Strain relief and the Apple power adapter

I followed somebody’s link (can’t remember whose1) to this Kickstarter project today. It’s for the Wrap_Up, a cable management device that clamps around your Apple power brick.

Wrap Up

I like the part that helps keep the thick cord (the one that plugs into the wall) in order, but I’m not too keen on how the thin cord is routed.

Here’s how the designers of the Wrap_Up describe the problem it’s trying to solve:

Type “Magsafe” into Google image search and you’ll find there are more than a few people who have had issues with their Apple power adapter. Making sure your cords stay safe, don’t tear, and stay bundled during travel are prevalent issues.

We invented and patented the Wrap_Up - a cover for your power adapter which provides a means to wrap up the cords dangling around your bag and also protects them from stress and fatigue cuts over time.

They show several photos of power adapters with the thin cord broken where it attaches to the brick. I actually followed their suggestion and did a Google Image search on magsafe. Most of the photos of broken cords had the break at the other end of the cord and were of the original design, not the current one. But there were photos like this, which was from Neil Turner’s blog.

Broken MagSafe cord

This kind of failure comes from repeatedly wrapping the thin cord around the flipout prongs of the brick and—this is the important part—making the first wrap too tight. The strain relief that Apple puts on the brick is a little too short and little too stiff to protect the cord from that kind of wrapping technique.

This is the right way to wrap the cord around the prongs.

Proper cord wrapping technique

Leave a nice big loop in the cord before making the first wrap around the prongs, and you won’t overstress the cord at the end of the strain relief.

And that’s what I don’t like about the Wrap_Up. Yes, it routes the cord away from the brick before allowing it to be wrapped around the prongs, but it does the routing through a hard piece of plastic. This doesn’t eliminate the sharp bend, it just moves it another fraction of an inch away from the brick.

To be fair to the Wrap_Up guys, they did put a curve on the inside of their strain relief piece, which I’m sure is their attempt to reduce the bending stress in the cord, but if the user pulls tight, the cord will bend sharply over the outer edge and will be no better off than if the Wrap_Up weren’t there.

Wrap_Up strain relief

I’m not trying to screw up anyone’s business here, and as I said, I do like the way they’re managing the thicker cord, but unless they can provide test results that prove their routing of the thinner cord prevents high bending stresses, I’m not buying it.

  1. Update: It was Shawn Blanc

6 Responses to “Strain relief and the Apple power adapter”

  1. Andrew White says:

    Years ago I went in to the Eaton Centre Apple store with my new blackbook to get a charging issue sorted. The lovely woman I dealt with showed me the wrap technique in the third image. She told me that was such a common point of failure that their manager had asked everyone to show a customer how to wrap their power cable when they brought in a portable.

  2. Dr. Drang says:

    Well, sure, Andrew, but now you have that advice coming from someone who, according to the piece of paper on my wall,

    has been admitted to the Degree of Doctor of Philosophy and is entitled to all rights and honors thereto appertaining.

    So you got that going for you. Which is nice.

  3. Jay Parlar says:

    Dr. Drag,

    That’s going to be my new stock response when I tell someone something, and they respond by saying they already knew it. One more use for my Ph.D.

  4. AC Kull says:

    You might also check out this product:

    Doesn’t really solve the strain issue on the thin cord, but it seems to work fairly well. I’ve had it for about a year now and it seems to be working OK for me. Still probably need to allow a little loop to keep the strain off of it.

  5. Andrew White says:

    Sorry, that wasn’t a “you’re late to the game”, more of an “Apple is aware of this point of failure, and it’s common, so they should fix it!”

  6. Dr. Drang says:

    No need to apologize, Andrew (how very Canadian of you). I wasn’t miffed by your comment, I just used it as an excuse to make a lame joke.