Swapping 60w & 85w MagSafe Power Adapters

sarah3585

macrumors regular
Original poster
Aug 12, 2007
230
0
Hello all.

I have a late 2008 MPB with a 85W Power Adapter. My other half has a 2009 Macbook pro with a 60W Adapter. These laptops are about 6 months apart, why the difference in adapter?

My BFs 60W recently packed up working (the rabbit nibbled it) so he's been using my 85W. Is this safe for his laptop? I've use to use his now and then, as I never noticed they were different. Was that safe?

Many thanks.

We both have 15" btw.
 
Last edited:

GuitarG20

macrumors 65816
Jun 3, 2011
1,020
1
I have a late 2008 MPB with a 85W Power Adapter. My other half has a 2009 Macbook pro with a 60W Adapter. These laptops are about 6 months apart, why the difference in adapter?

My BFs 60W recently packed up working (the rabbit nibbled it) so he's been using my 85W. Is this safe for his laptop? I've use to use his now and then, as I never noticed they were different. Was that safe?
1) the different watt adaptors are based off of different TDP usage by the processor. For example, in 2011, the 13" gets a 60, while the 15" and 17" get 85 because the 15" and 17" can use 85 or slightly more watts at full load, while the 13" is closer to 60W.

2) Yes, thats fine. The general rule is that you can use one with a larger Watt rating without any having problems. The sensors in the MagSafe will regulate wattage and voltage to keep it safe.
However, using a charger with less watt rating then the one your MBP came with can cause slow charging and may not keep the battery from being drained (yes, even when plugged in) if the computer is under load. For example, if I was running something that made my computer use 80W and I used a 60W charger, 20W would still be coming out of the battery. Something to consider if you're running under load and want to use a smaller watt rated charger.
 

dusk007

macrumors 68040
Dec 5, 2009
3,386
62
The only thing that really is important with charges is that they have the required voltage which is always the case if they are from the same company.
Everything else is up to a degree unimportant.

Too powerfull just means, heavy and inefficient at low load.
Too weak means either the computer crashes if it doesn't get the required current and the V drops or as with notebooks they suck all the missing power out of the battery.
 

snaky69

macrumors 603
Mar 14, 2008
5,904
484
Hello all.

I have a late 2008 MPB with a 85W Power Adapter. My other half has a 2009 Macbook pro with a 60W Adapter. These laptops are about 6 months apart, why the difference in adapter?

My BFs 60W recently packed up working (the rabbit nibbled it) so he's been using my 85W. Is this safe for his laptop? I've use to use his now and then, as I never noticed they were different. Was that safe?

Many thanks.
Let me guess, you have a 15", while your other half has a 13".

I'm good, right?

That's simply the wattage that comes with the different models, the 15" is more powerful and thus needs more electricity to work, plain and simple. You can use the 60W from the 13" and even the 45W from the MBA on your 15" MBP, but charging will take forever and a half.
 

sarah3585

macrumors regular
Original poster
Aug 12, 2007
230
0
Let me guess, you have a 15", while your other half has a 13".

I'm good, right?

That's simply the wattage that comes with the different models, the 15" is more powerful and thus needs more electricity to work, plain and simple. You can use the 60W from the 13" and even the 45W from the MBA on your 15" MBP, but charging will take forever and a half.
No we both have 15". Sorry I should have mentioned that in the OP. Seems odd :confused:
 

GGJstudios

macrumors Westmere
May 16, 2008
44,419
768
Power adapters for Intel-based Apple portables are available in 45W, 60W, and 85W varieties. Although you should always use the proper wattage adapter for your Apple portable, you can use an adapter of a higher wattage without issue.

