Wireless charging efficiency is lower than wired charging, and the number quoted usually includes or excludes different things. Before comparing two products, it is worth knowing where the losses sit: coupling, alignment, the coil and shielding, the conversion stages and the adapter.
Wireless charging efficiency: the five loss groups
Coupling, alignment, coil and shielding, conversion, and the adapter that feeds the whole chain.
The groups are sequential in the energy path, and the reported efficiency depends on where the measurement starts and ends. A figure measured from the transmitter input to the receiver output describes the coupling chain; a figure measured at the wall includes the adapter and the conversion stages.
Both are legitimate and they are not comparable, which is why the specification should state the boundaries of the measurement as well as the load and the alignment condition.
Loss group 1: coupling
The gap and the geometry decide how much of the field reaches the receiver.
Coupling falls with distance and with the difference between the transmitting and receiving coil geometries, which is why a case thickens the chain and why a smaller receiving coil changes the result. The loss here is physical and cannot be designed away entirely; it can be managed by geometry and by keeping the coils as close and as concentric as the product allows.
Loss group 2: alignment
Off-centre placement costs more than most packaging claims admit.
Coupling drops as the coils move apart, so a product that relies on the user placing the phone creates a distribution of results rather than a figure. A magnetic array fixes the position, which converts a distribution into a repeatable value; a coil array widens the usable area without fixing the position, which narrows the distribution without eliminating it. The specification should state which of the three applies.
Loss group 3: the coil and the shielding
Copper loss, ferrite loss and the field that is deliberately diverted.
The transmitting and receiving coils have resistance, the ferrite behind them absorbs some energy, and the shielding diverts field away from the electronics, which is necessary and not free. Thin designs push these three against each other: less ferrite means less protection and a different field distribution, while thinner wire raises the resistance. The result appears as heat in the same enclosure that has to release it.
Loss group 4: conversion
Two conversions per side, and each one costs something.
The transmitter converts the input to a high-frequency drive, and the receiver converts the induced voltage back to a regulated output for the device. Both stages have their own efficiency, and both are affected by the output level: a system running near its rated power usually converts better than one running at a fraction of it.
Loss group 5: the adapter
The figure from the wall includes a component that is often not the design’s.
The adapter supplied in the box has its own efficiency, and it is often a smaller unit chosen to meet a price point rather than the design’s operating optimum. A charger measured with a generous adapter looks better than the same charger measured with the one the customer receives, which is why the adapter specification belongs with the efficiency claim.
Where the adapter is not supplied, the claim should state the input required to reach the figure: the voltage, the current and whether the supply has to support a particular negotiation. Without that condition, the customer’s own adapter becomes part of the measurement and part of the complaint.
| Group | What it depends on | Design lever | How it shows |
|---|---|---|---|
| Coupling | Distance and coil geometry | Geometry and proximity | Delivered power at a given gap |
| Alignment | The user’s placement or the array | Magnetic reference or a wider area | The spread of results |
| Coil and shielding | Resistance, ferrite and field shaping | Coil design and shielding thickness | Temperature rise at full power |
| Conversion | Two stages per side | Component choice and operating point | Efficiency at defined loads |
| Adapter | The supply in the box | The adapter specification | The figure measured at the wall |
Making two figures comparable
Four conditions, and a figure without them is a claim.
The load at which the measurement was taken; the receiving device and the case condition; the alignment position; and the measurement boundary, meaning whether the figure starts at the wall or at the transmitter input. Stating those four makes the number comparable with another product, and it also explains why a customer measuring at the wall sees a lower figure than the one on the datasheet.
Why the loss ends up as heat
Every group above converts energy into temperature inside a small volume.
That is the practical consequence of the efficiency chain: the product has to release the losses through the same housing that carries the coils, and the thermal result is what limits the sustained output. The derating threshold is therefore connected to the efficiency figure, and the two belong in the same specification.
Where the effort pays
Three levers worth more than the rest.
Alignment, because it removes the loss that varies most between customers; the coil and shielding design, because it sets both the coupling and the thermal path; and the measurement conditions, because a figure stated properly can be defended while a figure without conditions becomes a complaint. Together they are the difference between a claim and a specification.
FAQ
Why is wireless charging less efficient than a cable?
Because energy crosses an air gap and is converted twice on each side. Coupling and alignment losses are physical, and the conversion stages add their own. The useful comparison is between two wireless products measured under the same conditions. Energy crosses an air gap and is converted twice on each side, so coupling and alignment losses are physical and the conversion stages add their own.
Does a case change the efficiency?
It increases the gap and, where it carries a magnet ring, contributes to the alignment. Both effects reduce the delivered power, which is why the case condition belongs in the measurement and in the packaging claim. It increases the gap and, where it carries a magnet ring, contributes to the alignment, so the case condition belongs in the measurement and the claim.
Should the figure include the adapter?
State the boundary either way. A figure from the wall includes the adapter and the conversion stages; a figure from the transmitter input describes the coupling chain. Both are useful and they are not interchangeable. A figure from the wall includes the adapter while a figure from the transmitter input describes the coupling chain, and the two are not interchangeable.
Can the losses be reduced by design?
Alignment and coil design can be improved, and the conversion stages can be chosen for the operating point. The coupling loss across the gap cannot be removed, only managed through geometry and proximity. Alignment and coil design can be improved and the conversion stages chosen for the operating point, while the coupling loss across the gap is managed rather than removed entirely.
Next step
Send the device list, the form factor and the target power to Wecent Group through the contact page. The reply states the delivered figure with its conditions, the alignment method, the thermal result and the derating threshold for the design. Related reading: wireless charger applications, OEM and ODM charger manufacturing and charger quality control. External references: WPC knowledge base, Wireless Power Consortium, IEC standards, EU energy-efficient products, UL standards and certification and TUV testing services.
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