EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: mapleLC on April 14, 2022, 12:04:01 am
-
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
-
This is common, DE-5000 goes to 20,000 uF for example https://www.ietlabs.com/pdf/Manuals/DE_5000_im.pdf (https://www.ietlabs.com/pdf/Manuals/DE_5000_im.pdf) Older units are usually less.
https://www.eevblog.com/forum/metrology/super-capacitor-meter/ (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.
-
This is common, DE-5000 goes to 20,000 uF for example https://www.ietlabs.com/pdf/Manuals/DE_5000_im.pdf (https://www.ietlabs.com/pdf/Manuals/DE_5000_im.pdf) Older units are usually less.
https://www.eevblog.com/forum/metrology/super-capacitor-meter/ (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.
Thank you for directing me there. I need to value match high value caps, thats the main reason.
-
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+.html (https://www.uni-trend.com/meters/html/product/General_Meters/DigitalMultimeters/UT61%20161%20Series/UT61E+.html)
220mF
-
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?
-
The Tonghui TH2830 specs claim a maximum capacitance reading of 10 Farads, while the Hioki IM3536 specs indicate 10 GigaFarads ???
We have both and offer to measure a large capacitance if someone sends a sample.
Best,
-
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.
-
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?
Match 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.
-
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.
-
https://www.eevblog.com/forum/metrology/super-capacitor-meter/ (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.
After 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?
-
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) / Currrent
Capacitance = in Farad
dV = Voltage delta (voltage change thru time of dT when the cap is being charged by the Current)
dT = Time during the operation
Current = in A = the "constant" current that is charging the cap during the measurement period
To give you the idea, your chart will be looked like this if the cap is charged with constant current.
(https://www.allaboutcircuits.com/uploads/articles/capacitor-voltage-current-2.png)
-
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,
-
Hioki IM3536 specs indicate 10 GigaFarads ???
Must 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 (https://www.hioki.com/download/32905)
-
After 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?
No, 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.
-
Hioki IM3536 specs indicate 10 GigaFarads ???
Must 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 (https://www.hioki.com/download/32905)
Yes, I suspect so :)
Since 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 indicates ???
Best,
-
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?
A 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. ;)