Super simple ESR meter with a resolution of 10 mOhms. - Page 1
Forum section: electronics / projects

author: iet
author_rank: Frequent Contributor
timestamp: May 12, 2025, 04:47:39 pm
content: A good friend of mine once sent me this circuit. It was lying in a folder for a long time until I accidentally saw it.The circuit is super simple, only 8 components. 3 resistors, 3 capacitors, 1 transistor and 1 transformer.The ESR meter works together with a digital multimeter in the diode measurement mode. This mode performs two functions: powering the meter and displaying the measured values ​​on the display in digital form. I had a cheap digital multimeter lying on the shelf for a long time, so I used it.The ESR meter is structurally made using a well-established technology - tweezers with polished brass tips. The entire assembly is made on a small board with ready-made holes.The requirements for the tweezers design are the same: good contact and minimal resistance of the connecting wires between the tips and the board. There are no special requirements for the components. Special attention should be paid only to the transformer. It is wound on a ferrite ring. Much depends on the type of ferrite used. Wires of the same or different diameters can be used for the windings.The measuring frequency, measuring voltage and zero setting range depend on the quality of the wound transformer. In our circuit, this is 1.000 on the multimeter display with the tweezers closed.

author: Shay
author_rank: Regular Contributor
timestamp: May 13, 2025, 01:22:00 am
content: Thank you for sharing, however you haven't explained how the circuit works or the turns ratio required. It would be good to explain how the circuit works.

author: iet
author_rank: Frequent Contributor
timestamp: May 13, 2025, 05:01:38 pm
content: Quote from: Shay on May 13, 2025, 01:22:00 amThe circuit uses a Hartley generator.https://www.electronics-tutorials.ws/oscillator/hartley.htmlIt generates oscillations with a frequency of 100 kHz. The frequency can be slightly higher or lower. This depends on the number of turns of windings II and III. The frequency can also be changed by selecting the capacitance of capacitor C1.On winding I, we get a low sinusoidal voltage of 100-600 mV, which is fed to the measured capacitor. The multimeter operates in the mode of measuring the forward voltage drop on the diode.My circuit worked the first time. I only had to tinker a little with the transformer. After measuring the resistors on the test board, I found out how the ESR meter works.The first digit after the dot corresponds to units of Ohms, the second to tenths of an Ohms, the third to hundredths of an Ohms.In my circuit, the number of turns:I: 1-0.45 mmII: 10-0.35 mmIII: 60-0.2 mm

author: Paul Price
author_rank: Super Contributor
timestamp: May 13, 2025, 06:32:43 pm
content: Congratulations! You've truly created a one-of-a-kind instrument!How did you manage to achieve such accuracy? I think its fantastic you can accurately do so much with so little parts and effort!Wait to JDiddy sees this!

author: kripton2035
author_rank: Super Contributor
timestamp: May 13, 2025, 06:39:25 pm
content: resolution <> accuracy !

author: tom66
author_rank: Super Contributor
timestamp: May 14, 2025, 08:39:34 am
content: Interesting idea, but would the reading not depend upon the current that the DMM forces (or tries to force into) the tester?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 14, 2025, 10:52:58 am
content: The series resistor at the terminals to the DUT makes it deficult to get high resolution. One may need some minimal resistance to make the oscillator oscillate at all.I would not expect high accuracy and some dependence on the DMM used. So it makes sense to add a resistor to an extra terminal (like 1 ohm, maybe also 10 ohm) to check the calibration with the actual meter.The idea is nice to check capacitors. This usually does not need high accuracy.

author: Paul Price
author_rank: Super Contributor
timestamp: May 14, 2025, 11:04:50 am
content: The real problem here for everyone interested in building something like this is the failure to standardize the oscillator core part identity which puts the whole apple cart on a tilt. Probably not an easy thing to find an anonymous core somewhere that works the same!Another problem is a failure of the OP to show the results of several tests with known resistors(for example .01 to 10-ohms) to show any indication of accuracy.That's why I said this device istruly a one-of-a-kindinstrument!This great invention, it is not at all easily duplicated, relying on finding the perfect matching unknown transformer core and this is the heart of this project.Both the magic core and multimeter are wild Jokers in this mysterious voodoo circuit called a Great ESR Meter Discovery.All Praise to JDiddy!

