capacitor
I have an unmarked SMD capacitor on a PCB and I want to identify the value of this SMD capacitor. I have an LCR meter (BK880) and I want to use it to measure directly the capacitance of this SMD capacitor.
Do I need to discharge the SMD capacitor before measuring it?
The only clue I can find might be this: -
It looks like you are seeing a +16% shift in value and X5R is not known for the greatest dielectric so this may be counted as some form of initial aging due to soldering. After all, it started about 8% down and it's gone 8% over. I'd expect X7R dielectric to be better (stabler) and C0G/NP0 to be better again.
Very large electrolytic capacitors are generally used at relatively low frequencies (below 1 kHz) to smooth fluctuating DC voltages such as in power supplies. At 100 kHz, the impedance of an 8200 uF capacitor is less then 1 milliohm. This is very difficult to measure accurately considering wire resistance and the effect of parasitic capacitance and inductance that are inherent in the construction of the capacitor and have significant impedances at 100 kHz. This is why the capacitance of electrolytic capacitors is usually specified at either 60 Hz, 120 Hz or 1000 Hz. It is also why electrolytic capacitors used as bypasses on high speed IC's are almost always placed in parallel with a much smaller capacitor that is more effective at high frequencies.
Best Answer
You need to desolder it from PCB before you can measure it, as capacitors cannot be measured in-circuit. And discharge it too, but a multimeter can be used to measure if it is already discharged.