Test an MOV??

[fastline]

In experience, it always seemed that if an MOV was bad, you knew it.... Exploded.... However, I wanted to determine if there are other failure modes and if they can be bench tested/approved? I am really fighting a controller and probably should check to be on the safe side if they indeed can fail without exploding..

 

[crutschow]

They could conceivably fail either short or open without exploding.

The short can be tested with an ohmmeter.

The open would require a high voltage supply to test.

 

[fastline]

DMM ohm test reads open. We do have a function generator but I do not think we can get the voltage required...Do you basically test the voltage drop across it?

 

[crutschow]

DMM ohm test reads open. We do have a function generator but I do not think we can get the voltage required...Do you basically test the voltage drop across it?

The MOV looks rather like a zener diode. So you put a large resistor in series to limit the current, apply a voltage above it's breakdown and measure the voltage across it. You can use a DC supply for that if you have one with a high enough voltage.

 

[fastline]

Maybe you can help with a datasheet on this one? PN is ZNR V14431U. Typical disc shape with radial leads. Made by Murata. Cannot find a sheet anywhere...

 

[crutschow]

Couldn't find anything on it either.

Is connected across the line?

If so the voltage rating is probably 10-20% above the peak AC line voltage.