Cost to run electricity for MBP

Discussion in 'MacBook Pro' started by whitedragon101, Apr 24, 2014.

  1. whitedragon101 macrumors 65816

    Sep 11, 2008
    I have an old PC (Athlon CPU+1GB RAM + 3 IDE HDD) I was going to use as a server. It has a 400w psu but will only be idling most of the time. I calculated :

    400w psu probaby drawing 150-200w
    150w for 24 hours a day 365 days a year = 1,314,000wh or 1,314kwh
    1kwh = approx 13p (UK)
    1,314 x 0.13 = £170.82 a year

    That seems like a lot


    1) Have I made any mistakes in the above calculation?

    2) Does anyone know the power draw range of a unibody (non retina) 15/17" MBP when its being used but not charging, so I can do a calc for my MBP?
  2. koerk macrumors regular


    Dec 14, 2013
    Install something like coconut battery or battery health and let the MBP run on battery only. In the programs it indicates the watt usage than. My MBA ranges from
    5 to 20 watt.
  3. blueroom macrumors 603


    Feb 15, 2009
    Toronto, Canada
    Buy a kill-a-watt and measure it. A typical household is full of wall vampires.

    The MagSafe on my rMBP 15" runs pretty cool most of the time, it's a very efficient switch mode supply. It's going to use very little current when the laptop is charged or disconnected.
  4. thundersteele macrumors 68030

    Oct 19, 2011
    Yeah but that is not how much energy you actually use. As you may have noticed, the charger can get quite warm, which tells you that not all of the energy it draws from the wall is provided to the laptop, some is lost in the conversion to low voltage and radiated off as heat.

    As a very conservative estimate, I would say it is save to assume that a mostly idle 15''/17'' MBP will not use more than 50 W, including loss from the charger. 20W-30W are probably more likely.
  5. koerk macrumors regular


    Dec 14, 2013

    Sounds logical, thanks. As already pointed out, in idle the MagSafe charger isn't really warming up so I guess the extra watts don't count that much then?!
  6. kgeier82 macrumors 65816

    Feb 18, 2008
    The math is simple.

    Magsafe can put out max 85w to the laptop. More typical output when idle/surfing is about 20-25watts usage.

    85/1000 * (electric rate per kWh)

    Thats the max the laptop will use per hour. Talking pennies.

    If you leave it on 12 hour a day, multiply those pennies by 12 and so forth.
  7. cbecklund macrumors newbie

    Aug 30, 2013
    While I'm no expert in computer usage, I doubt that your PC uses 150w to 200w at idle. I would think it would be more like 100 or less unless the PC is constantly doing something other than at idle. But I don't know, maybe it is that much
  8. leman macrumors G3

    Oct 14, 2008
    I don't think your Athlon based computer will draw more then 50-60 Watt on idle, unless is has a REALLY beefy GPU. As to laptop consumption: I am not sure if the following calculations make any sence, but according to coconutBattery, my rMBP (95Watt/hr battery) has gone through 742 load cycles in 599 days. This is total of 70.5 kWatt/hr. I estimate that my computer is running on battery in average 4 hours per day and I don't usually do any computer-intensive stuff when not plugged in, so this 'represents' my light usage. This means that I spent 70.5 kWatt/hr on 4*599=2400 hours, or somewhere in ballpark of 30 Watts. Probably less, because the battery power is spent on other stuff as well (even if your machine is on charger). Funnily enough, this estimate closely corresponds to the figures one usually find on the internet :D

    BTW, if you want to have a home server, it makes sense getting a cheap (maybe even second-hand) Atom system. It will be extremely power efficient (with Wake on Lan even more so) and the investment will pay off quite quickly. Performance-wise they will beat your Athlon.
  9. MCAsan macrumors 601


    Jul 9, 2012
    Get a MacMini Server. You know it don't have a 400watt PSU. ;)

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