Got an APC Smart-UPS? Measure real power with it.

Discussion in 'Power Supplies' started by NeoPTLD, Jun 28, 2007.

1. NeoPTLD Platinum Member

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When people are shopping for PC power supplies, most of them look at watts and maybe brands. While the max power is important, its important to know how much power you're really using in steady state for sizing UPS.

If you already have an APC Smart-UPS, you can measure power with it. It's difficult to measure AC power. Before you say, Volt x amps = watts, let me say this only applies to DC.

All but heaters and regular light bulbs need more sophisticated to calculate wattage.
To measure the REAL power, you need to figure out the area of the product of voltage times the current and average it over time(every sec or so). A power analyzer takes both measurements and calculate the answer and give it to you in real time. They do it digitally or with an analog integrator. Simply put, you can't do it with your multimeter. You can't even measure the current(amps) of a computer power supply unless your meter is a true RMS type.

VA = volts * amps
Watts = volts * amps * power factor, in the case of computers, this is roughly 2/3.

Ok, so you've got a SmartUPS.. Let's say your model is SUA750, which is rated at 500W/750VA. Connect it to a computer with a serial cable. If you don't have one, buy one from APC or make one. You just ought to cut a straight through serial cable (9pin type) and rearrange three wires.

UPS(male connector)<-->PC(female connector)
2-2
1-3
9-5

Open HyperTerminal
Use 2400 bps
Flow control Xon/Xoff
leave everything the default.

enter shift-Y to activate communication port.
enter shift-P and you'll get a true power reading percent.

So, if this reads "45.2", it means your wattage load is 45.2% of the SmartUPS' rated capacity. If you have a 750VA/500W UPS, you would multiply 0.452 and 500 to get 226W load.

I suggest you size the UPS to be around twice the combined idle power of all the devices you want to have on battery backup. This ensures you get a good runtime and prevent the UPS from overloading should the power go out while your computer is heavily pushed with games and such.

#1

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3. Zepper Elite Member

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Much easier to get a Kill A Watt meter (currently on special for Newegg members). Use to specify UPSes, etc.

.bh.

#2
4. NeoPTLD Platinum Member

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That's true, but for those who already have a Smart UPS, this is a feature worth exploiting. All it takes is a serial cable.

#3
5. Modelworks Lifer

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Or you can go to the apc web site and download the powerchute software.
It will tell you remaining run time, voltage input, ups load, etc.

AC utility power
100% battery
Charged
Self test passed 6/25/2007
119 volts input
18 minutes remaing run time. (currently wrong for my ups since I have multiple batteries attached, I have about 2 hours runtime, it bases run time on what the original battery size would be capable of)

#4

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Cool, thanks. I never think of my UPS, it just sits there doing its thing, but I would like to see exactly some the stuff going on there.

Cheers,
KT

#5
7. TungFree Golden Member

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So there is no way of ball parking say 2 hard drives, 2 DVD burners, and a video card/motherboard?
is an LCD monitor drawing power from the power supply? or just the Power protection with battery backup?

How do you become a New Egg member, I bought their video card is that what it takes?

#6
8. Zepper Elite Member

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http://email.newegg.com/a/hBGg...jBOHsUMA44Mvms4/nweg20 Here is the code for the Kill A Watt (only works for members): EMC621DPSIN And here is the link to the KAW: http://email.newegg.com/a/hBGe...jBODngEA44Mvmqn/nweg28 .

You might want to get a short 3-wire extension cord (like the ones they sell to use with large wall-warts) to use with it so it doesn't block the whole outlet.

oops, the deal ended yesterday (June 27). Sorry... But they have it on the deals quite often so it'll be back soon

.bh.

#7

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