4 Simple Ways to Tell If Your Varistor Is Failing

Varistors, abbreviated as VDRs, exhibit nonlinear voltage-current characteristics, meaning their resistance changes with applied voltage. They are compact, lightweight, have high voltage tolerance, fast response, large current capacity, stable performance, and can withstand various surge currents. Because of these advantages, VDRs are essential components in many electronic devices.

As voltage guardians in circuits, VDRs respond rapidly to high voltage, clamp excess voltage, absorb extra current, and protect electronics from transient overvoltage or surges, also providing lightning protection.

However, due to complex operating environments and frequent high-voltage impacts, VDRs can fail. When an electronic device malfunctions, here’s how to determine whether a VDR is still working properly:

1. Visual Inspection
Open the device and inspect the VDR on the circuit board. VDRs are typically encapsulated in epoxy resin.

If you notice swelling, cracks, discoloration, or detached leads, the VDR is damaged and must be replaced with the same model immediately.

2. Multimeter Testing
A multimeter can be used to test the VDR’s resistance.

• Set the multimeter to the X10K resistance range.
• Measure the VDR’s resistance.
  • If the reading shows infinite resistance, the VDR is functioning normally.
  • If the reading is very low, the VDR is damaged and must be replaced.

3. Oscilloscope Testing
An oscilloscope can also test a VDR.

• Apply a test current of 1 mA DC and measure the actual voltage across the VDR.
• If the voltage deviates significantly from the rated voltage, the VDR is faulty and should be replaced.

4. Replacement Method
You can also test a VDR by replacing it with a new one of the same model. If the circuit functions normally after replacement, the original VDR is confirmed to be defective.

By using these methods, you can accurately determine whether a VDR is operational. If a VDR is damaged, replace it promptly with the same model to ensure proper circuit protection.

This article is provided by JYH HSU (JEC) Electronics. JEC is a research, development, production, and sales-oriented company specializing in manufacturing and selling various electronic components such as capacitors and resistors.