There you go again. Lets see if I can make it simpler for
Mike so that Mike instead insults the scam plug-in protector
manufacturer. First you claim an indicator lamp can report a
'degraded' MOV as in Littelfuse AN9310:
A failed device is defined by a +-10% change in the
nominal varistor voltage at the 1 ma point. This does
not imply a non-protecting device, but rather a device
whose clamping voltage has been slightly altered.
But to prove that point, instead you post about a
'catastrophically' damaged MOV that was grossly undersized, as
defined by Littelfuse AN9772:
Varistors initially fail in a short-circuit mode when
subjected to surges beyond their peak current/energy
ratings. They also short-circuit when operated at
steady-state voltages well beyond their voltage ratings.
The catastrophically damaged MOV is also described in your
magazine article from
http://www.powerelectronics.com:
In an unlimited current condition, the MOV will first fail
short. Yet, due to the high amount of energy available,
it most often ruptures instantaneously.
The article then describes how an MOV can be disconnected
from a surge to protect the surge protector - appliance
protection be damned. What kind of protection is that when
the MOVs are undersized? Ineffective protection.
So yes, a catastrophically damaged MOV - because the surge
protector was grossly undersized - is indicated by a ruptured
thermal link and indicator lamp. An unacceptable failure mode
because the human installed a grossly undersized plug-in
protector.
But will that light report all types of MOV failures? No.
Because the normal and acceptable failure mode for properly
sized MOV surge protectors is 'degradation' as defined in
AN9310. A properly sized surge protector typically will not
fail catastrophically. And yet an indicator light will still
imply the degraded protector is good.
And so again, an indicator light can only report surge
protector failure when the surge protector was grossly
undersized - as are so many plug-in protectors. Properly
sized surge protectors typically do not fail catastrophically
- do not suffer from "sustained abnormal overvoltage, limited
current conditions". Why? Properly sized protectors are not
grossly undersized plug-in protectors selling at high
profits. Properly sized protectors, also, would never claim
effective protection when the plug-in UPS only has 160 joules.
So how does that light report normal degradation in properly
sized protector? No problem! Instead, sell grossly
undersized protectors. A grossly undersized protector will
only report a catastrophic type failure. Then the naive human
will say, "The surge protector sacrificed itself to protect my
computer". The human should instead say, "The surge protector
was so grossly undersized that it did not provide effective
protection AND indicated its catastrophic failure by even
lighting the indicator lamp LP1". The informed human will
then say, "Its a good thing my appliance was properly designed
with internal protection because this plug-in protector was
crap - grossly undersized".
What does the light report? It can report that a grossly
undersized protector failed catastrophically. But the light
cannot report a properly sized protector has failed normally -
has degraded. IOW the light cannot report that a protector is
good. Light only reports one failure mode - the unacceptable
failure mode. Light only reports that protector was grossly
undersized and therefore failed catastrophically.
So how do we make the indicator lamp useful? We make sure a
protector only fails catastrophically. We grossly undersized
the protector and get the naive to hype this protector. How
convenient since a grossly undersized protector can also mean
higher profits. Since appliances already have effective
internal protection, then the naive will recommend more of
these grossly undersized protectors. What a racket!