For instance If you have a MacBook (13-inch Late 2009) that normally uses a 60W adapter, you can also use an 85W adapter with that computer. You would not use a 45W adapter with that computer; it would not provide enough power for that MacBook. Using an adapter of higher wattage than the adapter that came with the computer will not cause the computer to charge more quickly or otherwise operate any differently than using the adapter that came with the computer.
This should answer most, if not all, of your battery questions:
 

Naimfan

Suspended
Jan 15, 2003
4,669
2,010
His 15" 2009 is the base model, then - the base 15" came with a 60 watt adapter, perhaps due to it not having a discrete graphics unit (it came with the nVidia 9400m).

As snaky69 said, you can safely interchange them.
 

chrfr

macrumors G3
Jul 11, 2009
9,233
3,198
His 15" 2009 is the base model, then - the base 15" came with a 60 watt adapter, perhaps due to it not having a discrete graphics unit (it came with the nVidia 9400m).

As snaky69 said, you can safely interchange them.
It is possible however, that if your 2008 computer is working hard, the 60W adapter may not be able to provide enough power to charge the battery and the computer will then run off the battery and the AC Adapter. The 60W adapter may also get quite warm if trying to charge the battery while the computer is running.
 

GuitarG20

macrumors 65816
Jun 3, 2011
1,020
1
It is possible however, that if your 2008 computer is working hard, the 60W adapter may not be able to provide enough power to charge the battery and the computer will then run off the battery and the AC Adapter. The 60W adapter may also get quite warm if trying to charge the battery while the computer is running.
i said that in my post...
 

mac jones

macrumors 68040
Apr 6, 2006
3,257
1
Yes use it. Totally safe.

For instance, I'm typing on a Macbook Air 13" that has a 85W adapter (for my Macbook pro) plugged in.

No sense in having multiple adapters if your using them one a t a time. I just carry the big one, and i'm covered.
 

GGJstudios

macrumors Westmere
May 16, 2008
44,419
768
The problem is that that answers none of the questions posed by the OP.
That's not true. The OP asked:
My BFs 60W recently packed up working (the rabbit nibbled it) so he's been using my 85W. Is this safe for his laptop? I've use to use his now and then, as I never noticed they were different. Was that safe?
My quoted excerpt from the Battery FAQ:
Although you should always use the proper wattage adapter for your Apple portable, you can use an adapter of a higher wattage without issue.
 

iThinkergoiMac

macrumors 68030
Jan 20, 2010
2,664
4
Terra
2) Yes, thats fine. The general rule is that you can use one with a larger Watt rating without any having problems. The sensors in the MagSafe will regulate wattage and voltage to keep it safe.
While your answer is (partially) correct, your reasoning is not. Wattage is "drawn" by the device, not "pushed" by the charger. You could put a 200W charger on your computer with no harm (this doesn't hold for something extreme like, say, 50,000W). Voltage, OTOH, is "pushed" by the charger. So hooking up the incorrect voltage will fry whatever you've hooked up if you're over, or do nothing (or make run slowly) if you're under.

Apart from the auto-switching capability of the charger to use either 120V or 240V, the charger does absolutely nothing to "regulate" the voltage. I don't know what it would do if you gave it 175V (though I expect it would work fine) and it would certainly fry itself if you gave it 360V.

So the voltage must be the same, but the wattage, as long as it meets the required minimum, doesn't really matter.

One benefit of using the 85W charger on a MBP that only needs a 60W charger is that your battery will charge quite a bit faster. I only have an 85W charger for my 13" MBP, and it doesn't take very long to charge the battery at all.
 

GGJstudios

macrumors Westmere
May 16, 2008
44,419
768
Thank you for correcting me. I didn't know that-it's good information.
I just have to say that your attitude is worthy of respect. Too many get ticked off and defensive when someone corrects misinformation. Making mistakes and receiving correction is how knowledge is acquired. Good work!
 

squeakr

macrumors 68000
Apr 22, 2010
1,603
1
While your answer is (partially) correct, your reasoning is not. Wattage is "drawn" by the device, not "pushed" by the charger. You could put a 200W charger on your computer with no harm (this doesn't hold for something extreme like, say, 50,000W). Voltage, OTOH, is "pushed" by the charger. So hooking up the incorrect voltage will fry whatever you've hooked up if you're over, or do nothing (or make run slowly) if you're under.

