ESR Meter

An ESR meter is a specialized electronic device used to measure the Equivalent Series Resistance (ESR) of capacitors—especially electrolytic ones—without needing to remove them from a circuit.

Here’s why that matters: over time, capacitors can degrade internally, increasing their ESR. Even if their capacitance value still looks fine, a high ESR can cause all sorts of problems in electronic circuits—like power supply instability, audio distortion, or complete failure to operate.

Unlike regular multimeters or capacitance testers, ESR meters apply a small AC signal (often at a few kHz) to detect this hidden resistance. That makes them incredibly handy for troubleshooting, especially in modern devices where bad capacitors can be sneaky culprits.

Want to know how to use one or maybe even build a simple version yourself?