Fundamentals of Electrical Practice: Capacitor Identification and Measurement

Fundamental Skills Training in Marine Electronics and Electrical Systems

I. Basic concepts of capacitance

A capacitor is physically a static charge storage medium, and the charge stored within the capacitor may be permanent. Capacitors have a wide range of uses. Capacitor is an indispensable electronic component in the field of electronics and electric power, mainly used for power supply filtering, signal filtering, signal coupling, resonance, filtering, compensation, charging and discharging, energy storage, isolation of DC and other circuits.

Figure 12-4 Symbols and Shapes of Capacitors

II. Measurement of capacitance (Pointer multimeter)

1. Measure the capacitor for leakage

● Large capacitors of 1000 μF or more:can be started with R×10Ω block to charge it quickly and make an initial estimate of the capacitor capacity, then change to the R×1kΩ Block continue to measure for a while, then the multimeter pointer should not return, and should stop at or very close to “∞”, otherwise there is a leakage phenomenon.

● Highly demanding capacitors below a few tens of microfarads:For example, the oscillating capacitor of the color TV switching power supply has very high leakage characteristics requirements. It can be used in R×1kΩ Switch to it after charging the gears. R×10 kΩ The meter needle should stop at “∞” without returning.

2. Estimation of microfarads (μF) capacitance capacity

Can be used empirically or with reference to a standard capacitor of the same capacity, according to the pointer swing of themaximum extentTo determine. The referenced standard capacitors do not have to have the same withstand voltage value, as long as the capacity is the same.

Example:To estimate a 100 μF/250 V capacitor, use a 100 μF/25 V capacitor as a reference, as long as the maximum amplitude of their pointer swings are the same, it can be concluded that the capacity is the same.

3. Estimated capacitance in picofarads (pF)

require the use of R×10kΩ The capacitance of a capacitor can only be measured above 1000 pF.

Judgment Criteria:For 1000 pF or slightly larger capacitors, a slight swing of the meter needle is considered sufficient capacity.

?️ Hands-on safety reminders:

Before measuring the capacitance, be sure to perform aDischarge processing(especially high-voltage large-capacity capacitors) to avoid damage to the multimeter or the risk of electric shock. Measurement with a pointer multimeter utilizes the charging and discharging characteristics of the battery inside the meter on the capacitor.