Wireless Charging heat loss: how to separate copper loss, ferrite loss, and metal heating.
A wireless charging system gets hot.
That part is clear.
The harder question is: what should be changed first to reduce the heating?
The coil? The ferrite shield? The nearby metal plate? The alignment between transmitter and receiver? The operating current?
A temperature distribution alone does not answer that. It only shows where the heat ends up. To fix the design, engineers need to understand where the heat is created.
In wireless charging, heat usually comes from three main sources:
- Copper loss in the transmitter and receiver coils
- Ferrite loss in shielding or flux-guiding parts
- Eddy-current heating in nearby conductive metal parts
These sources can sit close together. They can also heat each other through conduction. That is why a hot area in the final temperature field is not always the original source of the loss.
Simulation helps when it separates the system into objects and result types. Instead of only asking “where is it hot?”, engineers can ask a better question:
Which object is losing energy, and by which mechanism?
Image source: CENOS EV wireless charging use case: Temperature distribution of the charging coil
Start with temperature
Temperature distribution is the first useful view. It shows the thermal result of the whole setup.
In the CENOS electric vehicle wireless charging use case, the temperature field shows how heat builds up around the transmitter coil during the charging process. This is the right place to start because it shows the visible engineering problem.
But it does not yet say why the system is hot.
A transmitter coil can be hot because of its own copper loss. A ferrite plate can be hot because the magnetic field is too concentrated. A nearby conductive plate can be hot because the field is coupling into it instead of the receiver coil.
These are different problems. They need different fixes.
So the next step is to move from temperature field to loss separation.
1. Copper loss in the coils
Copper loss is usually the first suspect.
In wireless charging coils, current creates resistive loss. At higher frequencies, current is not distributed through the conductor in the same way as in a DC calculation. Skin effect and proximity effect can push current into areas of the conductor and increase local heating.
That is why coil heating should not be checked only through total temperature. Engineers should also inspect:
- current density in the transmitter coil
- current density in the receiver coil
- active power in each coil
- resistance and Q factor
- coil geometry, turns, strand count, and strand diameter
In the CENOS EV case, the transmitter coil setup includes 20 turns, 10 strands, and 46 A RMS current. Those values are not just setup details. They directly affect current distribution, field generation, and heat loss.
Image source: CENOS WCH Results Viewer: Selecting objects and result fields
Source: WCH Results Viewer
In the Results Viewer, engineers can inspect separate geometry objects and switch result fields such as temperature, current density, eddy losses, and other values. This matters because the coil should be checked as its own object, not only as part of the full temperature picture.
A good first check is:
Does the hot zone follow the coil current density?
If yes, the likely starting point is coil design. Engineers may need to review:
- conductor cross-section
- litz wire definition
- number of strands
- turn spacing
- operating current
- frequency
- cooling assumptions
- receiver load and matching
If current density is high in one local area, the fix is usually not ferrite material. The copper is telling you where the first problem sits.
2. Ferrite loss
Ferrite is often added to guide the magnetic field and reduce leakage. But ferrite is not a passive decoration layer. It changes the field, and it can become a loss source itself.
Ferrite-related loss can include hysteresis loss and eddy-current loss, depending on material properties, frequency, magnetic flux density, temperature, and geometry.
This is why engineers should inspect ferrite parts separately.
A useful check is:
Is the ferrite helping guide the field, or is it becoming a heat source?
In CENOS, geometry roles can be assigned to coils, ferrites, and conductors. Thermal analysis can also be enabled for the relevant objects. That lets engineers inspect ferrite temperature and stray losses as separate results instead of guessing from the final thermal map.
Image source: CENOS WCH Results Viewer. Performance plots including Q factor, mutual inductance, current, active power, coupling coefficients, and stray loss
Source: WCH Results Viewer
The EV use case includes a stray-loss diagram where losses are shown across system components, including conductors and ferrite materials.
Image source: CENOS EV wireless charging use case. Stray loss diagram
This is the key difference between “thermal analysis” and “loss analysis”.
A temperature plot may show that the region near the ferrite is warm. A stray-loss plot can show whether the ferrite is creating the heat or only receiving heat from nearby objects.
