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Power surges a problem?

by compuguy / June 9, 2004 5:53 AM PDT

I have a question about small power surges. All the outlets in the room with my computer are on the same circuit. I have a window air conditioner in my computer room. Whenever the compressor starts up or shuts off it seems that there is a small power surge. My desk lamp will flicker for an instant. I do not notice it doing anything to my computer or my monitor. Will these small surges be harmfull to my computer's motherboard and power supply? Should I invest in a UPS with power conditioning?

Thanks,
Kevin

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Since youy don't see any effect on the computer/monitor
by Ray Harinec / June 9, 2004 7:22 AM PDT

it would seem that the computer and monitor's power supply regulators are handling the surge with no problem. HOWEVER, let's consider the transient [it has short period spikes and longer period surges]. At compressor going ON, the inrush current drops the line voltage and as the inrush current reduces to normal run current the line voltage returns to normal smoothly.

The compressor going off can be more problematic. The sudden reduction in current in any wire with a finite inductance can cause large L di/dt voltage spikes [very short period, tens of nanoseconds to microseconds, but very high]. The input power is AC and thus is a sine wave that [for 120 V rms] hits a positive and a negative peak of 120 X 1.414 = + and -170 Volts. The waveform also passes through zero twice per cycle. Thus the instantaneous voltage when compressor goes off can be anywhere between 170 volts and zero and the porential transient can vary all over the place. [believe it or not it can get into the 1000 volt range.]

For these type of spike transients one should have a "surge" protector. Basically that is all that a "surge " protector provides protection for. A real line surge can contain far more energy than these devices can handle. Just get one that has the highest Joule rating [mine are in the 3000 joule range].

The UPS's can protect better against real line surges as opposed to spikes, but more useful for allowing the computer to run through momentary power outages.

The best solution for surges is to use the new power supplies which handle anywhere from 80 volts to 230 volts without the use of a switch. At 240 volts the peak is 340 volts, so using one of these supplies on a 120 VAC input provides huge amounts of protection against long period surges.

Each item has a different purpose, so all three are useful.

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Re:Power surges a problem?
by Willy / June 9, 2004 1:21 PM PDT

It pays to play it safe when its less costly for the long haul. The price of basic UPS and surge strips of quality makes while an investment are there to keep things running smoothly. The headaches you'll save yourself from are worth it. Use several surge device(s) that has a LED in order to know its working, besides the simple surges, there's always the possibility of major surges of unknown status present.

good luck -----Willy

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