Written By: Charles F. Kerchner, Jr., P.E.

Copyright 1984
Charles F. Kerchner, Jr.
All rights reserved
Last revised 13 May 1996

What? You say. Well let me try to explain.

With the proliferation of high-tech plug-in electronic equipment such as personal computers, it has become obvious to people that they only work reliably if the power line you plug them into is reliable and free of spikes, surges, noise, glitches, brownouts, and blackouts. Out of need comes innovation. Therefore, a whole series of new products have been introduced to the consumer - Power Conditioners and Uninterruptible Power Systems (UPS). There are several types of power conditioners - among them spike and surge suppressors or absorbers, EMI/RFI noise filters, voltage stabilizers, and voltage regulators. UPS units come in the continuous on-line type and the standby type. Continuous on-line units are very expensive and are not required for personal computers. With this raft of new products comes a deluge of new specifications and terminology and, unfortunately for the consumer, a lot of misleading advertising. So, how does "What's a Watt" fit into this picture? Well, as you might have guessed, a WATT is an electrical specification and, of course, all of the above mentioned equipment are electrical power devices. The confusion arises when people start advertising and/or promoting in their literature what you are going to get for your buck when you spend it. They know that you don't exactly know everything about what you need when you buy. After all, who can keep up with all this high- tech mumble-jumble anyway. Well, they take advantage of this. They don't lie. They just don't give you all the facts. So here is some information which should help you. A WATT is an electrical term for power, and power is the time rate of doing work. A WATT is not energy, but just how fast you are using energy. A 100 WATT light bulb uses energy twice as fast as a 50 WATT light bulb. This is why it gives more light. Energy is work x time. Remember that the key word is time. Work is the consumption of energy. Energy is what you pay for. The amount of energy in a voltage spike is what does the real damage and the amount of energy a protection device can absorb is the real measure of its worth. Energy is watts x time. The amount of energy a surge protector can absorb without damage is a fixed value determined by the size of the parts the designer specified into the surge protector when he designed it. This energy rating is rated in JOULES. Restating what we've learned. JOULES = WATTS x Time. In other words the JOULE rating is how much power for how long. A typical surge absorbing device like a metal oxide varistor (MOV) may be rated at 50 JOULES which is a constant for a given device. A 50 JOULE device costs more than a ten JOULE device. But look what a clever advertising copywriter can do to the spec game. Aha! says he, everyone knows what a WATT is. Everyone has bought a light bulb. Bigger bulbs give more light. Bigger is better. A little quick math and we can say, WATTS = JOULES/Time. Looking at that equation we can see that by dividing the constant rating, JOULES, by ever smaller and small amounts of time we can make the WATT rating bigger and bigger until it reaches infinity if we want. Thus, he can sell you (for more money) a 20 JOULE device by labeling it a 2,000,000 watt unit while another manufacturer is selling you a 50 JOULE device (for less money). The reason; he only labeled his device a 500,000 WATT unit. The problem is they are using different time bases for the surge duration. A typical surge duration is 100 microseconds. Some manufacturers use one millisecond. Other manufacturers use one microsecond. The answer is obvious. Don't buy surge suppressors based on WATTS. Buy them based on their JOULE rating. All reputable manufacturers know the JOULE rating of their units and it should be on their literature.

Now for another math game with the word WATT. Most computers use transformers and capacitors in their power supplies. These devices, unlike resistors and light bulbs, are very different in their electrical characteristics. Transformer and capacitor operated devices have an additional little known and understood, but never the less very important, spec called POWER FACTOR which is a number between zero and one. This POWER FACTOR represents the ratio of the energy used by the system to the energy required by the system to make it operate properly. Light bulbs use everything put in and thus have a POWER FACTOR of one. Computers do not. To deliver electrical energy to a working device it takes energy in the form of volts and amps. You can have lots of volts and no amps, or vice-versa, and no work is being done. In the U.S., standard electrical systems are rated at 120VAC for small plug-in appliances so the only thing we can vary to get more energy available to an electrical appliance is to raise the ampere rating of the wiring of the power supply feeding the device. Thus, the energy delivering capacity of a power system is measured VOLT-AMPS (VA). A typical household electrical circuit outlet is rated at 15 amps and thus has a rated VA capacity of 120Vx15A = 1800VA. If you exceed this limit for very long you will trip a circuit breaker or blow a fuse. Likewise for a UPS, a 200VA device has more capacity than a 100VA device and if you exceed its' rating you could blow a fuse or maybe it won't work properly when you need it. For a given device the VA rating can be considered constant and larger VA capacity units cost more money. Now, how does the term WATTS fit into this? Well, VA = WATTS/POWER FACTOR where VA is fixed by the equipment energy handling capacity. POWER FACTOR is defined as a number less than or equal to one. It can be visualized as the amount of energy which is actually used out of the total VOLTS and AMPS (VAs) circulating in the equipment. Thus, a computer may require 140VA to operate properly but actually only uses 70 WATTS so the POWER FACTOR is 70/140 = 0.5. Now, with some clever math we can see that WATTS = VA x POWER FACTOR. Now everyone knows that the WATT rating is on the label of every computer. So if you were going to buy a standby power system for your computer you simply read the power rating off the label, say 70 WATTS, then go out and order a 70 WATT standby UPS. Wrong! It is not that easy. Why? Because as we said WATTS = VA x POWER FACTOR. 70W = 140VA x 0.5 for the case of our example computer. So you see we need a 140VA (WATT?) unit to run a 70 WATT computer. Unfortunately a lot of UPS manufacturers are choosing a POWER FACTOR of 1.0 when they advertise their VA devices and are listing the rating in WATTS instead of in VA capacity. They do this because the term WATTS is more familiar to most users than VA and a 1.0 POWER FACTOR gives you the biggest value for the WATT rating. Remember the math game. However, this is confusing because it makes it appear to the consumer that he can buy a smaller unit (cheaper) than he really needs to run his computer. Example: 200VA x 1.0 = 200W. So the UPS manufacturer advertises it as a 200W unit when it really is a 200VA unit and could not handle a 200W computer which would probably require 400VA. So if you add up the labels on your equipment and it adds up to 180W you may feel safe in buying the 200W unit. However, as I said no computer devices have a power factor of 1.0. They have power factors much less than one, usually around .5 to .6. Therefore, if your system is consuming 180W you need a 180/.5 = 360VA standby UPS not a 200W unit. Obviously a 360VA unit costs more than a 200VA unit. Unfortunately, manufacturer's advertising is not making this clear and by doing this, they may be misleading the customer to buying too small a unit. Also, computer labeling may not be clear. A good label should have on it - volts, fuse-amps, volt-amps (VA), watts, and frequency. If specific VA ratings are given on the labels use them--add them up. In the absence of the specific VA spec you can estimate VA on the conservative side by multiplying fuse-amps times the voltage. If the VA rating is not on the label, check the manual in the technical specifications section. Or get a qualified technician to measure your amps under actual operating conditions and multiply that number times the volts to get your required VA capacity. Also, always buy a UPS unit with at least 20% extra capacity.

So, in summation let the buyer beware. Remember, when you order a surge suppressor check out the JOULE rating and when you buy a standby power system know the VA rating of your computer and the VA rating of the standby power system before you order. Don't let them talk WATTS to you, for you could wind up not knowing WHAT you bought, thinking you're getting a bargain but buying too small a unit.

Copyright ©1984
Charles F. Kerchner, Jr.
All Rights Reserved
Last Revised - 13 May 1996
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