>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.
My error, I had them confused with the GE surge suppressors many use and
have trouble with, the CL-90 for instance.
MOV is a GE registered trademark BTW.
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.
Already well covered in the literature.
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.
IMO placing them after the switch is the normal way of installing them. The
other option is as part of an external line filter/Spike suppressor which is
popular with the receiving end but those have proven to be prone to failure
resulting in smoke when least expected.
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
Ive been using HB line filters for decades on everything from home
electronics, vintage radios scattered around the house, vintage and modern
ham gear including amps, test equipment, etc. It started when I built a very
competitive contest station in the 80's and wanted to keep family and
neighbors out of my hair. It grew once consumer electronics became a scourge
and I became obsessed with a clean AC line as well as what was coming in on
feedlines and control cables.
Large full house MOV's are installed in the mains box right after the 200A
breaker.
Carl
KM1H
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