Electronics > Projects, Designs, and Technical Stuff

Easily replaceable MOV

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wraper:

--- Quote from: Alti on July 08, 2020, 08:49:52 pm ---
--- Quote from: Gyro on July 08, 2020, 06:36:47 pm ---Brand new MOVs don't explode catastrophically after 2 minutes!

--- End quote ---
That is why I always check "Best before" date.

--- End quote ---
There is no best before date for MOV. They don't degrade by sitting on the shelf. The same for most of other parts except that lead solderability degradation is a thing.

Bassman59:

--- Quote from: wraper on July 08, 2020, 08:52:11 pm ---
--- Quote from: Alti on July 08, 2020, 08:49:52 pm ---
--- Quote from: Gyro on July 08, 2020, 06:36:47 pm ---Brand new MOVs don't explode catastrophically after 2 minutes!

--- End quote ---
That is why I always check "Best before" date.

--- End quote ---
There is no best before date for MOV. They don't degrade by sitting on the shelf. The same of most of other parts except that lead solderability degradation is a thing.

--- End quote ---

They do degrade each time they suppress an overvoltage, though.

T3sl4co1l:
Yeah, MOVs usually come with rating curves -- big boy lightning surges are down in the 100s, or 10s or 1s of cycles lifetime range.  There is a limit, where lifetime goes towards infinity; it's just completely useless for surge protection purposes.  If you needed so little (a few J) protection, you'd put in a TVS instead.

Or, if you have an application where the pulse width is much longer than direct/induced lightning, in which case there is some economic argument in favor of them (MOVs are cheaper than TVSs, for the same energy capacity for long pulses).  That's like 10ms+ pulses.

(Interestingly enough, they do make TVSs for lightning suppression; they do not have a wear mechanism, they just fail shorted (or, if your fault current or fusing isn't very good, they'll probably still blow the fuck up... :-DD ) when absorbing too much energy.  Downside: they're a bit bigger than MOVs, and hella more expensive! :o )

Tim

wraper:

--- Quote from: Bassman59 on July 08, 2020, 10:42:26 pm ---They do degrade each time they suppress an overvoltage, though.

--- End quote ---
You just repeated what I said in the post #5.

trobbins:
MOV's do not degrade when suppressing an overvoltage below a rated level of absorbed energy - read the datasheet.  Typically a MOV has to be on a mains supply feed to get to transient levels that could cause degradation - not all applications are mains fed supplies, and not all transients on mains fed supplies would cause degradation.

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