LCR Meter for high value capacitors? - Page 1
Forum section: electronics / testgear

author: mapleLC
author_rank: Frequent Contributor
timestamp: April 14, 2022, 12:04:01 am
content: Hello, I discovered my LCR meter only measures to 2000uf - is this a common design limitation of these or is this something that was common among older units?I need to measure electrolytic caps in amplifiers that are sometimes 100,000uf, so it begs the question if an LCR meter is the wrong tool? I wouldn't need to measure above 15,000 that often.Please help me understand if I am using the wrong tool, or a tool that is tool old

author: thm_w
author_rank: Super Contributor
timestamp: April 14, 2022, 12:19:57 am
content: This is common, DE-5000 goes to 20,000 uF for examplehttps://www.ietlabs.com/pdf/Manuals/DE_5000_im.pdfOlder units are usually less.https://www.eevblog.com/forum/metrology/super-capacitor-meter/In reality you probably only care about ESR. That or AC ripple if you know what it should be.

author: mapleLC
author_rank: Frequent Contributor
timestamp: April 14, 2022, 12:26:03 am
content: Quote from: thm_w on April 14, 2022, 12:19:57 amThank you for directing me there. I need to value match high value caps, thats the main reason.

author: .rpv
author_rank: Contributor
timestamp: April 14, 2022, 12:40:33 am
content: it has to be an LCR?, some multimeters can reach really high values like the ut61e:https://www.uni-trend.com/meters/html/product/General_Meters/DigitalMultimeters/UT61%20161%20Series/UT61E+.html220mF

author: bdunham7
author_rank: Super Contributor
timestamp: April 14, 2022, 12:44:05 am
content: I think most handheld LCR meters will top out at 15-20mF. Mine says 15.91mF max in the specs, but does read over that, with somewhat suspect accuracy.DMMs usually use a different method than applied AC to measure capacitance and I have a bench and handheld that will do 100mF with reasonable accuracy.Just curious--why do you need to match such large capacitors?

author: mawyatt
author_rank: Super Contributor
timestamp: April 14, 2022, 01:12:22 am
content: The Tonghui TH2830 specs claim a maximum capacitance reading of 10 Farads, while the Hioki IM3536 specs indicate 10 GigaFaradsWe have both and offer to measure a large capacitance if someone sends a sample.Best,

author: gamalot
author_rank: Super Contributor
timestamp: April 14, 2022, 01:46:06 am
content: Most cheap LCRs have a minimum test frequency of 100Hz/120Hz, a 100,000uF capacitor has a capacitive reactance of 16 milliohms at 100Hz, to measure high capacitance you need a more precise (more expensive) circuit design, or lower frequencies.

author: mapleLC
author_rank: Frequent Contributor
timestamp: April 14, 2022, 02:45:27 am
content: Quote from: bdunham7 on April 14, 2022, 12:44:05 amMatch was not the right term. Match them to spec, I meant. I come across amplifiers with large caps, I need to measure them for tolerance and potential replacement.If there was a golden bullet where I could test them in circuit with certainty to know if replacement is needed, I would like to know about it. Its a job getting one of these coffee cans out and back in.

author: bdunham7
author_rank: Super Contributor
timestamp: April 14, 2022, 02:48:41 am
content: Some LCR meters like the BK 885/886 have an adjustable test voltage as low as 50mV and that allows you to test many capacitors in circuit.

author: mapleLC
author_rank: Frequent Contributor
timestamp: April 14, 2022, 02:49:44 am
content: Quote from: thm_w on April 14, 2022, 12:19:57 amAfter reading that thread, I am left with the same issue I kind of began with. How do I easily test a high value cap to determine its bad, out of spec, etc? Would an ESR meter really determine this for me?

author: BravoV
author_rank: Super Contributor
timestamp: April 14, 2022, 03:44:48 am
content: If this is just one off or ad hoc measurement for just few high value caps, with a "constant current" source (like bench PSU) and a DMM, and then with abit of patience to write down on a piece of paper, the voltage delta ( voltage change across the cap) divide by the current supplied to the cap, once charted few points, you will get the capacitance value.Usually the chart Voltage, Time will be diagonally straight line.Did that long time ago when I didn't have a proper LCR meter, and the result was pretty good.Formula :Capacitance = (dV / dT) / CurrrentCapacitance = in FaraddV = Voltage delta (voltage change thru time of dT when the cap is being charged by the Current)dT = Time during the operationCurrent = in A = the "constant" current that is charging the cap during the measurement periodTo give you the idea, your chart will be looked like this if the cap is charged with constant current.

author: mawyatt
author_rank: Super Contributor
timestamp: April 14, 2022, 01:37:34 pm
content: That's ^ a good method to find a large capacitance value. Another is to charge up the large cap to some value V, then discharge into a resistor R and measure the time T it takes for the cap voltage to reach 1/2 V.C then equals 1.44*T/R.Best,

author: RoGeorge
author_rank: Super Contributor
timestamp: April 14, 2022, 03:22:06 pm
content: Quote from: mawyatt on April 14, 2022, 01:12:22 amMust be a typo, in the datasheet chart at page 14 shows about 10 Farads, 50 Farads at most for the lowest frequency.https://www.hioki.com/download/32905

author: bdunham7
author_rank: Super Contributor
timestamp: April 14, 2022, 03:46:35 pm
content: Quote from: mapleLC on April 14, 2022, 02:49:44 amNo, an ESR meter won't spot all bad capacitors, not even close. If you measure capacitance, leakage and ESR, you'll spot most of them, and that's probably good enough for linear PSU filter caps.

author: mawyatt
author_rank: Super Contributor
timestamp: April 14, 2022, 04:03:29 pm
content: Quote from: RoGeorge on April 14, 2022, 03:22:06 pmYes, I suspect soSince the maximum test current limit is 100ma, and a voltage measurement of ~1mv would require a capacitive impedance of 10m ohms. So the measurement frequency would need to be ~1.6nHz and we would need to wait at least 20 years for a measurement result.Anyway, here's what the users manual indicatesBest,

author: indman
author_rank: Super Contributor
timestamp: April 14, 2022, 05:00:05 pm
content: Quote from: mapleLC on April 14, 2022, 12:04:01 amA simple DIY C/ESR Meter is ideal for this kind of measurement. The upper range of measured capacitances is - 999999uf.The measurement method is the charge of the capacitor with a stable current.