THE MOVS used in surge protectors have a normally high resistance to line voltages but then goe to a very low resitistance during high voltage surges ( before thay wear out ). jco
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of graywolf Sent: Friday, June 15, 2007 10:02 PM To: Pentax-Discuss Mail List Subject: Re: Lightning proof? Didn't think I was going to do a surge protector tutorial <grin>. On the cheap surge protectors about the only way is to take them apart and use an ohm meter on the MOV. On the expensive ones there is usually a green LED or something that tells you it is still good, if it goes out or turns red the MOV is bad. Please note that some of the cheap ones have a LED, but as far as I know all it tells you is that there is power at the plug. A MOV, like any varistor has a non-linear resistance, as the current goes up the resistance goes up exponentially damping the surge. If the surge is beyond the capability of the MOV it should blow acting as a fuse. The real expensive ones also supposedly have MOV's that work the opposite shorting the surge to ground as well. Sometimes that surge can peak faster than the MOV can react and a smaller surge gets through, and sometimes, not often, they can fuse instead of open when they blow. That is why I like to use a couple in series. The real reason for the extra one on the laser printer is to prevent back surges from damaging things between it and the other surge protectors. Laser printer fusors tend to pull a lot of current suddenly causing a surge although it is not as severe as a power-line is likely to be. Please note that I am living in the mountains and thunderstorms walk through this valley very frequently. When I lived in the lowlands I never actually experienced lightning damage to my equipment. And the recent damage was to network stuff which was not protected. 3 other of the 5 apartments in the building had more damage than I did. Luckily no fires. -- graywolf http://www.graywolfphoto.com http://webpages.charter.net/graywolf "Idiot Proof" <==> "Expert Proof" ----------------------------------- Feroze wrote: > Thanks, didn't know that...how do you test if a surge protector is > working other than the obvious way... > > Do UPS's also have mov's? > > Feroze > > J. C. O'Connell wrote: >> mov's get "used up" (not quite same thing as going bad, since this is >> inherent ) due to a number of small surges or one big one, leaving >> you with NO mov in effect. jco >> >> -----Original Message----- >> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf >> Of graywolf >> Sent: Friday, June 15, 2007 7:19 PM >> To: Pentax-Discuss Mail List >> Subject: Re: Lightning proof? >> >> >> Sometimes a surge partially gets past the first MOV. Also sometimes >> MOV's go bad. Just extra insurance in other words. >> >> MOV is short for Metal Oxide Varistor and is is the semiconductor >> inside the unit that actually deals with the surge. >> >> > -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
