Hi to all,
quite often, it happens to me that I have to measure the capacitance of large capacitors (1000uF- 22000uF), possibly with a reasonable precision. Unfortunately my beloved multimeter is only capable of measuring capacitances smaller than 220uF.
How can I measure those large values?
Thx a lot in advance to everyone for your precious hints
quite often, it happens to me that I have to measure the capacitance of large capacitors (1000uF- 22000uF), possibly with a reasonable precision. Unfortunately my beloved multimeter is only capable of measuring capacitances smaller than 220uF.
How can I measure those large values?
Thx a lot in advance to everyone for your precious hints
Measure the RC time constant, where the initial arbitrary charged DC voltage decays to 1/e = 0.38 of the initial value.
For 10 seconds to be one time constant, discharge the C with a resistor R = 10sec/C, where C is in Farads.
With a 10,000uF capacitor (0.01F) use R = 10sec/.01F = 1k
For 10 seconds to be one time constant, discharge the C with a resistor R = 10sec/C, where C is in Farads.
With a 10,000uF capacitor (0.01F) use R = 10sec/.01F = 1k
Great, what a quick answer!
Please, let me try to summarizea bit the process by myself, just to be sure I have understood properly.
Supposing to have to check/measure the actual capacitance of a cap of 10000uF nominal/63v:
. charge the cap to 50v DC (what I mean, not too far from the max voltage allowed, am I right?)
. put a 1kohm resistor (reasonably, how many watt?) between the cap leads
. measure the time needed to reach the voltage of 19vDC
. if this time is more or less 10 seconds, ok.
. Otherwise? Suppose for instance that the decaying time is 6 seconds, how can I calculate the actual capacitance? I guess that C=Time/R, so in that specific case C=0.006F. Is it correct?
THANKS a lot!
Please, let me try to summarizea bit the process by myself, just to be sure I have understood properly.
Supposing to have to check/measure the actual capacitance of a cap of 10000uF nominal/63v:
. charge the cap to 50v DC (what I mean, not too far from the max voltage allowed, am I right?)
. put a 1kohm resistor (reasonably, how many watt?) between the cap leads
. measure the time needed to reach the voltage of 19vDC
. if this time is more or less 10 seconds, ok.
. Otherwise? Suppose for instance that the decaying time is 6 seconds, how can I calculate the actual capacitance? I guess that C=Time/R, so in that specific case C=0.006F. Is it correct?
THANKS a lot!
Yes, the basic formula is T = R x C
and if you know any two of them, you can calculate the third.
Needless to say, R and T should be known reasonably accurately, so C will be accurate.
If T and R are each known to around 5%, then C could be calculated to about 10% accuracy.
and if you know any two of them, you can calculate the third.
Needless to say, R and T should be known reasonably accurately, so C will be accurate.
If T and R are each known to around 5%, then C could be calculated to about 10% accuracy.
Buy a bigger capacity meter if needed, they are cheap, if you cannot use the method described above,
Thanks NareshBrd, a possible solution. Any hints about an efficient/cheap capacitance meter of this kind?
There is an upper size limit on capacitance meters, some as low as 2000uF.
Here is one for larger capacitors, but it is more expensive.
https://bkpmedia.s3.us-west-1.amazonaws.com/downloads/datasheets/en-us/830C_890C_datasheet.pdf
Here is one for larger capacitors, but it is more expensive.
https://bkpmedia.s3.us-west-1.amazonaws.com/downloads/datasheets/en-us/830C_890C_datasheet.pdf
Look for 'graphic multimeter'
Random net sample:
https://www.amazon.in/Auto-Ranging-...fd088df2bbf83ebda2cb67a744856903&gad_source=1
Another type is sold as a kit, with separately sold box, it has a dot matrix 2" square (approx) display, quite cheap.
It is also a multi function meter...and seems to charge and discharge the capacitors, handy, my usual shop keeper has one for checking capacitors.
My Google-Fu is weak at the moment, I will post a picture later.
No ties to any sellers, as usual.
Random net sample:
https://www.amazon.in/Auto-Ranging-...fd088df2bbf83ebda2cb67a744856903&gad_source=1
Another type is sold as a kit, with separately sold box, it has a dot matrix 2" square (approx) display, quite cheap.
It is also a multi function meter...and seems to charge and discharge the capacitors, handy, my usual shop keeper has one for checking capacitors.
My Google-Fu is weak at the moment, I will post a picture later.
No ties to any sellers, as usual.
According to spec, this device can measure up to 100,000μF.
LCR-TC1 TC7 Colorful Display Multi functional TFT Backlight Transistor Tester For Diode Triode Capacitor Resistor Transistor
LCR-TC1 TC7 Colorful Display Multi functional TFT Backlight Transistor Tester For Diode Triode Capacitor Resistor Transistor
A test with actual voltages seems more accurate, i have a 6.5 multimeter with software to pc option, it can datalog, the exact voltage at any given time, so do the test , check the charts produced, and i will get fairly accurate voltage level with time stamp