ESR meters

One way to test electrolytic capacitors is to measure their capacitance. It does not tell the whole story of capacitor condition. Another usually more useful way to measure electrolytic capacitor condition is to use an ESR meter.

EEVblog #365 – ESR Meter Bad Cap Monitor Repair video gives you tips how to use ESR meter to find bad electrolytic capacitors:

An Equivalent Series Resistance Meter article has a good plan for DIY ESR meter. I have built it and found it well working. Building an ESR meter for Testing Electrolytic Capacitors has a nice table of ESR values you could expect from different capacitors and you can find another table here.

Here are links to some other ESR meter plans and information:

Wikipedia ESR meter page

The Most Useful Tool for Identifying Bad Capacitors

ESR meter page

Building an ESR meter for Testing Electrolytic Capacitors

Capacitor ESR Tester


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  2. tomi says:

    Testing caps with a DIY ESR meter

    The entire circuit is built on stripboard, and if you’re lucky enough to find the right parts in your random parts bin, you should be able to build this ESR meter with components just laying around.

    Building an ESR Meter
    Building a simple ESR meter for troubleshooting electrolytic capacitors.

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  7. Tomi Engdahl says:

    #135: Measure Capacitor ESR with an Oscilloscope and Function Generator

    This video discusses how to measure the ESR (equivalent series resistance) of a capacitor using an oscilloscope and function generator. All of the capacitors tested in this video were 220uF electrolytic caps. In reality, the resistance in the plates of a dried out electrolytic capacitor can’t be modeled as a simple series resistor, but for the purposes of identifying good from bad, this simplification works fine.

  8. Tomi Engdahl says:

    Getting a Handle on ESR with a Couple of DIY Meters

    Got a bunch of questionable electrolytic caps sitting in your junk bin? Looking to recap a vintage radio chassis? Then you might need to measure the equivalent series resistance of the capacitors, in which case this simple five-transistor ESR meter might come in handy.

    Even if you have no need for an ESR meter, [W2AEW]’s video below is a solid introduction to how ESR is determined. The circuit itself comes from EEVBlog forum user [Jay-Diddy_B] and is about as simple as such a circuit can get.

    #247: Circuit Fun: 5 Transistor ESR Meter circuit by EEVBlog user Jay_Diddy_B

  9. Tomi Engdahl says:

    Don’t let ESR waste power and cook capacitors

    There’s an important real-world aspect to the ideal capacitor, called its equivalent series resistance (ESR), which quantifies the capacitor’s effective resistance RS to RF currents.

    This ESR actually has multiple constituent elements, including the part contributed by the electrodes and terminal leads, as well as that due to the dielectric, plate material, electrolytic solution, all as measured at a particular frequency. If you look at ESR in terms of the actual series resistance, the leakage resistance, and the dielectric loss, ESR goes from being just a resistor in series with an ideal capacitor to something more complicated

    Why should we worry about ESR? For basic DC-only blocking circuits, ESR may have little impact. However, when you are designing a switching power supply or an RF circuit, ESR obviously affects your modeling, and real-world performance of the circuit.


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