>The problem with MOV's is they have a narrow current range where they
>are most efficient and either side of that the internal resistance and
heat
>goes up.
>
>Carl
>KM1H
>
Please could you expand on that, Carl? MOVs are non-conducting unless
they are actually limiting a surge, so I'm not sure how internal
resistance, heat and "efficiency" (in the normal engineering sense of
that word) come into it.
> They also have a finite life.
MOVs are sacrificial components. Their mission in life is to 'take a
bullet' from line surges to protect other, more valuable components
downstream. But their working life is closely related to the total
amount of energy they have absorbed... and as well as damage due to
large surges, there is also damage from long-term exposure to the much
larger numbers of small surges.
In a normal shack PA, the working life of an MOV can be greatly extended
by placing the MOV on the downstream side of the main power switch, so
it isn't exposed to any surges unless the amp is in use.
Also don't forget the benefits of a mains filter. As well as filtering
high-frequency impulses coming backward out of the power supply, the
filter will reflect most of the high-frequency components of any
incoming surges.
73 from Ian GM3SEK
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