How to Test if an Inductor is Working？

Inductors are key parts in power supplies, filters, and transformers. If an inductor fails, your circuit may overheat, make noise, or stop working. This guide shows you how to check if an inductor is good using basic and advanced methods.

1.Common Inductor Problems

Before testing, it helps to understand what can go wrong:

Open circuit -- Broken wire inside the coil.

Short circuit -- Wires touch each other due to damaged insulation.

Low inductance -- Cracked core or shifted windings.

Saturation -- Core can't handle DC current; inductance drops sharply.

High DC resistance -- Partly broken wire or corrosion causes extra heat.

Low Q factor -- High losses in the core or wire.

Short to core/shield -- Insulation fails between winding and core or shield.

 

2.Preliminary Checks – Visual & Mechanical

Before using any tester, look at the inductor:

-Cracks, burns, broken leads, melted plastic – replace it.

-Loose terminals – gently wiggle; they should be firm.

-For SMD types – check for cracked solder joints.

-Check labeling – make sure the value and rating are readable.

If you see damage, replace the inductor immediately.

 

3.Basic Electrical Tests with a Digital Multimeter (DMM)

 

A DMM is quick for basic checks.

 

3.1 DC Resistance (DCR) Test

-Set DMM to lowest resistance range (e.g., 200 Ω).

-Measure across the two terminals.

-Compare with the datasheet value.

What the reading means:

-Very low (e.g., <0.1 Ω) – normal for power inductors.

-Tens to hundreds of ohms – normal for small signal or RF chokes.

-Infinite (OL) – open circuit – inductor is dead.

-Zero ohms when DCR should be higher – possible shorted turns. A DMM cannot confirm this alone; use an LCR meter.

Note: A DMM cannot measure inductance. It only checks continuity and resistance.

 

3.2 Short to Core or Shield

-Set DMM to high resistance (e.g., 20 MΩ).

-Measure between a terminal and the core (or shield).

-Should show infinite – any finite resistance means insulation failure – replace.

 

4.Inductance Measurement – Using an LCR Meter

This is the most reliable test. It measures inductance (L) and quality factor (Q).

 

What you need：LCR meter (handheld or benchtop).

 

Steps:

-Set meter to inductance mode (L).

-Choose the test frequency from the datasheet (usually 100 Hz for power inductors, 1 kHz or 100 kHz for signal/RF). If not specified, use 1 kHz.

-Set test voltage to 1 Vrms or lower (avoid saturation).

-Connect the inductor (use Kelvin clips for parts under 10 µH).

-Write down the L and Q readings.

Pass/fail:

Inductance tolerance – Most inductors have ±20% or ±10%. If the reading is outside the specified range (e.g., a 100 µH inductor reads 45 µH), it is defective.

Q factor – Compare with datasheet. A Q value significantly lower than specified indicates high losses (e.g., damaged core or oxidized wire).

If the LCR meter shows "open" or extremely high inductance – The coil is open.

If it shows very low inductance but DCR is normal – There is likely a turn-to-turn short.

Pro tip: Always zero/calibrate the LCR meter before testing, especially for low-inductance components.

 

5.Saturation Current Test (Isat)

 

When DC current exceeds the rated value, the core saturates and inductance drops. A good inductor stays within spec up to its rated Isat.

 

How to test:

-You need a DC power supply and an LCR meter with bias capability (or a separate bias source).

-Slowly increase DC current from 0 to rated Isat, then a bit above.

-Record inductance at each current step.

What is normal?

At rated Isat, inductance drop should match the datasheet (e.g., 30% drop for power inductors). If inductance collapses much earlier or the part gets very hot, it fails.

Without an LCR meter: You can use an oscilloscope and a series resistor, but it's more complex and less accurate.

 

6.Self-Resonant Frequency (SRF) Test

Every inductor has a self-resonant frequency due to internal capacitance. Above SRF, it acts like a capacitor. A damaged inductor may have a lower SRF.

Simple method (signal generator + oscilloscope):

-Connect the inductor in series with a 50 Ω resistor (voltage divider).

-Sweep the frequency while watching the output voltage.

-Find the frequency where voltage across the inductor peaks – that's the SRF.

-Compare with datasheet.

If SRF is much lower than specified, the inductor may be wet or deformed.

 

7.Q Factor and Impedance Phase Angle

A good inductor has an impedance phase angle close to +90° (inductive) at the test frequency.

Using an LCR meter in Z-θ mode:

Phase angle (θ) should be between +70° and +90°.

If angle is near 0° or negative, the part is resistive or capacitive – defective.

 

8.Special Case: In-Circuit Testing

Testing an inductor while soldered on a board is tricky because other parts affect the reading.

Tips for in-circuit testing:

-Use a low-frequency LCR meter (100 Hz or 120 Hz) – other components have less effect.

-If possible, desolder one leg – this is the only sure way.

-Some advanced testers have an "in-circuit" mode.

-Use a DMM to check for shorts to ground. If a terminal shows near-zero ohms to ground, the short is likely elsewhere.

Golden rule: When in doubt, remove the inductor and test it off the board.

 

9.Summary – Step-by-Step Testing Flow

Step	Test	Tool	Pass Condition
1	Visual inspection	Eye	No cracks, burns, or broken leads
2	DCR check	DMM	Within datasheet range (not open, not zero if DCR > 0)
3	Insulation to core/shield	DMM (high ohms)	Infinite resistance
4	Inductance (L)	LCR meter	Within tolerance (±10% or ±20%)
5	Q factor	LCR meter	≥ specified minimum
6	Saturation test (if needed)	DC bias + LCR meter	Inductance drop ≤ datasheet limit at rated Isat
7	SRF (for RF/filter inductors)	Network analyzer	Matches datasheet

For production or incoming inspection: Always perform steps 1, 2, 4, and 5.

For troubleshooting a failed circuit: Perform all steps to pinpoint the failure mode.

 

10.When to Replace vs. When to Keep

Replace immediately: Open circuit, short to core, cracked core, melted bobbin, L out of tolerance, Q too low.

Use with caution (non-critical only): L slightly below lower limit (e.g., -22% instead of -20%). For power circuits, replace anyway.

Good to use: All tests pass and it works under load in your circuit.

 

Conclusion

Testing an inductor is not just about checking continuity. A truly "working" inductor must meet its inductance, Q, saturation, and frequency characteristics. For a quick production check, an LCR meter and a DMM are sufficient. For high‑reliability designs (automotive, medical, industrial), perform saturation and SRF tests as well.

This simplified guide gives you the essential steps to test inductors quickly and reliably. Always refer to the datasheet for exact values. If you need high-quality transformers, inductors, or cores, contact us for support.For more information, please contact us at sales@xfullstar.com