tedj@hpcilzb.HP.COM (Ted Johnson) (08/15/88)
I came in to work Fri. to see my Unix box belly-up. The power outlet had shorted together and was now putting out 204v instead of 120V (according to the electrician). Fortunately the fuses blew, so everything survived. But it was a pretty horrible experience nonetheless. But it makes me wonder..., WHY DOESN'T MY SE HAVE A FUSE????? Seems like the $.50 that a fuse costs would be worth it! Maybe someone at Apple can answer this...? Of course, I am protecting my SE with a Telemax surge protector, but I know of lots of people who just plug their puppy into the wall and hope for the best. -Ted "I've seen them crash *and* burn and sizzle too!"
svpillay@phoenix.Princeton.EDU (Kanthan Pillay) (08/16/88)
In article <870209@hpcilzb.HP.COM> tedj@hpcilzb.HP.COM (Ted Johnson) writes: > >I came in to work Fri. to see my Unix box belly-up. The power outlet >had shorted together and was now putting out 204v instead of 120V >(according to the electrician). Fortunately >the fuses blew, so everything survived. But it was a pretty >horrible experience nonetheless. > >But it makes me wonder..., WHY DOESN'T MY SE HAVE A FUSE????? >Seems like the $.50 that a fuse costs would be worth it! >Maybe someone at Apple can answer this...? > > >Of course, I am protecting my SE with a Telemax surge protector, >but I know of lots of people who just plug their puppy into the >wall and hope for the best. > >-Ted "I've seen them crash *and* burn and sizzle too!" For shame, Ted. How dare you compare a pathetic Unix box to your SE? (-: Seriously though, my understanding is that the SE will automatically adjust to voltages between 110 and 240 volts. The 204 volts would probably be a summer breeze to your SE. Of course I could be wrong. Kanthan. -- Do I really need a signature?
johns@calvin.EE.CORNELL.EDU (John Sahr) (08/17/88)
In article <870209@hpcilzb.HP.COM> tedj@hpcilzb.HP.COM (Ted Johnson) writes: > [] >But it makes me wonder..., WHY DOESN'T MY SE HAVE A FUSE????? >Seems like the $.50 that a fuse costs would be worth it! >Maybe someone at Apple can answer this...? I hope that someone at Apple will answer. However, the power supply in your SE or Mac II is unusual in that it will "eat" 110-240 volts without flipping any switches. It is a "switched-mode" type of power supply. We have run our Mac II on US 60 Hz 110 volt, and then plugged it into the Scandinavian power grid (50 Hz, 220 Volt). We did nothing but plug it in both times. Because the transistor/diode switch would probably blow up faster than any fuse if it failed, it might be pointless to put even a $.50 fuse in the SE or Mac II. There is very likely to be DC isolation from the AC grid in the form of a small, high frequency transformer. I am just guessing, based on what I've learned about these type of supplies. I am not affiliated in any way with Apple. John Sahr (johns@calvin) [opinions expressed are my own alone]
gnome@olivey.olivetti.com (Gary) (08/17/88)
From article <561@calvin.EE.CORNELL.EDU>, by johns@calvin.EE.CORNELL.EDU (John Sahr): > Because the transistor/diode switch would probably blow up faster than any > fuse if it failed, it might be pointless to put even a $.50 fuse in the > SE or Mac II... > I am just guessing, based on what I've learned about these type of supplies. > John Sahr (johns@calvin) [opinions expressed are my own alone] Fuses are very good in preventing certain types of failures from becoming fire hazards, but in general, they won't really protect a hell of a lot in a computer system. The semiconductors will blow much faster than a fuse. Don't forget, if I remember correctly, a fast-blow fuse will blow in 1 minute at 200% overload, others are much tougher to blow-out. They're great for dead-shorts (impulse power >10x the rated amount). Even with this point of view, I still over-fuse anything I have design responsibility on. I also believe in power-supply crowbar circuits -- a lot. Gary
paulf@Jessica.stanford.edu (Paul Flaherty) (08/17/88)
In article <27429@oliveb.olivetti.com> gnome@olivey.olivetti.com (Gary) writes: >Fuses are very good in preventing certain types of failures from >becoming fire hazards, but in general, they won't really protect >a hell of a lot in a computer system. The semiconductors will >blow much faster than a fuse. That's what crowbars are for. The firing time of a modern SCR is such that most overvoltage conditions can be clamped off before they damage the semiconductor stuff. A quick explaination for those who want to know: A crowbar circuit is designed to protect equipment from a failed power supply. It works by detecting an overvoltage condition and then shorting out the power supply; the short draws enough current to blow a fuse. The advantage of this technique is that an overvoltage condition lasts only for the trigger time of an SCR, which is small enough to protect most semicondutor circuitry. A power supply without a crowbar and fuse is a risky proposition. -=Paul Flaherty, N9FZX | "There is no distinctly American criminal class ->paulf@shasta.Stanford.EDU | except Congress." -- Mark Twain
flash@ee.qmc.ac.uk (Flash Sheridan) (08/18/88)
I happen to know that if your Mac+ hard disk explodes, your modem port dies. If your mainframe is struck by lightning, and your printer port is attached to it, it explodes too. Be careful to make sure both these things happened under warranty. (We pay double for our Macs here, but it sometimes saves the cost of a motherboard.) From: flash@ee.qmc.ac.uk (Flash Sheridan) Reply-To: sheridan@nss.cs.ucl.ac.uk or_perhaps_Reply_to: flash@cs.qmc.ac.uk
matthew@sunpix.UUCP ( Sun NCAA) (08/19/88)
In article <870209@hpcilzb.HP.COM>, tedj@hpcilzb.HP.COM (Ted Johnson) writes: > > I came in to work Fri. to see my Unix box belly-up. The power outlet > had shorted together and was now putting out 204v instead of 120V [stuuf deleted] > But it makes me wonder..., WHY DOESN'T MY SE HAVE A FUSE????? > Seems like the $.50 that a fuse costs would be worth it! > Maybe someone at Apple can answer this...? All Apple Computers use a switching power supply which has a natural feature of shutting down the internal power supply oscillator if the "OUTPUT" should become shorted, there-by stopping power transfer across the small transformer. This is all that is required by UL, and makes the machine much more reliable since it doesn't contain a fuse, which could fail (come on now, how may times have you replaced a fuse, Just because it blew?). -- Matthew Lee Stier (919) 469-8300| Sun Microsystems --- RTP, NC 27560| "Wisconsin Escapee" uucp: {medusa, rti}!sunpix!matthew |