In the overvoltage protection system of circuit boards, varistors play the role of “safety guards”. However, when electronic devices are struck by lightning or surges, this component is highly susceptible to damage. For maintenance engineers and electronics enthusiasts, mastering how to detect the quality of varistors is an essential skill, which directly affects the efficiency and accuracy of fault diagnosis. Usually, simple detection can help us quickly locate the cause of the device’s “strike”.
The most basic detection method is to use the resistance range of a multimeter. After the power is cut off and the discharge is completed, adjust the multimeter to a high range of megaohms and measure the two pins of the varistor. Under normal circumstances, its resistance should be infinite or display “OL” open circuit. If the measured resistance value is close to zero, it indicates that the component has broken down and short circuited; If a fixed low resistance value is measured, leakage or aging may have occurred. This is a commonly used method for entry-level testing of the quality of varistors. Although it can only determine extreme faults, it is very practical.
To more accurately detect the quality of varistors, dynamic testing is required. Due to the high resistance state of varistors below the nominal voltage and the sharp decrease in resistance value above the nominal voltage, we can use an adjustable power supply in series with a current limiting resistor to simulate overvoltage environments. Apply voltage to the component and slowly increase it, observing whether the current suddenly increases when the voltage approaches its nominal value (such as 560V). If the voltage increases but there is no current change, it indicates an internal open circuit failure, and this method can deeply verify its nonlinear protection characteristics.
In addition to measuring conduction characteristics, leakage current is also a key indicator for determining performance degradation. In the professional process of detecting the quality of varistors, it is necessary to apply the maximum continuous operating voltage (such as 0.83 times the varistor voltage) to the varistors and measure them in series with a microampere meter. If the leakage current exceeds the standard value (such as greater than 50 μ A), even if the static resistance is normal, it means that the performance of the component has declined and it will generate abnormal heat in the circuit, which urgently needs to be replaced. In summary, the method for detecting the quality of varistors needs to be selected based on the scenario: a multimeter can be used for rough measurement at the maintenance site, while specialized instruments are needed for precise verification during R&D quality inspection. As a professional electronic component supplier, Yuanlin Electronics not only provides high-quality and compliant varistor products, but also offers professional technical selection and testing guidance to customers, helping them easily solve various problems in circuit protection.