author: kripton2035
author_rank: Super Contributor
timestamp: May 14, 2025, 11:57:42 am
content: I'm rebuilding my esr meter repository, in a few weeks it will be online.I will include this one as well, along with all the remarks for building it ...

author: iet
author_rank: Frequent Contributor
timestamp: May 14, 2025, 02:22:11 pm
content: Quote from: tom66 on May 14, 2025, 08:39:34 amI have not noticed this yet. The current consumption is very small.

author: iet
author_rank: Frequent Contributor
timestamp: May 14, 2025, 02:24:36 pm
content: Quote from: Paul Price on May 14, 2025, 11:04:50 amOpen the LED lamp, there is a ferrite ring on the board.You can buy several types of ferrite rings, they are very cheap. Winding this transformer takes 10-20 minutes, depending on the diameter of the wire.

author: iet
author_rank: Frequent Contributor
timestamp: May 14, 2025, 03:07:10 pm
content: Quote from: Paul Price on May 14, 2025, 11:04:50 amTest board. Resistors.

author: iet
author_rank: Frequent Contributor
timestamp: May 14, 2025, 09:51:34 pm
content: Spent a little time "standardizing" the transformer. Green ferrite ring 14x8x5. Used for power filters of various devices. Three windings are wound with wire of the same diameter - 0.4 mm.I:1II:5II:30

author: PCB.Wiz
author_rank: Super Contributor
timestamp: May 15, 2025, 01:03:02 am
content: Quote from: iet on May 14, 2025, 03:07:10 pmIs that on the diode range ? (There is no diode showing on the LCD.)It seems to be trimmed to draw 1mA and then change uA with ESR, which makes it quite temperature and HFE dependent.It's cheap, so I guess users can zero manually at each use.

author: ledtester
author_rank: Super Contributor
timestamp: May 15, 2025, 06:52:41 am
content: Quote from: iet on May 14, 2025, 03:07:10 pmFrom the titles of the pics it seems we have the following relationship between ESR and displayed voltage:Vout = 1V + Rtest*0.1AQuote from: iet on May 12, 2025, 04:47:39 pmDoes the 1V come from the resistor R1? (which apparently has a value of 1 ohm)I would expect R1 and the test resistor to contribute the same towards Vout. Or, is R1 really 10 ohms?

author: Paul Price
author_rank: Super Contributor
timestamp: May 15, 2025, 09:03:12 am
content: Only a heartless troll would bite the core that feeds the ESR meter, but the OP first declares the toroid core is found within a lamp, but the first core surely it is not green and so as the new core, it is not matching the first picture the OP posted and has now a newly changed original circuit use purpose?Would the OP be so kind as to create a second instantiation of this instrument with another DVM and tell us how well it works?Would the OP be so kind as to show where one (or many) can easily find this newly described core?Has anyone else tried this recipe yet?

author: iet
author_rank: Frequent Contributor
timestamp: May 16, 2025, 02:26:24 pm
content: Quote from: PCB.Wiz on May 15, 2025, 01:03:02 amMultimeter switch in diode mode. This can be seen in the photo. It is not on the display.As for transistors. I am also interested in looking at different transistors in this circuit. Is there an effect of hfe and other parameters on the circuit operation. Well, and to analyze some other things that other participants in the topic talked about.Therefore, I am making a second test board with soldered pins.

author: iet
author_rank: Frequent Contributor
timestamp: May 29, 2025, 08:26:54 pm
content: Here I finished the second board. Everything works very well.

author: Analog Kid
author_rank: Super Contributor
timestamp: May 30, 2025, 02:58:01 am
content: I've taken the liberty of redrawing your schematic:but I'm not sure about the values of those two caps. C1 is 330what? And I can't really read what C2 is (1nF?).

author: Vovk_Z
author_rank: Super Contributor
timestamp: May 30, 2025, 11:59:04 am
content: Quote from: Analog Kid on May 30, 2025, 02:58:01 amSeems like '330' is 330 pF. I looks like old school type of marking. Just old school didn't use 'nF' at all (1 nF was '1000' or '0.001'. ), but now we do use it.As I remember, pF were without a dot, only integer numbers. uF were with decimal dot, so 10 uF was marked as '10.0'.

