How do I read varistor code?
Touch one meter probe to the free varistor lead and the other probe to the connected lead. Read the resistance on the meter. If it reads nearly infinite resistance, the varistor is still good. If it reads very low resistance, the varistor is blown.
What are metal oxide varistors?
A metal oxide varistor (MOV) is a device used as a component in electrical equipment. The word varistor is short for variable resistor. A resistor is a circuit that does not conduct electricity well. This is useful for controlling how much electric current travels to certain parts of electronic devices.
How do varistors fail?
Under different current conditions, failure modes include electrical puncture (see Figure 4), physical cracking (see Figure 5), and thermal runaway. Cracking happens because varistors are basically a ceramic material, and hitting them with a sharp high-amplitude surge is like hitting a dinner plate with a hammer.
How are varistors rated?
The energy rating is determined by volume, voltage rating by thickness or current flow path length, and current capability by area measured normal to the direction of current flow. Littelfuse Varistors are available with AC operating voltages from 2.5V to 6000V. Higher voltages are limited only by packaging ability.
Do varistors have polarity?
Does a varistor have polarity? In the case of metal oxide varistor, a zinc-oxide layer is basically sandwiched between two metal electrodes. As a result, there is no polarity.
What do varistors do?
Varistors are used to protect a circuit from high voltage surges. When a high voltage surge is applied to a circuit, the outcome is usually catastrophic to the circuit. A capacitor may be installed across the signal lines.
What are varistors made of?
Metal Oxide Varistors, or MOV’s are typically made from a small disk-shaped metal zinc oxide material. They are available in many values for specific voltage ranges.
How do varistors work?
When a voltage surge exceeding a specified voltage (varistor voltage) is applied, the varistor suppresses the voltage to protect the circuit. When the voltage surge does not exceed the varistor voltage, the varistor works as a capacitor.