[Amps] MOVs

[Roger]

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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