Step-by-Step: How to make a 5 volt and 7 volt wiring adapter out of a Molex Y adapter
July 19, 2001


Summary:
This guide will show you how to make a simple wiring adapter that allows you to quickly and easily switch between 5, 7, and 12 volts for your Molex based case and cpu fans.  With this adapter, it is easy to control fan speed and fan noise for optimal case and cpu cooling.
 

Ominous Warning: DSL/Cable Webserver is not responsible for any damage caused by this project.  Everything you do here is at your own risk.  Please use common sense and take all possible safety precautions.

If you're a computer enthusiast, then you probably have several fans in your computer.  Maybe 2 for your cpu, 1 for your graphics card, and 3-4 case fans?  That's probably a gross underestimation for some of you hard-core overclockers.

Almost all fans out there run on 12 volts.  However, you may find that the fan is too noisy at the full 12 volts.  What can you do?  Well you could live with it or you could lower the voltage of the fans so they don't make as much noise (tradeoff is they move less air).  The combinations we can extract from a typical 4 wire Molex connector are 5, 7, and 12 volts:
 

Volts
Fan speed/noise
12
100%
7
58%
5
42%

The decrease in fan speed is somewhat proportional to the decrease in the amount of noise made by the fan. Not exactly proportional, but this ain't rocket science.

Okay, so you cut the wires and re-solder them at 5 volts or 7 volts.  It's a tedious process of cutting the wires, stripping, soldering, putting heat shrink tubing, etc.  Then you find out the fan won't even spin up at 5 volts (some fans won't spin up at 5 volts), so you have to repeat the whole time consuming process and try it at 7 volts.  Re-cut, re-solder, re-tube = pain in the butt.  Wouldn't it be nice if you could switch from 12 volts to 5 volts then to 7 volts just by plugging them into an adapter?  Yeah, I think so too.

Here we'll go through a short and sweet guide on how to making a +5 volt and + 7 volt wiring adapter from a standard Molex Y power adapter.  The beauty of this little adapter is that you can make a bunch of these adapters and then use them to fine tune the airflow from in your case.  Maybe your front intake doesn't need to run at 12 volts, but your exhaust does.  With this adapter, you can make changes to your system easily and quickly without having to mess with soldering wires and all.  Once you fine tune the voltages of all your case fans, you can then solder all the fans to the proper voltages, or you can leave the adapters in place which is what I do.  Okay, so I'm lazy.

If your fans use the 3 prong header which plugs into your motherboard, you will need to buy a 3 to 4 wire adapter to use this mod.  However, by using the 3 to 4 wire adapter, you'll lose the ability to monitor your fan RPM from your motherboard.

Important: You must shut down your computer before you connect / disconnect / reconnect any wiring.  This should go without saying, but you never know.

A standard Molex connector has 4 wires that we are all familiar with.  All the diagrams are with the angled sides of the Molex connector facing up.

A Molex connector head looks like this (sort of):
 

Wire/Position 4 +5 volts
Wire/Position 3 Ground for 5 volts (0 volts)
Wire/Position 2 Ground for 12 volts (0 volts)
Wire/Position 1 +12 volts

The two middle black wires and both ground wires, one for the +5 volts and the other for +12 volts lines.  These lines are kept separate so there won't be interference between the +5 and +12 volt lines.

When you buy a fan with a Molex connector, the positive lead is connected to (wire 1) +12 volts and the negative lead is connected to (wire 2) ground for 12 volts.  We're gonna leave fan connector alone.  We will be doing the rewiring on the adapter.

+5 volts
To get 5 volts we'll be moving wire 4 to wire 1's position and wire 3 to wire 2's position

  • Position 4: Empty
  • Position 3: Empty
  • Position 2: Negative - Move (wire 3) black ground for +5 volts --> Position 2
  • Position 1: Positive - Move (wire 4) red +5 volts  --> Position 1
Positions 3 and 4 will be left empty - DO NOT randomly fill positions 3 and 4.  The potential for disaster is great if you accidentally plug this sucker into a hard disk or cd rom, so leave 3 and 4 empty.

+7 volts
To get 7 volts we will be using the +5 volt wire as the ground for the +12 volt wire (12 volts - 5 volts = 7 volts).  This "7 volt trick" is a bit unconventional and is a bit outside the specs of how power supplies are wired.  However, the are thousands of people (including myself) who are using this trick in their cases.  You shouldn't have any problems, but if you're not quite sure, you should test it out on an "expendable" piece of hardware.

