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HOW TO CHECK A CAPACITOR?

Views:4     Author:Ada     Publish Time: 2019-07-27      Origin:Site

Metalized Polypropylene Film Capacitoris an electrical device that stores an electrical charge. They are used on fan motors and compressors in hvac systems.It applied to running of single -phaseat 50Hz(60Hz) frequency for high efficiency compressor of refrigerator.A capacitor stores and releases electrical energy during every cycle change. A run capacitor is specifically sized to create the ideal phase shift for optimal running efficiency and power usage by the motor.


RETEKOOL make strict checking on every capacitor before delivery.

We 100% make sure that every capacitor folliwng the GB/T3667-1997 and IEC/EN60252:193 Certification Standard.


RETEKOOL investing substantiallyin advanced machinery and equipments: 

TE2660 endurance test device、TE2661 endurance testerd 、TE2616 capacitancemeasuringtester、TE2617 capacitance sorter、TE2670 insulation tester、TE2802 capacitor multiparameter 、automatic sorting system、 vernier caliper and micro-caliper etc.

We use these equipments to make the following 6 testing items:

1) Appearance and Marks-----Appearance should be good,no damage Marks should be clear

2) Capacitance------tolerance ±5%

3) Loss Tangent------tanδ≤0.0020(100Hz)

4) Withstand Voltage Between Terminals------Can stand AC800V,50/60Hz,60S

Without flashover and Permanent Breakdown

5) Withstand Voltage Between Terminal and can------2Ue+1000V,and not less than 2200VAC,no flashover and breakdown

6) Leakage test------tc+10℃,without leakage and distortion


The capacitor is a simple component with no moving parts.the only potential cause of failure is overheating,which causes expansion and the commonly seen bubbled top.


For start capacitor testing, a multimeter is required. Some digital meters have a capacitance setting. First the power supply should be shut off then the two terminals on the capacitor should be shorted across with a screwdriver. This will discharge the unit so you do not receive a shock. Disconnect the wires from the capacitor. Then, the leads of the meter are placed on the terminals and a reading is obtained. The reading you get should be within 6% of the rating on the capacitor. If your reading is more than 6% lower than the rating, the capacitor should be replaced.

If you have an analog type meter, the capacitor is checked with the meter set to measure resistance. Shut off the power, discharge the capacitor, and disconnect the wires attached to it. Then with the meter on the highest resistance setting, put the leads on the capacitor terminals. The resistance reading should start at zero and go up to maximum.Some obvious signs that the capacitor is bad are bulging of the unit or an oily substance leaking from it.

When testing a run capacitor, many techs pull the leads off and use the capacitance settings on their meters to test capacitors. When you’re constantly checking capacitors as a matter of regular testing and maintenance, testing the capacitors under load (while running) is a great way to confirm the capacitor is doing its job under real load conditions, which is also more accurate than taking the reading with the unit off.

When the unit is running, you are applying the actual voltage, amperage, and temperature the capacitor operates under every day, therefore giving you a more accurate reading. If your multimeter reads voltage and amperage accurately, this test does work. If the results aren’t matching up with your capacitor tester, you will want to check your multimeter against some other high-quality meters to see which reading is coming up incorrect, but the test under load procedure is sound math, and it works.

First, if you are used to doing capacitor checks during the cleaning stage of a preventive maintenance visit, you are going to need to change your practices and do your tests during the testing phase. These readings will be made at the same time you are taking other amperage and voltage readings during the run test.

Here are the steps:

1. Measure the amperage of just the start wire (wiring connecting to the start winding). This will be the wire between the capacitor and the compressor. In the case of 4-wire fan motors, it will usually be the brown wire — not the white-striped brown wire. In the case of a compressor with a dual capacitor, it will be the wire going to the HERM terminal. Note your amperage on this wire.

2. Now, take the amp reading you took on the start wire (wire from the capacitor), and multiply by 2,652 (some say 2,650, some 2,653, and some 2,654, but 2,652 is perfectly accurate). I remember 2,652 because 26 doubled equals 52.

3. Next, measure voltage across the capacitor. For a compressor that would be between HERM and C, this is the measured voltage across the start and run terminals on the motor.

4. Divide the total of the start wire amps times 2,652 by the voltage you just measured. This total is the capacitance. The complete formula is:

Start Winding Amps x 2,652 ÷  capacitor voltage = microfarads.

5. Read the nameplate MFD on the capacitors and compare to your actual readings. Many capacitors allow for a 6 percent +/- tolerance. If outside of that range, then replacement of the capacitor may be recommended. Always double check your math before you quote a customer.

6. Repeat this process on all of the run capacitors and you will have assurance whether they are fully functional under load or not.

7. Keep in mind that the capacitor currently installed may not be the correct capacitor. The motor or compressor may have been replaced, or someone may have put in the wrong size. When in doubt, refer to the data plate or specs on the specific motor or compressor.


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