How to Charge a 400V High Voltage Capacitor

Written by alexander rudinski
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How to Charge a 400V High Voltage Capacitor
Capacitors store energy in a circuit. (capacitor image by naolin from

In most electronics textbooks, students can read that capacitors store a charge, which can later be released. Unfortunately, this is completely wrong. Capacitors do not store charge, but rather energy in the form of potential difference between the two conductive plates separated by an insulator. This energy is transmitted to the capacitor by running electricity through it, which move electrons around the capacitor and creates a potential difference between the two plates. When this potential difference is released, a spike in voltage is seen, which can give the impression that a capacitor stores "charge" rather than energy.

Skill level:

Things you need

  • 16-gauge wire
  • 4-mfd resistor
  • 400V capacitor
  • 9V battery
  • Battery holder

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  1. 1

    Connect a switch to the positive terminal of the battery.

  2. 2

    After the switch, attach one terminal of the resistor using some of the wire.

  3. 3

    Connect the other side of the resistor to one side of the capacitor. If you are using a non-polarised capacitor, it doesn't matter what side you connect to the resistor. If you are using a polarised or electrolytic capacitor, connect the end of the resistor to the negative side.

  4. 4

    Wire the remaining lead from the capacitor to the negative terminal of the battery.

  5. 5

    Flip the switch to begin charging the capacitor. After five cycles the capacitor will be fully charged. The length of a cycle in seconds can be calculated by multiplying the resistance in ohms by the capacitance in farads.

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