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Battery issue or MagSafe power adapter issue?

MRU

MRU

macrumors Penryn
Original poster
Aug 23, 2005
25,368
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Just a general wondering but do you think the long battery charge times could actually be caused by the magsafe 45watt adapter ?

If they are not outputting the right power then it would obviously take longer to charge.

Now the only thing that makes me suspect this is simple, I ran down my battery till the warning came on and then plugged in the magsafe 45watt and it reported that it was going to take 8 hours 21 minutes to charge.

Now as an experiment I plugged in the macbook's 65watt power supply and took a look and it reported that it would take 2hr 27mins to charge.

Plugged in the 45watt and again over 8 hours reported to charge....

Surely this can't be a coincidence. Obviously the 65watt would be faster but not nearly 3-4x as fast.
 
TEG

TEG

macrumors 604
Jan 21, 2002
6,621
169
Langley, Washington
The problem had been documented and talked about ad nauseum. There is problem with the PMU in the Air when you recieve it. Reset it and everything should work out fine.

TEG
 
MRU

MRU

macrumors Penryn
Original poster
Aug 23, 2005
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TEG said:
The problem had been documented and talked about ad nauseum. There is problem with the PMU in the Air when you recieve it. Reset it and everything should work out fine.
Click to expand...


I am not a newb! :rolleyes:

And if you had read all the continuing threads on this matter you will realise that may people like myself have ran SMU reset a couple of times and it made no difference what so ever to our systems or battery charge times.
 
R

rroback

macrumors member
Jun 29, 2007
77
0
It's not too hard to do that math about charging. I'm not sure what the voltage/capacity of the air is, but I'll just do a rough calculation to show:
45 watt supply, at 15volts can supply 3 amps of current. (p=volts x current)
a 3 amp/hour battery requires 3 amps to charge in our hour, 1.5 amp supply would take two hours etc.

Some things to consider are the fact that the current supply is less then the capacity of the battery, slow charges actually help battery life, and that the stated power of the supply I'm guessing is not constant. Most lithium battery charges vary the current supply, so as the battery gets closer to max charge, it reduces the current. If the 45watt supply says 8 hours, a 65 watt supply should take

45*8=65*x
x= 5.53 or about 5.5 hours charge time. The fact it says 2 hours makes me believe there is more then just supply side current.
 
MRU

MRU

macrumors Penryn
Original poster
Aug 23, 2005
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^ exactly.

Add that also to the fact that the even though the Macbook 65 watt power supply is 20 watts more than the MBA's - the MBA only ever takes as much power as it needs out of the power supply, it does not suddenly take 20 watts more.

The computer takes the power from the power supply. The power supply doesn't force power into it.

This is what is making me wonder if its somthing to do with the power supply at least in this instance instead.
 
B

beatzfreak

macrumors 6502
Jan 11, 2006
349
3
NYC
Interesting. I was hoping someone would try the 65 watt with the air.

Do you have an Apple store near you? Maybe they could try it with another 45 watt power adapter.
 
Cybergypsy

Cybergypsy

macrumors 68040
May 16, 2006
3,094
0
Central Florida!
I use slim battery monitor, from empty it take less then 3 hours BUT when it about 65-75% full, the trickle charge starts and it jumps from 50 minutes left to charge to 1:50 minutes try it....but still quick
 
MRU

MRU

macrumors Penryn
Original poster
Aug 23, 2005
25,368
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a better place
teerexx52 said:
When I called Apple the tech guy said absolutely do not use other power adapters on the air.
Click to expand...

Why? You are not forcing more power into a computer, the computer takes what it need from the power supply or that is what I have read on Apples discussion boards.

Either way as an experiment it proved that there may be more to the issue than just calibration and smu resets.
 
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