How Does a Qi Wireless Charger Work?

Table of contents

What Is the Qi Standard?

How Does Wireless Charging Work?

Why Do Qi Wireless Chargers Generate Heat?

Why Is Qi Wireless Charging Slow?

Can You Build Your Own Qi Charger?

To understand how a Qi wireless charger works, we must first explore the Qi standard.

Different brands often use proprietary wireless charging protocols, which makes cross-brand compatibility a challenge. To address this, the Wireless Power Consortium (WPC) introduced the first version of the Qi standard in 2008. It was designed specifically for small electronic devices such as smartphones, earbuds, and smartwatches, allowing different brands to communicate in the same "wireless charging language." This breakthrough paved the way for truly universal wireless chargers. In short, a Qi charger is a standardized, cross-compatible solution for wireless charging across multiple devices.

Wireless charging is based on two key physical principles: 

• Magnetic effect of electric current: When electric current flows through a wire, it creates a magnetic field around it.

• Electromagnetic induction: When a conductor moves through a changing magnetic field—or when the magnetic field itself changes around a stationary conductor—it generates an electromotive force (EMF), which can drive current.

Inside a wireless charger is a copper coil. When alternating current (AC) flows through this coil, it creates an oscillating magnetic field. The device being charged also contains a coil, which acts as a receiver. For current to be induced in the receiving coil, a changing magnetic field is required. Since it's impractical to keep the coil physically moving, AC is used because it naturally produces a changing magnetic field. This changing field induces an alternating current in the receiver coil, which is then converted into direct current (DC) by a rectifier circuit inside the device to charge the battery.

Wireless charging involves multiple stages of energy conversion, and with each stage, some energy is inevitably lost. According to the law of conservation of energy, this lost energy doesn’t just vanish—it transforms into another form, most commonly heat. That’s why you might notice your phone or charger heating up during wireless charging.

Since the Qi standard is designed to prioritize compatibility, safety, and cross-device interoperability, the charging power is intentionally limited. The latest Qi 2 standard currently supports charging speeds of up to 15W. However, a faster version—Qi 2.2—is on the horizon, aiming to reach up to 25W. As of June 17, 2025, Granite River Labs (GRL) became the first WPC-authorized Qi 2.2 testing platform (source: GRL official announcement), indicating that the official rollout of Qi 2.2 may be imminent.

Theoretically, yes. Based on the principles of wireless charging, a DIY Qi charger only requires a control circuit and a coil. This opens up creative, customizable use cases—like embedding a wireless charger into a bedside table.

• Because DIY wireless chargers typically offer very low power output, around 5W. In contrast, commercially available chargers from professional manufacturers are optimized for higher efficiency and performance. Modern chargers support the latest Qi 2 standard and can deliver up to 15W of power.

• Many branded chargers also feature temperature monitoring and cooling mechanisms to keep the device from overheating during operation.

• Another key factor in wireless charging efficiency is coil alignment—the alignment between the charger and device coils. Many modern chargers now incorporate magnetic alignment technology (like MagSafe), which helps ensure proper positioning and reduces energy loss.

• There are also multi-device wireless chargers on the market, capable of powering a phone, earbuds, and a smartwatch simultaneously. These are a great choice for users who need to charge multiple devices simultaneously.