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AC and DC


Trace Inverter Stack and Generator


Most of the loads an "average" person wants to power are AC. The grid is AC, therefore common tools and appliances are AC. Many gadgets are actually running on DC, but come with a transormer (sometimes called a "wall wart") to allow use of household AC.

Solar electric panels produce DC. Batteries store only DC. Thus for an off-grid system we need to get from solar DC, to battery DC, to household AC. Also we may want to use generator AC or grid AC if we are connected to the grid. Sometimes we take this AC and store it in the batteries so this is another conversion, this time from AC to DC. Usually this is done with an inverter operating in reverse as an AC charger or it can be done with a separate charger. This is why some inverters are actually correctly called "inverter/chargers."

If you are setting up a solar system please be aware that an electrician may be unfamiliar with some components and techniques necessary for high current DC systems. This is simply because these things are not a concern in normal residential or even commercial work. With the right components and attitude, this will not be a problem.

DC-rated disconnects, cable, circuit breakers, etc, are not always sitting on the shelves at the local supply house. In some cases standard items will work and I will refer to those items when possible.

Note that a high-current DC system requires a greater attention to detail than a typical residential AC-only system. This is because:

1. DC electricity is harder on connections and has a greater tendency to arc than AC.
2. A series of DC connections must be perfect to avoid overall loss of power. There is no Megawatt grid pushing power through the system if there is a marginal connection.
3. DC circuits are typically operating at lower voltages than household AC, again putting a premium on correct connectors and adequate wire size.
4. DC circuits often operate at higher currents than are commonly found in residential wiring, putting a premium on safety.