[lug] Aging Surge Protectors

[Mr Viggy]

Yep, varistors are similar to resistors.  However, when the voltage
across them gets above a specific level, their resistance is reduced to
almost 0 (i.e. they short out).  And, yes, the material that they are
made of wears down over time, until they are completely open (they never
short out).

I'm not sure what high end units use, though.  In my applications, I
used MOV's across switches attached to steppers (needed to shunt off the
extra current when we swithced the stepper).  They probably use some 
kind of filter
(just guessing here), similar to a UPS system.

Viggy

> Wagner, Carl wrote:
> 
>> The way I understand it, the cheap units use MOV (metal oxide 
>> varistors) that
>> clamp down if you exceed the design voltage.  Every time it clamps 
>> down a portion
>> of the MOV is destroyed (not really sure about this).  The amount that 
>> is destroyed
>> is proportional to the magnitude of the over-voltage and duration.  So 
>> shelf life
>> should not matter, just the number of hits and magnitude, will affect it.
>>
>> As I said, this is how I understand it. I could be completely wrong 
>> though.
>>
>> I have no idea how high end units deal with over-voltage.
>>
>> You could probably do some google-ing to find more.
>>
>> Carl.
>>
>> -----Original Message-----
>> From: lug-bounces at lug.boulder.co.us
>> [mailto:lug-bounces at lug.boulder.co.us]On Behalf Of Timothy Klein
>> Sent: Friday, August 27, 2004 11:46 AM
>> To: Boulder (Colorado) Linux Users Group -- General Mailing List
>> Subject: Re: [lug] Aging Surge Protectors
>>
>>
>> On Friday 27 August 2004 11:01, Gordon Golding wrote:
>>
>>> This might come through twice - having trouble with email.
>>>
>>> I'm putting in some servers and client workstations - somebody just
>>> said that as surge protectors age, they lose their capacity to
>>> protect.
>>>
>>> Has anybody ever heard this?
>>
>>
>>
>> This is true, from my reading.  Something in the unit is consumed with 
>> use (don't remember what).  Some high end designs try to tell you when 
>> they fail, some really high end models use a more permanent design 
>> (the kind that clicks like mad -- it bleeds off current with a 
>> capacitor.  The standard ones shunt to ground, which can actually 
>> damage modems).  Cheaper models work for a time, and then fail silently.
>>
>> This is all from imperfect memory.
>>
>> Tim
> 
>