[Boatanchors] MOV Choice for 120 VAC and 230 VAC

[Ron]

There is no 'right' answer. On the one hand, you don't want 
the voltage rating of the MOV to be too high so it won't 
provide real protection. OTOH, you don't want it too low,
so a single spike will blow the MOV. 

My personal rule of thumb is to use 300V MOVs across the 
power line. By extension, I'd use 600V MOVs across 230V 
power lines. (MOV voltage rating above refers to peak 
voltage. Line voltage is in RMS).

As to the energy rating, the higher the better. The rating, 
stated in Joules, refers to maximum energy the MOV may 
dissipate each time it 'fires'. In addition, MOVs do not live 
forever. Their life is a complex function of their past --
number of times and amount of energy dissipated each time.

BTW, paralling MOVs provides increased energy rating -- 
in the ideal case, the sum of the energy ratings. In real life, 
rather less.

- Ron




________________________________
From: LEE BAHR <pulsarxp at embarqmail.com>
To: boatanchors at mailman.qth.net
Sent: Tue, March 16, 2010 2:10:01 AM
Subject: Re: [Boatanchors] MOV Choice for 120 VAC and 230 VAC

Is it wise to install a modern MOV across the primary of a boatanchor's 
power transformer input coil?  If so, which ones should I buy at Mouser out 
of the zillion of them for sale there.  (I'd be interested in both those 
used on 120 volts AC well as 230 volts AC).

I can't figure out which to buy.  Thanks for any input.  (I need to place an 
order at Mouser for some other stuff and will ad MOVs at the same time).

Lee, w0vt 

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