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01-02-2010, 07:11 PM   #1
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## determining wattage usage of electronics

I'm familiar with the amps x volts = watts. On many electronics, however, it gives a range for the volts, maybe 100-240 volts and then something like 1 amp for the current. Is this saying that the wattage in, say, Africa is higher than in the US? If it pulls 1 amp no matter, then would it be 120 watts (120 volts x 1 amp) in the US and 240 watts in Africa (240 volts x 1 amp)?

Thansk!

01-02-2010, 07:23 PM   #2
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It pulls whatever power it needs and tolerates a wide range of input voltages. The wide range implies that it is a switch-mode power supply, as opposed to a linear supply.

You could infer that the max power draw is 1A(120v) = 120 w and the current draw would probably be a half amp at 240v.

 01-02-2010, 09:05 PM #3 Idiot Emeritus   Join Date: Mar 2008 Location: Fernley, Nevada (near Reno) Posts: 1,849 Rewards Points: 1,492 Actual watts of any AC device is Volts X Amps X Power Factor. Both linear and switching power supplies usually have horrible power factor. Somewhere around 20-50%. Power Factor usually goes lower as voltage increases. Some are corrected, but usually only large ones (over 1 KW). The only way to know for sure is to use a watt meter, but it's pretty safe to assume the Power Factor to be 50%. In the above example, it'd be pretty safe to assume that a device marked 100-240 volts and 1 amp would consume less than 60 watts, more like 40. A better way is to look at its DC output. Say it's 12 volts and 2 amps. That's 24 watts (Power Factor has no effect on DC circuits). Figure about 25% more, and you're pretty close to the input power. In this case, it'd be about 30 watts. The input amp figures on power supplies are notoriously inaccurate. Rob

 Tags amp , current

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