author: iet
author_rank: Frequent Contributor
timestamp: May 31, 2025, 12:16:00 pm
content: Schematic for the second board. Element values ​​in the table. The changes made speed up the process of setting up the circuit. Protection against charged capacitors has been added.Additional information will be ready soon.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 31, 2025, 12:21:32 pm
content: you claim 10 milli ohms of resolution on a cheap 4 digits meter(s) ?

author: iMo
author_rank: Super Contributor
timestamp: May 31, 2025, 03:42:31 pm
content: Those EMI rings are either iron powder or ferrite ones.With OP's 110turns resonating at ~100kHz with 330pF the AL of the material should be around 640nH/turns^2 (that is close to the ferrite material 43).L = 110turns^2 * 640nH/turns^2 = aprox 7.7mH7.7mH in parallel with 330pF = aprox 100kHz (not counting the parasitics)PS: those oscillators have got the cold side winding (III) much lower number of turns than the hot side one (II - where the base is connected) usually. Not sure with the above one (it has 100turns on the cold side), it could be for some special purpose, however.

author: iet
author_rank: Frequent Contributor
timestamp: May 31, 2025, 04:48:20 pm
content: Quote from: coromonadalix on May 31, 2025, 12:21:32 pmIn the second message I wrote how the digital part of the multimeter works.

author: iet
author_rank: Frequent Contributor
timestamp: May 31, 2025, 04:50:29 pm
content: Quote from: iMo on May 31, 2025, 03:42:31 pmYou are a little ahead of me. The information on the transformer is not yet fully ready. It is necessary to find time for additional tests, and there is very little of it.Here the frequency turned out to be a little higher - 150 kHz. The inductance of the winding III-3.4 mH.On the second board I used a dark gray ferrite ring 12x4x6. Information about it was lost, now I am trying to restore it.

author: iMo
author_rank: Super Contributor
timestamp: May 31, 2025, 07:17:18 pm
content: FYI- a sim only.. Not easy to setup, indeed..V1 and R7 are the parts of the meter set to the diode measurement (plus minus, perhaps some have an, say, 1mA current source there). R6 is the esr of that 10u cap.R3 sets the 1.00V with 0ohm ESRR1 and R3 sets the spread..Mind everything there plays..

author: iet
author_rank: Frequent Contributor
timestamp: May 31, 2025, 11:29:50 pm
content: For a start, it's not bad. Yes, the circuit's operation depends on many things. But I've already set up my ESR meter and checked it on 1% resistors.

author: iMo
author_rank: Super Contributor
timestamp: June 01, 2025, 07:08:09 am
content: That looks pretty usable.. Are those voltages above "1.00V" in the diode range?Also mind the currents used for the diode measurement differ from meter to meter. I tried with my two meters and one is using 0.78mA, the second one 0.84mA (both measured with a 499ohm resistor).So you have to create a Guide how to setup it such we get those results as above..

author: Kleinstein
author_rank: Super Contributor
timestamp: June 01, 2025, 07:28:08 am
content: There is the adjustment for the base current. The 1 ohm resistor at the DUT connection is kind of used as reference and one would have to adjust the base current to get the 1 V reading with the build in 1 ohm. This step would largely compensate for different test currentsIf one needs more extreme ranges, one could have alternative windigs for the DUT. 3 windings would get 1/9 the reading.Depending on the core one could use more windings overall and than have 1 or 2 windings for the DUT to also extend the range to lower ESR.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 01, 2025, 09:01:20 am
content: Thanks for the schematic idea, nice little ESR tester!The response is logarithmic, which is good to distinguish between small ESR values, and to avoid range switching. Ideal for an analog voltmeter with a hand made logarithmic scale for direct ESR readings.The funny part is how the logarithmic scale is linear enough for reading fractions of ohms, when added to an existing 1\$\Omega\$.Now I wanna build one.

author: iet
author_rank: Frequent Contributor
timestamp: June 01, 2025, 09:20:29 am
content: Quote from: iMo on June 01, 2025, 07:08:09 amYes, we do all measurements in diode mode.As for multimeters. Yes, not all multimeters behave the same. Here you need to experiment. Either select a multimeter, or adjust the transformer.Regarding the Guide. The second scheme can be considered basic, it provides all the adjustments to speed up the setup process. Now the main thing is to try to "standardize" the ferrite and the transformer. To do this, you will need to wind 2-3 more transformers. When all these things are more or less determined, then the Guide will appear.

