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Due to limited linguistic and technical knowledge, I do not know (and can not find) the name for the 4 pin (or perhaps 3?) plugs that are used inside PC cases to deliver electricity.

My questions:

  1. What's the name of these cables? (they are used for connecting fans etc.)
  2. What's the difference between them and "Molex" cables?
  3. Is there a converter to attach to small 12V DC adapters' round end so that I can connect / run a fan externally?
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Those can be called molex as well. Actually, Molex manufactures the connectors (of course there's a lot of other brands now). But if you problem is to find the cables for buying, you can search something like "atx power supply molex cable" and you'l surelly find many. As for the adapter, how about making one? :) –  Sergio Aug 18 at 16:51
    
Thanks @Sergio!!! ;-) –  Phil Aug 18 at 16:57
    
Its a context specific name. Molex Power connector, for ATX systems. While the smaller ones are Floppy Power Connectors, as they are only present on Floppy drives. –  cde Aug 18 at 17:32

1 Answer 1

up vote 8 down vote accepted

These cable assemblies are typically used to deliver +5V and +12V DC to various components in the computer such as optical drives, hard drives, and fans. Molex (see Molex Connector) is the company that developed the typical connector found on the ends of these assemblies. Some people refer to the cable assembly itself as "Molex cables" but this is technically a misnomer.

Molex Fan Adapter

You can easily find adapters (pictured above) for connecting 3-pin (Molex KK-type) fans to these 4-pin connectors at your local computer store, or online. While I have not seen converters to connect DC power jacks, you can easily modify one by soldering your own power jack to it.

You can find the pinout easily online:

PC power supply harness pinout

With this information you can cut the appropriate wires and solder them to a DC power jack using the correct polarity. Be sure to use your meter to verify polarity if you're not sure.

More about DC Power Jacks: Electrical part question

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thanks a lot! Can you please tell why are there 3 or 4 cables hanging off these? DC adapters come with 2, no? How do I decide which one to connect if I strip off a DC adaptor? –  Phil Aug 18 at 16:58
    
PC power supplies typically are capable of supplying 200 or more watts, sufficient to power multiple hard drives, optical drives, etc. Manufacturers will usually provide cabling with several connectors intended for the end user to be able to add more devices without having to purchase splitters or new power supplies. Some computers (like mine at home) can have four or more hard drives in a RAID array, and having additional power connectors is necessary. –  JYelton Aug 18 at 17:02
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To address your question about DC power adapters having two wires, whereas the PC power cable has four, this is because the PC power supply is providing two voltages (5 and 12 DC) instead of one. The logic circuitry for a hard drive, for example, will operate on 5V, while the stepper motor may require 12V. I added a pinout to the answer. –  JYelton Aug 18 at 17:03
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The reason they have 2 ground wires is that it allows using the same gauge of wire for all the connections; with only a single ground wire a thicker wire would be needed to avoid overload when both the +5 and +12v lines were fully loaded. –  Dan Neely Aug 18 at 17:53
    
Thank you both, @JYelton and DanNeely. Finally, can you also please tell: If I want to have 12v, should I target the 12v end and any GND? Thanks! –  Phil Aug 19 at 0:49

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