How To Tell Positive and Negative Terminals of a Capacitor?

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Capacitors are passive components in electrical circuits; they hold the electrical energy in an electrical field. When the power is cut off, a capacitor is used as a battery in an electric circuit; they are energy storage components. The capacitor has two terminals, so how to identify the positive and negative terminals of a capacitor?

How To Identify the Positive and Negative Terminals of a Capacitor?

To identify the positive and the negative terminals of a capacitor, you have to look for a minus sign or a large stripe, or both on one of the capacitor’s sides. The negative lead is closest to the minus sign or the stripe, while the unlabeled lead is the positive one.

Another way to identify the positive and the negative terminals of a capacitor is the length of the two leads. The longer lead is the positive terminal, while the shorter lead is the negative terminal.

How To Identify the Value of the Capacitor?

To identify the value of a capacitor, you should look for the value written in the case of the capacitor; meanwhile, if your capacitor has a small size, there will be no space left for the value to be marked. So instead of the value being marked on the casing, the manufacturers use codes in small capacitors.

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How To Check a Capacitor?

To check a capacitor, you can do this in many methods, you can use the capacitance setting in the multimeter, you can use the multimeter without the capacitance mode, and use the time constant to test the capacitor; in addition, you can test the capacitor using the voltmeter or the analog multimeter.

Discharging The Capacitor

Before testing or checking a capacitor, you have to discharge it first because the capacitors can keep the charge even after being disconnected from the power supply. If a capacitor is not discharged correctly, and you intentionally touch the capacitor’s leads, it will discharge through you, and you may be shocked.

You can discharge a capacitor using a screwdriver or a discharge resistor; remember discharging a capacitor is a very important step before starting to test the capacitor. To discharge a capacitor, you can follow the following methods:

The Screwdriver Method

An important warning before using this method, it’s not recommended for beginners because when discharging the capacitor, there will be some sparks. Sparks can cause many injuries and burns; they may even damage other components.

Disconnect the capacitor from the printed circuit board “PCB,” then use the soldering iron to desolder, but you have to be careful not to touch its terminals. In the next step, grab a well-insulated screwdriver; it’s more preferred if it has a long handle, you should use only one hand. Finally, use your other hand to grab the capacitor.

Touch the terminals of the capacitor using the screwdriver’s metal part to discharge the capacitor. When the screwdriver touches the terminals, there be some sparks and a cracking sound; this means the capacitor is being discharged; repeat this step serval times to ensure that the capacitor is properly discharged.

The Discharge Resistor Method

This method is safer than the previous one and is more recommended when discharging a capacitor. It’s used in power supplies and other circuits, where the capacitor is placed in a parallel with a resistor known as the bleeder resistor. Then the power is turned off, so any remaining charge kept in the capacitor is discharged through the bleeder resistor.

To perform this method, bring a large resistor; for example, any resistor with a few kilos ohm will work properly. Connect the resistor in parallel with the capacitor to have the same start and end nodes. The charge will transfer from the capacitor and discharge through the resistor.

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1). A Multimeter With Capacitance Method

You would have to use a mid or high-end digital multimeter in this method because the capacitance mode is not available in low-end multimeters. In addition, this method is the quickest, easiest method to check any capacitor.

1. Remove the capacitor from the PCB and discharge it properly.
2. If the capacitor ratings are marked on its body, write them down to check them later, the capacitance unit is Farads or micro Farads, and the voltage rating unit is Volts.
3. Adjust your digital multimeter for capacitance mode.
4. If you have a polarized capacitor connected to the black-colored probe to the negative terminal, it’s the lead with the shorter length. Connect the red-colored probe to the positive terminal to the positive terminal; it’s the lead with the longer length.
5. If you have a non-polarized capacitor, you can connect any probe to any lead as it doesn’t matter because there is no polarity.
6. Compare the ratings from the capacitor, the ones you have written down, with the ratings that appeared on the digital screen of the multimeter. If the difference is a small value, the capacitor has a good condition; meanwhile, if the difference is large, the capacitor has a bad condition and must be replaced.

2). A Multimeter Without Capacitance Method

You can use this if you have a cheap or low-end multimeter and are unwilling to buy another mid or high-end one. The low-end multimeter doesn’t have the capacitance mode available in the mid or high-end one.

