electme wrote:
>
> hi & tfyt,
> i have a project for a 480vac motor & want to use mov's for transient
> protection.
> i have a few epcos 250vac movs
> rather than buy a mov for 480vac
> i was thinking of using 2 x 250v mov's in series
> will this work ?
> i assume that as the cycle rises & it reaches the transient voltage of the
> 1st mov the impedance will change & that the remaining voltage will not be
> enough to change the impedance of the 2nd mov , hence only if the voltage
> is above 500vac will both mov's impedances drop & short any transients
> (which is what i want to use them for).


If you put a resistor in parallel across each
MOV you will get equal volts across each MOV
until they start conducting. Conduction is on
a curve and once they start conducting they
should balance each other within reason.
It's a pretty ugly solution, why do you have
transient problems? Have you considered an
RC snubber? Much higher long term reliability
than a semiconductor. If you do go with the
MOV use a series resistor to soften the blow.
:o)
-Roman

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