Click to expand.Nitpick: this is not some unique or special property of Apple power supplies. All power supplies can be used at or below their maximum rated power (e.g. An 85W power supply can provide any power from 0W-85W), as long as the voltage is correct. The reason Apple's power supplies are interchangeable is that they all provide the same voltage. Additionally, the numbers you listed (45W, 60W, 85W) are simply the maximum ratings of the power supplies Apple shipped with each computer.

That doesn't mean the MBA uses 45W, and the MacBook Pro draws 85W. It all depends on load. You can power a MacBook Pro perfectly adequately on a 45W power supply, as long as the battery is charged and you're not doing anything CPU/GPU-intensitve. Nitpick: this is not some unique or special property of Apple power supplies.

All power supplies can be used at or below their maximum rated power (e.g. An 85W power supply can provide any power from 0W-85W), as long as the voltage is correct. The reason Apple's power supplies are interchangeable is that they all provide the same voltage. Additionally, the numbers you listed (45W, 60W, 85W) are simply the maximum ratings of the power supplies Apple shipped with each computer. That doesn't mean the MBA uses 45W, and the MacBook Pro draws 85W. It all depends on load.

You can power a MacBook Pro perfectly adequately on a 45W power supply, as long as the battery is charged and you're not doing anything CPU/GPU-intensitve. A: The macbook pro apple adapter (85w) actually put's out 16.5v just like the macbook adapter (60w) for normal usage.

But if you are a heavy graphics user, then it'll automatically up the voltage to 18.5 volts(85w). During our tests, we've found that not a whole lot of people tax their macbooks Pro to the max, so the 70w is actually enough for a lot of people. If you are within the 3%, your laptop will simply slow down or stop charging your battery. It will resume charging when you reduce CPU tasks. We also choose this voltage because of Airline wattage limitations.

Q: Your site seems out of date, you say N2(B) tip, but it should be N3(B). A: Please read above question.

N2(B) outputs 16.5v. We recommend N2(B) because of above answer to question, and to stay within limits of the power supplied on Airlines. N3(B) is recommended for those who are heavy CPU users, and not on airlines.

Hey fl89 Great thread - thank you. I was a bit surprised about the discouraging feedback you received in the beginning. It has been one year since your last post and I was wondering if you could give a short follow-up.

I would like to do something similar: Power my MBP from a 12V solar-charged lead acid battery. The most efficient way is to get good components and start soldering, it seems.

I would be especially curious if 18.5V turned out the right option or is the 16.5V (60W) option more suitable? As far as I understood, the power rating is programmed into the cable (not the power supply - cf.

So what happens if I only can find a 60W-rated cable and turn the voltage to 18.5V. After reading all of your links and some more, it seems to be more reasonable to go 16.5V and accept a battery drain when playing the latest shooter games. Great thread and links. I too was planning to tinker to build a mobile setup powered by the more common +12v from vehicles and standby battery packs used to start cars when their battery is dead.

refurb working Apple official adapters are available at OWC for $45-55 according to an email I got today. I had planned to use a DC-to-DC converter to step up the nominal +12v to nominal +18v (for example, the airline adapter Apple sells will power but not charge a laptop due to voltage being only +15v - EmPower).

lots of 'broken' adapters on ebay to scavenge for official MagSafe connectors Why? More efficient and less bulky than using +12vdc to 120vac converters and then using the Apple laptop chargers.

Also, many hard drives use simple +12vdc power, so was planning to generate regulated +12vdc from the battery source. Finally, investigated some lithium power packs if car battery power not available. Then would have to also worry about charging circuitry. Overall, an interesting project. Click to expand.My MagSafe transformer died after 4 weeks of use (it was a chinese knockoff I found on eBay for 20) As I didn't want to borrow my mom's charger for too long, I decided to try and make a new charger.

So I salvaged the MagSafe cable (and other components for other projects ^^) from my charger, and hooked it up to a DC-DC boost converter (you can find those on eBay relatively cheaply). I used a basic 12V transformer as power source, and after many verifications of the output voltage (18V instead of 18.5V, just to be sure), I took a deep breath and plugged the cable into my MacBook, and it worked just fine!! Although it's not really recommended, it works as a 'short-time' solution, as I don't have the time and money now to buy a genuine one.

Hope this helps!! Just reviving the thread here ^^ (it might be useful for someone!) My MagSafe transformer died after 4 weeks of use (it was a chinese knockoff I found on eBay for 20) As I didn't want to borrow my mom's charger for too long, I decided to try and make a new charger. So I salvaged the MagSafe cable (and other components for other projects ^^) from my charger, and hooked it up to a DC-DC boost converter (you can find those on eBay relatively cheaply). I used a basic 12V transformer as power source, and after many verifications of the output voltage (18V instead of 18.5V, just to be sure), I took a deep breath and plugged the cable into my MacBook, and it worked just fine!! Although it's not really recommended, it works as a 'short-time' solution, as I don't have the time and money now to buy a genuine one.

Promo Original Converter Magsafe To Magsafe 2 High Quality For Macbook Pro

Hope this helps!!

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