On May 29, 12:56 pm, Doug McNutt <[email protected]> wrote: > Analysis: > ... > The real problem with MOVs is that they will only handle a few hundred such > pulses > in their lifetime. Some manufacturers add a green LED to their boxes as an > indicator that the MOV has been damaged too many times.
Numerous pulses applied to an MOV only degrade it. A degraded MOV is not reported by that LED. That LED indicates the MOV was subjected to a surge massively in excess of what the manufacturer defines acceptable. A failed MOV also has its voltage changed by 10% (as stated in manufacturer datasheets). MOV is still functional and that light does not report the degradation. That light can only report a completely unacceptable failure - a one time massive current in excess of the manufacturer's Absolute Maximum Parameters. LED can only report one type of failure because the MOV was grossly undersized. Using same datasheets, a 270 volt spike on a 200 joule MOV for 1 millisecond will degrade that MOV in two pulses. Obviously that 270 volts spike will be less when conducted through that MOV. 270 volts for 1 millisecond through a light bulb is not a valid analysis. Your analysis must put that voltage across the MOV. Since current limit for that 270 volt spike is not known, then insufficient information exists to perform an analysis. This worst case analysis for a 200 joules MOV can only withstand two 270 volts spikes - from manufacturer datasheets. Surges are current - not voltage events. Voltage will rise as necessary to conduct that current. Two kilovolt isolation in a network card or power supply is not exceeded if that current has some other path to earth. Just like the church steeple. Lightning voltage (and therefore energy dissipation) is minimal on a church steeple if conducted to earth by Franklin's invention. 'Whole house' protector also does diverting to earth for a computer's power supply. UPS does not. ATX power supply (like all appliances) has internal protection. But that protection can be overwhelmed (voltage will increase) IF surge current is not diverted to earth. A dike cannot stop a flood. But a dike works if the flood has a downriver path. Same principle applies to a computer's power supply when downriver is a properly earthed 'whole house' protector. Bottom line: a protector is only as effective as its earth ground. Which is why all facilities that cannot suffer damage connect protectors short to an even better earthing electrode. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed Low End Mac's G3-5 List, a group for those using G3, G4, and G5 desktop Macs - with a particular focus on Power Macs. The list FAQ is at http://lowendmac.com/lists/g-list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/g3-5-list?hl=en Low End Mac RSS feed at feed://lowendmac.com/feed.xml -~----------~----~----~----~------~----~------~--~---
