Qi is the open wireless-charging standard created by the Wireless Power Consortium, and it works by magnetic induction: a coil in the charger creates a field that a matching coil in the phone turns back into current. The wattage printed on a charger is its maximum, not what every phone receives. The phone negotiates its own rate, so a 15 W charger delivers 15 W only to a phone built to accept it. Apple's own guidance is that many Qi-certified chargers charge an iPhone at up to 7.5 W; faster wireless charging on iPhone comes from magnetically aligned systems such as MagSafe and Qi2, which the WPC says brought 15 W to certified devices. Four things slow any Qi charger down: a thick or metal case, anything between phone and coil, poor alignment, and heat — when a battery runs warm, the phone limits charging on its own.
What does the wattage on a wireless charger actually mean?
It is a ceiling. A wireless charger and a phone talk to each other before any real power flows, and the phone decides how much it will take. That is why the same charger can fill one phone quickly and another at half the rate: the charger is not being slow, the phone is being conservative.
Apple is unusually direct about this. Its support page says that many Qi-certified chargers charge an iPhone running the latest iOS at up to 7.5 watts. A charger rated at 15 W is not wasted on an iPhone — it simply is not the limit. Plenty of Android phones do accept 15 W over standard Qi, which is why the same charger can be a genuine fast charger on one desk and an ordinary one on the next.
| Phone and charger | What decides the speed |
|---|---|
| iPhone on a standard Qi charger | The phone — up to 7.5 W, per Apple. |
| iPhone on MagSafe or a Qi2 magnetic charger | Magnetic alignment lets the phone accept more; Qi2 brought 15 W to certified devices. |
| Android phone that supports 15 W Qi | Up to the charger's rating, if the phone's own limit is 15 W or more. |
| Any phone with a thick, metal or battery case | Often less than rated, or not at all — take the case off to test. |
How does Qi work?
Qi uses magnetic induction. A copper coil in the charger carries an alternating current, which creates a changing magnetic field; a second coil in the phone sits inside that field and turns it back into current that charges the battery. Nothing is plugged into the phone, but the two coils have to be close and roughly lined up for the transfer to be efficient.
The Wireless Power Consortium, the body that maintains the standard, says Qi launched in 2010 and that more than 13,000 Qi-certified products are on the market. Certification means a product has been through an authorised lab for safety and interoperability — the reason one charger works with phones from different makers at all.
What changed with Qi2 and magnets?
Alignment. A standard Qi pad works best when you put the phone in the right spot, and a phone that is a centimetre off charges slower and runs warmer. Qi2 adds a magnetic ring that snaps the phone into exactly the right place every time. The WPC describes Qi2 as bringing 15 W charging to certified devices with better energy efficiency because the alignment is perfect, and a later version, branded Qi2 25W, as raising that further. Apple's MagSafe works on the same principle.
If you buy a charger mainly for raw speed on a recent iPhone, a certified magnetic charger is the tool for the job. If you want a charger that lives on your desk and is worth looking at, standard Qi is fine — the difference is minutes, not hours.
Why won't my phone charge on a wireless charger?
- The case. Apple lists thick cases, metal cases and battery cases as the usual reason an iPhone charges slowly or not at all. Test once with the case off.
- Something in between. Cards, magnetic mounts and key fobs reduce performance, and Apple warns that the field can damage magnetic strips and RFID chips in bank cards, badges and passports. Take them out of a wallet case before charging.
- The phone moved. A vibrating notification can shift the phone off the coil, and the charger stops. Apple suggests turning off vibration or using Do Not Disturb if it keeps happening.
- It is plugged in. An iPhone connected to USB charges over USB and ignores the wireless charger.
Is it normal for wireless charging to get warm?
Yes, within limits. Induction is less efficient than a cable, and the lost energy shows up as warmth. Apple notes that the iPhone may get slightly warmer and that, to protect the battery, software may limit charging above 80 percent when the battery is too warm, resuming when it cools. Moving phone and charger somewhere cooler — out of direct sun, off a radiator shelf — is the fix.
Good chargers help from their side too. The Solis Core Reactor detects when a phone is placed on it and has built-in temperature control, so it is not pushing power into a phone that is not there or one that is running hot.
Which power adapter should I use?
The one the charger asks for. A wireless charger cannot give out more than it receives, so an underpowered adapter caps it before the phone ever gets a say. Apple's advice is to use the adapter supplied with the accessory or one the manufacturer recommends. The Core Reactor takes a 5 V/2 A or 9 V/2 A input; a 9 V/2 A adapter gives it the headroom for its full 15 W output.
A charger worth leaving on the desk
Most wireless pads are black discs hidden behind a monitor. The Solis Core Reactor goes the other way: a 164 × 164 × 154 mm reactor replica in CNC-machined aluminium alloy over a PC and ABS core, 600 g, with a copper-toned coil array and an engraved ring. Lean a phone against its face and it charges at up to 15 W on phones that support it and up to 7.5 W on iPhone; take the phone away and the core glows blue, with a start-up sound and a pulse effect on a double-tap.
Solis Core Reactor — 15W Wireless Charger, Light & Sound
CNC-machined aluminium reactor replica that charges Qi phones at up to 15 W, with a blue core glow, start-up sound and double-tap pulse.
$129.00 — view product →
It sits in our collector collection alongside other pieces that do a real job. The functional collectibles gift guide compares them side by side.
Frequently asked questions
Will a 15 W wireless charger charge my iPhone at 15 W?
Not on standard Qi. Apple says many Qi-certified chargers charge an iPhone at up to 7.5 W. Faster wireless charging on iPhone comes from magnetically aligned chargers — MagSafe or certified Qi2 — which the WPC says brought 15 W to certified devices.
Does a wireless charger work through a phone case?
Through most thin plastic or silicone cases, yes. Apple lists thick cases, metal cases and battery cases as common reasons an iPhone charges slowly or not at all, and warns against cards or magnetic mounts between the phone and the charger.
Can wireless charging damage my bank cards?
It can. Apple warns that objects between the phone and the charger might damage magnetic strips or RFID chips in credit cards, security badges, passports and key fobs. Take them out of a wallet case before charging.
Why does my phone stop charging at 80% on a wireless charger?
Heat. Apple says that if the battery gets too warm, software might limit charging above 80 percent to protect it, and charging resumes once it cools. Move the phone and charger somewhere cooler.
What adapter does the Solis Core Reactor need?
A 5 V/2 A or 9 V/2 A USB adapter. One cable powers the reactor; after that the phone needs no cable. Use a 9 V/2 A adapter to give it room for its full 15 W output.
Which phones work with the Solis Core Reactor?
Qi phones: iPhone 8 and newer, Samsung Galaxy, Google Pixel and most current Android phones. iPhones charge at up to 7.5 W; phones that support 15 W Qi charge at up to 15 W.
Sources
Written by the Solis Fortune editorial team. Specifications quoted are the published manufacturer figures for the products linked above; where a supplier publishes no figure we say so rather than estimate one. Regulatory summaries are general information, not legal advice — check the rules that apply where you live before you buy.