ESR Meter Construction and Implementation

The post discusses a simple ESR meter circuit which can be used for identifying bad capacitors in an electronic circuit without removing them practically from the circuit board. The idea was requested by Manual Sofian

Technical Specifications

Do you have a schematic about ESR meter. Technicians recommend me to check the electrolytic first every time I come up with a dead circuit, But I don't know how to measure it.

Thank you in advance for your answer.

The Design

ESR which stands for Equivalent Series Resistance is a negligibly small resistance value that normally becomes a part of all capacitors and inductors and appear in series with their actual unit values, however in electrolytic capacitors especially, due to aging, the ESR value could go on increasing to abnormal levels adversely affecting the overall quality and response of the involved circuit.

The developing ESR in a particular capacitor may gradually increase from as low as a few milliohms to as high as 10 ohms, affecting the circuit response severely.

However the above explained ESR may not necessarily mean that the capacitor's capacitance would also be affected, in fact the capacitance value could remain intact and good, yet have the capacitor's performance deteriorating.

It is due to this scenario a normal capacitance meter entirely fails to detect a bad capacitor affected with high ESR value and a technician finds the capacitors to be OK in terms of its capacitance value which in turn makes troubleshooting extremely difficult.

Where normal capacitance meters and Ohm meters become totally ineffective in measuring or detecting abnormal ESR in faulty capacitors, an ESR meter becomes extremely handy for identifying such misleading devices.

Circuit Diagram

An ESR meter can be used to determine the health of a doubtful capacitor while troubleshooting an old electronic circuit or unit.

Moreover the good thing about these measuring instruments is that it can be used to measure the ESR of a capacitor without the need of removing or isolating the caapcitor from the circuit board making things pretty easy for the user.

The following figure shows a simple ESR meter circuit which can be built and used for the proposed measurements.

ESR meter circuit

How it Works

The circuit may be understood in the following manner:

TR1 along with the attached NPN transistor forms a simple feed back triggered blocking oscillator which oscillates at some very high frequency.

The oscillations induce a proportionate magnitude of voltage across the 5 turns secondary of the transformer, and this induced high frequency voltage is applied across the capacitor in question.

An opamp can also be seen attached with the above low voltage high frequency feed and is configured as a current amplifier.

With no ESR or in case of a new good capacitor the meter is set to indicate a full scale deflection indicating a minimum ESR across the capacitor which proportionately comes down toward zero for different capacitors having different amounts of ESR levels.

Lower ESR causes relatively higher current to develop across the inverting sensing input of the opamp which is correspondingly displayed in the meter with a higher degree of deflection and vice versa.

The upper BC547 transistor is introduced as a common collector voltage regulator stage in order to operate the oscillator stage with a lower 1.5 V so that the other electronic device in the circuit board around the capacitor under test is kept under zero stress from the test frequency from the ESR meter.

The calibration process of the meter is easy. Keeping the test leads shorted together the 100k preset near the uA meter is adjusted until a full scale deflection is achieved on the meter dial.

After this, different capacitors with high ESR values could be verified in the meter with correspondingly lower degrees of deflection as explained in the previous section of this article.

The transformer is built over any ferrite ring, using any thin magnet wire with the shown number of turns.

Need Help? Please send your queries through Comments for quick replies!


Gururaj Acharya said…
Hello Mr.Swagatham,
The esr circuit presented by your is boon for amatuer hobbyist like me as it helps to identify bad caps from salvaged caps.
I heard that ferrite transformer from mobile chargers or pc power supplies too can be used.
Gururaj Acharya said…
Circuits for transistor check and capacitance check too would be helpful.
Swagatam said…
Thank Gururaj,

yes any type of ferrite core can be tried for the transformer
Swagatam said…
yes those circuits are already included in this blog, you can search them through the given search boxes
imanul sofian said…
Dear Mr. Swagatam,
Thank you for designing the circuit. You truly are a helpful man.
Swagatam said…
Thank you dear Imanul,

you are most welcome!
bir bal said…
Very useful
Est miter circuit
Thanks,sir ji
Swagatam said…
you are welcome birbal, and dhodhy
rodan tablatin said…
how to determine if the capacitor is good or bad? tnx
Swag said…
there will be no deflection in the meter...
rodantablatin said…
sir what is the exact numbers and letters of ic 741 . .tnx
Swag said…
Rodan, any 741 IC will do, the prefixes are not important.
rodantablatin said…
ok sir . .can you give me the pcb design of the esr tester?if its ok sir?
Swag said…
I may try if possible....
rodan tablatin said…
good day sir . . i use the anolog meter for the meter and i test the cap .the pointer didnt move . .i have no potentiometer . .
rodan tablatin said…
good day sir i tried your design no deflection in good caps
Swag said…
Hi Rodan, I am sorry it will be difficult for me to troubleshoot your circuit because the design is too elaborate and might need quite many examinations and tweaking to make it work perfectly.
Susilo said…
Hello mr Swagatam
How to connect power supply the esr circuit above ? Is it need ground or just positive and negative supply?thanks
Swag said…
Hi Susilo, I have updated the diagram with the negative supply line, please check it out.
Susilo said…
Ok,thanks mr.Swagatam

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