Classic Computer Magazine Archive COMPUTE! ISSUE 131 / JULY 1991 / PAGE 73

What to do when the lights go out? (PC hardware tips) (column)
by Mark Minasi

Last month, I talked about power protection and some lower-cost power-protection devices. This month, I'll finish the topic with a discussion of battery-backup devices.

In addition to protection from short power irregularities, you may need backup power. I've lived in a number of places in the northeastern United States where summer lightning storms will kill the power for just a second--enough to erase your memory and make the digital clocks blink. Unlike the devices I discussed last month, no transformer or MOV (Metal Oxide Varistor) can help you here. You need something that has a built-in battery, something with enough power to carry you through until the juice comes back on, or at least with enough power to allow you to gracefully exit your applications and shut off your computer. To that end, there are two kinds of devices in this category: SPSs (Standby Power Supplies) and UPSs (uninterruptible Power Supplies). Both use batteries, but there's a fundamental difference between the ways they yse them.

Not to Worry?

"Hang on a minute," I hear you cry. "Who needs a UPS? Isn't that overkill?" Actually, I'd say No.

Here's the bad news: Electrical power is getting worse in the United States. Nobody wants a power plant in his or her backyard, coal-burning plants cause acid rain, nukes scare just about everybody, and wind/tide/geothermal/you-name-it alternative sources of energy aren't really going anywhere. We're not building new sources of electricty, but we're continuing to create new drains on the country's power network. Power demand continues to grow, while electrical generation capacity grows much more slowly. The net result is that we're going to see more brownouts, blackouts, spikes, and surges throughout the 1990s.

The good news? Uh . . . there isn't any. The world is changing. Expect power in our country to take on a distinctly Third World look. (How do I know? I was a senior economist with a national laboratory working for the United States Department of Energy for several years in the early 1980s.) From your PC's point of view, electrical power is like air--it soon dies without it, and dirty power makes it sick. That could mean permanent hardware damage, data loss, or momentary misreads.

This all seems strange and counterintuitive because power in the 1980s was fairly clean and reliable, leading to the common wisdom that you just plug your PC into the wall and it'll go. Also, most household appliances are fairly robust about the kind of power they'll accept: Plug a toaster in just about anywhere, and it works fine. A new consensus will develop by the mid 1990s that everyone needs power protection.

UPS and Downs

Your backup options are standby power supplies (SPSs) and uninterruptible power supplies (UPSs). They use fundamentally different approaches to solving power problems. SPSs charge the batteries while watching the current level. (See Figure 1.) While utility power is normal, the SPS is fairly irrelevant, letting spikes, surges, and low voltage pass right through to your PC. A few SPSs have MOVs--the kamikaze components in surge protectors that I discussed last month--but, in general, they do nothing except when the power disappears altogether.

If the power drops, the SPS activates itself and supplies power until its batteries run down. (See Figure 2.) Note well that a fast power switch must occur here, and it's important to find out what the switching time is. Four ms or under is fine. In my experience, 14 ms isn't fast enough.

A UPS constantly runs power from the line current to a battery, then from the battery to the PC. (See Figure 3.) This is superior to an SPS because there's no switching time involved. Also, this means that any surges affect the battery-charging mechanism, not the computer. A UPS is, then, a surge suppressor as well.

A UPS or SPS has to convert the battery's DC current to the AC current that your PC requires. AC is supposed to look like a sine wave. Cheaper UPS and SPS models produce square waves. (See Figure 4.) Square waves are bad because they include high-frequency noise which can hamper your computer's operation. Worse, some peripherals (printers in particular) can't handle square-wave AC; their power supplies burn up. So, when examining UPSs, ask whether they use square wave or sine wave.

A sine-wave UPS is the only way to really eliminate most power problems. The reason everyone doesn't have one is cost; a good one costs over $1,000, like the excellent Minuteman systems from Para Systems (sine-wave MM500/1 UPS--$1,399, AT300 SPS--$339; 1455 LeMay Drive, Carrollton, Texas 75007; 800-238-7272).

Plan B

A decent compromise can be found in a fast (4 ms) square-wave SPS I know I said square waves are bad for your peripherals, but consider this: How often will the SPS actually be providing power? Not very often--remember that it only supplies power when the line voltage drops out, which is probably not a common occurrence. The brief minute or two each month of square-wave power that your peripherals end up getting won't kill them. And you'll save a pile of money over a UPS.

On the other hand, remember that a UPS is always online and so must produce sine-wave output, but UPSs have the benefit of providing surge protection by breaking down and reassembling the power. SPSs don't provide this protection; you still have to worry about surge protection when you buy an SPS, but not if you buy a UPS. So make the choice that your budget allows.

Or you might buy a unique product, called the InnerSource, from PC Power and Cooling Systems (31510 Mountain Way, Bonsall, California 92003; 619-723-9513). The InnerSource replaces your current power supply with a combination power supply and UPS. It's a nifty device--it takes no more space than the power supply that's already in your PC and provides 10 to 15 minutes of backup power. (It also includes a connector to power your monitor.) You get low-voltage protection, surge and spike protection, and blackout insurance--all for $395. This isn't a bad deal (as I said last month, a decent power conditioner would cost $200, and this does a lot more). And while this sounds like a unique idea, every single battery-powered laptop incorporates a similar system--so I suppose you could buy only laptops as a means of combatting power problems. To summarize:

* It it's an SPS, it must switch in 4 ms or less.

* If it's an SPS, square-wave output is acceptable.

* It it's a UPS, it must have sine-wave output.

Power of Misinformation

Shopping for a UPS can be a real education--not in power-protection devices, but in misinformation. You'd think Saddam Hussein's public-relations minister wrote some of the UPS brochures I've seen. One story in particular really highlights what I mean.

A few years ago, a power-protection company--I won't mention any names--ran some full-page ads claiming to have the answer to low-cost power protection: a $200-$300 UPS. Wow, I thought, and called them up to find out more. I was directed to a regional distributor, who took my call and did his best to answer my questions.

"This sounds like a terrific deal on a UPS," I said. "Does it produce sine-wave output or square-wave output?"

"I'm afraid the information I have doesn't include the answer to your question," the distributor's technical manager replied. He didn't have the answers to a lot of other questions, so I started smelling a rat.

So I ventured, "How about the switching time? What's the switching time?"

He perked up, pleased to have the answer to a question. "Four milliseconds," he proudly answered. I replied that he wasn't selling a UPS, but an SPS. His answer? "Oh, you mean it's not an online UPS. Yeah, that's true. It's not an online UPS." I've heard similar dodges from vendors since that conversation, so be careful when examining power-backup products.