If ferrite loss is high, engineers may need to review:
- ferrite material grade
- shield thickness
- shield segmentation
- ferrite coverage area
- distance between ferrite and coil
- local magnetic flux density
- operating frequency
The fix may be a ferrite change, but not always. Sometimes ferrite loss rises because alignment is poor and the field path is no longer what the design expected.
3. Metal heating near the charger
Nearby metal is one of the more unpleasant sources of heat loss because it may not be part of the charging function at all.
It may be:
- a housing part
- a bracket
- a backplate
- a vehicle structure
- a metal shield
- a screw
- a phone component
- a foreign object
- a conductive plate in the wrong place
In the EV use case, misalignment caused the receiver coil to sit almost outside the magnetic field from the transmitter coil. Instead of coupling well with the receiver, the transmitter field coupled with the conductive plate. That caused poor coupling and increased losses in the conductive plate.
Image source: CENOS EV wireless charging use case. Magnetic field distribution with misalignment
This is a practical warning.
If a conductive part is close to the active field, it can become a hidden heater. The coil may look like the problem because the charger is hot, but the real issue may be that the field is coupling into the wrong object.
A useful check is:
Which conductive object shows eddy loss when the receiver is shifted, tilted, or moved away?
This matters for electric vehicles, mobile devices, robots, and micro-mobility chargers. The product rarely gives engineers perfect alignment. The system has to tolerate the positions that users, vehicles, robots, and docking stations will create in use.
Mobile phone charging: localized heat can come from placement
The CENOS mobile phone wireless charging case shows a temperature range from 33.2°C to 39.5°C. The important point is not only the number. It is the pattern.
The temperature field changes with coil placement and alignment. Misalignment reduces coupling, wastes more energy as heat, and can create localized overheating.
Image source: CENOS mobile phone wireless charging case. Temperature distribution from 33.2°C to 39.5°C
This is why “the device gets warm” is not enough information.
The system may heat because:
- transmitter and receiver coils are shifted
- magnets or alignment parts change the field path
- the receiver is too far from the transmitter
- metal inside the device sits inside a high-field region
- the coil design creates local current concentration
- the ferrite does not guide the field well enough
The fix depends on which of these is true.
External research says the same thing: losses must be separated
This is not only a CENOS point.
A UCL paper on ferrite-cored wireless energy transfer systems compared conductive and magnetic shielding materials using finite element modeling. The study found that magnetic shield material affects self-inductance, coupling coefficient, and losses in the system. It also showed that the right shielding choice depends on the coil system, not on a universal rule.
External research comparing eddy-current losses for different resonant coil geometries and shield materials. The results show why shielding choice cannot be treated as a generic add-on, material and geometry both change where losses appear.
Image source: UCL Discovery — “Ferrite-cored wireless energy transfer systems” Source: https://discovery.ucl.ac.uk/id/eprint/10089844/
Another thermal study of coupled resonant coils for EV wireless charging modeled transmitter and receiver coils and analyzed temperature distribution. In that study, the copper coil case reached a maximum temperature of about 74.982°C, and the authors connected thermal behavior to coil material, core layer material, and heat transfer conditions.
Image source: Wen et al., “Thermal Analysis of Coupled Resonant Coils for an Electric Vehicle Wireless Charging System,” World Electric Vehicle Journal, 2022
Source: Thermal Analysis of Coupled Resonant Coils for an Electric Vehicle Wireless Charging System
Foreign object research also confirms the risk of conductive objects. A 2024 paper on metal and living foreign object detection for EV wireless charging notes that metal foreign objects in an alternating magnetic field can heat through eddy currents and may create fire risk.
Image source: Cai et al., “Research on Metal and Living Foreign Object Detection Method for Electric Vehicle Wireless Charging System,” World Electric Vehicle Journal, 2024.
Source: https://www.mdpi.com/2032-6653/15/1/34
The practical conclusion is consistent:
A wireless charging thermal problem should be analyzed by object and by loss type, not only by final temperature.
Client proof: Tiler used CENOS to study misalignment
A relevant CENOS wireless charging client story comes from Tiler, a Dutch company working on wireless charging for micro-mobility.
Tiler uses the vehicle kickstand as the receiver and a pavement tile as the transmitter. That creates a demanding alignment problem because the system must work across a wide displacement range.
