How to Discharge a Capacitor with a Multimeter

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Did you know that a charged capacitor’s short circuit gives a substantial danger of burning out the electrical part and other circuit components? You will also find the danger of electrocution and burning. The higher the voltage and capacitance of the capacitor, the more the risk it could have in the case of a short circuit. 

Your job is to ensure the capacitor is properly discharged before you withdraw it from the circuit. 

What is a Capacitor? How Does it Work?

Capacitors are two-electrode devices divided by a dielectric material in which electric charges of the same magnitude and opposite potentials build up. You will find many different types of capacitors, each of which might be divided into subtypes. 

The easiest devices are composed of two metal parts with a dielectric material—like ceramic material, air, or saturated paper—squeezed in between them. Further, plates are the metal parts applied to keep electrical energy. 

The stage of electricity deposition begins when voltage is applied to the capacitor surfaces, more as it does in battery cells. Further, the electrical charge on the capacitor plates lingers while the voltage source is disconnected, owing to electrostatic attraction.

The accrued charges are of the same magnitude. However, their potentials are quite different. The approach of safely discharging the capacitor is very close to that of charging it. You see, DC voltage is included to capacitor terminals along with a given capacity—a charge that is the product of voltage and capacitance—is deposited in the capacitor.

Farads are then utilized to measure capacitance. A charge of one coulomb generates one volt in a capacitor along with a capacitance of one farad. Take note that one farad is such a huge number. That’s why capacitors in electrical engineering and electronics are normally measured in millifarads, microfarads, nanofarads, and picofarads. 

What are the Important Parameters to Discharge a Capacitor?

You need to learn the capacitor’s specifications to learn how to discharge it. The rated voltage, capacitance resistance, rated capacitance, and dielectric loss are the major criteria of a capacitor. Always keep that in mind. 

Any capacitor has such key attributes:

  • Temperature coefficient
  • Pulse load capability
  • Rated power and frequency 
  • Resistance to insulation
  • Permissible AC voltage
  • Climate dimensions and class

The most crucial parameter when preparing a capacitor discharge is capacitance. 

The capacitance determined by the production company is a nominal capacitance, which is nearly challenging to obtain. In fact, the capacitance value is caused by a wide array of environmental aspects. Hence, the capacitance is determined with a percentage tolerance—for example, the percentage variance of the real capacitance from the rating value.

The capacitor’s failure is the amount of energy lost because of its action under alternating voltage and is signified by a loss tangent. Such losses are typically greater than dielectric losses and are connected to the electrode’s losses and the capacitor unit’s frequency or temperature. 

What’s the Proper Way of Discharging a Capacitor?

Bear in mind that capacitor discharge is identified by the form and capacitance of the capacitor. Those more than one farad must be discharged with a caution as a short circuit may lead to not just capacitor damage but also electric and fire shock. 

The capacitor’s secure discharge is as basic as adding some resistance load to the terminals, which will dissipate the energy included in the capacitor. 

A high resistance receiver could be utilized to discharge the capacitor. Moreover, the charge included in the plates will take a longer time to discharge. However, the plates will be totally discharged. Meanwhile, a lower capacitance capacitor might be discharged through assembling a unique discharging tool that involves a serially connected resistor and capacitor. 

You need to pay attention to the discharge period of the capacitor and the necessary power of the resistor while creating such a device. 

How Do You Discharge a Capacitor with a Digital Multimeter?

To avoid any issues when discharging a capacitor, you must utilize a digital multimeter to identify the stores’ electric charge of the capacitor before you use a screwdriver or any other tools.

  1. Start by setting your digital multimeter to the all-out DC voltage setting.
  2. Connect the lead of the capacitor to the probes of the multimeter.
  3. Interpret the numbers on the multimeter monitor while holding the probes.

Using a screwdriver 

You may have already read that shorting the terminals of the capacitor using pliers or screwdriver is a simple method of discharging it. Most technicians will put a screwdriver between the two terminals of the capacitor and call it a day. However, only capacitors with a voltage below ten volts and a few microfarads can operate with that system.

You don’t need to charge the capacitor if its stored voltage is less than 10 volts, as it can easily discharge by itself. Meanwhile, you can discharge the capacitor with a short circuit or a screwdriver if the multimeter readings are below 50 volts. 

Remember that this process is only ideal for discharging low voltage capacitors. Here’s what you need to do.

  1. Take your capacitor on one side and an insulated screwdriver on the other side
  2. Make sure the coating of the screwdriver handle is in great shape. There shouldn’t be any tears, defects, gaps, or mishaps in the rubber or plastic. For a few electrical tasks, don’t use a screwdriver with a stretched handle. 
  3. Place the screwdriver between the two leads of the capacitor. 
  4. There will be a spark. If there is, it means an electric discharge is happening. 

Final Thoughts

You can find a fast way to discharge a capacitor. Nonetheless, that’s only suitable for capacitors with low voltage. Shorting the terminals of a high-voltage capacitor is risky as the current generated is quite huge, not to mention the user being electrocuted or burned, all of which might lead to serious injury or, worse, death. 

Is it essential for a capacitor to discharge self-sufficiently? Yes, it can discharge on its own if a capacitor is not wired to other charging systems or wired to some external power.

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