shawn@eddie.mit.edu (Shawn F. Mckay) (05/29/91)
Howdy. We run a fairly average size (perhaps medium) computer room here, and we would like to find a power cutoff that when the power feed to the machine room "dips", or drops altogether, it will finish the dip by cutting power, and remain in this state until a human turns it back on. Has anyone heard of anything like this? We know about power conditioners for about $9,000.00, but need only this simple function. There *must* be something out there that does this, we would dearly love a pointer. Thanks for any help, - Shawn
jgd@Dixie.Com (John G. DeArmond) (05/29/91)
shawn@eddie.mit.edu (Shawn F. Mckay) writes: >Howdy. We run a fairly average size (perhaps medium) >computer room here, and we would like to find a power >cutoff that when the power feed to the machine room >"dips", or drops altogether, it will finish the dip >by cutting power, and remain in this state until a >human turns it back on. >Has anyone heard of anything like this? We know about >power conditioners for about $9,000.00, but need only >this simple function. There *must* be something out >there that does this, we would dearly love a pointer. This task is either trivially easy or just plain easy depending on how fast you want the detection to be. The trivially easy case is if you want to drop the line when power dips enough to allow a relay to de-energize. I've built a blue-million so-called "green boxes", so named because I used an illuminated green oiltite machine pushbutton as the reset. I usually build the circuit into a small junction box with a duplex outlet on one side and a power cord on the other. The circuit is based around an ordinary NEMA motor contactor of the appropriate rating for the load and equipped with a seal-in contact - standard 3 wire control equipment. The circuit is as follows: Line main contact -----------------| |------------------- to load | | |------| |--------| manual pushbutton | | |----------| |----| seal-in contact | relay coil | | --------------------------------------- to load neutral For voltages other than 115, you would need the appropriate pilot voltage supply, typically through a small instrument transformer. The equipment is energized by momentarily pushing the pushbutton which energizes the contactor. This applies power to the load and also makes up the seal-in contact which then supplies current to the contactor coil. The pushbutton is released and the relay is held in by current flow through the seal-in contact. When power drops long enough for the contactor to open, the seal-in contact also opens which maintains the contactor in the open state until the button is again pressed. I recommend using a lighted pushbutton and hooking the lamp across the contactor coil so that it is illuminated when the contactor is closed. If you must catch single cycle failures or small multiple cycle failures, then a bit more complicated circuitry is called for. The easist is to pick up the power fail line if available from the power supply and operate a pilot relay connected to the above configuration such that the contactor is opened if the power fail lead goes active. If that signal is not available from the computer, dropped cycle detectors are available from companies that make switchboard instrumentation such as GE, Westinghouse, and Ohio Semitronics. I'm rather fond of OS's products. You can find 'em in the EEM or in a Thomas Register. I should add that the green box solution has solved the overwhelming majority of power line induced failures on the equipment connected to the boxes. It completely eliminates the stress from multiple-reclose breaker chugging which is the most common gross power line problem. One last note, you can buy the green box functionality in a couple of brands of surge protection. One brand that comes to mind is the Panamax. This is a good supressor because it comes with a lifetime $1 million insurance policy against any attached equipment being damaged by surges. Hope this helps, John -- John De Armond, WD4OQC | "Purveyors of speed to the Trade" (tm) Rapid Deployment System, Inc. | Home of the Nidgets (tm) Marietta, Ga | {emory,uunet}!rsiatl!jgd | "Vote early, Vote often"