Help tracing failed capacitors (ESR Meter) - Page 1
Forum section: electronics / beginners

author: Geoff Mutton
author_rank: Newbie
timestamp: June 18, 2020, 10:14:29 am
content: Hello folks,First post and just wanted to say how great a resource this place seems.I've been watching the YouTube videos and its led me here. Already learned a lot!I have basic Electronics knowledge - although my degree was quite some years ago now!I've just bought an ESR Meter and am stumped at whether:A) I've got a faulty unitB) I just don't know how to use it properly!I have a board that I've pulled from a faulty device that has some clearly bad capacitors (leaky earwax-looking deposits all over the place).I decided to go through the entire board to test everything out and bought a MESR-100 ESR Meter for testing in-circuit (https://www.amazon.co.uk/MESR-100-AutoRanging-Circuit-Capacitor-MESR100/dp/B00UTBXLGAI decided to try testing on an easy to access "looks fine" cap.It's 16V and 47uF, which the table tells me should be healthy up to a maximum of 1.6 Ohms ESRWhen I pressed the probes on the solder points, the meter jumped every half second or so between wildly different values (0.3, 9.98, Overflow, 1.53 etc etc).Thinking this might be a bad one to start on, I moved to another and had the same behaviour - in fact every one I tried was the same.Does anyone have any idea if I've overlooked something simple here?I'm staring to wish I'd gone for the Peak Electronics ESR-70, but don't want to spend more money if I'm simply doing something wrong or not understanding the process.https://uk.farnell.com/peak-electronic-design/esr70/esr-meter-w-audible-alert-capacitor/dp/2917878#anchorTechnicalDOCSThanks in advance for your help!

author: Geoff Mutton
author_rank: Newbie
timestamp: June 18, 2020, 12:00:35 pm
content: OK - I think the probes on this thing are not the best - but I'm getting somewhere if I press down harder than I'd be expecting to.Bonus question: Can an ESR value significantly lower than expected also be an indicator of problems?I have a 10uF 16V cap that my table tells me is good up to 8 Ohms ESR and I'm reading 1.2This is one of the most visually suspect ones on the whole board - so I'm almost hoping it's dead!

author: ceoxrad
author_rank: Regular Contributor
timestamp: June 18, 2020, 12:05:59 pm
content: Hi Geoff.The figures on those tables are very broad and do not take into account different types of capacitors (low esr types, for example). An esr way lower than the ones listed usually is fine, especially if is a large electrolytic in a switching power supply. If you are unsure you can always desolder the part and check it out of circuit.I you are trying to repair the board i think that a photo of it might be of good use.

author: Geoff Mutton
author_rank: Newbie
timestamp: June 18, 2020, 02:54:02 pm
content: I'm having trouble uploading pics - let me work that out and I'll get back to you!

author: kripton2035
author_rank: Super Contributor
timestamp: June 18, 2020, 03:04:26 pm
content: not sure but I recall the peak esr70 is not ok for in circuit testing.at this price, better get a deree de5000 lcr meter, it works in circuit, and is very precisearound $100 directly from japan. don"t forget to buy the tweezers probe with itmore info :http://kripton2035.free.fr/LCR%20meters/lcr-deree5000-cl.htmlmore esr meters to build yourself :http://kripton2035.free.fr/esr-repository.html

author: Ice-Tea
author_rank: Super Contributor
timestamp: June 18, 2020, 03:05:41 pm
content: Keep in mind there may be several caps in parallel on the board. Which may influence your measurements greatly.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 18, 2020, 11:44:18 pm
content: If you have doubt about your ESR meter, then take some good caps, add some series resistors, and measure them.If you want a better meter, then consider the Der DE-5000. It's one of the cheapest "real" RLC meters, and has plenty of accuracy for almost any application.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: June 19, 2020, 12:13:45 am
content: This is a nice video to watch about how to do this stuff:

author: bob91343
author_rank: Super Contributor
timestamp: June 19, 2020, 12:38:52 am
content: It seems to me that there is too much emphasis placed on ESR. People build and buy devices to measure it and then scratch their heads while asking about the results of measurement.In general, ESR is higher when a capacitor has questionable termination. This may be due to previously excessive current flow, or mechanical damage. Other than those two, there are few reasons a capacitor will measure too high an ESR. And what is too high? That depends on the circuit in which it's used.Leakage is also a concern, and ESR meters don't measure it.The capacitance is usually the important parameter. ESL is important too and, like ESR, has to do with capacitor termination and design.When designing a circuit, ESR can be important, so you decide just how important, and use a capacitor that takes care of it. Other than that, it's not a particularly important parameter to measure.So the question arises, is this test being run to evaluate a capacitor for a given design, or is it being run to see if a particular capacitor is good?Like most rules of thumb, the numbers you get may or may not be significant. It depends on the application.I have measured capacitors over a wide frequency range, and most of them are not even still capacitors at high enough frequency. The worst offenders are aluminum electrolytic capacitors, which cease to be capacitive as the high end of the audio range is approached.As I have said many times, there is no substitute for understanding the physics and knowing just what you want. Test equipment, like your fingers, are just tools and shouldn't be decision makers without consulting one's brain.