Introduction:

Before I start with the guide, let me just say a big thanks to Cliff Anderson of Fanbus for all the great products and stuff that he's been making and showing to the overclocking freaks all around the world for the 9 months he's been in business. Most of you would know that Cliff is the father of Fanbus and also know by now that he's quitting the Fanbus business to concentrate on his other commitments in life, mainly his family. Here's to you bud! And this guide is my way of saying thanks to you!

Back to the guide then! If you remember the previous guide on the Dual Voltage Baybus, which incorporates the 5V and 12V supply from the PSU, you'll noticed that I've mentioned that some fans, like my 120mm Sunons, aren't really comfortable or have problems running/starting at 5V. And some would agree that 5V isn't much of a power to actually move a considerable amount of air. So, out of that necessity, comes invention, with what is commonly known as the "7V Trick".

As usual, I am assuming that you guys are already familiar with basic electronics and wiring diagrams. And also the use of simple tools like the soldering iron and the hand drill. So I'll skip a few steps. Let's get to it then!

A common case fan runs on 12VDC. This is achieved by connecting the positive lead from the fan (usually a red wire), to the 12V wire (yellow) of the Molex connector on your PSU and also connecting the negative (black) lead of the fan to the Ground (Black) wire from the same Molex connector. See picture below.

12V fan wiring diagram

Now, to achieve 7V, all you need to do is connect the 5V wire (Red) from the Molex to the negative lead of the fan, instead of the normal ground wire. So by pitting the 5V against the 12V line, the 5V line is now acting as a "ground', thus cancelling 5V from 12V giving you 7V. See picture below.

7V fan wiring diagram

The 7V achieved is low enough to reduce the noise produce by your fans, but at the same time, providing a much comfortable voltage for your fan to start and continue running, and to churn out a considerable amount of air flow. Now that you've learn how to get the 7V, let's get to the fun stuff. Wiring your switches up and using Dual LEDs to indicate the diferent voltages! As usual, the list of parts!

• DPDT (Double Pole, Double Throw) switches

• Blue and Red LEDs (1.5V, 0.015A)

• LED Holders

• 750 & 240 Ohms resistors

• some wires

• Kit box and spring wire clips for the Fanbus

• a 5.25" faceplate from your PC

Mark out switches and LEDs locations on the faceplate, use a drill and drill the holes required for it. You'll end up with something similar to the picture below.

Items required Click to enlarge

Faceplate done Click to enlarge

If you've read the 5V/12V Baybus guide, you'll see that there's a picture showing you the grouping of the 6 terminals on the switch. At first, I thought I could just swap the 12V wire locations with the Ground, but after doing so, the blue LED that was supposed to indicate 7V did not light up. I spent another hour or so figuring out the wiring setup and came up with the following. I can't really explain to you why this is so, but just keep in mind that different brand and make of switches will the terminal groupings a little different. Test, test and test!

Dual position Dual throw switch
Click to enlarge

Terminal groupings Click to enlarge Important!

Wiring setup for the circuit Click to enlarge Important!

As you will be running on dual voltage, you will need two different resistor values. Here's the formula again. Note : The LED indicating 7V is connected to the 5V line, not the "7V" line. The "7V" is only supplied to the fans!

Voltage = 1.5V, Amp = 0.015 A. Therefore, to calculate resistance needed for a 12V line-in;

Ohm = (Mains Voltage - LED Voltage) / LED Amperes, so;
Ohm = (12 Volts - 1.5 Volts) / 0.015 A
= 700 Ohms or 750 Ohms

Voltage = 1.5V, Amp = 0.015 A. Therefore, to calculate resistance needed for a 5V line-in;

Ohm = (Mains Voltage - LED Voltage) / LED Amperes, so;
Ohm = (5 Volts - 1.5 Volts) / 0.015 A
= 233.33 Ohms or 240 Ohms

Once you have confirmed that the wiring is correct, proceed to start soldering the wires onto the terminals. And don't forget to slide on the heat shrink tube first before soldering the wires.

Groupings of terminals
Click to enlarge