Tiler CTO Joris Koudijs said:
“Tiler explored multiple simulation tools, but found CENOS to be the most user friendly by far. It is really quick to setup multiple studies and iterate the design quickly. We also simulated the designs we have in production already and found very good correlation.”
In the same case story, Tiler achieved an average K of 0.5 and Q of 700+ over a displacement of 3x the size of the receiver.
That connects directly to heat-loss separation. If the charger must tolerate misalignment, the design team needs to know whether losses move into the coil, ferrite, or nearby metal as the position changes.
A practical loss-separation process
Here is a practical way to inspect a hot wireless charging system.
1. Check the full temperature field
Start with the full thermal view. Locate the hot zones.
Do not make a design change yet.
At this stage, the goal is only to identify where the system temperature rises.
2. Inspect each coil separately
Select the transmitter coil and receiver coil as separate objects.
Check:
- current density
- active power
- resistance
- Q factor
- local temperature
- plot over line through suspicious zones
If the hot area follows high current density, the first design review should focus on coil geometry, conductor definition, current, frequency, or cooling assumptions.
3. Inspect ferrite objects separately
Select ferrite parts.
Check:
- ferrite temperature
- stray loss
- magnetic flux density near ferrite
- whether loss changes with position or gap
- whether the ferrite is saturated or overworked locally
If ferrite loss is high, review material, thickness, segmentation, and placement.
4. Inspect nearby conductive parts
Select conductive objects that are not meant to receive energy.
Check:
- eddy losses
- local temperature
- magnetic field distribution around the part
- loss changes under misalignment
- loss changes with air gap
If a nearby metal part heats up, the coil may be doing its job badly because the field is coupling into the wrong object.
5. Compare aligned and misaligned cases
Run at least one aligned case and one worst-position case.
For EVs, this may mean lateral offset, vertical distance, and tilt. For phones, it may mean shifted placement or magnetic alignment variation. For robots and micro-mobility chargers, it may mean imperfect docking.
The question is not only whether coupling drops.
The better question is:
Where do the losses move when alignment gets worse?
What to change first
Once the loss source is clear, the design decision becomes more direct.
Change coil geometry when:
- current density is locally high
- active power loss is high in the coil
- Q factor drops
- coil heating matches the current-density pattern
- turn spacing or conductor definition creates local concentration
Typical changes include turn spacing, strand count, conductor size, coil diameter, receiver load, and frequency.
Change ferrite design when:
- ferrite loss is high
- magnetic flux is concentrated in one part of the ferrite
- ferrite temperature rises before nearby objects heat up
- shield coverage sends the field into a poor path
- ferrite placement improves coupling but increases thermal risk
Typical changes include ferrite grade, thickness, segmentation, coverage, and distance from the coil.
Change surrounding metal or packaging when:
- eddy losses appear in brackets, plates, housing, screws, or nearby conductive parts
- misalignment increases conductive-object heating
- a metal part heats even when coil losses are acceptable
- the field couples with a conductive plate instead of the receiver coil
Typical changes include moving metal parts, adding shielding, changing material, adding distance, cutting slots to interrupt eddy-current paths, or adjusting coil/ferrite placement.
Treat misalignment as the likely cause when:
- coupling coefficient drops
- mutual inductance changes sharply
- conductive-object loss rises with offset
- temperature becomes local instead of evenly distributed
- the hot zone moves when receiver position changes
This is especially important in EV charging, mobile phones, robots, and micro-mobility systems. These systems live in imperfect positioning. The design must survive that.
Final takeaway
Heat in wireless charging is not one problem.
It is the result of several loss sources interacting in the same compact space.
A temperature plot shows the symptom. Current density helps explain coil copper loss. Stray-loss plots help separate ferrite and conductor losses. Eddy-loss views show whether nearby metal is stealing energy and turning it into heat. Alignment studies show when losses move from the intended receiver path into the wrong object.
That is the point of simulation here.
Not to make a prettier thermal picture. To decide what to change first.
For engineers working on wireless charging systems, that difference matters. It can save unnecessary prototype rounds, reduce late design changes, and give the team a clearer route from hot system to solid design.
