A typical cause of "sags" or "brownouts" (these are bvery inaccurate terms) is reclosers on big power substations. A recloser is something like a large circuit breaker. If it senses a fault, it will interrrupt the power for a certain amount of time, and then reclose (reconnect). If the fault is still there, the recloser interrupts again, for a longer time. Hopoefully the fault will clear in up to three tries. The most common types of faults in power systems are squirrels, birds, and sticks that momentarily become barbeque. These faults clear themselves quickly. A tree branch falling across a power line in a wet rain could easily short it for a bit. If the power system simply threw a breaker when these faults happened, we'd never have any power at all for very long Every power system company sets their reclosers differently. A local power engineer told me that in my city, reclosers are set to interrupt for 64 milliseconds, then a few hundred milliseconds on the second throw, then seven seconds on the third try. After that they open. THIS HAS MAJOR IMPLICATIONS FOR YOU POWER SUPPLY DESIGNERS. Can your system ride through a 64 millisecond dropout without hiccupping? I test all my appliances with a "brownout generator" (again, mis-named, it generates drop-outs) that interrupts power from 64 milliseconds to 7 seconds repeatedly. THe appliance must not energize a heating element when in an idle state. I don't mind if it reboots, but I do mind if Cyrrillic characters appear on the LCD display that is supposed to display English, or the front panel controls lock up. -- Lawrence Lile Senior Project Engineer Toastmaster, Inc. Division of Salton, Inc. 573-446-5661 voice 573-446-5676 fax Micro Eng Sent by: pic microcontroller discussion list 04/25/2003 12:54 PM Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: Subject: [EE]: AC power surges/sags Does anyone know how many cycles are typically affected when there is a power surge on the AC line or a sag? I'm guessing it depends on how severe the surge is...but in the case of a sag, where alot of stuff is being powered up at the same time, how many cycles would depend on what the load is...inductive/capacitve and what it takes to recover. So in the case of a PC power supply...what would it look like? _________________________________________________________________ Help STOP SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body