On 1/24/2014 1:37 AM, Jim Brown wrote:
On 1/23/2014 10:02 AM, Carl wrote:
Inductive industrial equipment use big MOV's for spike suppression on
single and 3 phase lines of many voltages.
Again, the problem comes with interconnected equipment when the MOV
dumps the spike onto ground. Won't repeat previous email. :)
We had some 50,000 Joule MOVs "across" a pair of back to back 1200 amp
SCRs. The "chip in those SCRs was no chip. It was a round slice of
Silicon about 1.5 inches in diameter. The gate was easily seen. When
one of those MOVs failed, it was a spectacular ball of fire and Loud.
The MOV were shaped like a trapazoid about 3/4 of an inch thick on a
1/8th inch Aluminum plate. The MOV would vaporize. There were no
particles flying around. The wire connections which were either #6 or
#8 would be pointing straight out as if they had been pulled...hard! The
only thing left was that Al back plate.
I never saw a pair of SCRs survive, so I'm not sure what good they did.
I use a pair of large Littlefuse MOV's as a whole house limiter and
right at the main panel.
That's an excellent application.
Lines that are used with electronics when on generator power are also
treated with MOV's and .01/2KV buffer rated disc caps.
They would be far more expensive, but wouldn't back to back zener diodes
, or strings of heavily rated zeners be more effective?
I have a bunch of stud mounted zeners in the junk box and it seems like
that'd be a good place for them.
73
Roger (K8RI)
>>
Some things that are common practice are bad practice. Like "The Pin One
Problem" -- cable shields that go to a circuit board rather than to the
shielding enclosure. Like power cords whose green wire goes to the
mounting lug of a terminal strip that is insulated from the chassis by
paint. I'm sure you can cite plenty more examples. :)
73, Jim K9YC
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