DC and AC Power: Why Batteries Need an Inverter

Your battery and your wall outlet speak different electrical languages. The battery gives out direct current, or DC. The outlet gives alternating current, or AC. An inverter translates.

What DC is

With direct current, "the electric current flows in a constant direction"¹. A battery cell is the classic example. Wikipedia calls an electrochemical cell "a prime example of DC power"¹.

Solar panels are the same. Both batteries and solar systems "can produce only DC"¹. That's why a home with panels and a battery needs conversion somewhere in the chain.

What AC is

Alternating current is "electric current that periodically reverses direction"². Picture water that sloshes back and forth in a pipe instead of flowing one way. The direction flips many times each second, and the number of flips is the frequency.

Frequency and voltage differ by place. Premises in most of the world get a supply of between 220 and 240 volts at 50 hertz, and North America is the biggest exception³. Your inverter has to match the local supply, or your appliances may not like it. The label page shows where to find these figures.

Why the battery can't just plug in

Most appliances are designed around the wall supply. They expect AC at a set voltage and frequency. Hand them steady DC and a plug-in device may simply not work, or it may be damaged. Don't connect household appliances to a bare battery.

An inverter fixes this. It flips the direction of the battery's flow back and forth, fast enough to imitate the wall supply. See what an inverter does for the larger picture.

Some gear does run on DC. Many portable power stations have DC ports, such as USB sockets, so phones and small devices can skip the conversion. Check which ports yours has in its manual.

What this means when you shop

DC and AC both show up on spec sheets, and they mean different things.

• DC figures describe the battery side: its voltage and how much it can store.
• AC figures describe what the inverter delivers to your outlets.
• A mismatch is possible: a battery may store plenty, but the inverter may cap how much you can draw at once.
• A system labeled for one voltage won't suit equipment built for another, since supply voltages differ by region³.

Ask which side a number belongs to. A listing that gives a bare number without saying DC or AC leaves out something you need.

Keep the wiring to a pro

The inverter's AC side connects to a home's circuits at household voltage. Wiring a battery or inverter into a house, a switchboard or a transfer switch is licensed electrician work. It's not a weekend job. Follow your product's manual, and use a qualified person for any permanent connection.

The same goes for the battery side. Don't open a battery, rebuild its cells or change how it's built. Only the maker's manual says what an owner may touch.

Next, learn how the converted power is shaped: pure vs modified sine wave.