How to measure ESR? - Page 1
Forum section: electronics / projects

author: OM222O
author_rank: Frequent Contributor
timestamp: May 03, 2019, 02:52:32 pm
content: I've done a lot of googling, but I've either seen schematics provided for an ESR meter with no explanation of how it works, or some videos which involved a signal generator and an oscilloscope ... I highly doubt the commercial products use the signal generator + scope technique as it would be very expensive to build into one small instrumentplease share your comments down below

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 03, 2019, 03:11:05 pm
content: ESR is just Rs, usually measured at 100 kHz. Try my page here-http://www.conradhoffman.com/cap_losses.htmYou can convert loss, which can be in terms of Rs, dissipation factor or several other things, to any other form, if you also have value and frequency, so ESR is just a quick calculation away if you have the results from any LCR meter that also gives loss, but not all will do it at 100 kHz. That's why one-trick-pony ESR meters exist. Regardless, if you can set up to find the series resistance at 100 kHz, using a bridge or just current and voltage, you can get ESR. IMO, ESR isn't all that useful to anybody other than switching power supply designers. You need three things to evaluate a cap- value, loss and DC leakage at rated voltage. I realize that's contrary to the popularity of ESR meters, and they can be useful for a quick check, but they can also lead you astray or miss problems that you need to find. IMHO, it's so easy to build a bridge (or buy a cheap LCR board on eBay) that I'm surprised more people don't do it.

author: OM222O
author_rank: Frequent Contributor
timestamp: May 03, 2019, 03:33:43 pm
content: I have seen selectable frequency on a few designs so I might give that a try.'To measure losses as you said, can I just use a known resistance in series with the cap and measure the voltage across it, hence getting the power it dissipates vs the input power. then calculate the difference which is power dissipated by capI'm not sure what sort of values I should be expecting and if the difference is large or small.maybe there is an easier way of calculating the difference in power?

author: Tek Tech
author_rank: Contributor
timestamp: May 04, 2019, 06:07:40 am
content: Check out this project, with a nice explanation:http://vk6tt.blogspot.com/2016/04/capacitor-esr-meter.htmlUpdate:http://vk6tt.blogspot.com/2017/03/esr-meter-update-and-pcb.html

author: MarkF
author_rank: Super Contributor
timestamp: May 04, 2019, 06:14:35 am
content: Look here for a little project

author: soldar
author_rank: Super Contributor
timestamp: May 04, 2019, 07:15:09 am
content: Depends on the level of precision you need but if you just need a rough reference of whether a cap is good or bad and want a very simple circuit with just one IC you can Google - kakopa esr -

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 04, 2019, 08:06:56 am
content: ESR is the real part of the impedance.Simple*, make a synchronous RF detector circuit. Apply excitation (presumably, sine wave at some test frequency and amplitude), and measure the complementary parameter (i.e., if supplying current, measure the voltage; or vice versa; or for a general source impedance, measure the ratio of voltages = ratio of impedances).*In the canonical RF sense. Implementation is left as an exercise for the student, etc. etc.The usual approach, usually differs in these ways:1. Excitation is square wave, so the frequency content includes harmonics.2. Detection by magnitude, not in-phase only, so the impedance |Z| gets measured instead.3. The measurement is done at some fixed frequency, usually ~100kHz.Measuring |Z| is only okay when X_C and X_ESL << ESR.Measuring with a square wave is only okay if this remains true for all the harmonics of significance. That is, for the Nth harmonic, X_ESL goes up as N, but the amplitude goes as 1/N, so it's a wash. As long as all those harmonics stay below the signal due to ESR, it's okay. Eventually, ESL will win out, but no square wave has infinite harmonics, there's always an upper cutoff (where harmonics transition from going as 1/N to 1/N^2 and more). Hopefully, the circuit is designed to filter the square wave a bit, to reject the ESL signal by some reasonable frequency.Fixed frequency is a range problem. For the ESR signal to dominate, the frequency must be above 1 / (2*pi*ESR*C). Likewise, ESL must be less than ESR / (2*pi*BW), where BW is the signal chain's bandwidth.Note that it doesn't matter, where in signal chain the filtering is applied. The signal source can be filtered, or the detector can be filtered, or both. The total is all that matters. Note that, for a sine wave source, BW is quite small (the width of the sine wave, more or less), which is why it's the gold standard.So, all together -- for a typical use-case that's only concerned with electrolytic capacitors over 10uF or so, with modest lead lengths, the typical design is alright. It falls over when the capacitance is small, or the ESR is very small, or the ESL is exaggerated.And, it's not too hard to make a proper one, following a canonical RF design -- you set up a local oscillator, a buffer amp and a balanced mixer, plus whatever coupling transformers or differential amps are needed to sense the signal and perform level-shifting and all that. The in-phase component corresponds to resistance, so just filter the mixer's output and read out the voltage.You can even set up a quadrature oscillator (or phase shifter, or..) to measure reactance instead. Note you can only measure total reactance at the given frequency -- while it might be positive or negative (implying overall inductance or capacitance), you need multiple frequencies to disambiguate where inductors and capacitors are. But even if not going to that trouble, you can still draw the equivalent circuit (R in series or parallel with L or C) at that frequency, it just might not be applicable over a wide range of frequencies, that's all.Tim

