Can oscilloscopes check the health of capacitors? - Page 1
Forum section: electronics / beginners

author: vinlove
author_rank: Frequent Contributor
timestamp: January 15, 2023, 07:07:52 pm
content: I have a cheap nonane Made in China 5 Mhz bandwidth handheld oscilloscope, and wondering if it can be used to check & test capacitors health or condition for reliable uses.If so, what are the methods? Any good youtube links for that process? If not, what would be the best method or tools for the process?

author: jonpaul
author_rank: Super Contributor
timestamp: January 15, 2023, 07:42:55 pm
content: cap V, uF, type ?j

author: james_s
author_rank: Super Contributor
timestamp: January 15, 2023, 07:48:55 pm
content: Not really, an oscilloscope is not the proper tool for testing any passive components.

author: tggzzz
author_rank: Super Contributor
timestamp: January 15, 2023, 08:07:53 pm
content: You can use a scope to test ESR in a way that is relevant to SMPSs.Apply a square wave amplitude V through a known resistor R and watch the voltage across the capacitor.If the ESR is zero in an ideal capacitor, then when the output changes initially the voltage across the capacitor won't change, and the current will initially be I=V/R. Now add ESR of Resr, and there will be an initial voltage step across the collector's terminals of Vesr=I*Resr, which will be followed by the textbook exponential voltage change.

author: Stray Electron
author_rank: Super Contributor
timestamp: January 15, 2023, 08:18:02 pm
content: Quote from: vinlove on January 15, 2023, 07:07:52 pmI think Dave did a video on this. Check his blog site. If not, I'm sure that there's a video about testing caps on U-tube.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 15, 2023, 08:32:00 pm
content: #135: Measure Capacitor ESR with an Oscilloscope and Function Generatorw2aew

author: jonpaul
author_rank: Super Contributor
timestamp: January 15, 2023, 11:58:36 pm
content: 1970s, 1980s some Hameg analog scopes had a component checker, with a V/I lissijous figure.Diodes, semiconductor, had a curve as in the video, capacitors an elipse.Just a mains frequency test, a few volts/ ma but very useful.HM203 and HM103 had itJon

author: vinlove
author_rank: Frequent Contributor
timestamp: January 16, 2023, 12:04:07 am
content: Quote from: tggzzz on January 15, 2023, 08:07:53 pmNot sure if my 5Mhz handheld scope can send out square signals to external parts. Maybe it can .. I am not sure. I am just back from the hobby break for a couple of years doing the other hobby. Feel like I forgot all I used to know in electronics, which wasn't much first place.https://www.amazon.com/dp/B07R6Q1YMB?ref=vse_pfo_vdp

author: vinlove
author_rank: Frequent Contributor
timestamp: January 16, 2023, 12:06:17 am
content: Quote from: jonpaul on January 15, 2023, 11:58:36 pmThat would have been useful functionalities. Why have they done away with them? Maybe there are tons of the dedicated tools for checking the parts out now?

author: vinlove
author_rank: Frequent Contributor
timestamp: January 16, 2023, 12:07:05 am
content: Quote from: james_s on January 15, 2023, 07:48:55 pmEvery type of capacitors.

author: vinlove
author_rank: Frequent Contributor
timestamp: January 16, 2023, 12:12:29 am
content: Quote from: james_s on January 15, 2023, 07:48:55 pmOk, maybe better just go and buy L/C meter, or parts checking meter or even just Capacitance meter?I used to have a part checking meter (Made in China, had bought one a few years ago from eBay) - upon powering on and checking a part, it told what the part was, and also the value of it including resistors and transistors as well as capacitors, but it blew up one day.

author: tggzzz
author_rank: Super Contributor
timestamp: January 16, 2023, 12:16:28 am
content: Quote from: vinlove on January 16, 2023, 12:04:07 amIf you don't have any signal source, then the characterstics of any capacitor are unknowable. Or any other component for that matter.A square wave oscillator is about the simplest source of signals you can make!

author: rstofer
author_rank: Super Contributor
timestamp: January 16, 2023, 02:23:45 am
content: Even the inexpensive Aneng 8008 DMM has a capacitance scale. It will also generate square waves.https://www.amazon.com/ANENG-AN8008-Multimeter-Resistance-Capacitance/dp/B076GZK62BThe Arduino tone() function is another source of square waves.https://www.arduino.cc/reference/en/language/functions/advanced-io/tone/

author: themadhippy
author_rank: Super Contributor
timestamp: January 16, 2023, 02:39:36 am
content: Dont the device your using to access this forum allow you to add software to produce tones?

author: james_s
author_rank: Super Contributor
timestamp: January 16, 2023, 03:56:13 am
content: Quote from: vinlove on January 16, 2023, 12:12:29 amThat depends on what you're interested in measuring. Those $20 universal component checkers are pretty effective at testing capacitors. If you're doing repair work a dedicated ESR meter is a worthwhile tool to have. I bought my Capacitor Wizard almost 25 years ago when they were $200 and it has paid for itself many times over, but there are much cheaper options available now that work well enough.I should have been more clear, there are ways you can use an oscilloscope in combination with some additional hardware to test capacitors and other components so it's not that it can't be done, but generally I'd say it isn't the right tool for the job. It's a bit like using a pipe wrench to pound a nail.Those curve tracer adapters people mention require XY mode, so unless your little scope has that feature it's not going to work.

