MOV metal oxide varistors testing

Thread Starter

SamEricson

Joined Apr 25, 2015
196
They use these MOV metal oxide varistors for light ballast circuits
They are these very small and the color is blue

With the circuit turned off, how do you test and check MOV varistor compoents?

I put my ohm meter across a MOV varistor and I got no ohm resistance reading it just said O.L overload.

How do I know if the MOV varistor is shorted or open or good?

PIC#1
https://www.google.com/search?q=inc...y.com%2Findex.php%3Fshowtopic%3D65748;576;190

PIC#2
https://www.google.com/search?q=inc...ighting-accessories%2F2025332911.html;720;502
 

Potato Pudding

Joined Jun 11, 2010
688
The test for a metal oxide varistor is to take it above its breakdown with a low current high voltage, to see if it conducts and what the clamp voltage is.
Treat it like two zener diodes cathode to cathode in a package with their anodes exposed.
Not recommended for anyone that... well if you needed to ask you probably should not bother trying. High voltage for a ballast is going to be in a don't go there zone unless you are extremely certain what you are doing, need to know really badly, and take the precautions required.

The overload test you got with your ohmmeter is the most important test and a good sign. It means they are not shorted.
 

Thread Starter

SamEricson

Joined Apr 25, 2015
196
So how does an electronic technician test MOV varistors? to know if they are open? or working

I would have to remove them for the circuit and do what? apply an AC or DC voltage across the MOV component leads?

Also I tried to use a huntron to measure the MOV varistor signature and i got no component signature from it.
 

Potato Pudding

Joined Jun 11, 2010
688
I can't explain it more clearly.

The only part I will repeat and clarify is that it is not safe for you to fully test the MOV in a ballast. Please don't try.
 

Thread Starter

SamEricson

Joined Apr 25, 2015
196
yes i will remove the MOV for testing. I will test the MOV out of circuit

It's true there is no way for an electronic technician to test MOV in circuit right? only out of circuit tests?
 

devisree

Joined Apr 26, 2016
1
Varistor acts as a dielectric, the device has a capacitance that depends directly on its area and varies inversely with its thickness. Therefore, the capacitance of a Varistor is a function of its voltage and energy ratings. It is important to take care of electrical history of varistor, short both ends of varistor to discharge and measure the capacitance after removing the short.

Many thanks,
Theyvees
 
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