Re: IIc keeps tripping the circuit breaker

[mjmahon@aol.com (Michael J. Mahon)]

Tom Zuchowski replied:

>"Michael J. Mahon" <mjmahon@aol.com> wrote in message
>20020810231829.26975.00003981@mb-fi.aol.com">news:20020810231829.26975.00003981@mb-fi.aol.com...
>> Tom Zuchowski replied:
>>
>> >Uh, I suppose they turn into black smoking charcoal by opening up? I
>would
>> >have supposed that was a result of the heat generated from a shorted
>> >condition . . .
>>
>> More likely from absorbing a significant triansient.  They are supposed
>> to convert that energy into heat.  Of course, where I live, we don't have
>> thunderstorms to speak of, and I don't plug them into an elevator circuit,
>> so there isn't much to absorb.  ;-)
>>
>.aol.com/MJMahon/
>
>That is not my understanding of what MOV's do, but I don't doubt that I
>could be wrong. I don't understand why they are mounted across hot and
>neutral (or ground) if their purpose is to convert a transient to heat. I
>thought their purpose was to shunt the transient to ground, which will of
>course generate a lot of heat if the transient is big enough.

MOVs have a high resistance until their voltage threshold is exceeded,
when they begin to exhibit a low resistance.  The purpose is to shunt
regulate voltage spikes in excess of their rated voltage, but with total
energy less than their rated energy absorption capacity.

A transient can come across line and neutral or it can be on one or both
relative to ground.  This is why "better" surge supressors (absorbers)
have 3 MOVs.

They can only absorb a modest amount of energy (which is their
rating in joules).  But, in some percentage of cases, they will absorb
enough of the energy to spare the line filter capacitors or the diode
bridge in your power supply.  ;-)

-michael

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