When an EV battery system needs to operate in cold conditions, adding a heater is usually not the difficult part.
The difficult part is making the heater work efficiently, uniformly, and reliably within a limited mechanical space.
A heater may have the correct voltage and power rating on paper, but still perform poorly after installation because of thermal resistance, poor contact, uneven heat distribution, or an unsuitable control strategy.
This is where thick film heating technology becomes interesting.
Rather than treating a thick film heater as a simple replacement for a PTC heater, it is more useful to look at it as a heating element that can be designed around the thermal structure of the battery system.
The Real Problem: Heating the Battery Is Not Just About Heater Power
Consider a simplified EV battery heating system.
The battery starts at a low temperature and needs to reach a target operating range before charging or high-power operation.
A common engineering approach is to calculate the required heating power and then select a heater.
But the actual thermal response depends on much more than wattage:
- Initial temperature
- Target temperature
- Battery or coolant mass
- Heat loss to the environment
- Thermal resistance
- Contact area
- Heating time
- Heater location
- Temperature sensor location
- Control strategy
Two heaters with the same 1 kW rating can therefore produce very different system-level results.
The first design question should be:
Where should the heat be introduced into the thermal system?
1. Start With the Heat Transfer Path
For EV battery thermal management, there are several possible heating paths.
A heater may transfer heat directly to a metal thermal plate, heat a coolant circuit, or be integrated into a dedicated thermal structure.
The shorter and better controlled the heat transfer path is, the easier it is to achieve predictable thermal performance.
For example:
Heater → thermal plate → battery module
has a different thermal behavior from:
Heater → coolant → pump → cold plate → battery module
Neither architecture is automatically better.
The right choice depends on the battery pack design and the required heating response.
This is one reason thick film heaters can be useful: the heating element can be designed as part of a compact thermal structure rather than treated as a generic external component.
2. Don't Optimize Only for Maximum Temperature
A common mistake in heater design is focusing on the maximum heater temperature.
For battery applications, temperature distribution is often more important than maximum temperature.
Suppose a heating element produces sufficient total power but concentrates too much heat in one area.
The result may be:
- Local hot spots
- Uneven battery temperature
- Increased thermal stress
- More complicated control requirements
- Reduced effective heating efficiency
The heating pattern should therefore be considered during the heater design stage.
With thick film technology, the resistance pattern can be designed according to the required heating area and power distribution.
This gives engineers more freedom to match the heater layout to the thermal structure.
3. Power Density Needs to Match the Thermal Structure
Higher power density is not automatically better.
If the heater produces high heat flux but the thermal interface cannot transfer that heat away effectively, the heater surface temperature can rise much faster than the target component temperature.
In other words:
Electrical power ≠ useful thermal power at the battery.
A simplified thermal path can be considered as:
Heater → interface → substrate → coolant / thermal plate → battery
Every interface introduces thermal resistance.
Therefore, when designing a thick film heater, power density should be evaluated together with:
- Substrate material
- Heating area
- Contact area
- Thermal interface material
- Coolant flow rate, when applicable
- Surface temperature
- Heat dissipation capability
This system-level approach is much more useful than selecting a heater based only on its wattage.
4. Why Thick Film Heating Can Be Useful
Thick film heaters use a printed resistive heating element on a suitable substrate.
This construction provides several useful characteristics for EV thermal applications.
Compact construction
The heating circuit can be integrated into a relatively compact structure, which is useful when packaging space is limited.
High power density
The resistance pattern can be designed to concentrate heating power within a defined area.
Fast thermal response
A properly designed structure can reduce unnecessary thermal mass between the heating element and the target.
Custom geometry
The heater can be designed around the available mechanical structure rather than being limited to a standard rectangular heating pad.
Integration with metal structures
Metal substrates can provide a useful thermal path while also offering mechanical rigidity.
These characteristics make thick film technology worth evaluating for battery thermal management systems where packaging and thermal response are important design constraints.
More information about customized thick film heating structures is available on FLD's Thick Film Heater product page.
5. Thick Film vs. PTC: Think in Terms of System Requirements
It is tempting to ask:
Is a thick film heater better than a PTC heater?
