# Given power info on a CRT monitor, how can I calculate power consumption (kWh)?

I have a Dell CRT Screen and the only info I have is this:

AC input
voltage: 90 to 264 VAC
frequency: 50 or 60 Hz + 3Hz
current: 1.5A max. (RMS) at 120 VAC; or 0.8A max. (RMS) at 220 VAC

How can I calculate the energy consumption in Watt-hours for an hour (or better, a day)?

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r0ca, this is much more specific and to-the-point than your question from yesterday, so i'm leaving it open. but stop posting the same question multiple times. if you need to rephrase a question, use the "edit" function. – quack quixote Apr 7 '10 at 17:50
Oops! NOTE THAT Sathya's answer is WRONG. Yes, the formula is correct, etc, however you CANNOT get power consumption from specifications. What you get from specifications is the rated worst-case, NOT actual. The goal of the specifications is to tell you what the system is rated for. Take an automobile, for example; just because it's rated capacity is 2500 lbs does not mean that that's what it carries every day. The tires, while rated at 750 lbs each does NOT mean they (collectively) carry 3000 lbs all they time. Do not confuse rating from actual load... – Richard T Apr 7 '10 at 18:28

Power is Voltage times Current, and power consumption is measured by Power times Time.

Note that your CRT's specs show that it will draw one of two currents depending on your location's mains voltage. If your area uses 120V AC, your CRT will draw a maximum of 1.5A; if your area uses 220V AC, your CRT will draw a maximum of 0.8A.

Power consumption for 1 hour:

``````= Voltage * Current * Time
= 220 V * 0.8 A * 1 hour = 176 Watt-hour
= 176 / 1000 = 0.176 Kilo Watt-hour
``````

To find the consumption for one day, multiply by 24:

``````0.176 * 24 = 4.224 kiloWatt-hours
``````

This assumes that the monitor is on for all 24-hours. If the CRT is under standby mode, then the power consumption will be lower.

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it also assumes 220V, though it's not hard to adjust for locations that provide 120V AC. – quack quixote Apr 7 '10 at 17:47
For modern computer hardware with switched-mode power supplies, the power consumption should be (and according to the posted specs, is) very similar regardless of mains voltage. – coneslayer Apr 7 '10 at 17:51
@coneslayer: sure. i'm just pointing out that Sathya's calculation grabs a certain set of values from the specs, and that you could perform the same calculation with the other set of values. – quack quixote Apr 7 '10 at 18:01
Guys! I'm impressed by that! Thank you so much! – r0ca Apr 7 '10 at 18:09
Oops! NOTE THAT Sathya's answer is WRONG. (posted again, here, for visibility.) Yes, the formula is correct, etc, however you CANNOT get power consumption from specifications. What you get from specifications is the rated worst-case, NOT actual. The goal of the specifications is to tell you what the system is rated for. Take an automobile, for example; just because it's rated capacity is 2500 lbs does not mean that that's what it carries every day. The tires, while rated at 750 lbs each does NOT mean they (collectively) carry 3000 lbs all they time. Do not confuse rating from actual load... – Richard T Apr 7 '10 at 18:28
• 1.5 Amps at 120 Volts = 1.5 * 120 = 180 Watts
• Watts / 1000 = Kilowatts
• Kilowatts * Hours = Kilowatt Hours

Therefore:

• 180 / 1000 = .18 KwH per hour
• .18 * 24 = 4.32 KwH per day

if running at Max amperage

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Wow, nice answer! Thanks!!! – r0ca Apr 7 '10 at 18:09

I used to have three 21" pro monitors. They came with 3A fuses. One day a fuse blew and I tried a 1A fuse. It blew as well. So each monitor used more than 240W.
Ohms law is `V x A = W`

So 240V x 1A = 240W and the fuse blew, but a 3A fuse was ok (240V x 3A = 720W), so it's greater than 240W but less than 720W - that's quite a range, and also you have to bear in mind that this will peak with a surge when the monitor is turned on - I think 250W each monitor would be a good estimate.

I changed them for three 26" 16:10's which are 52W each so quite a saving from 750W apx total down to 156W :)

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