MOV's (was Re: Spark Gap)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Pyrotrons-at-aol-dot-com>

Hi all....

MOV = Metal Oxide Varistor.

They are placed directly across a component that is to be protected.

Usually little colored disk-like things, with 2 wire leads that can be 
soldered.

The special metal oxide in them "clamps" the voltage when it reaches a 
certain point, much like a very small lightning surge arrestor (they are 
filled with metal oxide also....lots of it). Say like on a 14.4kV 
pig.......you'll probably find a 15kV arrestor on it? (not sure about this). 
Anyhow, the arrestor starts conducting at 15kV. So when lightning hits it, it 
conducts, and shorts the strike to ground instead of it going through a 
transformer winding to ground (frying the thing).

And so a small MOV for stuff like NST's, MOSFET transistors (Aron uses GOBS 
of these for mosfets) and thousands of other things. I've seen them rated 
from 10V up to 480V.

Not sure about the specifics of an MOV "conduction" curve, but I know they 
start conducting at a certain voltage, then quit conducting when the voltage 
goes back down.

Fantastic devices.

Justin Hays
KC5PNP
Email: pyrotrons-at-aol-dot-com
Webpage: www.hvguy-dot-com