Why does a charger fail the high-temperature operating test?

Main answer · Wecent Editorial Team

Short answer: A charger fails a high-temperature test when parts get too hot for their rating or the case exceeds its temperature limit. The usual causes are a thermal design that has too little margin, components with low temperature ratings, poor heat paths and enclosures with little airflow. Find the hot spot with thermocouples or an infrared camera, then improve cooling or reduce losses.

What the test does

The charger is run at full load in a warm chamber, typically at a raised ambient temperature, to see whether it stays within limits. Parts and the outside case have maximum temperatures. When ambient is high, there is less margin.

Common causes of failure

• Not enough margin. The design is close to the limit at room temperature.
• Hot components. Transformer, switching devices or rectifiers run too hot.
• Low-rated parts. Capacitors or other parts rated for a lower temperature.
• Poor heat paths. No pad, spreader or contact to the case.
• Sealed case. Little airflow and no way to lose heat.
• Component spread. Some units run hotter than others.
• High load. The test load is more demanding than expected.

How to investigate

1. Attach thermocouples to the hot parts and the case.
2. Repeat the test while recording temperature over time.
3. Use an infrared camera outside the chamber to locate hot areas.
4. Compare failed units with passing units.
5. Check the load and ambient temperature for correct settings.

Fixes

• Increase efficiency, so less energy is wasted.
• Improve heat conduction to the case and spread the heat.
• Move hot parts apart.
• Choose components with higher temperature ratings.
• Add ventilation where the design allows it.
• Reduce the maximum output or add controlled derating.

Derating

A charger can lower its output as it heats up. This protects it, but affects the user’s experience, and may be acceptable if described clearly.

Record

Keep the test conditions, temperatures and fixes in the design file.

Quick summary

Find the hot spot, improve heat paths and ratings, add margin and retest.

Example plan for a fix

First measure and rank the hottest parts. Then change one thing at a time: a better thermal pad, a larger heat-spreading area or a higher-rated capacitor. Retest after each change and record the effect. This methodical approach shows which change worked, and keeps the cost of the fix as low as possible.

Plan for variation

Do not rely on one passing unit. Test at least several samples from different builds, because component spread can move one unit over the limit while another passes. Add a margin so that production units pass as well.

Where this answer says to confirm with Wecent, the detail is not published on the product page and has to come from the datasheet or the factory. General facts come from the regulators, standards bodies or device makers named in the text.