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Re: [Amps] MOVs

To: amps@contesting.com
Subject: Re: [Amps] MOVs
From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
Date: Fri, 24 Jan 2014 12:14:37 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>
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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