author: iet
author_rank: Frequent Contributor
timestamp: June 01, 2025, 09:22:23 am
content: Quote from: Kleinstein on June 01, 2025, 07:28:08 amA good idea about expanding the range to reduce ESR. Here we logically approach the question, what range do we need? In the direction of increasing or decreasing, taking into account the realities of today. I just don't want to waste time on something that will not be used in practice.A question for you and everyone who is interested in the problems of measuring the ESR of capacitors.

author: iet
author_rank: Frequent Contributor
timestamp: June 01, 2025, 09:24:19 am
content: Here, for example, is measuring the ESR of a 1 uF 50v capacitor.

author: iMo
author_rank: Super Contributor
timestamp: June 01, 2025, 10:23:08 am
content: I think the optimal range would be from 1.00V to 1.99V for ESRs from 0 to 9.9ohm where the scale will be highly none linear from 1ohm up. The schematics is too volatile to any part's parameters in there to expect some precise results, imho. A good indicator for everyday use (provided there is the Guide).

author: iMo
author_rank: Super Contributor
timestamp: June 02, 2025, 07:56:56 am
content: Another SIM..0-15ohm RESR gives 1.0-2.0V..PS: a small MCU with built-in 10b ADC and simple PWM output feeding a moving coil meter would do the linearisation trick..

author: Kleinstein
author_rank: Super Contributor
timestamp: June 02, 2025, 08:27:17 am
content: Quote from: iMo on June 01, 2025, 10:23:08 amIt depends on the transformer how linear the circuit would be. A nonlinear response is possible, especially at higher ESR. The transformer losses would be something like a parallel loss resistance. An extra winding with more turns could help for higher ESR.The shown range is still good enough for testing the usual electrolytic capacitors. For those tests one also does not need high accuracy - there are no accurate values to compare to anyway.

author: iMo
author_rank: Super Contributor
timestamp: June 02, 2025, 11:30:51 am
content: .. I've spent 4hours with experimenting..Tried:L1 1t, 2t, 3t, 4tC1 1n, 2n2, 3n3, 6n8C2 180p, 330p, 470p, 1n2, 2n2R3 trimmer 330k (has to be split fixed+trimmer)Best settings found (max spread, linearity regardless):Diode mode:Frequency 116.6kHz with open probesProbes:Open 1922Shorted 1000 (set by the R3)RESR:0ohm 10000.02ohm 10000.22ohm 10121ohm 11044.7ohm 124710ohm 146927ohm 179268ohm 1801

author: iet
author_rank: Frequent Contributor
timestamp: June 02, 2025, 09:06:10 pm
content: Your board is working, that's good.What parameters did you get?Range, frequency, measuring voltage?What did you get when measuring a 100 mOhms resistor?Connect a 100 or 50 Ohms trimmer. Or even better, 10 Ohms instead of R1 1 Ohms.Try reducing L2 to 10t.Or add 1-3 turns to L1.

author: iMo
author_rank: Super Contributor
timestamp: June 03, 2025, 07:25:48 am
content: Quote from: iet on June 02, 2025, 09:06:10 pmI've updated above.The meter is rather an "indicator", imho, not a precision meter. For example when you touches the transistor with fingers for couple of seconds the value shown by the meter drops by say 20mV. To replicate the meter is not an easy task..With my parts it shows values from 1.005V to 1.650V based on capacitors measured, that fits the reality (from quality foils to tantalum low value drops). Of course the scale is highly none linear..The frequency is too high (117kHz in my case) for high value elyts, too.

author: Sacodepatatas
author_rank: Regular Contributor
timestamp: June 03, 2025, 09:01:42 am
content: Quote from: iMo on June 03, 2025, 07:25:48 amSome variations could be used for improving the design... A TL431 could be used instead of a BJT, for thermal stability (but taking into account that Vref≈2.5V instead of Vbe≈0.5...0.7V). The oscillator could be built using a 32.768kHz Xtal and tune it with the transformer at the 3rd harmonic (98.3KHz). This way, measures would be much more consistents.