Apart from the auto-switching capability of the charger to use either 120V or 240V, the charger does absolutely nothing to "regulate" the voltage. I don't know what it would do if you gave it 175V (though I expect it would work fine) and it would certainly fry itself if you gave it 360V.

So the voltage must be the same, but the wattage, as long as it meets the required minimum, doesn't really matter.

One benefit of using the 85W charger on a MBP that only needs a 60W charger is that your battery will charge quite a bit faster. I only have an 85W charger for my 13" MBP, and it doesn't take very long to charge the battery at all.
Your answer too is not fully correct. Voltage is a difference of potential created within the supply, and the supply does regulate the voltage since it is a step-down transformer. By this nature, it takes a given input voltage and regulates the voltage from the given input stepped down to the correct output voltage. Although voltage must be correct, so must amperage (the flow of current) within reason, as if more amperage is output by the charger then a serious over current condition occurs which has to be shunted off somehow, in either the form of heat, reflected power resulting in heat, or a short to some other component in the system.
 

iThinkergoiMac

macrumors 68030
Jan 20, 2010
2,664
4
Terra
Your answer too is not fully correct. Voltage is a difference of potential created within the supply, and the supply does regulate the voltage since it is a step-down transformer. By this nature, it takes a given input voltage and regulates the voltage from the given input stepped down to the correct output voltage. Although voltage must be correct, so must amperage (the flow of current) within reason, as if more amperage is output by the charger then a serious over current condition occurs which has to be shunted off somehow, in either the form of heat, reflected power resulting in heat, or a short to some other component in the system.
I see my days of working at RadioShack have not made me a master of the knowledge of electricity (no surprise there). Thanks! :)
 

Silvrbill

macrumors member
Dec 20, 2013
52
2
Your answer too is not fully correct. Voltage is a difference of potential created within the supply, and the supply does regulate the voltage since it is a step-down transformer. By this nature, it takes a given input voltage and regulates the voltage from the given input stepped down to the correct output voltage. Although voltage must be correct, so must amperage (the flow of current) within reason, as if more amperage is output by the charger then a serious over current condition occurs which has to be shunted off somehow, in either the form of heat, reflected power resulting in heat, or a short to some other component in the system.
The voltage does not need to be spot on. The charger will work correctly within a given range, it doesn't need exactly 120v or 230v. Anywhere in-between will be just fine. As far as amperage (current) goes the charger will not put out any more current than the device draws from it. Without a load there is no current. Current does not flow through the charger at will, it must be "drawn" from it for a specific purpose. There is no threat of over current to the device from using too small or too large of a charger. The charger will ONLY produce what it's capable of, no more. The threat of using too small of a charger is that the device may want more current that the charger can supply. Then you have a case of the charger becoming hot and possibly starting a fire.
 

TheIguana

macrumors 6502a
Sep 26, 2004
656
389
Canada
Then your BF was using an underpowered power brick.

15 and 17" MBPs have always used 85W bricks.
Nope, there was one model the 2009 mid MacBook Pro (15-inch, 2.53GHz, Mid 2009) that shipped with a 60 watt adapter. It only had integrated graphics in the form of an Nvidia 9400m, which is part of the reason it didn't need the beefier 85 watt charger. Apple has got a great support doc on all the models and what the minimum charger they need are: http://support.apple.com/en-ca/HT2346

Getting back to the OPs original question: it is safe to use the 85 watt adapter with either of your Macs. If the Mac only needs 60 watts of power it will reduce the output to meet the computers needs. If it needs 85 watts then it will provide it.

In my case we have a mixture of 13" and 15" MBP in our house and I have almost exclusively gone with 85 watt MagSafes to simplify things as there is no question of whether the adapter will be able to provide enough power.
 
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