---------------------- multipart/mixed attachment Date: Wed, 5 Aug 1998 23:53:06 -0400 From: "Elian Degen" <degen@telcel.net.ve> Subject: RV:computers * Stuff Snipped *=20 Sorry to correct you, it comes from turning it on and of, but it is not = a thermal shock, it is a rapture effect, it is the same principle used = in the old car=B4s ignition system, ( the ones that used points in the = distribuitor ) whenever you open a circuit there is an arc that produces = a peak of very high voltage and low amperage, and that is fatal for all = IC=B4s (integrated circuits) as it is static electricity, that is why it = is very important to have a voltage regulator, a good grounding and use = the computer switch to turn it off ( computer switches are designed to = send any arc to ground. * More Stuffed Snipped *=20 Jory Writes: I don't normally get into debates on the Internet because it's usually a = waste of my time however the above statement is one of those "Urban = Legend" things that circulate around and serve only to misinform the = general public. I'll leave the piano stuff to you folks, since I'm no = expert on pianos, however, as an electrical engineer with 15 years of = experience I can say without hesitation that the statement above is = false. The affect Elian is referring to is referred to in engineering circles = as "Inductive Kick". I've never heard of "rapture effect" outside of = discussions of religion. From high school physics you might remember = that the voltage across an inductor is the inductance in Henry's times = the time rate of change of current or di/dt. When you open a switch the = current tries to go to zero instantaneously meaning di/dt goes to = infinity. In practice the voltage doesn't do to infinity because there = are no perfect inductors in real life. Another way to think of it is that an inductor is surrounded by a = magnetic field. As the current is shut off the magnetic field collapses = causing a very large voltage to appear across the inductor much like a = changing magnetic field in a generator induces a current in the rotor = winding. You may also remember something from physics about how = inductors try to keep current constant and capacitors try to keep = voltage constant. All of these are saying the same thing. You all have witnessed "Inductive Kick" in action. Have you every = noticed how the lights get really bright momentarily when older = refrigerators, air conditioners, power equipment, etc are turned off? = That's inductive kick in action. You might also have seen arcing in the = switch when you shut off a power saw or some like that. You might also = have noticed that certain relays, switches, etc are rated for "20 Amps, = 10 Amps Inductive". This is because the inductive kick tends to eat the = contacts of the switch as the voltage goes up and the switch arcs over. Elian is correct about car ignition, except that all cars even modern = ones use the same principle to generate a spark for the ignition. When = the points close the ignition coil (an inductor by the way) is = "charged", that is a magnetic field is generated around it. When the = points open the inductive kick creates a very large voltage (several = thousand volts) that creates a spark at the spark plug that ignites the = air/fuel mixture in the cylinder. Modern cars use something called an = igniter, instead of points, but the principle is the same. So what does this have to do with computers? No much and that's the = point. If even the computer power supply was very inductive (which for = many reasons mostly having to do with power conservation they are not = really allowed to be inductive) the inductive kick would appear across = the power switch not the electronics. It would be very bad if ANY of = the AC line voltage was present on the components inside the computer. = In fact, Underwriter's Laboratory or other regulatory agency would not = register such a product. There are many, many standard engineering = practices backed up by testing to assure that you, the user, are safe, = and AC line voltage inside the box where they could get onto your mouse = for example is simply not tolerated. You can sleep better at night = knowing that there is a whole set of regulations designed with the sole = intent of keeping the user safe. Study, after study on the reliability of electronic circuits has shown = that temperature cycling is the major killer of electronics. In fact, = Highly Accelerated Life Test (HALT) systems designed to quickly "age" = products to failure rapidly temperature cycle the system being "aged" = while vibrating it. For example, connectors tend to get loose and = oxidize under many temperature cycles. The most reliable parts of your = computer are the semiconductors. To have an IC die is quite unusual. = The mechanical parts usually go first unless the semiconductors are not = properly cooled. Since most computer manufacturers are using HALT = testing, you the consumer, can be assured that it would be very hard = kill your computer by turning it on and off. You are FAR more likely to = have the computer go obsolete than to die. Of course if you're buying a = clone computer from a high school kid that "builds" them in his garage, = then anything could happen. I'm referring to computers made by major = manufacturers. Sorry this turned into another lecture, but I want to do my part to = stomp out this "Urban Legend". I hope I haven't offended you Elian. I = mean no offense. Jory ---------------------- multipart/mixed attachment A non-text attachment was scrubbed... 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