On 12/12/2011 9:04 AM, "Carl, WCØV" wrote: > What isn't mentioned is the fact that MOVs are rated by the TOTAL energy > in Joules that they will absorb in their lifetime before they fail. The > energy absorbed from spikes is cumulative and when the rating is > exceeded, boom. > They are also responsible for nasty noise generated by the crowbar > action on the spikes in making them square waves - the sum of all > possible harmonics. I > used to have to deal with these things when customers would use them > in front of servoamplifiers. The noise from the square waves drove us > crazy until we found the MOVs and removed them.
YES! We learned about this in the pro audio world as well, and did the same thing to search out and destroy them. And yes, they are insidious, in everything from copy machines to printers and even power supplies. I found some in an Astron power supply when they failed. The WORST thing about MOV-based protectors is that they CAUSE destructive failures of equipment that is interconnected by low voltage wiring when that equipment is plugged into different power outlets, even when all of the outlets are "protected." That's because they dump the surge into the green wire that serves each outlet, the length, and thus the voltage drop due to the surge to each outlet is different, and the DIFFERENCE blows up the equipment. That's why MOVs are ONLY a good thing at the service entrance. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