That is usually the wrong engineering question.
PTC heaters have important advantages and are already widely used in automotive applications.
The better question is:
Which heater architecture fits the thermal system being designed?
A PTC solution can be attractive when its self-regulating characteristics and established system architecture fit the application.
Thick film heating becomes particularly interesting when the design requires:
- Compact integration
- Customized heating geometry
- High heating power in a limited area
- Direct integration with a thermal structure
- Controlled heat distribution
- Fast thermal response
The comparison should therefore be made at the system level, not simply by comparing heater specifications.
6. Temperature Sensors Should Be Designed With the Heater
Another issue that is often overlooked is sensor location.
The temperature measured by a sensor is not necessarily the actual temperature of the heating element.
For example:
Heater temperature ≠ thermal plate temperature ≠ coolant temperature ≠ battery temperature
If the sensor is positioned too far from the heating area, the control system may respond too slowly.
If it is placed too close to the heater, it may detect the heater temperature before the battery or coolant has reached the required temperature.
The sensor position should therefore be considered together with:
- Heater layout
- Heat transfer direction
- Thermal mass
- Expected temperature gradient
- Control response
For a battery heating system, this can be just as important as selecting the heater's rated power.
7. Mechanical Design Matters More Than It Looks
EV battery systems experience vibration, thermal cycling, and changes in temperature over long operating periods.
The heater therefore needs to remain mechanically stable after repeated heating and cooling cycles.
Important design factors include:
- Substrate selection
- Mounting method
- Thermal expansion
- Surface flatness
- Contact pressure
- Insulation
- Environmental protection
- Connection design
A heater that performs well during a laboratory test may behave differently after integration into a vehicle system.
This is why heater development should include both thermal and mechanical considerations from the beginning.
8. A Better Way to Select a Thick Film Heater
Instead of starting with:
"I need a 500 W heater."
Start with the thermal requirement.
For example:
Step 1 — Define the target
What needs to be heated?
Battery module, thermal plate, coolant, or another component?
Step 2 — Define the temperature range
Determine:
- Starting temperature
- Target temperature
- Maximum allowable temperature
Step 3 — Estimate heating power
Consider the thermal mass and required heating time, then account for heat loss.
Step 4 — Define the available installation space
Determine the maximum:
- Length
- Width
- Thickness
- Connection position
Step 5 — Design the heat transfer path
Identify how heat moves from the heater to the battery system.
Step 6 — Select the heater structure
Evaluate substrate, resistance pattern, heating area, insulation, and mounting method.
Step 7 — Design temperature control
Define sensor location, control method, and over-temperature protection.
This approach usually produces a more reliable design than selecting a standard heater first and trying to adapt it afterward.
When Should You Consider Thick Film Heating?
Thick film heating is particularly worth considering when several of these conditions exist at the same time:
Limited installation space
High heating power requirement
Fast thermal response
Customized heating geometry
Direct integration with a thermal structure
Controlled heat distribution
It is not necessarily the best solution for every EV battery application.
For applications where flexibility and conformable installation are more important, silicone heaters may be more suitable. For extremely thin and flexible heating requirements, polyimide heaters are another option.
The important point is to select the heater according to the thermal architecture, not simply according to the heater type.
Final Thoughts
Designing an EV battery heater is fundamentally a thermal-system problem.
The heater power is only one part of the equation.
A successful design needs to consider the complete path from electrical input to the final heat delivered to the battery or coolant.
Thick film heating can be a strong candidate when the system requires a compact, high-power-density heating element that can be integrated closely with the thermal structure.
For engineers working on a new battery thermal management project, the most useful starting point is not:
"Which heater should I buy?"
It is:
"Where does the heat need to go, how quickly does it need to get there, and what mechanical space is available?"
Once those questions are clear, the appropriate heater technology becomes much easier to determine.
If you are developing a customized EV battery heating solution, FLD works with OEM/ODM customers on heater dimensions, electrical specifications, heating patterns, substrate selection, and application-specific requirements. You can learn more about the company's custom thick film heater solutions.
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