Thermal management is often the difference between a magnetic component that works on the bench and one that fails in the field. Transformers and inductors heat up from both core loss and copper loss, and every 10°C rise cuts magnet wire insulation life roughly in half.
This guide covers thermal design principles for power magnetics, key measurements, and practical cooling strategies.
Shaanxi SiRui Technology Co., Ltd. engineers design every custom transformer and inductor with thermal analysis and prototype verification. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. Where the Heat Comes From
- Core loss: hysteresis and eddy current loss, uniform in core volume
- Copper loss: I²R loss concentrated in windings
- Proximity effect: additional AC resistance at high frequency (can dominate)
2. Temperature Limits
| Component | Max Temperature |
|---|---|
| Magnet wire (Class B) | 130°C |
| Magnet wire (Class F) | 155°C |
| Magnet wire (Class H) | 180°C |
| Ferrite core (Curie point) | ~200°C |
| Bobbin / plastic | 105–130°C |
Design rule: keep hot spot at least 20–30°C below insulation rating.
3. Cooling Strategies
- Increase core size: more surface area for heat dissipation
- Thermal pad: between component and PCB/chassis
- Forced air: fans dramatically reduce thermal resistance
- Potting: improves conduction, choose carefully to avoid trapping heat
- High-temp insulation: Class F/H wire for hot applications
4. Measuring Temperature
- Thermocouple: embedded in winding during construction (most accurate)
- Thermal camera: surface temp only (underestimates hot spot by 10–20°C)
- Temperature rise test: run at rated load until stable
5. Common Mistakes
- Underestimating proximity loss (AC resistance 2–5× DC at high freq)
- Designing for 100°C ambient without derating
- Only measuring surface, not internal hot spot
- Ignoring PCB copper as heat sink
- No thermal margin (design at 80% of rated loss)
6. Sirui-Tech Thermal Design
- Loss modeling (core + copper)
- Thermal resistance estimation
- Prototype temperature testing before production
- Class F/H insulation for high-temperature applications
Conclusion
Thermal design is as important as electrical design for magnetic components. Balance core loss and copper loss, keep hot spot below insulation rating with margin, and verify with prototype testing.
Need a thermally optimized design? Contact Sirui-Tech at sales@sirui-tech.com with your power level and ambient temperature.