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How do you test an MOV?
A MOV can be tested with a small applied current (such as 1mA) and that voltage compared with the datasheet specification. For example, a Bourns MOV-07D221K should drop 198V minimum, 220V nominal 242V maximum at 1mA.
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 the working principle of MOV?
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.
Does MOV wear out?
The MOV is the heart of surge suppressors. The role of the MOV is to divert surge current. However, MOVs wear out with use. As more surges are diverted, the MOVs life span shortens, and failure becomes imminent.
How can you tell if a MOV is good or bad?
An ohmmeter will only tell you if a MOV is bad by indicating conductivity, typically a short. A good MOV will always measure “open” with an ohmmeter, but this is not a definitive test. It is not easy to tell if the MOV is good.
How can you test the resistance of a MOV?
Normally, the MOV has very high electrical resistance. If lightning strikes a nearby power line, the high voltage causes the MOV to become a shunt, preventing the electrical surge from harming sensitive equipment. After this happens, the device’s fuse will blow. You can test an MOV simply by testing its resistance.
Is it OK to do open circuit test on MOV?
Open circuit test is the main problem. However, successive operation of the MOV causes internal micro short-circuiting, so open-circuit typically happens in a rather destructive manner 😉 If you do not get a low reading in diode check mode than it is most of the time OK.
How to identify a metal oxide varistor ( MOV )?
Identify the metal oxide varistor. In most smaller equipment, it is a two-lead, coin-sized device, similar to a disc capacitor with a bright color, such as red, yellow or blue. Note if the MOV appears to have burn or scorch marks, indicating damage.