This article originally appeared in TidBITS on 1999-09-20 at 12:00 p.m.
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Don't Interrupt! A UPS Saves the Day

by Adam C. Engst

We've all ponied up hundreds of dollars for utility programs that promise to twiddle the bits on our hard disks or prevent crashes or make us more productive. What would you say if I told you there is a product you can buy for between $100 and $300 that is guaranteed to increase your productivity, prevent crashes and hard disk corruption, and extend the life of your Macintosh and peripherals? Then what would you say if I told you that this product is compatible with every Macintosh and every version of the Mac OS, not to mention any PCs you might happen to have around?

Such a product exists, and although it's not sexy, it will do all the things promised above. I'm talking about an uninterruptible power supply, better known as a UPS (not the folks with the trademark brown trucks).

A UPS increases your productivity by enabling you to work safely on those blustery days when the power flickers at every gust of wind. There have been days when I wouldn't have dared to turn on expensive computer equipment without a UPS. The hours gained during those days add up fast when you're calculating productivity increases, especially when stormy days occur near deadlines.

In terms of preventing crashes and hard disk corruption, anything that eliminates large sags or surges beyond the tolerances of your computer's power supply (not to mention total power failures) can keep your computer running smoothly. I bought our first UPS back in 1992 after losing my main 105 MB hard disk to a power flutter caused by a drunk driver hitting an electric pole. Luckily, I had decent backups, but I still had to replace the hard disk.


Sags and surges that don't exceed power supply tolerances also take a toll on the computer's components. We talk a lot about continuing to use old Macs; one reason they're still running is that we protect them with a UPS.

What Goes UPS... The theory behind a UPS is simple: plug your computer and peripherals into a large battery and then plug that battery into the wall. As long as the power from the wall is present, the battery does nothing. But as soon as the wall power disappears, whether for a fraction of a second or 10 minutes, the battery starts providing your equipment with clean power.

You may be thinking, "Ah, my PowerBook has a battery, so it already has a mini-UPS in it." Yes and no. Any laptop with a battery will work fine when the power goes out, but PowerBooks have no circuitry to filter dirty power or protect from sags or surges. We recently moved Tonya's Power Mac 7600 and its UPS to another part of the house, leaving the PowerBook Duo 230 without a UPS. Now, whenever the power flickers badly, the Duo freezes, even though it continues to run fine if you just unplug it from the wall. Older PowerBooks may work better in similar situations - according to a repair technician at Westwind Computing, the PowerBook 100-series machines ran entirely from battery power and trickle-charged the battery when plugged in. Newer PowerBooks, though, run from wall power when plugged in, switching to battery power only when you unplug them. Another advantage of a PowerBook is that a surge is more likely to damage the AC adapter before hurting the PowerBook itself.

The technology inside a UPS is quite sophisticated. A UPS must be able to switch from wall power to battery power quickly - between two and eight milliseconds - so the computer doesn't notice the changeover. (High-end UPS models run from battery all the time, eliminating even this changeover time.) Almost every UPS builds in surge suppression and line noise filters to ensure that the power reaching your equipment is clean. Some UPS models also have options for protecting your modem and motherboard from lightning strikes that hit local telephone lines. Such telephone line protection reportedly does work for ISDN and DSL connections, but not all UPS models support two-line (four-wire) telephone cables.

UPS and Downs -- We tend not to think much about electric power except when it stops working, but it is more variable than most people realize. You can categorize different types of power issues in at least five ways.



Pick-UPS Sticks -- Choosing the right UPS model for your needs can be tricky. The hardest part is determining the electrical load your computer system will place on the UPS when the power fails. There are two methods you can use to determine load. The easy way is to use something like the APC UPS Selector, which recommends UPS models based on the equipment you have.

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Alternatively, look on the back or bottom of each of your devices for power draw ratings in either amps or watts. If power draw is listed in amps, multiply it by your line voltage (120 volts for North America, 230 volts for Europe, etc.) to find the volt-amp (VA) load. If the power draw is instead listed in watts, multiply by 1.4 to find volt-amps. The problem with this manual calculation is that manufacturers tend to be conservative and publish the maximum power draw possible, which would in turn cause you to buy a larger UPS than necessary.

