energy consumption of AEBS and Airport Express

Question

Level 1

30 points

energy consumption of AEBS and Airport Express

Hi,

I just obtained a AEBS and it works great. I also have an Airport Express Station to extend the range, otherwise I cannot access the WIFI from the "far" regions of garden (only maybe 25 meteres from the AEBS in the flat, but many walls, however, I still find it odd that I need an additional, Airport Express Station, which makes the whole thing pretty expensive!).
I unplugged the Airport Express in the other room for environmental and saving money reasons when not used. If unplugged, the AEBS flashes yellow, which is a bit annoying and I am thinking whether I should leave the Airport Expressed plugged so I get rid of the flashing at the AEBS.

OK, long text, short question: Does anyone know the monthly energy consumption of the Airport Express Station and the AEBS? I would like to know whether it is worth to unplug the stations when not used or not.

thanks a lot,

D.

ibook G4, Mac OS X (10.4.9)

Posted on May 8, 2007 11:30 PM

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Answer 1

Tesserax

Level 10

157,980 points

May 9, 2007 7:47 AM in response to MacFriend

Does anyone know the monthly energy consumption of the Airport Express Station and the AEBS?

According to the AirPort Express & AirPort Extreme Technology Overview documents, they draw 0.2A & 0.4A respectively. (ref: http://www.apple.com/support/manuals/airport/)

Since Watts = Amps x Volts, substituting 230V (standard in the UK?), gives the following:
Wax = 0.2 x 230 = 46W
Waebs = 0.4 x 230 = 92W

Not sure what your current utilities rates are, but as you can see, these devices power consumption would be roughly equivalent to either a 50W or 100W light bulb.

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Answer 2

MacFriend Author

Level 1

30 points

May 9, 2007 8:54 AM in response to Tesserax

Hi,

thanks for the quick reply! I found that in London 1 kWh costs 15p. One month with 31 days has 744 hours. This makes 34.2 kWh for the Airport Express and 68.5 kWh for the AEBS or roughly 102 kWh per month together.
This would mean the Airport Express costs 5.13 Pounds and the AEBS 10.28 Pounds a month or 15.40 Pounds together! Seems quite a lot or do I make a mistake???

D.

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Answer 3

Tesserax

Level 10

157,980 points

May 9, 2007 9:15 AM in response to MacFriend

The math appears right, but I agree, those costs seem excessive...as theoretically it should be the same as what it would cost to leave 50W or 100W light bulbs on, 24 x 7, each month.

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Answer 4

May 9, 2007 10:23 PM in response to Tesserax

I followed the link above but did not see the technology overview document available. Unfortunately the current/power draw is not specified in the manual for the Express.

However usually it is power draw that is constant, not current draw. So if the 0.2 and 0.4A estimates where for the US, they would be approximately 1/2 that for the UK, assuming 230V service.

120v * 0.2A = 24watts (mind you in the US you really usually get between 110v and 115v out of an outlet)

In the UK it would still only need 24 watts of power, cause power is what does the work, voltage and current is just how you work out how to get the power. So:

230v *?A = 24w or 24/230 = 0.1A (close enough).

In other words, it will be about 1/2 of what you came up with originally, 7GBP or so for the two for one month, which still is pricey, but not quite as bad.

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Answer 5

MacFriend Author

Level 1

30 points

May 10, 2007 12:55 AM in response to Shawn Parr

Thanks for the answer. I looked on the power converter of the AEBS and it says the output is 12V and 1.8 A. This would make only 21.6 W for the AEBS. Is the rest consumed by the transformation? However, Airport Express should be definitely lower than AEBS, which would mean that it might be still less.

I now try to find a current analyser and measure the power directly. As soon as I have numbers, I will post them (but this may take some time).

D.

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Answer 6

May 10, 2007 10:33 AM in response to MacFriend

To address your Question. Some power is consumed by the transformer in the power supply. This is why it gets warm. But this is a percentage of total wattage coming from the wall, determined by the efficiency of the transformer (and other electronics in the power supply).

Electrically speaking, however, a transformer of 100% efficiency obeys the following equation (Where V is voltage and I is Current in Amps)

Vin * Iin = Vout * Iout

So in a US household using an AEBS the equation would be:

110V * 0.2A = 12V * 1.8A

Sure, the transformer is not 100% efficient, but the current being drawn from the wall is nowhere near 1.8A. Even if the transformer was only 50% efficient it would draw only 0.4A from the wall.

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