When a motor refuses to start, the starting capacitor may be the culprit. This capacitor provides the extra boost needed to overcome the initial inertia of the motor. If the capacitor fails, the motor will not have enough power to start. Testing a starting capacitor is a relatively simple procedure that can be performed with a few basic tools.
Before accessing or testing any electrical component, be sure to first disconnect the appliance from its power source. Take the necessary safety precautions to avoid electric shock by wearing rubber gloves and working in a dry environment. You will need a multimeter for the continuity tests. Set the dial on the multimeter to the lowest resistance scale, usually 200 ohms or 2 Kohms.
The first step is to disconnect the capacitor from the motor. Once the capacitor is disconnected, you can check for continuity between the terminals. If there is no continuity, the capacitor is bad and needs to be replaced. Another way to test a starting capacitor is to charge it up and then discharge it. To charge the capacitor, connect it to a DC power source for a few seconds. Then, disconnect the power source and use the multimeter to measure the voltage across the capacitor. If the voltage is not the same as the voltage of the power source, the capacitor is bad and needs to be replaced.
Identify the Starting Capacitor
The starting capacitor, also known as the run capacitor, is a critical component in many electrical devices, particularly those with motors. It provides an initial boost of power to the motor, helping it to overcome the inertia and start rotating. Identifying the starting capacitor is essential for troubleshooting and repair.
Starting capacitors are typically cylindrical in shape and have two terminals. They are often labeled with their capacitance value (in microfarads, µF) and voltage rating. They are usually located near the motor, but may also be mounted on the device’s frame or inside the control box.
To identify the starting capacitor, follow these steps:
- Unplug the device from the power source for safety.
- Locate the motor. The starting capacitor is typically mounted near the motor.
- Look for a cylindrical component with two terminals and a capacitance value labeled on it.
- If you can’t find the capacitor near the motor, check the device’s frame or control box.
If you are unsure which component is the starting capacitor, consult the device’s manual or contact the manufacturer for assistance.
Prepare Your Multimeter
To test a starting capacitor, you will need a multimeter. A multimeter is a device that can measure voltage, current, and resistance. To use a multimeter, you will need to set it to the correct setting. You will also need to connect the multimeter to the capacitor.
Select the Correct Setting
The first step is to select the correct setting on the multimeter. You will need to set the multimeter to the “capacitance” setting. This setting is usually denoted by a symbol that looks like a capital letter “C”. Once you have selected the correct setting, you will need to connect the multimeter to the capacitor.
Connect the Multimeter
To connect the multimeter to the capacitor, you will need to use two test leads. The black test lead should be connected to the negative terminal of the capacitor. The red test lead should be connected to the positive terminal of the capacitor. Once you have connected the test leads, you can begin testing the capacitor.
Set the Range
Before you begin testing the capacitor, you need to set the range on the multimeter. The range is the maximum value that the multimeter can measure. You will need to set the range to a value that is higher than the capacitance of the capacitor. For example, if the capacitor is rated for 100 microfarads, you will need to set the range to 200 microfarads.
Read the Measurement
Once you have set the range, you can begin reading the measurement. The measurement will be displayed on the multimeter’s display. The measurement will tell you the capacitance of the capacitor. If the capacitance is within the acceptable range, then the capacitor is good. If the capacitance is not within the acceptable range, then the capacitor is bad.
| Step | Description |
|---|---|
| 1 | Set the multimeter to the “capacitance” setting. |
| 2 | Connect the black test lead to the negative terminal of the capacitor. |
| 3 | Connect the red test lead to the positive terminal of the capacitor. |
| 4 | Set the range on the multimeter to a value that is higher than the capacitance of the capacitor. |
| 5 | Read the measurement on the multimeter’s display. |
Check for Short Circuits
Using a multimeter, check for continuity between the capacitor’s terminals. If the meter reads a short circuit (zero resistance), the capacitor is faulty and should be replaced.
Another way to check for short circuits is to discharge the capacitor and then connect it to a 12-volt battery. If the capacitor is shorted, it will draw a large current from the battery, causing the battery to quickly discharge. A good capacitor will initially draw a small current, which will gradually decrease as the capacitor charges.
Here’s a step-by-step guide on how to check for short circuits using a multimeter:
| Step | Action |
|---|---|
| 1 | Set the multimeter to the lowest resistance setting. |
| 2 | Touch one probe of the multimeter to each terminal of the capacitor. |
| 3 | If the multimeter reads a short circuit (zero resistance), the capacitor is faulty and should be replaced. |
Measure Resistance
Before measuring the resistance, discharge the capacitor by shorting its terminals with an insulated screwdriver or multimeter leads. Once discharged, set your multimeter to the ohms (Ω) scale. Connect one multimeter lead to each capacitor terminal. A good capacitor will have a very high resistance, typically in the megaohms (MΩ) range. If the resistance is low (less than 1 MΩ), the capacitor is likely shorted and should be replaced.
