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The terms used to measure the electricity that powers modern homes and businesses can be confusing and a bit overwhelming.
Watts, volts, amps…
What do they measure and why?
Understanding the difference between these terms can be a challenge.
Another fundamental electrical concept to grasp is the difference between AC (alternating current) and DC (direct current).
While AC and DC electricity may seem similar, there are essential distinctions.
The primary difference between AC and DC is that AC electricity flows in two directions (alternating back and forth), while DC electricity only flows in one direction.
Why does that matter?
Let’s take a closer look.
What Is Alternating Current (AC)?
Most homes and commercial buildings rely on alternating current, or AC. So much so that AC is often called “household electricity.”
Modern appliances and consumer electronics like computers and smartphones actually run on DC current, primarily because transistors require it to function. But devices transform AC electricity from your home wiring into DC using an adapter or converter.
So what does alternating current actually mean?
An alternating current is an electrical current that changes direction periodically. Instead of flowing in a single, constant direction like direct current (DC), AC switches between positive and negative.
This switching action happens quickly — standard alternating current in the US runs at 60 Hz, meaning it changes direction 120 times per second.
In addition, the voltage supplied by AC power varies significantly by country. For example, a standard AC wall plug in the US delivers 120V at 60 Hz. In the UK, a household plug provides 230V at 50 Hz.
The difference in mains electricity voltages is crucial to note when traveling. Devices like smartphones and laptops are typically designed to handle voltages between 110V-240V.
However, many appliances are not. If you plug a device rated for 120V into a 240V socket, you will likely blow a fuse (or worse, fry the machine altogether).
How AC Current Works
Alternating current has traditionally been produced by mechanical generators converting kinetic (hydroelectric or wind) or thermal (fossil fuels or nuclear) energy into electricity using electromagnetic induction.
AC electricity’s voltage reverses polarity (changes direction) from positive to negative in fixed intervals measured by Hertz (Hz). Each Hz equals one positive cycle and one negative cycle. For example, in North America, where the standard AC voltage is 110V @ 60 Hz, the current changes direction 120 times per second.
The rapid oscillation of alternating current facilitates long-distance electricity transmission, making AC the global standard for electrical grid infrastructure.
AC’s primary benefit over DC is that it is easily modifiable by a transformer from extremely high voltages — transmitted through the utility grid from power plants over power lines — to low voltages for safe use.
Advantages of AC Current
- Significantly less expensive to modify voltage with transformers than with DC
- Less power loss over distances up to about 600 miles (1000 km)
- Much thinner cables are required for power lines
- Easier to interrupt than DC electricity (such as with a fuse or circuit breaker)
- No concerns about correctly connecting household plugs to positive/negative currents
Disadvantages of AC Current
- Less efficient for transmitting electricity over extremely long distances than HVDC transmission (high-voltage direct current)
- More dangerous to work with at high voltages
What Is Direct Current (DC)?
Unlike AC, direct current electricity always flows in the same direction. The polarity is constant — it doesn’t oscillate between positive and negative — and the voltage also doesn’t vary.
DC is also sometimes used to produce types of electrical current where the polarity is constant, but the voltage varies over time using a rectifier.
Transistors don’t operate using AC electricity, so almost all modern appliances and consumer electronics actually run on DC — not AC power. A rectifier (or adapter) is required to convert the AC electricity from an outlet into DC electricity.
DC power sources have two terminals — positive and negative — and electricity always flows in one direction between the two.
How DC Current Works
Direct current power doesn’t fluctuate in polarity or change direction like AC electricity. DC electricity has two poles (positive and negative), and current flows in one direction from the power source to a battery or DC-powered appliance. Or from a solar panel to an on or off-grid solar power system.
DC offers a constant flow of electricity, allowing it to charge solar or other types of batteries effectively. Depending on your system, you may need a DC-to-DC battery converter to adjust the voltage up or down to meet the device’s requirements.
Advantages of DC Current
- Solar panels capture DC electricity using the photovoltaic effect. DC is then converted to AC by a portable power station or inverter and other balance of system components
- Required for charging solar and other types of batteries
- DC generators are more straightforward in design that AC
- More efficient than AC for transmitting electricity over extremely long distances (such as through undersea cables)
- Current flows in one direction with consistent polarity, making it a stable source of electricity
Disadvantages of DC Current
- Cannot be used with a transformer, meaning DC can’t be transmitted at high voltage over power lines than stepped down for household and commercial use
- Typically less efficient than AC for many applications — including use in electrical generators
- Ineffective for transmitting electricity from a power station over extremely long distances using HVDC
What Is the Difference Between DC and AC Current?
The main difference between AC and DC is that AC alternates while DC remains constant. Alternating current switches directions rapidly, while direct current flows in one direction only. This is the primary difference between AC and DC and impacts how each is used and how the electricity is generated.
In the 1890s, AC began to replace DC as the preferred current for transmitting electricity from power plants to homes and businesses throughout the US. AC electricity is much easier than DC to convert from high to low voltages, making it far more efficient for transmitting electricity through power lines and the utility grid infrastructure.
However, direct current has made a serious comeback in recent decades. The transistors found in computers, smartphones, and many other electronic devices run on DC power — as do rechargeable batteries. The outlets in your home are almost guaranteed to supply AC electricity, but it’s converted by appliances into DC as necessary.
Additionally, solar panels capture DC electricity which in off-grid systems is stored in a solar battery and converted to AC. since it’s easier to control.
Portable power stations like the RIVER 2 Series or larger home backup systems and whole home generators like the DELTA Series store DC electricity in long-lasting LiFePO4 batteries. It’s also an ideal choice for portable devices like phones and laptops.
AC and DC electricity are both essential components of the way we use electricity. With the growing adoption of Electric and Hybrid vehicles and clean, renewable solar power, DC power plays a more significant role in our society each day.
Frequently Asked Questions
Direct current (or DC) is better than alternating current (AC) for some applications — such as storing electricity in batteries. AC electricity still remains the current of choice for most homes and businesses because of existing grid infrastructure and because it’s cheaper and easier to transmit than DC.
The “strength” of electricity is measured by metrics like volts, amps, and watts. Direct current (or DC) isn’t inherently stronger than alternating current (or AC). AC is easier to convert from high voltage power lines to 120V household electricity using a transformer, making it the primary choice for grid infrastructure. But DC is being used in more applications — like solar power and EVs — every day.
Alternating current (AC) and direct current (DC) both play essential roles in our daily lives.
While AC powers our on-grid infrastructures and most homes and commercial buildings, DC is the backbone of our battery-powered electronic devices from smartphones to EVs — and clean, renewable solar electricity.
At EcoFlow, we provide portable power solutions and solar generators, leveraging the advantages of both AC and DC power. Many of our devices can be charged using both AC and DC simultaneously.