author: iet
author_rank: Frequent Contributor
timestamp: June 03, 2025, 10:45:00 am
content: Quote from: iMo on June 03, 2025, 07:25:48 amThis is the key word, with your values.Your ratings on the diagram are slightly different from mine. For example, C1, C2 are in the opposite order. Q1 may also be different.The transformer windings are wound with a thicker wire and the number of turns is also different.I don't know what kind of ferrite you have, this also matters a lot. Try other types of ferrite rings, without touching the other elements.If possible, wind the transformer with a thinner wire, increasing the number of turns of L3 to 100, while maintaining the proportionality of the L2 winding 10 turns. Because the more turns of L3, the higher the accuracy. I came to this conclusion experimentally.The oscilloscope plays a special role here, you can observe the waveform, frequency and voltage.One more important point. The frequency of the measuring signal should not differ without load and with load.

author: iet
author_rank: Frequent Contributor
timestamp: June 03, 2025, 05:25:37 pm
content: Quote from: iMo on June 03, 2025, 07:25:48 am117 kHz is not a high frequency. On the second board, I started with 300 kHz, gradually decreasing to 150 kHz. I haven't managed to get it any lower yet. I'm making another transformer with a thinner wire. Here, the frequency doesn't affect the measurements very much. This is visible when comparing the measurement results at 100 kHz with the Pro1 Plus.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 04, 2025, 07:48:46 am
content: This ESR adapter is one of the finickiest and unreproducible circuits I've ever seen.Lost half a day simulating it in LTspice, and couldn't make it to indicate between 1V and 2V.BTW, in practice might need 2 anti-parallel diodes connected at the input measuring turn(s), to discharge the capacitor for just in case there is still some voltage left, or else the DC kick might kill the transistor because of the turns ratio. Even with diodes, a 0.6-1V might already be too much. Seen a nice trick to prevent this in a patent, with 2 secondaries in anti-parallel (and with diodes between the antiparallel turns), like this:From patenthttps://patents.google.com/patent/US6677764Another nice to have would be a 0.68uF/250V or bigger in series with the 1\$\Omega\$, so to be able to measure ESR for powered circuits, or to measure the ESR of batteries.

author: iMo
author_rank: Super Contributor
timestamp: June 04, 2025, 09:10:55 am
content: I started to mess with it because it has the galvanic isolation from the DUT and no power supply. Also it seems it oscillates well under wide range of various values.That are the PROS.The CONS are the many degrees of freedom to tackle in order to get it working "somehow linear" in entire typical "diode range" of a handheld DMM.The TC of the transistor there is say -2mV/C, so messing with 10mV resolution/precision/accuracy has no sense unless you can keep the stuff at <5C temperature stability.Another PROS I found is it oscillates at pretty large variation of any parameters. So you can almost always set "1000" with the R3. The other parameters will set the output range from 1000 + XX..XXX based on values used (assuming 1999 the max).The linearity and scale is a different thing. The most "stable" parameter seems to be the L2/L3/C1 frequency itself. Any other params have rather big impact on the setting.The output "spread" (the actual range from 1000 to 1XXX) is mostly given by the R3 setting, C2 value, the L1 number of turns and the value of R1 (considering the L2 and L3 ratio kept fixed).You may perhaps find a "somehow linear" range at the very beginning (like 1000..10XX) but I have not found it from 1000 to 1100, not talking to 1999. Also the simulation as well as experiment show there is a none-linearity in the non-linearity at the very beginning as well (at some part's values the output voltage starts to go down from 1000 with small RESR values and then goes up with larger values of the RESR).What I see as a potential solution is to use that oscillator with a small MCU compensating for the TC as well as for those none-linearity, driving a small display or an analog meter.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: June 04, 2025, 09:57:38 am
content: Quote from: RoGeorge on June 04, 2025, 07:48:46 amHehe, yes, it is fussy. I had some sim runs even work ‘backwards’ with reverse scale.Some leakage inductance seemed to help.The real plus here is it gives a ~100kHz injection which is where many caps spec ESR.It is so variable, for practical use it needs a set of cal resistors which are easy enough to include.