Capacitance Measurement
Most multimeters do not have a capacitance measurement function. However, you can use an analog capacitance meter or a dedicated capacitor tester to measure capacitance. Connect the meter to the capacitor terminals and read the capacitance value directly from the meter display.
Check for Shorts and Opens
To check for shorts, set your multimeter to the continuity scale. Connect one multimeter lead to each capacitor terminal. If the multimeter beeps, the capacitor is shorted and should be replaced. To check for opens, set your multimeter to the ohms (Ω) scale. Connect one multimeter lead to each capacitor terminal. If the multimeter reads infinite resistance (OL), the capacitor is open and should be replaced.
| Test | Expected Result | Action |
|---|---|---|
| Resistance | Very high resistance (MΩ) | Good capacitor |
| Capacitance | Matches specified value | Good capacitor |
| Shorts | No beeping | Good capacitor |
| Opens | No infinite resistance (OL) | Good capacitor |
Assess Capacitance Value
Measuring the capacitance value of a starting capacitor is crucial to ensure its functionality. Utilize the following steps with caution:
1. Safety First: Disconnect the capacitor from all power sources and discharge any residual voltage before handling it.
2. Gather Your Tools: You’ll need a digital multimeter with a capacitance measurement function, probe wires, and a non-conductive surface.
3. Ground Yourself: Wear an anti-static wrist strap or touch a grounded surface to prevent electrostatic discharge.
4. Set Up the Multimeter: Select the capacitance measurement range appropriate for the capacitor’s expected value (typically microfarads).
5. Connect the Probes: Touch the positive probe to the marked terminal on the capacitor and the negative probe to the unmarked terminal. Ensure solid contact and hold the probes steady.
The multimeter will display the capacitance value in microfarads (μF). Compare the measured value to the capacitor’s rated capacitance, which is usually printed on its body. A significant deviation indicates a faulty capacitor that needs replacement.
| Expected Capacitor Range | Deviation Threshold |
|---|---|
| 1-10 μF | ±20% |
| 10-100 μF | ±15% |
| Over 100 μF | ±10% |
Note: It’s recommended to repeat the measurement several times to ensure accuracy. If the measured value consistently differs from the rated capacitance, replace the capacitor promptly.
Adjust Capacitance if Necessary
Once the capacitor has been tested and found to be faulty, it can be replaced with a new one. The new capacitor should have the same capacitance as the old one. If the capacitance is too low, the motor will not start. If the capacitance is too high, the motor will overheat and burn out. In some cases, it may be necessary to adjust the capacitance of the capacitor.
To adjust the capacitance of a capacitor, use a capacitance meter. The capacitance meter will measure the capacitance of the capacitor and display the value on a digital display. If the capacitance is too low, add a capacitor in parallel with the existing capacitor. If the capacitance is too high, remove a capacitor from the parallel combination.
The following table shows the steps on how to adjust the capacitance of a capacitor:
| Step | Description |
|---|---|
| 1 | Measure the capacitance of the capacitor using a capacitance meter. |
| 2 | If the capacitance is too low, add a capacitor in parallel with the existing capacitor. |
| 3 | If the capacitance is too high, remove a capacitor from the parallel combination. |
| 4 | Retest the capacitance of the capacitor. |
| 5 | Repeat steps 2-4 until the capacitance is within the desired range. |
Check for Continuity
After charging the capacitor, use your multimeter’s continuity setting to test the capacitor. This setting usually has a symbol that looks like a sound wave or diode. If your multimeter doesn’t have a continuity setting, you can use the lowest Ohms setting.
Touch the multimeter’s probes to the capacitor’s terminals. If the capacitor is good, you’ll hear a beep or see the resistance reading drop to zero. If you don’t hear a beep or the resistance reading doesn’t change, the capacitor is bad and needs to be replaced.
Here’s a table to summarize the results of the continuity test:
| Multimeter Reading | Capacitor Condition |
|---|---|
| Beep or Resistance Reading = 0 | Good capacitor |
| No Beep or Resistance Reading Doesn’t Change | Bad capacitor |
Evaluate External Terminals
Inspect the external terminals of the starting capacitor for any signs of damage. Look for any corrosion, cracks, or loose connections. If the terminals appear damaged, the capacitor may be faulty and should be replaced.
Check the resistance between the terminals using a multimeter. With the multimeter set to the resistance setting, connect one probe to each terminal. The resistance should be very high, typically in the range of several megaohms (MΩ). If the resistance reading is low (less than 1 MΩ), the capacitor may be shorted internally and should be replaced.
Checking Capacitance
To check the capacitance of the starting capacitor, you will need a capacitance meter. Connect the probes of the capacitance meter to the terminals of the capacitor. The display of the capacitance meter should indicate the capacitance value of the capacitor. Compare the measured capacitance value to the specified value indicated on the capacitor. If the measured value is significantly different from the specified value, the capacitor may be faulty and should be replaced.
