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iBook power plug polarity

Message #1 - Posted 2007/03/04 - DougL

Well, that's just part of the question.

First, some context. I have a Kensington universal car/air adapter for my G4 iBook. That's what lets me plug my iBook into a car cigarette lighter port, or an airplane seat port. In this Kensington adaptor, the DC-DC converter part is separate from the big fat plug that goes into those ports. So, stupid me, when I pulled it from by airplane seat, I left the big fat plug behind in the seat outlet.

Now, I would like to just cut off the connector that Kensington uses to connect to their own "big fat plug" (the one I left behind), and hardwire one on (saving me about $70 minus the $1 cost of the big fat plug). But I want to make sure to get the polarity right. The rather weird Kensington connector oddly has two large pins (which are connected to the cable) and two small pins which are not. Anyone know which is +12 and which is ground? (One of the two large pins on that connector has what appears, though the clear plastic housing, to be connected to the cable core, and the other to the sheath, which might be a strong clue. Am I going to destroy the Kensington DC-DC converter by getting my +12 and ground reversed on its input?

Another way to do it is just to hook it up, hope for the best, and see what comes out the iBook end of the Kensington power cable. But what am I supposed to see there on that jack? From some fragmentary discussion I've seen, the 2-conductor pin (inside the shield) has +24 on the inner part of the shaft, and ground on the outer part. The shield powers the little light in the connector, and I figure if I get the shaft polarity right, that will be OK by default.

Is this right?

I guess I can handle killing my adapter, but I really don't want to kill my iBook.


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