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.*

**What is ESR**

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.

### UPDATING a Simpler Alternative

The op amp based circuit given below looks complex, no doubt, therefore after some thinking I could come up with this simple idea for assessing the ESR of any capacitor quickly.

However for this you will have to first calculate the how much resistance the particular capacitor possesses ideally, using the following formula:

**Xc = 1 / [2(pi)fC]**

- where Xc = reactance (resistance in Ohms),
- pi = 22/7
- f = frequency (take 100 Hz for this application)
- C = capacitor value in Farads

The Xc value will give you the equivalent resistance (ideal value) of the capacitor.

Next, find the current through Ohm's law:

I = V / R, Here V will be 12 x 1.41 = 16.92V, R will be replaced with Xc as achieved from the the above formula.

Once you find the ideal current rating of the capacitor, you can then use the following practical circuit to compare the result with the above calculated value.

For this you will need the following materials:

- 0-12V/220V transformer
- 4 diodes 1N4007
- 0-1 amp FSD moving coil meter, or any standard ammeter

The above circuit will provide a direct reading regarding how much current the capacitor is able to deliver through it.

Note down the current measured from the above set up, and the current achieved from the formula.

Finally, use Ohm's law again, to evaluate the resistances from the two current (I) readings.

R = V / I where voltage V will be 12 x 1.41 = 16.92, "I" will be as per the readings.

### Obtaining Ideal Value of a Capacitor Quickly

In the above example if you don't wish to go through the calculations, you can use the following benchmark value for getting the ideal reactance of a capacitor, for the comparison.

As per the formula, the ideal reactance of a 1 uF capacitor is around 1600 Ohms at 100 Hz. We can take this value as the yardstick, and evaluate the value of any desired capacitor through a simple inverse cross multiplication as shown below.

Suppose we want to get the ideal value of a 10uF capacitor, quite simply it would be:

1/10 = x/1600

x = 1600/10 = 160 ohms

Now we can compare this result, with the result obtained by solving the ammeter current in Ohms law. The difference will tell us regarding the effective ESR of the capacitor.

**NOTE: The voltage and the frequency used in the formula and the practical method must be identical. **

### Using an Op Amp for Making a Simple ESR Meter

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 capacitor 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.

**Circuit Diagram**

## 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.

Olgun says

Hello!Swagatam

In your explanations above, you say that R = V / I will be 12 V.Is the V voltage the voltage at the 4 diode outputs 1n4007?Or is the secondary winding output voltage of the transformer?

Can you use this circuit to measure and calculate a sample capacitor esr value?

Swagatam says

The voltage will be 12 x 1.41 = 16.92V

Olgun says

I installed the simple circuit shown above. I used a 0-12V / 220V transformer.Connected to a condenser of 330 microfarad-200V.I switched the digital multimeter to milliamp.Since the capacitor is charged immediately, it is difficult to read the current drawn in the ammeter.It shows the ammeter value for a very short time and then no current flow.Therefore, it is necessary to read the current drawn by the capacitor very quickly.I found the value of the 330uF-200V capacitor as follows; R=U/I=12,36/0.0188=657,44ohm Xc=4,82ohm.The esr value of this capacitor = 657.44-4.82 = 652.62ohm. Is this result correct?

Swagatam says

Olgun, I have changed the procedure slightly, so please do it again using the new procedure.

But 330uF is too big, please first confirm using a small non polar capacitor like 1uF.

Olgun says

OK.I’il try it according to the new procedure.I’il contact you again for results.

Olgun says

Hello!

10uf-50v ı installed a capacitor according to the new procedure.I read 32.6 ma from the ammeter.The voltage of the circuit is 12,53×1.41 = 17,667v

Xc = 159,23 ohm R = U / I = 17,667 / 0,0326 = 541,9 ohm

According to these results, what is the ESR value of the capacitor?

Swagatam says

electrolytic will not work with AC, if you are using electrolytic then you must put two in series, whose effective uF will become 5uF. By the way, a 10uF will allow around 500mA current, because a 1uF gives 50mA practically, therefore I recommended to first test using 1uF non polar cap.

Olgun says

Is this circuit only for determining the ESR value of non-polar capacitors?

Can this circuit not be used for electrolytic capacitors?If so, the circuit has no value.The important thing is to learn the ESR value of electrolytic capacitors.Isn’t that right for you?

Swagatam says

In the shown transformer set up electrolytic capacitor cannot be used because the current is AC. By putting two 10uF capacitor in series you create a single 5uF non polar capacitor which becomes suitable for the use. You can connect +/+ or -/- poles of the two capacitors and connect the other ends in the shown position of the circuit, and check how much current it delivers. Once you get the value then you can proceed with the other steps for a 5uF capacitor.

This is a manual method that I have devised so that we can get a clear idea regarding what exactly goes on through each steps.

Olgun says

When I use an electrolytic capacitor, I need to make a series connection.Is this true?

To determine the esr value of a 10 microfarad electrolytic capacitor, it is necessary to connect another 10 microfarad capacitor to it in series.Is that what you want to say?

Josh says

Hi

I need a circuit for a fish tank heater.

It must keep the water at 30 degrees, and switch off and as soon as the temperature drops below 30 degrees the heater must switch back on.

Regards

Swagatam says

You can try the second last circuit form this article:

https://www.homemade-circuits.com/how-to-build-simple-electronic/

I would be deleting this comment soon since it’s not related to ESR meter.

electro kar says

hi sir

is there any way to upload a picture from final circuit?

from 2 side of circuit?

any video that shows hot it works?

Swagatam says

Hi electro kar, sorry I do not have a video for this at the moment!

Susilo says

Hello mr Swagatam

How to connect power supply the esr circuit above ? Is it need ground or just positive and negative supply?thanks

Swag says

Hi Susilo, I have updated the diagram with the negative supply line, please check it out.

Susilo says

Ok,thanks mr.Swagatam

rodan tablatin says

good day sir i tried your design no deflection in good caps

Swag says

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.

Olgun says

What is the frequency to be used in measuring ESR? The Xc value found with 100hz will be different from the calculated value at 100khz.

Swagatam says

The shown will show whether the capacitor is good or not, which will be applicable for all frequencies. If you want to confirm for 100kHz then you can change the set up for 100kHz

rodantablatin says

ok sir . .can you give me the pcb design of the esr tester?if its ok sir?

Swag says

I may try if possible….

rodan tablatin says

good day sir . . i use the anolog meter for the meter and i test the cap .the pointer didnt move . .i have no potentiometer . .

rodantablatin says

sir what is the exact numbers and letters of ic 741 . .tnx

Swag says

Rodan, any 741 IC will do, the prefixes are not important.

rodan tablatin says

how to determine if the capacitor is good or bad? tnx

Swag says

there will be no deflection in the meter…

bir bal says

Very useful

Est miter circuit

Thanks,sir ji

Swagatam says

you are welcome birbal, and dhodhy

Dhodhy Purwakarta says

Esr good thank for you

imanul sofian says

Dear Mr. Swagatam,

Thank you for designing the circuit. You truly are a helpful man.

Swagatam says

Thank you dear Imanul,

you are most welcome!

Gururaj Acharya says

Circuits for transistor check and capacitance check too would be helpful.

Swagatam says

yes those circuits are already included in this blog, you can search them through the given search boxes

Gururaj Acharya says

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.

Swagatam says

Thank Gururaj,

yes any type of ferrite core can be tried for the transformer