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+--- Thread: Cutting and splicing a mac mini power cord (/thread-1071.html)
- fish2live - May 13, 2010
I've installed my mac mini on the boat and tested it by powering the mini with its normal power brick. Now the time has come to cut the cord up and splice it to the power output of a Carnetix PSU. I am hesitant to cut the cord until I know what it looks like inside.
I've already cut and spliced the power cord to my LCD monitor. That cord resembled a coax cable inside, with a braided outer conductor. Since there were still only two conductors, it was simple enough to gather the braided outer to one side and splice it to one power lead.
The mini power plug appears to have 5 conductors. Since the plug is non-directional, that must mean there are actually 3 conductors. (+, -, ground?) Am I going to find 3 wires in that cord, or 2 wires with a ground shield?
- bobetter - May 13, 2010
the info you need should be here:
http://www.blisstonia.com/eolson/notes/kensingtonmacmini.php
- bobetter - May 14, 2010
Your other option is to get one of these kit, it's already got the proper Molex connector on it for the Carnetix supply and you save your 110v supply.
http://store.mp3car.com/MacPac_Power_Cable_Kit_For_the_NEW_Mac_Mini_p/cbl-086.htm
- fish2live - May 14, 2010
I know about the macpac cables, but they aren't available for several more weeks and I can't wait around for one of them. In fact, the Carnetix instructions are fairly detailed for powering other motherboards, but for the mac mini they only show how to use the macpac cable. I asked Carnetix for advice or instructions on splicing the innards and they said that they had none.
The link to the Kensington adapter notes is very instructive. Those notes conflict with a picture that I found on Flickr. The pic shows the braided shield of the mini cable going to the white isense wire of the power supply. The notes page says that a thin gray wire must be attached to the isense wire for the mac to boot. Oddly, the notes relay this information from Carnetix but I have not been able to get it from them directly.
So what about that braided shield? I see braided shields in other wires and I never know what to do with them. In one place, the multiplexer, I'm supposed to attach the braided shield to the shield (or is it float?) terminal. Should it be attached to ground in other cases?
- bobetter - May 14, 2010
It's been a while since I installed a Mini/Carnetix system but to the best of my recollection, you should have a (+) (red), (-) (blk), an iSense (wht) and the shield in the Mac Pwr cable. Don't confuse the shield (ground) with (-). The shield, if connected, should go to a ground, not a (-).
These wires should connect to the Carnetix Molex as per the manual. You will also have to connect the yellow (ign) wire from the Carnetix power input harness to one of the input reds.
- fish2live - May 14, 2010
Well, I had already spliced the red and black before the two previous posts in this thread, so I took it to the boat and tried it that way. Despite the notes' warning about the mac not booting without the isense wire, it definitely does run without it.
The shield is indeed confusing, as is the whole subject of grounding. The entire boat is grounded to the engine and keel cooler, and most ground wires just tie into a negative bus bar, which is also tied to the engine. If I understand this installation correctly though, I should attach the wire shield to the negative bus bar because the red and black wires of the power supply output don't allow stray currents to leave the computer. It's like a relief valve.
I haven't attached the shield to anything yet, but I can easily run another wire past the power supply and back to a negative bus bar.
- bobetter - May 15, 2010
Sounds like you're good to go then!!
I am not totally clear on what the iSense circuit does....I assume it is related to power management and fans, etc. and probably should be connected. I know there were some issues with the Carnetix supplies when Apple went to the Core 2 Duo boxes in terms of terminating the iSense circuit properly.....
In terms of the shield....in a power circuit, the shield is inhibiting RF noise from emminating (sp) from the red/black. In order for it to do it's job properly, any currents induced in it need to have a place to go, usually the ground.
In a signal circuit, the shield is doing the same thing but in a differential circuit (2 wires, 1 positive and 1 negative) it is also providing a 0 volt reference to the 2 signal legs. GPSNavX, who is much more organized than I, has a great diagram of differential vs single-ended circuits.
....hope this helps...
- bstamerjon - May 16, 2010
About shielded wires, Ground only one end!!!!
Large passenger and car carrying vessel that I work on had a problem with installation of a "monitoring system", and the contracted installer grounded both ends of the shielded cables which made them capacitors, and we were seeing 40v on a 24v system. Much head scratching ensued, system was disconnected, and plans were made by experts to make it work, some day.