My daughter called this evening. She has a 13.5" MacBook (2006, 1.83 GHz) and the power adapter blew. She bought a new one and was going to attach it when she noticed that the replacement is 85 watt. Her machine uses a 60 watt.

She wanted to know if she could use it.

I told her I wasn't sure. I didn't know if the wattage meant the amount the adapter is capable of delivering but that the machine would only draw what it needs...or...if the output was a constant 85 watts and that her machine would be getting more than necessary, with the possibility of internal component damage.

Should she have an adapter with matching wattage?

ryck

According to Intel-Based Apple Portables: Identifying the right power adapter:

Thanks. She has subsequently dropped a note with a JPEG of the unit (which I would include but I don't have a website) and it shows that it is the cable itself, not the adapter, that blew.

The fault is at the adapter end of the cable, where the Maglink cable exits the adapter and is just past the strain relief. The cable has been blown right out, and has the burnt look of a dead short such as you see with a shorted A/C cable, so I'm assuming it's cable fatigue from being wrapped/unwrapped for storage.

This may be a goofy question, but I have to ask: Is there any chance that something in the computer itself would cause a malfunction in the adapter which then blew the cable? The logical side of me says the adapter simply converts the 120V A/C to something else, which then goes one-way to the Maglink end but.....

ryck

My son bought a new power adaptor for his Macbook Pro at the Apple Store a couple of weeks ago and was told they are recommending the 85 watt adaptor to everyone regardless of which MacBook or MacBook Pro the user has. So I think your daughter is safe on that question.

As to cause of the burnout, my first suspicion would be physical damage to the power cord such as getting pinched in the hinge of a briefcase or snagged in a zipper as you initially surmised. But there are others, such as V1 who are more qualified to comment on the possibility of an internal short causing the burnout.

Was your son given a reason for the recommendation? (The two are listed at the same $79 in the Apple Store, so corporate greed can't be blamed.)

Related question: Does the 85W adaptor draw more AC power than does the 60W?

> "I'm assuming it's cable fatigue from being wrapped/unwrapped for storage."

Virtual1 has posted (more or less) that using those watchmacallits on the power block for wrapping the cable is a recipe for disaster. (I know that my natural tendency is to pull a bit harder on the cable than I probably ought to in order to get things "just so.")

Yes. In the note I sent back to my daughter, I said:

"Looking at the JPEG, I see the blown section is just where the cable strain relief ends. That's the plastic piece that goes around the cable and extends from the adapter about a 1/2 inch. It appears that you likely fold the cable there, at a right angle, when you wrap it for storage.

If so, don't do that.

You should allow the cable to come out about an inch and have it gently curve to where you wrap it. There are a number of wires (probably four) inside the cable and, if it's bent at a right angle, a couple of the wires have to travel farther than the other two.

I know it sounds strange, because the distance is so tiny, but after many, many, folds the wires will finally break. If they then touch the others you have a "short" and kaboom."

Maybe I should send an amending note with the recommendation that she simply coil the cable and skip the wrapping.

ryck

The reason given is the 85 watt adaptor will work on any Macbook or Macbook Pro that has a magSafe connection whereas the smaller power supplies will not. At this particular store it appeared they were stocking the 85 watt adaptor exclusively, but neither of us investigated that closely.

Makes sense, particularly inventory-wise; thanks.

watts (and current) are supplied on-demand. the power supply need only be able to meet or exceed the rating to work. Voltage and frequency need to match however.

Apple's original macbooks shipped with a paltry 60w adapter. it's perfectly fine to run them off the 85w adapters. you may need to run a firmware update if the machine is behind on its updates, since the new magsafes won't be recognized by the original mobo's firmware.

Also the latest are the ones that run the cord away at 90 deg, sometimes that can cause problems with other cables or arrangements, or if the case is bent (mbp) it may not meet properly.

I've always thought it would be a good idea for Apple to either replace or augment the default strain-protector with a relatively stiff spring about 1 1/2 - 2" long.

Any thoughts?

Ya, it wouldn't look nearly as stylish and clean as the current solution. And that's a big thing to overcome in redesigning an Apple product.