author: iMo
author_rank: Super Contributor
timestamp: June 05, 2025, 07:39:46 am
content: FYI - I've tried a different approach - with fixed L1 and R1 I "tuned" the stuff by changing the R3 and C2 (with my parts as above).So far: L1=4t, R1=1ohm, C1=680p foil, C2=2n2 ceramic.During the session the 1000 setpoint fluctuates +/- 4..RESR diode meter0 1000 (set by R3)0.22 1013 wirewound0.60 1077 wirewound1 11282 12276.7 143616.7 171726.7 1601 (??)43.7 1770open OL

author: iet
author_rank: Frequent Contributor
timestamp: June 07, 2025, 08:50:05 am
content: The third board. I managed to find a multi-turn trimmer resistor of 10 Ohms. Now all three resistors are multi-turn trimmers. The transformer is on the same ferrite, just wound with a slightly thinner wire. Transistor BC548B. Everything was immediately well adjusted with three trimmer resistors. I did not touch anything else. Now about the main thing.The board is almost standardized. We can confidently say about the repeatability of the transformer in relation to the measurement results. C1, C2 as in the diagram. I will experiment with transistors more.Linearity in the range of 1-10 Ohms has improved. Which was not possible to get before.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 07, 2025, 09:18:08 am
content: A 330 Whats capacitor

author: iet
author_rank: Frequent Contributor
timestamp: June 07, 2025, 10:12:11 am
content: C1:330pF.Reply 20.

author: iet
author_rank: Frequent Contributor
timestamp: June 09, 2025, 07:48:09 pm
content: I tried some transistors on the board. Not all work well.Here are 2 in the list of poorly working transistors: 2N2222A, 2N3904.

author: iet
author_rank: Frequent Contributor
timestamp: June 10, 2025, 06:28:10 pm
content: I tested the ESR meter with a high quality multimeter. It seems to work well.

author: iet
author_rank: Frequent Contributor
timestamp: June 13, 2025, 11:05:04 am
content: I spent a little time to make sure that the circuit really works with a more expensive multimeter. Yes, it works quite well, which naturally significantly expands its capabilities. The range turned out to be 1-500 mOhms. In this circuit, in addition to frequency, range and adaptation to a specific multimeter, calibration plays a key role. The essence of calibration is to achieve proportionality of measurements, that is, 1, 10, 100, 1000 mOhms should be measured correctly. Zero stability mainly depends on the stability of the transistor. The smaller the temperature drift, the better. In addition, the characteristics of the transistor affect the zero adjustment, in our case 1.000. You need to experiment with transistors.In my circuit the frequency is 150 kHz. It is necessary to look for another ferrite and reduce the frequency to 100 kHz. R1-2.5 R. Trimmers: R2-100 k. R3-250 k. Q1-C945. Transformer 100/10/6.You can make two tweezers, for regular and lower-impedance measurements. This also applies to multimeters.The real range is 1-10000 mOhms. Everyone can choose for themselves what suits them best.

author: iet
author_rank: Frequent Contributor
timestamp: June 14, 2025, 08:52:00 am
content: Measuring resistors and capacitors with very low ESR.

author: iet
author_rank: Frequent Contributor
timestamp: June 17, 2025, 05:54:18 pm
content: After a series of experiments, it was possible to find out that the frequency depends on the type of ferrite. At the same time, the method for determining the dependence of the ferrite type on the frequency turned out to be very simple. We put the multimeter probes on the ring diagonally and measure the resistance. I found a ferrite ring with lower resistance. Now the frequency has significantly decreased and, depending on the selected parameters, is regulated within 70-130 kHz. I took the ferrite ring from this choke.https://product.tdk.com/system/files/dam/doc/product/emc/emc/line-filter/data_sheet/30/db/ind_2008/b82791g_h_k.pdf

author: iet
author_rank: Frequent Contributor
timestamp: June 19, 2025, 07:45:08 am
content: Now we return to the ferrite ring from the LED lamp. I have already posted the photo.The ferrite ring is dark gray. The resistance is quite low. Setting the zero and calibration took 1 minute. Calibration was set automatically in the main operating range: 10-1000 mOhms.Current consumption without load: 65-95 uA. With load: 450-650 uA. Depending on the multimeter.The ESR meter works with my 4 multimeters. That is, using R1, R2, R3, you can set zero (1.000) for different multimeters without touching the transformer.Now I can say with complete confidence that after all the work done over the course of a month, I got an absolutely repeatable, easy to configure, with an automatic range and protection from charged capacitors, super simple ESR meter.The values ​​for all components highlighted in the table on the right are valid for the multimeter in the first post. The characteristics of the ferrite ring and the inductance of the transformer windings are given.Schematic.

