Reforming Electrolytic Capacitors Variac

5 min read Jun 26, 2024
Reforming Electrolytic Capacitors Variac

Reforming Electrolytic Capacitors with a Variac: A Step-by-Step Guide


Electrolytic capacitors are a crucial component in many electronic circuits, providing filteration, regulation, and energy storage. However, over time, they can deteriorate, leading to reduced performance, reliability issues, and even complete failure. One method to revitalize electrolytic capacitors is by reforming them using a variac. In this article, we will explore the process of reforming electrolytic capacitors with a variac and provide a step-by-step guide to get you started.

Understanding Electrolytic Capacitor Deterioration

Electrolytic capacitors consist of two aluminum foils separated by an electrolyte, which can be a liquid or a solid. Over time, the electrolyte can evaporate, leading to a decrease in capacitance, increased equivalent series resistance (ESR), and a higher risk of failure. Other factors contributing to deterioration include:

  • High temperatures
  • Voltage stress
  • Current overload
  • Age

Reforming Electrolytic Capacitors with a Variac

A variac (variable auto-transformer) is a variable voltage transformer that can be used to reform electrolytic capacitors by gradually increasing the voltage to the capacitor while monitoring its current and voltage characteristics.


Before starting the reforming process, ensure you have:

  • A variac with a suitable voltage range for your capacitor
  • A multimeter with voltage and current measurement capabilities
  • A non-inductive load resistor (e.g., a 1 kΩ resistor)
  • The electrolytic capacitor to be reformed

Step-by-Step Reforming Process

Step 1: Connect the Circuit

Connect the variac, multimeter, and load resistor in series with the electrolytic capacitor, as shown below:

  |  Variac  |
  | Multimeter |
  |  Load Resistor  |
  |  Electrolytic  |
  |  Capacitor    |

Step 2: Set the Initial Voltage

Set the variac to a voltage lower than the capacitor's rated voltage. This will prevent excessive current flow and reduce the risk of damage.

Step 3: Monitor Current and Voltage

Turn on the variac and monitor the current and voltage across the capacitor using the multimeter. Record the values.

Step 4: Gradually Increase the Voltage

Gradually increase the voltage in small increments (e.g., 1-2 V) every 10-15 minutes, while continuously monitoring the current and voltage. If the current increases rapidly or the voltage drops significantly, reduce the voltage and wait for a few minutes before proceeding.

Step 5: Reach the Rated Voltage

Continue increasing the voltage until you reach the capacitor's rated voltage.

Step 6: Monitor and Test

Monitor the capacitor's current and voltage characteristics for at least an hour. Test the capacitor's capacitance and ESR using a capacitance meter or an impedance analyzer.

Safety Precautions

When working with electrolytic capacitors and a variac, ensure you:

  • Follow proper safety procedures when handling electrical equipment
  • Use a non-inductive load resistor to prevent resonance
  • Avoid applying excessive voltage or current, which can damage the capacitor
  • Keep the work area well-ventilated and clear of flammable materials


Reforming electrolytic capacitors with a variac can be an effective method to revitalize deteriorated capacitors. By following the step-by-step guide outlined in this article, you can restore your electrolytic capacitors to their optimal performance. Remember to exercise caution and follow proper safety procedures when working with electrical equipment.

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