How Qi Wireless Charging Works, From Qi to Qi2
Qi chargers move power through a magnetic field between two coils. This guide explains the coils, the feedback, the power levels and what Qi2 adds.
In this article
Qi (pronounced "chee") wireless charging sends power from a charging pad to a device through a magnetic field, with no plug in the device. Two coils do the work: one in the charger and one in the device. This article explains how that works, how the pad and device talk to each other, and how the standard has grown from 5 watts to Qi2 with magnets.
Two coils and a changing magnetic field
Qi uses electromagnetic induction between flat coils. According to Wikipedia's article on the standard, the charger contains a transmitting coil that produces an oscillating magnetic field. A receiving coil in the device picks up that field and produces an electric current, which charges the battery.
The coils need to sit close together; the article says close spacing keeps the transfer efficient. That is why a phone has to rest on the pad rather than a few centimetres away. Wikipedia says Qi transmitters typically start at 140 kHz and can adjust their frequency to suit the distance between coils, with reference designs operating anywhere from 105 to 205 kHz.
How the phone talks back
The charger needs to know how much power the device wants. The device tells it using backscatter modulation: it varies how it loads the magnetic field, and the charger watches for those small changes and adjusts the power it sends. No separate radio link is needed for this basic control.
Safety: detecting objects that should not be heated
A magnetic field can warm metal objects. Wikipedia records that foreign object detection first appeared in version 1.1 of the specification, to stop nearby metal such as coins from heating up. Version 1.2 improved its sensitivity, and version 2.2 added a check based on the Q-factor and power-loss calibration. The article does not describe the detection method in detail.
Who runs the standard
Qi is developed by the Wireless Power Consortium (WPC). Wikipedia dates version 1.0 to July 2010. The consortium's own site says Qi launched in 2010, that more than 13,000 Qi Certified products are on the market, and that only certified products may show the Qi or Qi2 logo. Certification involves safety and interoperability testing at independent authorised labs.
Power levels over the versions
- Baseline profile: 5 W, from the first versions in 2010 to 2012.
- Extended Power Profile: 15 W, introduced with version 1.2 in October 2015.
- Version 1.2.3 (February 2017): allowed negotiation up to 30 W.
- Medium power: 30 to 65 W as of 2019, according to Wikipedia.
- Ki, for kitchen appliances: 1 kW in 2015, raised to 2.2 kW in 2024.
- Qi2 (version 2.0, April 2023): 15 W with magnetic alignment.
- Qi 2.2 (April 2025): up to 25 W. Version 2.2.1 in July 2025 introduced the "Qi2 25 W" branding.
Dates in the list come from Wikipedia's version table. The consortium states that Qi2 25 W launched in July 2025 as v2.2.1 and delivers nearly 70 per cent more power than Qi2 15 W; it says this can take a smartphone battery from 0 to 50 per cent in about 30 minutes.
What Qi2 changes
Earlier Qi relied on the user placing the device correctly, and a misaligned coil wastes energy. Qi2 adds a ring of magnets so the device snaps into position. Wikipedia says the magnetic ring is based on Apple's MagSafe. The consortium says the alignment makes charging more efficient and easier to use, and that the magnetic hold also supports accessories such as AR and VR headsets and add-ons that attach to the back of a phone.
Limits
Because the coils must be near each other, wireless charging is a short-range technology. Neither source used here gives efficiency figures, so this article does not compare it with a cable. Wikipedia also lists version 2.3 from December 2025, which adds reporting of system gain changes, but the sources do not say how that affects ordinary users. For the power your own phone and charger support, check the maker's specifications.
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