If you're considering buying powerful UPS models to run multiple computers, note that it can be more cost effective to buy several lower-rated UPS models and attach fewer devices to each UPS. If nothing else, every UPS has a limited number of power outlets, and the AC adapters used by some peripherals tend to block multiple outlets. You can buy an inexpensive power strip to add more outlets, but the UPS manufacturers don't recommend plugging a surge suppressor into a UPS. It is acceptable to plug a UPS into a surge suppressor if you have extremely dirty power and wish to filter some of the worst surges and spikes before letting them through to your more-expensive UPS.

Some UPS models also provide one or more outlets that have surge protection, but aren't backed by the battery. That's so you can attach equipment like a laser printer to a UPS, something that's otherwise prohibited. A laser printer in use draws enough power to overload the UPS just when you need it the most. Plus, laser printers can cause power fluctuations, so you don't want them on the same side of the surge suppression as the rest of your equipment.

UPS batteries last about five years, after which they must be replaced. Battery replacement should be relatively easy in modern UPS models, but it may be difficult or impossible in older models, as was the case with my first UPS, which is now just a heavy power strip. Many of the sites I researched recently when buying batteries for my cell phone and camcorder also sell UPS batteries (see "Finding the Power Online: Buying Batteries" in TidBITS-494).

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Finally, you might wonder what happens when the power fails when you're not around to turn off your equipment. As soon as the UPS can no longer provide the necessary power to your equipment, it shuts off, and you lose all unsaved work. That's not good, but at least the UPS continues to filter power and won't turn on again until it can provide sufficient power. Modern Macs won't turn on automatically after a power failure unless you set them to do so with the Energy Saver control panel's Server Settings preferences. In some older Macs, use the Auto Power On/Off control panel instead, and in some still older soft-power Macs, you could lock the power button on by pushing in and turning it with a screwdriver.

There is software that notices power has failed and gracefully shuts the Mac down. APC includes free PowerChute software that can shut down a single Mac. Best Power's NetWatch Basic software costs $99, and Powerware has LanSafe III, which is free with several UPS models and can gracefully shut down a Mac, monitor voltage, and send notification of problems via email. There may be other packages, but most power monitoring software has been developed for Windows and Unix, with Macintosh versions being uncommon.


However, Tripp Lite has just announced Macintosh software that promises to allow users to view operating conditions, load, capacity, and other UPS information within a graphical interface. Macintosh users will also reportedly be able to set a shutdown delay to work through short power failures, perform a test of the UPS, reboot the UPS, and toggle outlets from the Mac. The software is free with all of Tripp Lite's UPS models. Future enhancements for the software include native USB support (they currently convert from serial to USB) and network management so you can manage multiple UPS devices on your network.


Finally, there's the question of which brand of UPS to buy. APC seems to be the most popular manufacturer, to judge from anecdotal evidence, with Tripp Lite also being well-known. Other UPS brands I've seen include Best Power and Powerware (formerly known as Exide), and Yahoo lists even more. Prices are generally comparable across brands, with most smaller UPS models between $100 and $300. When you're ordering a UPS, keep in mind that they're heavy, so shipping costs can add up fast.

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I realize this is a great deal of information to internalize, so here's a quick summary of the questions to ask while researching:

Setting It UPS -- When you receive your UPS, it's a good idea to plug it in and let it charge before attaching your equipment (my APC Back-UPS 600 recommended a 6 hour charge). Even though the UPS may ship fully charged from the factory, there's no telling how long it has sat in a warehouse.

If you want, you can use the power switch on the UPS to turn your entire system on and off; the surge suppression capabilities of the UPS are active even if the switch is off.

If you don't need to use your computer during violent localized thunderstorms or times when you know the power will fluctuate, it never hurts to unplug the UPS - and thus all of your equipment - from the wall. We also do that when we travel for extended periods, since you never know what might happen while you're away. All of the UPS manufacturers insure your equipment against power-related damage, but who needs the hassle of replacing an entire system and restoring files from backup?

My UPS beeps to indicate a power problem about once every two weeks. Sometimes I see the lights dim briefly at the same time; other times the UPS's warning is the only indication that something has happened. Once every few months, we lose power entirely, at which point I save open documents and shut off my power-hungry monitors. If the power doesn't return after a few minutes, I perform a blind shutdown by pressing the Power key and then Return. In times like those, I remember just why it is that I've made sure that every desktop Mac we own has a UPS. Keep the power flowing - use a UPS.

[I'd like to thank Marc Sarrel <> for starting the discussion on TidBITS Talk that finally prompted me to write about this important topic and for contributing the results of his research.]