Apple’s MagSafe power supply connector is one of the rare inventions that I wish I had thought of. Once you see one, it is an obvious solution to a common problem. It is much more convenient than standard power connectors, and has the advantage of easily breaking away if someone trips over your power cord. Despite the genius of the connector design, the rest of the power supply has a major flaw: poor stress relief.

MagSafe power supply

Flexible cables need stress relief where they connect to solid objects to avoid damage to the cable or the electrical connection. The MagSafe power brick’s stress relief on the outgoing DC cable is primarily designed to keep the cable from pulling away from the electrical connections. It does this well. It misses the other purpose of minimizing the stress of the bending cable near the rigid block. The stress relief portion of the cable is overly rigid, creating a spot where the cable can easily kink, damaging the wires inside. The solution is to add an additional little bit of thinner stress relief. This will eliminate the most likely point for the cable to be damaged. The incoming AC cable is an excellent example of good stress relief, so it is odd that the DC cable has this flaw.

MagSafe stress relief sketch

There will always be some who abuse hardware by make the cable bend too tight, or pulling on the cord, so no fix can be perfect. But the stress relief problem on the MagSafe power supplies is bad enough that even someone as careful as I am not to damage an expensive power adaptor ended up with a broken cord. It got to the point that the cord partially melted at the stress point. I had hoped it would be a simple fix: pop the case open, shorten the cord an inch, put it back together. Unfortunately, the brick is glued together. Apparently the best way to open it up is to Dremel around the seam. Once the repair is complete, either re-case the circuit, or tape the case back together. This is not an acceptable repair. Fortunately, Apple recognizes the problem as a safety hazard and—in cases where the damage is from wear, not abuse—is replacing the power supplies even after the warranty runs out. I had to drive to the nearest Apple store (over an hour away) to have it replaced. For some reason they don’t allow the local Apple repair shop to swap them out. Now I have a new power supply, and can get back to work.

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