Lesson 9: Power cable installation – Build my own computer


In lesson 9 we’ll continue the process to build my own computer and install the power supply into the case. Then we’ll connect the power cables to the motherboard and disc drives.

Installing the Power Supply into the case 

On some cases the power supply is installed at the top of the case above the motherboard. On these cases you should turn the power supply so the air intake is at the bottom. In this case the power supply goes below the motherboard at the bottom of the case. With bottom mounted power supplies you should turn it so the air intake faces upward. However if the case is vented at the bottom you can turn the power supply over so it can get cool air from the outside of the case.

The power supply is secured to the case with 4 screws. Hold the power supply in place and match up the power supplies screw holes with the holes on the case.

Insert the first screw at the top and the second, at the opposite, bottom corner. Leave them loose until all the screws are in and then tighten them down.

Check the power supply for a slider next to the primary power switch. If it has a slider, set it to 115V or 230V depending on your local power requirements. 115V is standard for the US. Most modern power supplies don’t have a switch and detect the voltage automatically.

Wait to connect the power supply to the outlet until the computer is fully put together.

There are 6 types of connectors on an ATX12V 2.3 or EPS12V 2.91 power supply.

  • The first is a 24 pin connector that provides the main source of power to the motherboard.
    Some power supplies come with a 20 plus 4 pin connector and you can remove 4 of the pins by breaking them off incase your motherboard only needs the 20 pins.
  • The second is a 4 or 8 pin plug that connects to the motherboard. Some power supplies come with 2 4 pin plugs that you can combine to create an 8 pin plug.
  • The 3rd is a 4 pin plug, also called Molex, which connects to some fans, hard drives, DVD and Blu-ray drives.
  • 4th is a smaller 4 pin plug used to power a floppy drive.
  • 5th a flat SATA power connector for SATA drives
  • 6th a 6 or 6 plus 2 pin PCI Express video card power connector.
    Not all video cards require a connection to the power supply.
    Most video cards that do require the 6 or 6 plus 2 pin connectors will come with a 4 pin molex to 6 or 6 plus 2 pin adapter.

All of the power plugs are keyed, so you can’t put them in upside down.

Modular Power Supplies

If you have a modular power supply, decide which of the cables you will need and save the rest for future use.  Read the manual for the power supply to make sure you plug the cables into the correct spots on the power supply.

Molex connections

We don’t have any drives or fans that take a 4 pin molex connection in this build.  If you need to use a molex cable the connection is keyed so it will only go in one way. It sometimes takes some extra pressure.

Connecting power cables to the components

We’ll connect the three fans that came pre-installed in the case to the 3 pin fan headers on the motherboard.{unreg}

If there aren’t enough Molex connectors, Y power adapters that split the power from 1 Molex connector into 2 are available.

On our modular power supply we’ll connect a SATA power cable to the power supply and route the cable to the other side of the case. We’ll connect one of the cables to the SSD and another to the HDD. I’ll route the end of the cable back into the main part of the case and connect it to the DVD burner.

On this power supply the 20 or 24 pin and 4 or 8 pin power cables are permanently attached to the PSU. I’ll route them through to the other side of the case and bring the 24 pin cable back through to connect it to the motherboard. I’ll take the 8 pin plug to the other side of the case, to the top and bring it through, above the motherboard to the 8 pin plug. It is very common to forget to connect this power cable. Make a point to remember this connection.

Again, all of the connections are keyed, so the plugs will only go in one way.

Our video card does require a 6 pin PCI Express power connection. I’ll connect a PCI Express power cable and route it through the other side and then back and connect it to the 6 pin PCI Express connection on the video card.

Removing cables

If you need to remove the main power cable, the 4 or 8 pin plugs, or the PCI Express power connectors, there is a tab to hold down while you pull.

That’s it, our build my own computer is assembled. In the next lesson we’ll power on the computer.