, right now. These AC-DC transformers convert the alternating current into a positive and negative current on the appropriate wires. Each has a rating clearly marked on the power supply that shows the maximum output voltage, and amperage.
How do you Make AC power DC power? A bridging Circuit.
The power from the wall is AC power, Alternating Current, or a positive and negative voltage on one wire, alternating at 50 - 60 times a second. The other wire is the return path to ground. The return path allows for a safe circuit to form, and the power can flow. To separate the positive and negative voltage from each other, a series of 4 diodes are needed and a bridging circuit. Basically the design routes AC power, through one of 4 one way doors, to the positive or negative wire, making it into DC power. This DC power can then be used to charges batteries, run DC motors, etc. Below is an example of a circuit that makes a DC power supply:
Holes in a bridging circuit
A battery should be used to fill in the gaps left in a bridging circuit. Basically a bridging circuit takes both positive and negative power from the same wire, and separates it. However, as the power switches back and forth, small gaps are left. If you look at a bridging circuit diagram it would look something like the one to the right. At 60 hz, there would be 120 holes per second in the power available (the dotted line) as the system switches through positive and negative Alternating Current. A battery takes the peaks as a charge, and fills the valleys as seen by the solid line in the diagram. Yet again, the UPS design foils a circuitry problem.
This page is designed to start you on your educated way. This information is in no way complete, nor does it include safety information. You must take the time to understand that power at these voltages and with these circuits can be hazardous, even kill you. Please take the time to learn to do this safely.