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View Full Version : Battery issue or MagSafe power adapter issue?




MacRumorUser
Feb 12, 2008, 04:14 PM
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
Feb 12, 2008, 04:21 PM
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

MacRumorUser
Feb 12, 2008, 04:25 PM
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.



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.

rroback
Feb 12, 2008, 05:30 PM
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.

MacRumorUser
Feb 12, 2008, 05:34 PM
^ 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.

beatzfreak
Feb 12, 2008, 05:47 PM
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
Feb 12, 2008, 05:50 PM
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

MacRumorUser
Feb 12, 2008, 06:39 PM
Do you have an Apple store near you? Maybe they could try it with another 45 watt power adapter.

Unfortunetly in Ireland we have the Apple Euro HQ, but not one single Apple Store in the whole country :(

teerexx52
Feb 12, 2008, 06:49 PM
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.

When I called Apple the tech guy said absolutely do not use other power adapters on the air.

MacRumorUser
Feb 12, 2008, 06:53 PM
When I called Apple the tech guy said absolutely do not use other power adapters on the air.

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.

watermelon
Feb 12, 2008, 07:10 PM
I used the macbook pro charger on mine, made NO difference in the charge time- still >5 hours.