author: kripton2035
author_rank: Super Contributor
timestamp: May 04, 2019, 10:13:09 am
content: here complete detailed article of old poptronix esr meter .http://kripton2035.free.fr/analog%20esr/esr-poptronix.htmlothers with explainations :http://kripton2035.free.fr/analog%20esr/esr-lowohm-silic.html

author: The Electrician
author_rank: Frequent Contributor
timestamp: May 04, 2019, 10:19:01 am
content: Quote from: OM222O on May 03, 2019, 02:52:32 pmCheck out this:https://literature.cdn.keysight.com/litweb/pdf/5950-3000.pdf

author: OM222O
author_rank: Frequent Contributor
timestamp: May 04, 2019, 12:09:52 pm
content: the "auto balanced bridge" method seems extremely easy to implementI might give it a try (100KHz so using an op amp, not complicated phase detectors and whatnot). the only question would be what are some nominal voltages for Vs and resistances for Rr?

author: The Electrician
author_rank: Frequent Contributor
timestamp: May 04, 2019, 02:39:41 pm
content: Since Vs will be the voltage applied to the DUT, and it's an AC voltage, when measuring electrolytics we don't want to apply a reverse voltage of more than a volt or so to the DUT, so Vs in that case will typically be .5 VAC. Maybe lower if doing in circuit testing with semiconductors in the circuit that we don't want to turn on.When measuring inductors, we might want to apply a higher voltage to the DUT. Some Keysight meters such as the E4980A can apply up to 20 VAC.Since Rr is a range switching resistor, its value should be near the magnitude of the DUT's impedance.

author: daisizhou
author_rank: Super Contributor
timestamp: May 04, 2019, 02:58:43 pm
content: https://www.eevblog.com/forum/projects/led-lamp-bead-display-esr-test-meter/new/#newI am planning to make

author: OM222O
author_rank: Frequent Contributor
timestamp: May 04, 2019, 03:38:22 pm
content: Quote from: The Electrician on May 04, 2019, 02:39:41 pmYes that makes sense! thanks a lot for the info!Quote from: daisizhou on May 04, 2019, 02:58:43 pmplease update your post when you finished the project

author: Shock
author_rank: Super Contributor
timestamp: May 04, 2019, 06:47:15 pm
content: http://www.kerrywong.com/2015/11/23/esr-measurement-using-multimeter-and-function-generator/

author: Shock
author_rank: Super Contributor
timestamp: May 04, 2019, 07:31:51 pm
content: If you are interested in a simple design forum member Jay_Diddy_B has one here with a written overview. It's 100kHz and has input voltage protection and a low build cost. Requires a multimeter to read the measurement.https://www.eevblog.com/forum/projects/esr-meter-adapter-design-and-construction/If you are interested in a kitset or off the shelf. Chinese ones start from $20 upwards. I'd recommend though a Bob Parker ESR meter design. Altronics, EVB and Anatek sell them for around $100, these can be cheaply modified to have better input voltage protection.The DER EE DE-5000 (LCR meter) also measures ESR and has multi frequency support, you're looking at also around $100. Not the simplest for in circuit testing and no decent input protection, a good value instrument however, hard to beat features and accuracy for $100.

author: OM222O
author_rank: Frequent Contributor
timestamp: May 04, 2019, 08:08:27 pm
content: Quote from: Shock on May 04, 2019, 07:31:51 pmhe also designed the 5 transistor ESR meter which somebody else postedhe must love designing ESR metersI would still like to try to create one from scratch using the bridge method which I mentioned earlier, as It's a great opportunity to learn something that I'm not very familiar with!