MagSafe Power Adapters Are Safe with All Mac Laptops

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After years of speculation, user reports, and conflicting information, we have discovered official confirmation from Apple that it is safe to use any wattage MagSafe power adapter with any MagSafe-equipped laptop.

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This 65-watt MagSafe Power Adapter can be used on a 45-watt MacBook Air without issue.

As discussed on Mac Geek Gab 355, while it may be “safe” to do so, it’s worth noting that it may not always be effective.  A higher wattage adapter will charge a lower-wattage computer just fine (for example, an 85-watt 15-inch MacBook Pro adapter used on a 45-watt MacBook Air) but a lower wattage adapter may not charge a higher wattage laptop (a 45-watt MacBook Air adapter connected to an 85-watt 15-inch MacBook Pro).  In the former situation, the computer will charge, but will not charge any faster than if the stock adapter is used.  In the latter situation, the adapter will not charge the machine at all while in use, and will only trickle-charge the machine while asleep.

All of this information and more is available in article HT2346 over at Apple’s Support Page.

Comments

geoduck

A higher wattage adapter will charge a lower-wattage computer just fine

Yes, exactly. Current is how much a device will draw. A charger has a current capacity and will work below that. This is an argument I’ve had a number of times with users over the years. They keep thinking that the charger or power supply will push too much into the device.

Example, yesterday the power supply for my Airport died. It’s 12v 1.5A. I didn’t have one but I have a brick and cord from a monitor that is 12v 5A and it works just fine.

Generally you don’t want to go smaller than original but larger is fine.

The only time I worry about it is if there is too much disparity between original and the replacement. I don’t think I would use that 5A power supply on a device that drew 0.25A. I’d be a little worried that the big power supply would not be precise enough and could damage the delicate low power device. In any event it likely wouldn’t plug in anyway.

aardman

Is there a risk of overheating the charger and causing a fire if you plug it into a higher rated device?  (In the same way that you can melt an extension cord if it’s not rated for the appliance plugged into it?)

Windsor Smith

Current is how much a device will draw. A charger has a current capacity and will work below that. This is an argument I?ve had a number of times with users over the years. They keep thinking that the charger or power supply will push too much into the device.

I see your point about current, but don’t we still have to be very careful to match the voltage?

I realize that’s probably not an issue with MagSafe adapters, because I’m sure Apple has the presence of mind to put physically incompatible connectors on the outputs of power adapters with different voltages. I’m thinking in more general terms, like in a situation where you’re using one of those configurable “universal” power adapters.

geoduck

Is there a risk of overheating the charger and causing a fire if you plug it into a higher rated device?

Theoretically yes. I once fried a wall brick by plugging it into something that drew more current than it could supply. (The wall brick looked the same and I didn’t realize that the current was different from the one I was replacing.). It got hot and melted/shorted out. In the case of the MagSafe I’d hope that Apple put some kind of current limiter in the system to prevent that, but I don’t know for sure. I’d feel the brick every few minutes to see if it’s getting hot.

don?t we still have to be very careful to match the voltage?

Absolutely. Using a power supply with the wrong voltage is a sure fire way to fry the device. If it’s too high then ~zap~. If it’s too low then it’s a brownout condition and that is hard on circuits especially motors etc. If it says 12 volt then 16 won’t do. If it says 14.75 volt then 8 won’t do.

geoduck

Actually let me correct myself a bit. Mostly what I’ve been talking about is a regular power supply for a device, like the Airport I mentioned earlier. The power supply makes available, the device draws, and as long as the voltage and current match all is well.

Battery chargers are a bit different. In that case the power supply does “push” the electricity into the battery, You still want to match the voltage but you can safely “trickle charge” batteries at lower current than rated. In fact trickle charging is better than charging too fast, which can cause the cells to overheat and burst.

Most laptops I’ve worked on, and I assume that current MacBooks and Pros are this way, use the battery to buffer the incoming power. The device runs off of the battery all the time, when it’s on the charger more electricity is going into the battery than the system is using so it charges, just more slowly. This is why, as stated in the article, if you use a lower rated charger the system will run but the battery will not gain anything until the system shuts down and stops drawing. It can’t keep up.

Apple Document HT2346 just clarifies that any MagSafe charger, even one with a lower current rating, will work safely with any Apple ‘book. This is not necessarily true of other companies systems. You can fry other brands of batteries and laptops by using the wrong charger.

haineux

If you use an Apple MagSafe charger to charge an Apple MacBook, it should not overheat.

As far as voltage goes, the adapters are specified to work correctly when connected to 100-240 volts, 50-60Hz.

So as long as the above are met, you should be safe. Because the tech note confirms this, I suspect that Apple has tested all the combinations.

That being said, use your common sense: don’t put the adapter, say, under a rug, where the heat could build up. And if you notice that the adapter is getting very hot, by all means unplug it!

Windsor Smith

As far as voltage goes, the adapters are specified to work correctly when connected to 100-240 volts, 50-60Hz.

Just to clarify: The voltages geoduck and I were talking about are on the DC output side of the power adapter, not the AC input side. Many (all?) power adapters these days can be plugged into virtually any outlet in the world, but the devices (MacBooks, Airports, etc.) that they supply typically have much narrower voltage tolerances, so we have to be careful about mixing and matching power adapters. It’s nice to know that Apple’s MagSafe adapters work across its whole line.

WetcoastBob

Been charging a 2006 15” MBP with a 45w charger for years.  Takes a little longer to charge but works fine.

haineux

Many (all?) power adapters these days can be plugged into virtually any outlet in the world.

Let’s be abundantly clear: It is acceptable to connect any Apple MagSafe power adapter to any Apple MacBook. Both the adapter and the computer have power management microprocessor chips to discuss the situation, and decide what to do.

To wit:

Been charging a 2006 15? MBP with a 45w charger for years.? Takes a little longer to charge but works fine.

In most cases, the power adapter can power the computer AND recharge the computer’s battery, but that can vary. A 45W charger might not be able to charge a 17” MacBook Pro. It might or might not be able to run the CPU (allowing the battery to be disconnected and maintain its charge), depending on the needs of the computer—and that can change over time. Using lots of fancy graphics, or spinning the DVD drive could cause the MBP to use both the battery and the power adapter, and usually, if the power adapter gets too hot, it will shut itself down.

If so, the MacBook should alert the user with what’s going on.

What Apple is confirming is that it’s OK to connect any Apple MagSafe adapter to any MacBook. It might not be able to help, but it won’t hurt.

(And yes, there’s always an exception: In very rare cases, the power adapter could have a hardware flaw that makes it malfunction—so use your common sense: The power adapter can get warm to the touch, so don’t put it under a rug or a blanket—and if the adapter seems very hot, disconnect it!)

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