How Does Wireless Charging Work? Induction, Coils and Magnets Explained
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Wireless charging can look like magic, but it relies on a principle discovered in the 1800s: electromagnetic induction. A coil in the charger creates a changing magnetic field, and a coil in your phone turns that field back into electricity. Here’s how it works step by step.
For the basics of what wireless charging is and the standards involved, see what is wireless charging.
Table of Contents
Step by Step: From Wall Outlet to Battery
- Power in: the charger plugs into a wall adapter or a car’s USB port.
- Transmitter coil: the charger sends alternating current through a flat copper coil.
- Magnetic field: the alternating current creates a rapidly changing magnetic field above the charger.
- Receiver coil: a matching coil inside the phone sits in that field, which induces an alternating current in it.
- Conversion: the phone converts that current to DC and feeds its battery charging circuit.
Apple confirms that wireless charging uses magnetic induction to charge iPhone.
The Digital Handshake
Qi chargers don’t just blast power. The charger and phone communicate first to confirm a compatible device is present and agree on how much power to send. Qi chargers are also designed to detect stray metal objects and reduce or stop power, which is one reason certified chargers are worth paying for. The WPC says only certified products can display the Qi or Qi2 logo.
Why Alignment Matters
The coils need to line up closely. If the phone is off-center, less power transfers and more turns into heat. That’s the problem magnets solve. The Wireless Power Consortium says Qi2 devices use magnetic attachment to align devices and chargers for better efficiency and faster charging. Apple’s MagSafe does the same for iPhone.
Why Wireless Charging Gets Warm
Some energy is always lost as heat during induction, more so when coils are misaligned or there’s a gap. Heat matters because batteries charge more slowly when warm. Apple says iPhone software might limit charging above 80 percent if the battery gets too warm.
What Blocks Wireless Charging
- Thick cases or wallet cases that add distance
- Metal cases, plates or rings between the phone and charger
- Credit cards and key fobs, which Apple says may be damaged
- A phone connected to USB, since Apple says iPhone charges through USB instead when plugged in
Wireless Charging in the Car
Car wireless chargers work the same way, but heat from the sun and navigation can slow charging. Mounts with cooling fans or thermoelectric coolers help. See our picks for car wireless chargers.
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Frequently Asked Questions
Does wireless charging use magnets?
It uses magnetic fields to transfer power. Qi2 and MagSafe chargers also use physical magnets for alignment.
Why is wireless charging slower?
Some energy is lost as heat, and chargers limit power to keep phones cool. Qi2 25W chargers are faster than older Qi pads.
Can wireless charging work from a distance?
Consumer wireless chargers work only at very short range, with the phone on or attached to the charger.
Is wireless charging bad for my battery?
Heat is the main concern. Use certified chargers, avoid thick cases and keep the phone cool.
The Bottom Line
Wireless charging works by magnetic induction: a coil in the charger creates a changing magnetic field, and a coil in the phone converts it back into electricity. Good alignment, a thin case and a cool phone make it faster and more efficient.
