How is varistor value calculated?
The simplest ways of determining the current duration are simulation or measurement (τ = t*r). The time constant can also be calculated to an approximation with equation 13. Here the varistor resistance of voltage class K20 is calculated for 1 A.
How do I choose a varistor?
Choose a varistor with an energy absorption rating that equals or slightly exceeds the energy values associated with the event the circuit may experience. If, however, the transient voltage is due to an external event, the magnitude of the source energy is unknown.
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.
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 .
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 is the purpose of a varistor?
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.
Are varistors polarity sensitive?
The copper-oxide varistor exhibited a varying resistance in dependence on the polarity and magnitude of applied voltage.
What is a MOV circuit?
An MOV is a voltage dependent device which has an electrical behavior similar to back to back zener diodes. ▪ When exposed to high voltage transients, the MOV’s resistance. changes from a near open circuit to a very low value, thus clamping the transient voltage to a safe level.
How do you test a MOV in a circuit?
Turn the multimeter on and set its function knob to read resistance. Touch the meter probe tips to the MOV’s leads and measure its resistance. If it has a resistance much under 100 ohms, it has blown. Desolder and remove the remaining lead and remove the MOV from the equipment.
What is MOV in a surge 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.
How does varistor protect circuit?
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. When a voltage surge exceeding a specified voltage (varistor voltage) is applied, the varistor suppresses the voltage to protect the circuit.
How do I test a MOV varistor?
Touch the meter probe tips to the MOV’s leads and measure its resistance. If it has a resistance much under 100 ohms, it has blown. Desolder and remove the remaining lead and remove the MOV from the equipment. If the part has resistance over one million ohms, it is still good.