How do you test a varistor?
How do you test for varistor? 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.
How do I know if my varistor is bad?
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 I test a MOV varistor with a multimeter?
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.
How do you calculate MOV?
The current rating of the MOV could be twice that of the SMPS rating, meaning if the SMPS wattage is rated at 24 watts at the secondary, then the primary could be calculated as 24/285 = 0.084 amps, therefore the MOV current could be anywhere above 0.084 x 2 = 0.168 amps or 200mA.
What happens when a varistor fails?
Varistors need to absorb the energy deposited by temporary overvoltage, switching surges, or lightning impulses. The energy absorption capability can be divided into thermal energy absorption capability and impulse energy absorption capability. …
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.
Should a varistor have continuity?
A continuity test shouldn’t cause a beep, because a varistor has much greater resistance than, say, a fuse. Try it on the Ohms range of the meter. The varistor is presumably an inrush current limiter whose resistance drops as it heats up.
Are varistors polarity sensitive?
How do I select a MOV varistor?
- Step 1: To find the voltage rating of the MOV, allow for 20% headroom to account for voltage swell and power-supply tolerances: 24 V dc × 1.2 = 28.8 V dc.
- Step 2: To determine which MOV disc size to use, first identify the MOV series that minimally meet the 1000-A surge requirement.
What is 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.
Why would a varistor burn out?
Varistors can be destroyed by too many surges. They wear out a little with each surge above the threshold and some day they are completely destroyed. Over-voltage is also a common problem. The varistors burned but also let the fuse blow and so save the connected equipment.
What is varistor working principle?
A varistor remains non-conductive as a shunt-mode device during normal operation when the voltage across it remains well below its “clamping voltage”, thus varistors are typically used for suppressing line voltage surges. Follow-through current resulting from a strike may melt, burn, or even vaporize the varistor.
How can you test the resistance of a varistor?
With the varistor removed from the circuit, you can now measure its resistance. Turn the multimeter on and set it to read resistance times 1000 ohms. Touch one meter probe to the free varistor lead and the other probe to the connected lead.
Which is the most common type of varistor?
A varistor is a device with a non-linear volt-ampere characteristic. When the voltage applied to the varistor is lower than its threshold value, the current flowing through it is extremely small, which is equivalent to a resistor with infinite resistance, vice versa. The most common varistor is a metal oxide varistor (MOV).
How is a varistor like a shock absorber?
A varistor is an electronic component that protects expensive devices from harmful power surges, much like a shock absorber. For example if there is a power surge, the varistor, normally having a very high resistance, responds to the voltage spike by absorbing its energy with a very low resistance.
What are the voltages of metal oxide varistors?
The metal oxide varistors offer a choice of varistor voltages from 18 V to 1800 V and Vrms voltages from 11 V to 1100 V. The devices have a high current handling, high energy absorption capability and fast response times to protect against transient faults up to rated limits.