Your Mac will only pull as much power as it needs. The voltages are the same. The difference is in the wattage. Here's an adapter you may need: http://store.apple.com/us/product/MD504ZM/A/magsafe-to-magsafe-2-converter?fnode=0d317b129be286b5c61c7dceedbc67d3e4d0c86c99c0f2f42bec8437222567de79d8aa78045589c0f33a17ff1df6c0a75f68574f6ac71c85a6a3c8717a5a00fbb9fd86892ce093754a1bdb81851ea7811bc23b90a64429a85df6ad2c6a549eedbbab0280006f86bb2071eead57110d98