What power cord adapter can we use for both a 13" Macbook and a 17" Macbook Pro?

The power (Wattage) requirement of the Macbook Pro is higher (the adapter is rated 85W, while the one for the 13"is rated 60W), so you must use the 85W adapter. These regulated power supplies are able to maintain the voltage (V) constant, while the current (I) is adjusted according to the needs of the equipment being powered. Since P=V x I, if V is kept regulated at 10 Volts, the maximum current supported by the 60W adaptor will be 6 Amps, while the 85W adapter will supply up to 8.5 Amps. So, using the 85W with the 13" does not constitute a problem (on the contrary, the power adapter will run cooler), but if you use the 60W with the Macbook Pro, the current drained from the adaptor will exceed its specs, the adapter will overheat and its life spam will be shortened considerably.

• Answered by Francisco L from Weston
• Jan 12, 2010
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Actually, I never realized until today that there are both 60W and 85W versions. I've been using a 60W version with my 15" MacBook Pro which has a battery that no longer holds more than 25 minutes worth of charge (a whole other unhappy story.) It works fine, though the adapter does get pretty hot. Not sure whether it's a better or worse idea than using an 85W for both - perhaps it's what gave my battery the final push over the edge? - but it can be done.

• Answered by Julie S from New York
• Nov 23, 2009
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