Designing a transformer or inductor is only half the job—you need to verify it performs as calculated. Electrical testing of magnetic components ensures that inductance, saturation current, loss and thermal performance meet the design specification before production.
This guide covers the key tests for transformers and inductors, the equipment needed, and what the results tell you.
Shaanxi SiRui Technology Co., Ltd. tests every custom magnetic component before shipment. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. Basic Electrical Tests
- Inductance: LCR meter at low signal; verify turns count and core material
- DCR: milliohm meter; compare with calculated winding resistance
- Turns ratio: for transformers, measure voltage ratio
- Insulation resistance: high voltage between winding and core
2. Saturation Current Test
Apply increasing DC current and measure inductance. Plot L vs I_DC to find the current at which inductance drops 10% or 30% (Isat). This is the most critical test for power inductors. Isat must exceed peak current design with margin.
3. Core Loss Measurement
- Back-to-back method: two identical transformers, one drives, one loads
- Power analyzer: measure input and output power at operating conditions
- Calorimetric: temperature rise (most accurate but slow)
4. Thermal Test
Run at rated load until temperature stabilizes. Measure winding temperature (thermocouple) and surface (thermal camera). Acceptance: 20–30°C below insulation class limit.
5. Hi-Pot (Dielectric Withstand) Test
Apply 2–4 kV between primary and secondary for 1 minute. Critical for isolation transformers, gate drive transformers, and medical devices.
6. Test Equipment Summary
| Test | Equipment |
|---|---|
| Inductance / impedance | LCR meter, impedance analyzer |
| DCR | Milliohm meter |
| Saturation | DC source + LCR, saturation analyzer |
| Loss | Power analyzer, oscilloscope + current probe |
| Temperature | Thermocouple, thermal camera |
| Hi-pot | Dielectric withstand tester |
7. Common Test Failures
- Low inductance: wrong core, wrong turns, gap too large
- High DCR: too thin wire, broken winding
- Early saturation: core not suited for DC bias
- High loss at frequency: core material loss too high
- Hi-pot failure: insulation breakdown, winding touching core
8. Sirui-Tech Testing
Every custom component is tested before shipment: inductance, DCR, turns ratio, hi-pot, visual and dimensional inspection. For prototypes, we also perform thermal testing and saturation characterization.
Conclusion
Testing magnetic components verifies that your design performs as calculated. Inductance, DCR and saturation are minimum tests. For safety-critical isolation, hi-pot is non-negotiable. Thermal testing confirms real-operation performance.
Need tested custom magnetics? Contact Sirui-Tech at sales@sirui-tech.com—we test every unit before delivery.