What Is Fast Charging, and How Does It Work?

OnePlus 30W wall chargerOnePlus

Today, most major versions of phones have improved charging speeds. How do fast chargers work and how do they get even faster? Find out here.

The rapid charge boom

Almost all recent flagship phones on the market offer some type of fast charging. Manufacturers often throw numbers like “80% in 30 minutes” or “a full charge in less than an hour” when marketing their latest devices.

The widespread adoption of fast charging is a response to the growing use of the phone, with many people needing to charge their phones more than once a day. It is also a necessity. As the size of the phones increases each year, they need larger batteries to keep up with additional energy consumption. Without fast charging, we will have to wait hours for our phones to charge.

At the most basic level, fast charging simply increases the number of watts (W) delivered to a phone battery. A basic USB port sends 2.5 W to the connected device, and faster chargers increase this amount. Current generation devices generally have 15 W power bricks right out of the box. Some manufacturers offer 50 W, 80 W and 100 W chargers.

For the end user, it’s as simple as using a compatible fast charger for their phone. However, for manufacturers, it’s not as simple as using a higher power supply brick.

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The fast charge process

Before going any further, you should take note of a simple formula. The power, or power, is calculated following the current (A or amperes) multiplied by the voltage (V or volts). Current is the amount of electrical current carried, while voltage is the force that drives this current. Therefore, the 3A / 5V load will provide 15W of power.

One thing you will notice is that many manufacturers tout their ability to perform a quick partial charge, such as being able to charge 50-80% of the battery in half an hour. This is due to the way the rechargeable lithium-ion battery inside the phones receives current. If you’ve ever watched how a battery is charged, you’ll notice that the charging speed becomes progressively slower over time.

The charging process can be divided into three parts. Take a look at the table “Figure 1: Lithium-ion charging steps” in this article Battery University for more technical details. In short, this is what it shows:

Step 1 – Constant current: The voltage increases towards its peak, while the current remains constant at a high level. This is the phase where a large amount of energy is quickly delivered to the device.
Step 2 – Saturation: This is the phase when the voltage reaches its peak and the current drops.
Step 3 – Trickle / Topping: The battery is fully charged. During this phase, the power will drain slowly, or periodically charge a small amount of top-up when the phone consumes the battery.

The power and duration of each process depends on the fast charge standard. A standard is an established charging process that corresponds to a particular device, charger and output power. Different manufacturers are developing different charging standards capable of varying the outputs and charging times.

Fast charge standards

Qualcomm Charge Standard Quick Charge 4Qualcomm

Here are the different fast charging standards that have been implemented in mobile phones:

USB power supply: Every mobile phone has a charging cable that uses USB – even the Lightning cables for Apple iPhones have a USB connection at the other end. USB 2.0, which has been a common specification for two decades, has a maximum output power of 2.5 W. Because USB ports need to provide more power, the USB-PD standard was created. The USB-PD has a maximum power of 100 W and is used for a wide range of devices, including most flagship mobile phones. All USB 4 devices will include USB-PD technology, which we hope will help normalize this.
Qualcomm fast charge: Qualcomm is the most used chipset for flagship Android devices, and their latest processors are compatible with their proprietary Quick Charge standard. The newest Quick Charge 4+ has a maximum output power of 100 W.
Samsung Adaptive Fast Charging: This standard is used by Samsung devices, especially their Galaxy range. This standard has a maximum output power of 18 W and automatically changes the charging speeds to preserve the longevity of the battery.
OnePlus Warp charge: OnePlus uses the proprietary Warp Charging standard, which charges their devices up to 30W. Instead of increasing the voltage like most other standards, unlike the other options on this list, 30W full speed charging is also available.
Oppo Super VOOC charge: Oppo uses a proprietary standard that charges their devices up to 50 W.

Most companies that do not have their own charging technology use USB-PD or Qualcomm Quick Charge, or adapt it to their specific device. Companies like Apple, LG, Samsung and Google use these standards for their flagship phones.

Most of these solutions increase charging speeds by increasing the voltage of their adapters. The outlier is the Oppo and OnePlus solutions, which dramatically increase current rather than voltage. The rapid charging of these devices requires the use of their proprietary cables.

RELATED: USB4: what’s different and why it’s important

The future of charging

Charging technology is constantly improving as manufacturers continue to increase charging speeds. Over the next few years, more companies will experiment with charging technology and new standards will emerge in the industry. However, it is likely that most of these standards still use USB-PD as the backbone.

There is also the emergence of wireless fast charge. Wireless transmission of large amounts of energy can become dangerous without proper thermal management. Wireless charging is still much slower than wired connection, as tech companies are still figuring out how to handle the heat. This is why companies like OnePlus have released 30W wireless loads with large fans to provide sufficient air flow.

RELATED: How does wireless charging work?

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