Wireless charging is a short-range transformer: the pad creates an alternating magnetic field, the phone’s coil catches it, and the phone converts the induced current back to DC. This article walks through the physics, the Qi and Qi2 standards, and the trade-offs that decide whether wireless makes sense for your product.
How Wireless Charging Works in 3 Steps
Everything else in wireless charging is engineering on top of these three steps:
- The pad’s coil creates a magnetic field. An alternating current through the pad’s coil generates an alternating magnetic field around it.
- The device’s coil catches it. A second coil inside the phone sits over the first; the changing field induces an alternating current in that coil.
- The device rectifies it into DC. The current is converted to stable DC, monitored, and fed to the battery under charge control.
That is why alignment matters so much: it is a loosely coupled transformer, and every millimetre of misalignment drops the coupling and slows charging.
Electromagnetic Induction Explained
The principle is Faraday’s law of induction — the same physics inside every transformer and electric generator. An alternating magnetic field through a coil induces a voltage in that coil. In a wireless charger the coupling is intentionally loose, with coils a few millimetres apart, which is exactly why coil alignment dominates real-world performance: move the phone off-centre and efficiency falls fast. For the full background, the Wikipedia article on inductive charging covers the physics, and HowStuffWorks explains the everyday version.
Qi, Qi2 and Magnetic Power Profile (MPP)
The Qi standard, maintained by the Wireless Power Consortium (WPC), defines how pads and devices talk. For years, Qi relied on the user lining up the coils by eye. Qi2 removes that problem with the Magnetic Power Profile (MPP) — a built-in magnet ring that snaps the phone into perfect alignment, the idea Apple popularised as MagSafe.
What this means in practice:
- iPhone: Qi2-certified chargers deliver up to 15W to current iPhones, with magnetic alignment across Qi2 and MagSafe accessories.
- Android: Qi2 brings the same magnetic alignment and standardised fast charging to Android — a new opportunity for accessory brands. Our Qi2 for Android timeline for OEMs covers the roadmap.
- FCC note: wireless chargers are intentional radiators in the US, so an FCC ID is required in addition to safety marks.
Efficiency, Heat and Charging Speed Trade-offs
Wireless charging trades convenience for efficiency. Typical system efficiency is roughly 70–85%, depending on alignment and coil design, against 90%+ for a good wired charger, and the lost energy becomes heat in both the pad and the phone. That is why wireless fast charging stays well below wired speeds and why phones throttle wireless power when hot.
For a product designer this means three decisions: speed vs heat (a 15W pad needs better thermals than a 7.5W one), convenience vs efficiency, and cost vs alignment reliability (magnets cost more but make charging dependable).
Wireless Charging in OEM Products (Pads, Docks, Power Banks)
Wireless charging is a product category, not a single product. The platforms most often OEM’d, and the jobs they are picked for:
| Platform | Typical output | Best for |
|---|---|---|
| Single-coil pad | 7.5–15W Qi/Qi2 | Entry SKU, bedside, desk |
| 2-in-1 / 3-in-1 dock | Phone + earbuds + watch | Nightstand, travel, gifting |
| Magnetic power bank | 15W output + battery | On-the-go, highest margin |
| Car magnetic mount | 7.5–15W | Driving |
For the multi-device category, our guide to multi-device wireless charging pads explains how to pick a platform, and the Qi2 3-in-1 magnetic wireless charger page shows a shipping example.
Wireless Charging Speed by Phone: iPhone and Android
Wireless speed is set by the phone, not the pad, and the two ecosystems differ. This is the realistic picture in 2026.
- iPhone — up to 15W with Qi2/MagSafe-certified chargers on supported models; standard Qi delivers 7.5W.
- Android — varies by brand; many support 10–15W on Qi, and Qi2 is bringing 15W+ and magnetic alignment to the ecosystem.
- Proprietary speeds — some brands push 50W+ wireless with proprietary chargers, which only work with that brand.
The practical rule: match the pad’s standard to the phone, and ignore headline wattages that need a proprietary charger.
Qi2 25W vs 15W: What’s the Real Speed
“Qi2 25W” appears on chargers, but the speed you get depends on the phone and the profile — not just the pad.
Qi2 defines the magnetic alignment profile; the delivered power is negotiated per device. iPhones cap at 15W today, and 25W-class output benefits Android phones that support it. A Qi2 pad labelled 25W still charges an iPhone at 15W, so match the pad to your phone’s supported profile rather than buying the biggest number.
Why Wireless Charging Gets Hot and How to Fix It
Heat is wireless charging’s biggest drawback, and most of it comes from misalignment and conversion loss.
- Fix the alignment — off-centre coils waste energy as heat; Qi2 magnets solve this, and repositioning helps on plain Qi.
- Remove thick cases — extra distance between coils drops efficiency and raises temperature.
- Avoid charging in sun or on fabric — heat builds up and slows the charge.
- Use a certified pad — quality pads manage heat with better coil and thermal design.
FAQ
Does wireless charging damage the battery? Not inherently. Heat is the main battery stressor; certified chargers with good thermal design manage it.
Can I use any Qi charger with an iPhone? Any Qi charger works, but only Qi2/MagSafe-certified ones reach 15W with magnetic alignment on supported models.
Why is my phone getting hot on a wireless charger? Loose coupling and misalignment waste energy as heat. Reposition the phone and use a certified pad.
Is wireless charging slower than wired? Usually yes — wireless tops out around 15W for mainstream phones while wired fast charging can exceed 100W.
Can I OEM a wireless charger? Yes. MOQ from 200 pcs, with logo, finish, cable and certification handling customizable. Browse the wireless charger collection and start from the OEM/ODM customization page.
References: WPC, Wikipedia inductive charging, ChargerLAB, and EE Times for wireless technology coverage.