What is direct current? In this article, we delve into the world of direct current. You will learn what direct current is, how it differs from alternating current, where it is used, and what role it will play in the future of our power supply.
The basics
Direct current is a form of electric current in which the electrons always flow from the source to the load in the same direction. Imagine a water pipe: With direct current, the water (the electrons) only flows through the pipe in one direction at a time. The electrical voltage remains constant or changes only very slightly. This leads to an even current flow.
Direct current vs. alternating current
In contrast to direct current, alternating current (AC) changes its direction of flow cyclically. In Europe it does this 50 times per second, in North America 60 times per second. The voltage and current pulsate in waves. If you imagine water flowing in a water pipe, the water would constantly reverse its direction of flow with alternating current.
Thomas Alva Edison backed direct current
The “war of the currents”
The so-called “war of the currents" over the choice between direct current (DC) and alternating current (AC) broke out at the end of the 19th century. Thomas Alva Edison backed direct current and built the first electricity grids based on it.
Nikola Tesla and George Westinghouse favored alternating current because its voltage can be transformed efficiently. The high voltages enabled low-loss long-distance transmission, while low voltages were safe for the loads. This advantage led to the implementation of alternating current as the large-scale power supply system.
Comparison of properties
To really understand direct current, it is essential to differentiate it from alternating current (AC).
| Direct current (DC) | Alternating current (AC) | |
|---|---|---|
| Flow direction | Always the same direction from the source to the load | Changes cyclically |
| Voltage | Constant | Changes cyclically, sinusoidal wave form |
| Transformation | More complex and less efficient | Simple and efficient with transformers |
| Transmission | Good for short distances or extra-high voltage direct current transmission (HVDCT) for long distances | Ideal for transmission over long distances in the grid |
| Applications | Batteries, electronics, LEDs, electrolysis, e-cars, household appliances, industry | Public power supply |
Applications in everyday life and technology
- Mobile electronic devices: Smartphones, tablets, laptops, MP3 players, digital cameras, and similar portable devices are powered by direct current. Their internal batteries and rechargeable batteries supply direct current. The power supply units convert the alternating current from the socket into direct current for charging.
- Vehicles: Automobiles use a 12 V DC system for lighting, radio, power windows, and other electrical components. Electric cars store energy in high-voltage batteries that supply direct current. DC charging (fast charging) of electric cars at charging stations is another important field of application in which direct current is fed directly into the vehicle battery.
- LED lighting: Light-emitting diodes (LEDs) require direct current to function. Many household LED lamps therefore have a built-in rectifier that converts the alternating current from the socket.
- Renewable energies: Solar systems primarily generate direct current. This must be converted into alternating current so that it can be fed into the grid and used to operate household appliances. Wind turbines can also generate direct current internally before it is transformed for grid integration.
- Industrial processes: Direct current is indispensable in electrolysis (e.g., for the production of aluminum) and electroplating (coating of metals). Many welding processes also use direct current.
- IT infrastructure: Data centers and servers are increasingly using DC power supplies, as this can reduce conversion losses and increase efficiency.
- High-voltage direct current transmission (HVDCT): For the transmission of large amounts of electrical energy over very long distances or under water, direct current is often more efficient than alternating current. HVDC lines are used, for example, to transport wind power from offshore systems and solar power from remote regions over hundreds of kilometers. Here, alternating current is first converted into high-voltage direct current, transmitted and then converted back into alternating current at the destination.
Frequently Asked Questions regarding direct current
Is 12 V always direct current?
No, the specification of a voltage such as “12 V” does not say anything about whether it is direct current or alternating current.
However, in most everyday applications where 12 V is used, it is actually direct current. Examples of this include:
- Car batteries
- Small power supply units (e.g., routers, external hard drives)
- Solar panel systems
There are also 12 V AC power sources, e.g., for certain lighting systems (halogen lamps with AC transformer) and some specialized industrial applications. Voltage (volts) is a measure of the "pressure" of the electricity. The type of current (direct or alternating current) describes the direction of flow.
Is heavy current direct current?
No, the term “heavy current” is used almost exclusively for alternating current, or more precisely for three-phase current.
“Heavy current” refers to electrical systems and devices with a higher power and voltage than the usual household current (single-phase alternating current). In households, heavy current is typically found at special red sockets (CEE sockets), which are used for electric stoves, instantaneous water heaters, and workshop machinery, for example. These supply three-phase alternating current with a voltage of 400 V.
Summary
Although alternating current is at the heart of our global power grid and can be transmitted efficiently over long distances, direct current is experiencing a renaissance. This is due in particular to the need to integrate renewable energies and to further develop electrical engineering in areas such as e-mobility and IT infrastructure. Understanding the difference between these two types of electricity is key to understanding how our modern electrical world works.
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