Here are the typical capacitance values for different types of starting capacitors:
| Capacitor Type | Capacitance Range |
|---|---|
| Electrolytic | 2-100 µF |
| Film | 1-100 µF |
| Ceramic | 0.1-10 µF |
Test for Voltage Drop
This test is used to check the voltage drop across the capacitor. A higher voltage drop indicates a higher resistance, which can result in reduced starting torque. To perform this test:
- Disconnect the capacitor from the starting circuit.
- Connect a voltmeter across the capacitor terminals.
- Apply a voltage of 12 volts DC to the capacitor.
- Measure the voltage drop across the capacitor after 1 minute.
- Compare the measured voltage drop to the specified voltage drop value for the capacitor.
The following steps will refine the Test for Voltage Drop subsection to an extent that exceeds 300 words:
- Calculate the expected voltage drop. This value can be found in the capacitor’s datasheet or can be calculated using the formula:
Voltage drop = Capacitor value (μF) x Voltage applied (V) x Time (s) / Resistance (Ω)
- Set up the test circuit. Connect the voltmeter and capacitor in series, as shown in the diagram below:
[Image of a circuit diagram showing a voltmeter connected in series with a capacitor]
-
Apply the voltage. Apply a voltage of 12 volts DC to the circuit.
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Wait for the capacitor to charge. Wait for 1 minute to allow the capacitor to fully charge.
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Measure the voltage drop. Record the voltage drop across the capacitor using the voltmeter.
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Compare the results. Compare the measured voltage drop to the expected voltage drop. If the measured voltage drop is significantly higher than the expected voltage drop, this indicates a high resistance in the capacitor.
-
Repeat the test with different capacitors. If you have multiple capacitors, repeat the test on each capacitor to identify any outliers.
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Consider the operating conditions. The voltage drop test should be performed under the same operating conditions as the capacitor will be used in. This includes temperature, voltage, and frequency.
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Document the results. Record the measured voltage drop, the expected voltage drop, and the operating conditions for each capacitor tested.
Verify Functionality in Circuit
Here’s how to verify the functionality of a starting capacitor while it’s connected within a motor circuit:
1. Safety Precautions:
Always follow safety protocols when working with electricity. Ensure the power is disconnected and the motor is fully discharged before proceeding.
2. Identify Capacitor:
Locate the starting capacitor in the motor circuit, typically connected in parallel with the start winding.
3. Discharge Capacitor:
Using a screwdriver or insulated tool, momentarily touch the capacitor terminals together to discharge any residual voltage.
4. Check Wiring Connections:
Visually inspect the wiring connections to ensure they are secure and free of damage.
5. Disconnect Capacitor:
Carefully disconnect one terminal of the capacitor from the circuit.
6. Set Multimeter:
Set your digital multimeter to the capacitance measurement mode.
7. Measure Capacitance:
Touch the multimeter leads to the disconnected capacitor terminals.
8. Compare Readings:
Check if the measured capacitance value falls within the specified range.
9. Replace If Needed:
If the measured capacitance is significantly lower than the specified value or open (0.00 F), replace the capacitor.
10. Run Motor with Capacitor:
Reconnect the capacitor to the circuit and energize the motor. Observe if the motor starts and operates smoothly. If it struggles to start or exhibits poor performance, the capacitor may need further diagnosis or replacement.
| Capacitance Range | Motor Size | Typical Capacitor Value |
|---|---|---|
| 2-10 μF | Small motors (<1 hp) | 4 μF |
| 10-30 μF | Medium motors (1-5 hp) | 20 μF |
| 30-100 μF | Large motors (>5 hp) | 60 μF |
How to Test a Starting Capacitor
Introduction
A starting capacitor is an electrical component that is used to provide additional power to an electric motor when it is starting up. It is typically connected in parallel with the motor and is charged up when the motor is not running. When the motor is started, the capacitor discharges its stored energy into the motor, providing extra power to help it get started.
Testing a Starting Capacitor
To test a starting capacitor, you will need a multimeter that is capable of measuring capacitance.
- Disconnect the capacitor from the motor.
- Set the multimeter to the capacitance range.
- Touch the probes of the multimeter to the terminals of the capacitor.
- The multimeter will display the capacitance of the capacitor in microfarads (µF).
If the capacitance of the capacitor is less than 80% of the rated capacitance, the capacitor is considered to be failed and should be replaced.
People Also Ask About How to Test a Starting Capacitor
What is the purpose of a starting capacitor?
A starting capacitor is used to provide additional power to an electric motor when it is starting up.
How do I know if my starting capacitor is bad?
You can test your starting capacitor using a multimeter to measure its capacitance. If the capacitance is less than 80% of the rated capacitance, the capacitor is considered to be failed and should be replaced.
How do I replace a starting capacitor?
To replace a starting capacitor, you will need to disconnect the old capacitor from the motor and connect the new capacitor in its place. Be sure to match the capacitance of the new capacitor to the capacitance of the old capacitor.
What are the safety precautions when testing a starting capacitor?
When testing a starting capacitor, be sure to discharge the capacitor before touching it. To do this, you can short the terminals of the capacitor together with a screwdriver.
