Testing a capacitor with a basic analogue (needle type) ohmmeter is a fast method for determining the viability of the electrical device. In most cases, the analogue meter will show the strength and level of storage capacity left in the capacitor. The most important factor in testing the capacitor is to always discharge the main terminals. The very nature of the device means that it will accumulate a charge even when it is not attached to an electrical source.
- Skill level:
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Things you need
- Screwdriver with an insulated handle
- Analogue or needle type ohmmeter
Remove all electrical power to the capacitor. Make note of any wires connected to the top terminals of the capacitor.
Touch the metal end of the screwdriver to both terminals on the capacitor simultaneously. Hold the screwdriver in place for 3 seconds. The capacitor is now discharged. Remove the wires from the metal terminals.
Switch the ohmmeter to the "ohm" position on the face of the meter. If applicable, the switch may also have to be set to "RX1." This symbol means that all readings on the meter are at a one to one ratio.
Insert the red lead into the connector marked "ohm." Place the black lead into the connector identified as "com." Touch the metal ends of the two leads together. Note the needle on the face of the meter. It should deflect all the way to the right. This position is zero (0) ohms. Separate the two leads. The meter should move back to the far left. This is infinite ohms, or a wide-open circuit.
Touch the red lead to one capacitor terminal, and the black lead to the other terminal. The needle should slowly rise toward the zero ohm position, then slowly move back toward the left. This signifies a good capacitor. If the needle moves at a uniform speed, the capacitor is properly charging and then discharging.
Reverse the leads from the meter to the terminals on the capacitor. The needle on the face of the meter should perform in the same manner as described in step 5. If the meter moves immediately to the right, zero ohms, and does not fall back to the left, the capacitor is shorted. If the needle on the meter never moves, there is a wide open or an internal break to the capacitor. Both of these last two readings indicate that the capacitor is bad and needs to be replaced.
Tips and warnings
- Testing a capacitor with a digital multimeter is easy. Place the switch on the face of the meter into the capacitor mode. This may be identified by either the word "cap" or a symbol that resembles "-)|-." Touch the red lead to one terminal and the black lead to the other terminal on the capacitor. The meter will read either "good" or "bad."
- Never work on or service any electrical equipment while it is energised with electricity. A severe electrical shock will occur, causing a serious burn or injury.
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