Why is Metal Oxide Varistor applied?

Definition: The most commonly used form of a varistor is the Metal Oxide Varistor, which is also a voltage dependant and non-linear resistor connected to the electrical and electronic circuits to protect against the switch, lightning surges, and to achieve high suppression of transient voltage.

What is the purpose of an MOV?

A Metal Oxide Varistor (MOV) is a protection component used in power supply circuits that is powered directly from AC mains. It is used to protect the circuit from high voltage spikes by varying its resistance.

What is MOV fuse?

A Metal Oxide Varistor or MOV is the blue or orange-colored circular component that you can commonly spot on the AC Input side of any Power Supply Circuit. Hence MOVs are normally used in parallel with a fuse, to protect circuits from high voltage spikes.

What is MOV suppressor?

Metal Oxide Varistors (MOVs) are bidirectional and non-linear surge suppressor devices that are widely used for limiting voltage during a surge or transient event in a broad variety of applications. An MOV also features non-ohmic current-voltage characteristics that are similar to that of a diode.

How does a MOV varistor work?

An MOV is a voltage dependent device which has an electrical behavior similar to back to back zener diodes. changes from a near open circuit to a very low value, thus clamping the transient voltage to a safe level. pulse is absorbed by the Varistor, thereby protecting vulnerable circuit components.

What happens when a varistor fails?

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.

What are varistors used for?

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. However, this capacitor cannot suppress voltage surges.

What are varistors made of?

The most common modern type of varistor is the metal-oxide varistor (MOV). This type contains a ceramic mass of zinc oxide grains, in a matrix of other metal oxides, such as small amounts of bismuth, cobalt, manganese oxides, sandwiched between two metal plates, which constitute the electrodes of the device.

What happens when MOV fails?

The prominent failure mode for the MOV is sustained overvoltage. Under these conditions, the MOV begins to conduct power frequency (50 Hz to 60 Hz) current. The MOV ultimately reaches its maximum energy capacity and enters thermal runaway.

How do you calculate MOV?

Estimate the MOV’s energy rating in units of joules. This is the electrical energy that the MOV can safely absorb at least once before failing. You can calculate the energy by multiplying peak surge volts by amps, and then by seconds of time. For example, 1,000 volts x .

How do MOV fail?

How does an MOV fail? When subjected to stresses above its ratings, an MOV can fail as a short circuit. If applied conditions significantly exceed the energy rating of the device, and current is not limited, the MOV may be completely destroyed.

How do you check if a varistor is working?

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.