1. Remove the capacitor from the PCB and discharge it properly.
2. Adjust the multimeter to the Ohm or the resistance mode; in manual multimeters, the resistance mode can have many ranges; you can choose a high range, for example, 200 KΩ to 20 KΩ.
3. If you have a polarized capacitor connected to the black-colored probe to the negative terminal, it’s the lead with the shorter length. Connect the red-colored probe to the positive terminal to the positive terminal; it’s the lead with the longer length.
4. If you have a non-polarized capacitor, you can connect any probe to any lead as it doesn’t matter because there is no polarity.
5. Observe the multimeter readings; the multimeter will show a reading for a short time, then it will change to infinity or an open circuit. You have to write down the reading that appeared for a short time to compare it later.
6. Remove the capacitor from the multimeter and repeat the previous steps several times.
7. If the results that appear each time are similar, the capacitor has a good condition; if not, then the capacitor has a bad condition.

3). Measuring Time Constant to Test the Capacitor Method

You can use this method only if you know the capacitance value, and then you use the capacitance to check whether the capacitor has a bad or good condition.

1. Remove the capacitor from the PCB and discharge it properly.
2. Connect the capacitor with a resistor of 10KΩ in series.
3. Use a power supply with known voltage to complete the circuit.
4. Turn on the power supply, and calculate the time the capacitor needs to charge 63.2% of the supply voltage; for example, if you have a 24 volts power supply, it would reach 15.168 volts.
5. Use the resistance and the time to calculate the capacitance and compare it to the value you already knew.
6. If the difference is a small value, the capacitor has a good condition; meanwhile, if the difference is large, the capacitor has a bad condition and must be replaced.

4). Simple Voltmeter to Test the Capacitor Method

1. Remove the capacitor from the PCB and discharge it properly.
2. Look for the capacitor’s voltage rating; it should be marked beside its capacitance rating; it can be 50V, 25V, or 16V. The voltage rating refers to the maximum voltage the capacitor can be subjected to.
3. Connect the capacitor to a power supply that has a voltage less than the capacitor’s voltage rating; for example, if the capacitor voltage rating is 16 volts, the power supply should be around 9 volts.
4. Use the power supply to charge the capacitor for a short time, 5-6 seconds.
5. Adjust the multimeter to DC voltmeter mode, and connect the multimeter’s probes to the capacitor.
6. If you have a polarized capacitor connected to the black-colored probe to the negative terminal, it’s the lead with the shorter length. Connect the red-colored probe to the positive terminal to the positive terminal; it’s the lead with the longer length.
7. If you have a non-polarized capacitor, you can connect any probe to any lead as it doesn’t matter because there is no polarity.
8. The initial reading on the multimeter should be similar to or close to that of the supply source.
9. If the difference is a small value, the capacitor has a good condition; meanwhile, if the difference is large, the capacitor has a bad condition and must be replaced.

5). Analog Multimeter to Test the Capacitor Method

1. Remove the capacitor from the PCB and discharge it properly.
2. Adjust the multimeter to the Ohm or the resistance mode; in manual multimeters, the resistance mode can have many ranges; you can choose a high range, for example, 200 KΩ to 20 KΩ.
3. If you have a polarized capacitor connected to the black-colored probe to the negative terminal, it’s the lead with the shorter length. Connect the red-colored probe to the positive terminal to the positive terminal; it’s the lead with the longer length.
4. If you have a non-polarized capacitor, you can connect any probe to any lead as it doesn’t matter because there is no polarity.
5. If your capacitor is in good condition, the resistance reading will appear at a small value first and then gradually increase.
6. If your capacitor has a bad condition, the resistance reading will always appear low.
7. If there is no reading or the analog doesn’t move, you have an open capacitor.

Conclusion

To sum up, you can know which lead is the positive and which is negative in any capacitor through two methods:

• You have to look for a minus sign, a large stripe, or both on one of the capacitor’s sides. The negative lead is closest to the minus sign or the stripe, while the unlabeled lead is the positive one.
• The length of the two leads. The longer lead is the positive terminal, while the shorter lead is the negative terminal.

To identify the value of a capacitor, you should look for the value written in the case of the capacitor; meanwhile, if your capacitor has a small size, there will be no space left for the value to be marked. So instead of the value being marked on the casing, the manufacturers use codes in small capacitors.

If you want to test your capacitor, you must discharge it first for your safety from the sparks and shocks; you can do it with a screwdriver; however, it’s not recommended to do it this way if you are a beginner. The more recommended and safer method is connecting a parallel resistor with the capacitor to discharge through it.