author: iMo
author_rank: Super Contributor
timestamp: June 19, 2025, 10:28:37 am
content: With those AL=1200nH/t^2, your toroid looks like PC50 MnZn composition when grey (TDK), as well as similar to the material 77 MnZn ferrite when almost black (Fairrite)..

author: iet
author_rank: Frequent Contributor
timestamp: June 21, 2025, 08:08:19 am
content: This is well written in the article and is confirmed in practice. In LED lamps, Mn-Zn ferrite rings are used. Therefore, we can get a frequency at the level of 100 kHz. This is what we need.https://product.tdk.com/system/files/dam/doc/content/emc-guidebook/en/eemc_basic_06.pdf

author: iet
author_rank: Frequent Contributor
timestamp: June 24, 2025, 09:30:44 pm
content: I wound and tested two more transformers from LED lamps.These are ferrite rings with a resistance of 1k,60k.Ferrite ring R=1k.Works poorly. Constant drift. Some delay in establishing results. Problem with zero adjustment with the UT161E multimeter.Ferrite ring R=30 k (Reply 54).Ferrite ring R=60k.Works very well. Fast calibration, good accuracy. High measurement speed. Works well with different multimeters. Compared to the ferrite ring 30k, higher linearity up to 10 R. The only ferrite ring with which it was possible to expand the range to 15 R. At the same time, the error increases.8 R-6.3 R10 R-7.35 R15 R-9.5 RInductance.I-5/50 uHII-10/170 uHIII-100/14 mH

author: iet
author_rank: Frequent Contributor
timestamp: June 26, 2025, 08:01:45 pm
content: Now it is very simple and convenient to install any transformer without touching the other elements of the circuit. Setting up the ESR meter takes only a few minutes. Here are tweezers with a ferrite ring R=60k. Frequency 120 kHz. I covered the transformer with varnish so that the turns do not move.

author: DavidAlfa
author_rank: Super Contributor
timestamp: June 26, 2025, 08:06:34 pm
content: Nice!Would this also measure resistors, i.e. to identify shorts?

author: iet
author_rank: Frequent Contributor
timestamp: June 26, 2025, 09:14:15 pm
content: Yes, it can detect short circuit up to 10 mOhms with cheap multimeters.

author: iet
author_rank: Frequent Contributor
timestamp: June 28, 2025, 07:30:22 am
content: Short in capacitor.

author: iet
author_rank: Frequent Contributor
timestamp: June 30, 2025, 03:58:51 pm
content: Let's return to the question of resolution/accuracy.Let's consider this using the example of Low Impedance NCC KZE electrolytic capacitors.https://chemi-con.com/wp-content/uploads/2021/05/KZE-Series.pdfIf we open the datasheet, we will see that all values ​​below 100 mOhms are given with a resolution of 1 mOhms. But these values ​​are given as maximum. That is, they can be from some minimum value to the maximum.Let's take a specific example. 1200 μF/16 V capacitor. ESRmax. -22 mOhms.The resolution of the ESR meter S1.V3 is 10 mOhms. That is, it will confidently show a value of 10 mOhms with an ESR of the capacitor of 10-14 mOhms. Which is what we see in the photo. And if we measure the ESR with a higher resolution, we will get a result of 11 mOhms. This means that I can fully trust the S1.V3 meter, taking into account the difference of 4 mOhms. It should be noted that 15 mOhms is a relatively uncertain state, in which the meter can show 10 or 20 mOhms.

author: iet
author_rank: Frequent Contributor
timestamp: July 03, 2025, 11:09:15 am
content: When measuring different types of capacitors, there is a certain conflict associated with the resolution of the ESR meter. Naturally, the higher the resolution, the better. As for this circuit, it has good versatility. That is, the resolution of the ESR meter depends on the multimeter used. Such versatility helps out in the case of measuring the parameters of solid polymer capacitors in the absence of a datasheet. This situation happened when I was repairing my charger. First, I measured the ESR with KMTA1-05 and got 1.000. When I connected UT161E, everything became clear. The way out of this conflict is quite simple. Either quickly adjust the meter with trimmers for another multimeter, or make two meters for different multimeters.