How much actual AC current does the 85W MacbookPro charger draw at 220V?

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How much actual AC current does the 85W MacbookPro charger draw at 220V?

Hi. I need to know the actual current drawn by the 85watt MacBook Pro AC charger from 220V 60Hz.

I am designing rooms and libraries that will typically have 10 to 30 Macbook Pro's in use. I need to design the power outlets they will use.

I know the actual value will vary with load (The MacBook's use situation).

I know the actual value will vary depending on the battery charge state when the Macbook is plugged in.

I know the maximum value would be at 85 watts OUTPUT from the charger, and that the charger is not 100% efficient, but is probably 85-90 percent efficient. Maybe.

At the moment I'm in a hotel in the Middle East with no test equipment..

So: Has anybody measured the AC current on a Macbook at 220V, like in Europe, Australia, Middle East, China?? Ideally I'd like it with a discharged battery, and maybe with a fully charged battery and just a browser running. (For the extremes??)

Any data, sugggestions, (Contacts at Apple???) would be appreciated..

Thanks!
terry@terryking.us ...On the Red Sea in Jeddah

MacBook Pro - misc different, Mac OS X (10.5.7)

Posted on Aug 30, 2009 9:06 AM

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Answer 1

Aug 30, 2009 7:12 PM in response to TerryKing

You should remember your school lessons :-))

Power = voltage multiplied by current or P=VI

So we have the maximum watts of 85 so we have P.

We have the voltage 220v so we have V.

Therefore if P=VI, I=P/V

85/220 = 0.386363636363636 amps

Hope that helps.

Phil

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Answer 2

TerryKing Author

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Sep 1, 2009 12:08 PM in response to Philip Tyler

Thanks, people, for the help and information..

My working number until I can actually do measurements, will be approximately:

- Phil's number: 85/220 = 0.386 / .90 = .43 Amps

This is based on a estimate of the charger's efficiency being 90%. Based on the temperature rise of the charger case, my rough estimate of the power dissipated there is 5 to 10 watts. Very roughly. So it's probably close...

So, back to my original need and question:

How many 15 inch MacBook Pros that are actively recharging batteries while being used for web surfing can I run on a 220Volt 16Amp circuit??

Answer: About 32. We may well have 25 from time to time, probably never 32. So I'm cool.. for now..

And I'm betting, based on other experience, that 25 kids won't plug their charger in during the same 2 or 3 AC cycles, so the surge current will be OK also.

But don't do this: Put out a string of multi-outlet strips, connect all the computers, and THEN flip the single power switch. That surge probably WILL trip the circuit breaker.

Whoever gets a decent AC ammeter on one of these chargers first, please post results here.

Thanks from the Middle East.
terry@terryking.us

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Answer 3

TerryKing Author

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Sep 1, 2009 8:17 PM in response to carl wolf

Carl, Apple says the charger delivers 18.5 V at 4.6 Amps at it's output.
18.5 * 4.6 = 85.1 which is the 'labeled' output.

The input will be more because the efficiency is less than 100%.

I'll be happy with the actual current the charger will draw from the AC line. What we've got now is close enough to keep me out of trouble.

Regards, Terry King ...On the Red Sea near Jeddah

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Answer 4

carl wolf

Level 6

14,631 points

Aug 30, 2009 5:36 PM in response to TerryKing

85 watts, maximum. The power adapter efficiency, including the DC output cable gauge and length, has already been figured into the equation. The power adapter was designed to deliver 85W, with an AC input voltage of 100-240, and a line frequency of 50-60Hz.

There are very few instances that the computer will draw 85 watts. As you mentioned, the actual current draw will depend, and it's up to you to decide if you want to assume all computers are drawing 85W all of the time, or a "typical computer" drawing 30W most of the time.

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Answer 5

Sep 1, 2009 5:46 AM in response to Philip Tyler

The label on the adapter itself states, +"Input: 100-240~1.5A (1,5A) 50-60 Hz"+. Therefore, based on the rating the maximum current draw from the adapter is 1.5 amps.

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Answer 6

Sep 1, 2009 6:04 AM in response to neuroanatomist

The figure of 1.5 amps is probably the maximum initial 'surge' current when you plug the device in, once it is running it will drop down.
All electrical devices when first plugged in usually have a 'surge' current then settle down, hence the old fashioned surge fuses which would take a much higher current for a very short time.

Phil

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Answer 7

carl wolf

Level 6

14,631 points

Sep 1, 2009 3:26 PM in response to TerryKing

Terry,
What answer is going to satisfy you? You have the maximum and typical current draws. What else do you need? The efficiency of the power adapter has already been figured in, and you don't have to do it again. You can't calculate the power adapter efficiency by measuring the case temperature.

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