If you try to run a 50watt device from a 25watt source the source power
supply is going to either overheat or be current limited such that the
device will get only 25watt of power. Apple supplies current limit. Just
because your MacBookPro can draw 85w of power doesn't mean the 45w
supply starts to overheat, it just gives it all it has and no more. So
using a 45w or 60w power supply for an 85w machine might be enough to
limp along on but not enough to charge your batteries at the same time.
The reverse case is also safe. Using a larger supply on a smaller mac
shouldn't hurt anything. Just because your supply can crank out more
amps doesn't mean the device will make use of it. Just like the power
available from the power company has a lot more amps than you can
(safely) use it doesn't mean your coffee pot will start to melt. Only if
they started sending you the wrong voltage would things go awry.
The main problem with DC power supplies is getting the wrong voltage. If
your device needed 6 volts and you plug in a 12 volt supply you may fry
its innards. Doesn't matter what the current draw is. So in the case of
swapping power supplies between models, all the voltages are the same.
Apple has a FAQ on this topic here:
http://support.apple.com/kb/HT2346
and I recall a similar thread coming up elsewhere because the apple
airplane adapter apparently could only produce enough power to operate
the machine without charging the batteries. Apparently the airlines
limited power on their jacks to the point where drawing any more would
pop their circuit breakers. I guess it was designed with iPods, not
laptops in mind.
CB
On 8/20/11 5:41 PM, Christopher-Mark Gilland wrote:
Tim wrote:
3. You may get away with things for a while, but I recommend that you
use the proper rated power supply, especially if you have any warranty
left on the machine.
I highly agree. It's never that great of an idea, in my opinion to
mix-match chargers, that's only asking for trouble in the long run.
Now, if you have to products same make same model same everything,
then, that's a different story, but...
Chris.
----- Original Message ----- From: "Tim Kilburn" <[email protected]>
To: <[email protected]>
Sent: Saturday, August 20, 2011 5:35 PM
Subject: Re: charger Compadibility
Hi all,
They will all work with each other although, electrically, there are
some things you should note:
1. If a unit is expecting a 45 watt power supply and you give it an
85 watt power supply, you may decrease the life of both the battery
and the charging unit. consider that you're pushing almost twice the
wattage into the charging unit as it is rated for. In some cases this
will burn the unit out faster, and in some cases, it will simply burn
it out immediately. Also, consider that heat is one of the most
damaging factors in battery life, if an increased amount of power is
being pushed onto the battery, it will heat up more, thus, the battery
will get hotter during charging probably reducing its life.
2. The other direction, charging with a 45 watt when expecting an 85
watt power supply, does not hurt anything really. It will simply make
the charging process take longer.
3. You may get away with things for a while, but I recommend that you
use the proper rated power supply, especially if you have any warranty
left on the machine.
Later…
On 2011-08-15, at 8:00 AM, Chris Blouch wrote:
While not quite the same setup my MacBook Pro charger works just fine
in my wife's old little MacBook and vice versa. Main thing is that
her power supply is not quite as big (physically and wattage) so it
takes longer to charge up my laptop if I'm using her power supply. I
would assume similar things with the Air and your MacBookPro where
the Air uses a 45 watt power supply:
http://www.apple.com/macbookair/specs.html
While the current MacBookPro has an 85w power supply
http://www.apple.com/macbookpro/specs.html
So I think whomever you passed the MacBookPro along to would
appreciate getting the correct larger power supply.
CB
On 8/14/11 7:55 PM, Mike Arrigo wrote:
It should be, the macbook pro is a higher wattage charger, so,
assuming it fits, it should work, though of course it won't charge
any faster.
On Aug 14, 2011, at 1:08 PM, Dan Roy wrote:
I am expecting my new macbook air to arrive tomorrow. Does anybody
know if the charger from the macbook pro is compatible with the 1
from the macbook air.
If I do sell the macbook pro, if the chargers are compatible, I can
package the macbook pro with the brand new charger. Knowing my
luck, this won't work. I just wanted to check and see if anyone
knew for sure?
If this is considered off topic, you can reply to me at:
[email protected] thanks.
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Tim Kilburn
Fort McMurray, AB Canada
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