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  1. #1


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    Power draw of Imac
    I am currently trying to switch to an Imac but have held off a purchase for now til I get clarification of power draw.
    I work often from my motorhome, so I would use the Imac through an inverter, therefore how much power the Imac draws is very relevant to me.
    The Apple site tells me the 21 inch 2.5gig Imac draws 205 watts, which is only .8 of an amp. That seems way too low. However when I tested it drew 10 amps through the inverter.

    My friend has a 2 year old 3.1gig 21 inch Imac, and when I tested that, it drew only 6 amps through the inverter.
    Can anyone shed any light on the current draw and why there is such discrepancy please?

  2. #2

    chscag's Avatar
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    How are you testing the current draw? I have never seen a computer, Mac or PC that would draw 10 Amps or 6 Amps. An electric heater yes, computer no.

  3. #3


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    What is the voltage at the inverter where you're measuring 10A?

    Apple's maximum figure of 205W is 1.7A at 120V (North American household voltage) or .85A at 240V (Most other places' household voltage) but 17A at the 12V that is common for vehicle power outlets.

    10A @ 12V = 120W, which would be consistent with moderate usage.

  4. #4


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    Quote Originally Posted by technologist View Post
    What is the voltage at the inverter where you're measuring 10A?

    Apple's maximum figure of 205W is 1.7A at 120V (North American household voltage) or .85A at 240V (Most other places' household voltage) but 17A at the 12V that is common for vehicle power outlets.

    10A @ 12V = 120W, which would be consistent with moderate usage.
    Voltage at inverter was 13.4.
    However my laptop is 1.4 amps at 240v, yet draws 6amps at the inverter. So I kind of assumed that as the Imac was only .85 amps at 240v, it would also be less at the inverter.
    Indeed my friends 3.1 gig model was 6.2 amps peak draw, but the 2.5 new model was 10.1

  5. #5


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    Quote Originally Posted by chscag View Post
    How are you testing the current draw? I have never seen a computer, Mac or PC that would draw 10 Amps or 6 Amps. An electric heater yes, computer no.
    I am testing with an inline ammeter. Any computer is going to draw at least 6 amps through an inverter. The least I've seen was a 15 inch Dell that drew 4.2 amps.

  6. #6

    chscag's Avatar
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    I guess we're forgetting that an inverter has to change a DC current to a useable AC one in order for the computer or other accessory to operate properly. I'm not familiar with motor homes but I thought that when you parked it at a motor park it could be plugged in to an AC receptacle to provide power throughout?

  7. #7

    Demapples's Avatar
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    An RV, like a boat on shore power, gets 120V AC from the outside, then inside the vehicle some appliances are 120V AC and some 12V DC (in North America). A converter converts 120V AC to 12V (or whatever) DC. The boat or RV can get DC from vehicle alternator/batteries or a converter. An inverter converts DC to AC. At least that's the terminology I've become accustomed to, but I guess technically it can get hairy.

    A laptop power supply converts 120V AC to ~14V DC.

    In an RV or boat running on 12-14V DC from alternator/batteries, an inverter converts the 12V DC to 120V AC, then the laptop power supply converter converts 120V AC to 14V DC.

    Amps = Watts / Volts

    All this is pretty vital for working out how to power computers on small boats. Another reason to like the iPad (10 watt charger).
    Longtime Windows, then onto slippery slope with iPod/iTunes in 2006, then Apple TV, iPad, iMac, iPhone, rejuvenated a discarded MacBook and, finally, Apple Watch. Happy camper.

  8. #8


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    Quote Originally Posted by Demapples View Post
    An RV, like a boat on shore power, gets 120V AC from the outside, then inside the vehicle some appliances are 120V AC and some 12V DC (in North America). A converter converts 120V AC to 12V (or whatever) DC. The boat or RV can get DC from vehicle alternator/batteries or a converter. An inverter converts DC to AC. At least that's the terminology I've become accustomed to, but I guess technically it can get hairy.

    A laptop power supply converts 120V AC to ~14V DC.

    In an RV or boat running on 12-14V DC from alternator/batteries, an inverter converts the 12V DC to 120V AC, then the laptop power supply converter converts 120V AC to 14V DC.

    Amps = Watts / Volts

    All this is pretty vital for working out how to power computers on small boats. Another reason to like the iPad (10 watt charger).
    Well, without wanting to get lost in the detail, I often use the inverter as for many reasons I don't have mains,
    My main query is about how much the Imac draws when using the inverter, as opposed to me friend's 2 year old Imac which draws 4 amps less on the inverter.
    Are newer ones simply using more power?

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