author: G-son
author_rank: Regular Contributor
timestamp: January 16, 2023, 10:19:40 am
content: If I'm not mistaken, you can determine the capacitance of a capacitor using just a voltage source, a resistor, and the scope to check the time it takes to charge the cap to a specific voltage. Don't remember the formula, but "time constant calculator" and "capacitor" together may give you the answers for that in google.ESR is a bit more difficult, as it requires a signal generator.

author: EPAIII
author_rank: Super Contributor
timestamp: January 16, 2023, 11:04:16 am
content: For many decades I just used the resistance scales on analog multimeters (Simpson 270) to check capacitors. After a while you get accustomed to the amount the needle initially kicks and where it finally settles at.About a year ago I purchased one of the universal component checkers that James talks about and found it is great for checking old and used capacitors. It even measures the ESR. I wish I had one or more of them 50 years ago.Just one; they are all over the internet:https://www.amazon.com/Organizer-Multifunction-Transistor-Capacitor-Inductance/dp/B07T6FKHM6/ref=sr_1_3?keywords=universal+component+tester&qid=1673866910&sr=8-3Quote from: james_s on January 16, 2023, 03:56:13 am

author: rstofer
author_rank: Super Contributor
timestamp: January 16, 2023, 05:25:59 pm
content: Quote from: G-son on January 16, 2023, 10:19:40 amSee attached which shows a capacitor charging (10k 0.1 ufd -> 1 time constant is 1 ms). Note how close to 1ms the voltage reaches about 63%. I can play with this resistor/capacitor circuit all day!Measurements are taken from rising edge of the square wave.There's an explanation of capacitor charging here:https://www.electronics-tutorials.ws/rc/rc_1.htmlBasically, you want to know when the capacitor voltage is 63% of the applied voltage as this occurs at 1 time constant. Given a measured time to get to 63% and a given resistor, you can work backwards to get C.Vout = Vsource * (1 - e-t/RC) R is in Ohms, C is in Farads, t is in secondsThe product RC is sometimes called Tau - the time constant. You want to adjust the resistor to get t / Tau = 1. Once you do, simply solve for C from t / Tau = 1 and Tau = RC so t / RC = 1. For my example above t = 1 ms, R = 10k and C = 0.1 ufd (but we're going to calculate the value) so:10-3/ (104* C) = 1 so C = 10-3/ 104or 10-7Farads or 0.1 ufd. Just what we expected.To clear up any confusion on scientific notation:10-3is 1 ms104is 10k10-7is 0.1 ufdI use this because I learned the subject using a slide rule and I do most of the math in my head. It's easier when using scientific notation.

author: bidrohini
author_rank: Regular Contributor
timestamp: January 17, 2023, 02:02:39 am
content: These answers may help too:https://www.eevblog.com/forum/beginners/testing-bad-capacitor-in-live-circuit-with-oscilloscope/

author: MrAl
author_rank: Super Contributor
timestamp: January 17, 2023, 03:00:23 am
content: Quote from: vinlove on January 15, 2023, 07:07:52 pmHi,Here is a drawing of a good cap vs bad cap.You need a square wave to excite the cap with through a resistor of some value (see drawing).You can test both ESR and capacitance.I had several commercial products go bad because of the aging electrolytic caps. Mostly in the power supply section of a product.

author: vinlove
author_rank: Frequent Contributor
timestamp: January 17, 2023, 09:39:00 am
content: OK, points taken. You need a circuit for taking in voltage input with resistor and the capacitor to be checked out in order to use Oscilloscope to test it.I ended up getting this universal component checker from Amazon for cheap, and it seems working ok.

author: vinlove
author_rank: Frequent Contributor
timestamp: January 17, 2023, 09:44:00 am
content: I am using an old Desktop Apple Mac PC for accessing the forums, so it won't generate waves or voltages unless it is added with some sort of peripherals even with the apps downloaded. But I am not keen on it.Just need a small handheld device dedicated for the job, and my Oscilloscope was a 5 Mhz handheld one, which would have been handy, but it doesn't have any output functions. It only has inputs via usual BNC port. I suppose Oscilloscopes are for monitoring voltage on time variants, so makes sense on all the points.

author: vinlove
author_rank: Frequent Contributor
timestamp: January 17, 2023, 09:45:42 am
content: deleted - repeated msg

author: vinlove
author_rank: Frequent Contributor
timestamp: January 17, 2023, 09:46:59 am
content: deleted - repeated msg.I edited my msg, and saved it, and it is generating the above msg in quote repeatedly. A forum bug alert, or is it my browser?

author: tggzzz
author_rank: Super Contributor
timestamp: January 17, 2023, 09:48:59 am
content: Quote from: vinlove on January 17, 2023, 09:39:00 amPut the scope across the capacitor leads, observe the waveform being applied, and think about how that tester is using that to infer the capacitor's properties.Then think about how you could have created an equivalent tester.Such thought experiments are fun and useful.