johnim@euler.Berkeley.EDU (John Im) (10/01/90)
Okay. This is my first time posting, so please excuse any and all irregularities. My problem is that there seems to be only one power line feeding all the rooms (3 of them) in the section of the house I'm in. What this means, is that whenever a space heater is turned on, the line voltage drops. I measured it this weekend, with two space heaters on (in different rooms), and the line voltage dropped by 15-20 V. Surprisingly, my Mac was still functioning as usual. I had it printing a document and a few other things to see if anything would be affected, but everything was fine. So what's the problem, you ask? Well, I'm wondering if this is causing any undue strain on the power supply. I'd sure hate to have to replace it (I just bought the Mac this summer). By the way, someone suggested I buy a UPS, but that is not an option. Since the heaters stay on for 5-15 min periods, depending on how cold it is, I'd run down the battery on a 500VA UPS pretty fast. Now, there are some with a step-up transformer that will keep the voltage at a steady 120V, but they are a bit out of my price range right now. So can anyone tell me if this'll burn out my power supply or something? Anyone from Apple out there? Thanks. - John
russotto@eng.umd.edu (Matthew T. Russotto) (10/02/90)
In article <28368@pasteur.Berkeley.EDU> johnim@euler.Berkeley.EDU.UUCP (John Im) writes: >Okay. This is my first time posting, so please excuse any and all >irregularities. > >My problem is that there seems to be only one power line feeding all the rooms >(3 of them) in the section of the house I'm in. What this means, is that >whenever a space heater is turned on, the line voltage drops. I measured it >this weekend, with two space heaters on (in different rooms), and the line >voltage dropped by 15-20 V. Surprisingly, my Mac was still functioning as >usual. I had it printing a document and a few other things to see if >anything would be affected, but everything was fine. Mac II power supply is rated from 90-170V (and another range around 220). Check the specs on the mac model you have--- if it is similiar, you probably don't have any problem. (Specs should be in the owners manual). >By the way, someone suggested I buy a UPS, but that is not an option. Since >the heaters stay on for 5-15 min periods, depending on how cold it is, I'd run >down the battery on a 500VA UPS pretty fast. Now, there are some with a >step-up transformer that will keep the voltage at a steady 120V, but they are >a bit out of my price range right now. Wouldn't a UPS (true UPS, not SPS) deplete more slowly if it was getting power off the line? (i.e. since a true UPS is always running off the battery, a drop in line voltage would merely make it charge less efficiently). >So can anyone tell me if this'll burn out my power supply or something? >Anyone from Apple out there? -- Matthew T. Russotto russotto@eng.umd.edu russotto@wam.umd.edu .sig under construction, like the rest of this campus.
esf00@uts.amdahl.com (Elliott S Frank) (10/12/90)
>In article <28368@pasteur.Berkeley.EDU> johnim@euler.Berkeley.EDU.UUCP >(John Im) writes: > >>By the way, someone suggested I buy a UPS, but that is not an option. Since >>the heaters stay on for 5-15 min periods, depending on how cold it is, I'd run >>down the battery on a 500VA UPS pretty fast. Now, there are some with a >>step-up transformer that will keep the voltage at a steady 120V, but they are >>a bit out of my price range right now. > >>So can anyone tell me if this'll burn out my power supply or something? >>Anyone from Apple out there? It's not a problem. I've been doing some reading on power supply design, and most of your concerns *are* non-issues. Modern switching-mode power supplies only draw current at the peak (and valley) of the voltage cycle. If there's sufficient voltage for the power supply to operate, it will be able to draw current. Your mac is really looking for the 5v that comes out of the power supply, not the crud that you are feeding the power supply. If you've got a Plus (I deleted the orginal article), you do have a problem, as the Plus has an analog supply instead of a switcher. Poor line voltage regulation is not good for the health of the Plus' power supply. A UPS just puts some combination of battery, inverter, and switching in from of the mac's powr plug. If the wall voltage is sufficient to keep the battery charger operating, you won't be drawing down the UPS battery. A UPS rated at 500 VA for 10 minutes will probably drive a mac for longer than that, depending on your display. Take a look in the new "Hardware Specifications ..." book -- I remember (dimly :-)) that all macs are under 200 VA rated. The highest current load is drawn when the mac is turned on. After that, it's much less. A voltage stabilizer is interesting, but given that all modern (post-Plus) macs have switching-mode power supplies, it adds no real value. A surge suppressor (the higher rated the better: there are surge suppressors rated for 300 joule surges) is worthwhile insurance. If one of those heaters has a chattering thermostat, it will probably toss spikes onto the line with abandon. The best surge supressor that you can afford will save you a visit or two to the repair shop over the winter. -- Elliott Frank ...!{uunet,sun}!amdahl!esf00 (408) 746-6384 or ....!esf00@amdahl.com [the above opinions are strictly mine, if anyone's.] [the above signature may or may not be repeated, depending upon some inscrutable property of the mailer-of-the-week.]