We'll move wire 4 to position 2.  That's it.

  • Position 4: Empty
  • Position 3: Empty
  • Position 2: Negative - Move (wire 4) red +5 volts  --> Position 2
  • Position 1: Positive - No change - Leave this wire alone (wire 1) yellow +12 volts
Again: Positions 3 and 4 will be left empty - DO NOT randomly fill positions 3 and 4.  The potential for disaster is great if you accidentally plug this sucker into a hard disk or cd rom, so leave 3 and 4 empty.

Does all that make sense?  If not, don't worry, we'll walk though it.

One last thing to remember is that many fans come with pass through connectors so you can attach another device to the power chain.  However, if you use this adapter, the voltage coming out of the pass through will be either 5 volts or 7 volts.  This is fine if you want to power more fans at that voltage, but you CANNOT connect the pass through to a regular peripheral like a hard disk or CDROM.  You could potentially damage the device by giving it a nonstandard voltage.

Important: All the diagrams are with the angled side of the Molex connector facing up.

Materials: 

  • Molex Y power adapter
  • Flat head eyeglass type screwdriver or other small flat head screwdriver
  • Wire clippers
Okay, first go pick up a couple of these Molex Y power adapters.  If you have some laying around, great.  If you don't, you can get these cheap at computer shows and various mom and pop computer shops.  If you decide to go to a retail store like Best Buy or CompUSA, expect to pay a lot more.

First thing we need to do is to label the different heads of our adapter.  Using a Sharpie or permanent marker, label the main head "Full" and the legs of the adapter "5" and "7".  This way you'll won't get confused about which head you're working on.

We'll first work on the +5 volt head.  Here's the plan:  Remove all 4 wires and then reinsert (wire 4) red +5 volts into position 1.  Reinsert (wire 3) black ground for +5 volts into position 2.

  • Position 4: Empty
  • Position 3: Empty
  • Position 2: Negative - Move (wire 3) black ground for +5 volts --> Position 2
  • Position 1: Positive - Move (wire 4) red +5 volts --> Position 1
At the end of each wire, there is a metal head with one or two prongs that lock the metal head into the plastic Molex head.  Using a very thin, eyeglasses type flat head screwdriver, bend the prongs until they are flush with the body of the metal head.  After you do this, the wire and metal head should slide right out of the plastic Molex head.  Do this with all 4 wires.

Here is a close up of the metal head with the two prongs sticking out.  Your particular adapter may have one or two prongs.  Since you bent the prongs flush with the rest of the metal head in order to remove it, you must now reverse the process and bend out the prongs before you reinsert the wire back into the plastic Molex head.  It should look something like this.

Here is what the +5 volt head should look like.  The red wire is in position 1 and the black ground wire for the +5 is in position 2.  Make sure that the black wire is the (wire 3) ground for +5 volts and not the black wire (wire 2) ground for +12 volts.  (Even if you made this mistake, it probably wouldn't make a difference, but let's follow specs shall we?)  After you are sure you connected the correct wires, cut off the remaining yellow and black wires using wire cutters.  Do not insert them into positions 3 and 4.

Now for the 7 volt head.

  • Position 4: Empty
  • Position 3: Empty
  • Position 2: Negative - Move (wire 4) red +5 volts --> Position 2
  • Position 1: Positive - Leave this wire alone (wire 1) yellow +12 volts
Remove the wires from positions 2, 3, and 4.  Leave the yellow wire in position 1.  Move the red wire to position 2.  After you are sure you connected the correct wires, cut off the remaining 2 black wires using wire cutters.  Do not insert them into positions 3 and 4.

Here are the +5 volt and +7 volt heads.  You could also make this adapter with two +5 volt or two +7 volt heads.  Or one +5 volt and one +12 volt head.  Or one +7 volt and one +12 volt head.  You get the picture.

You are done.  This is a picture of the finished product.  Note that for the +5 volt head, the ground wire comes from them +5 volt ground.

If you're really careful (or anal) you can bust out your trusty multimeter (voltmeter) and take a reading from the two heads to make sure the voltages and polarity are correct.  I would show you a picture of the readings, but my multimeter happens to have a blown fuse from my last Frankensteinien experiment.  Hehe, bad sign?

Make as many of these adapters as you need.  You'd be surprised at how useful they are when you're experimenting with different fan setups.