This Instructable will take you through the steps to power a simple computer fan from your wall outlet. The materials that you will need include the following.
1 x 12VDC computer Fan ($7.00 from Amazon)
1 x 12.6 V Transformer ($5.49 from radio shack)
4 x Diode (found in unused electronics around the house)
1 x Switch (found in an old lava lamp)
1 x Outlet Connector (found in old electronics)
Step 1: Assemble Your Full Wave Rectifer
Simple diodes can be found in almost any electronic device. I was able to find 4 in an old battery charger that I don't have any use for anymore. Desolder these, or order some online. Then, solder them together according to the diagram. These will restrict the current flow and create DC power from the AC power in your wall outlet. I have attached an image of what my finished rectifier looks like.
Remember that in a diode, the grey strip is pointing in the direction that current can flow. This will be the same direction as the arrow in the schematic view.
Step 2: Rectify Your Transformer
Buy yourself a transformer that is large enough to power your fan. Note that your fan will have an input current rating that will probably be around .32A like mine. As long as the transformer is rated to output more current than this, your setup will work. The transformer that I used for this was rated for 1.2A so everything should be fine.
Solder the two leads of the secondary side of the transformer onto the left and right side of your rectifier as it is shown in the previous diagram. This will ensure that the top node is always positive and the bottom node is always negative. The top and bottom of your rectifier should still be unconnected to anything.
Step 3: Power Your Transformer
Take your power cable and strip back the outer casing. Inside you will find two smaller insulated wires. Strip these back and then solder the wires onto the two primary connections on the transformer. Orientation does not matter for this step. If you have a switch attached to your power chord this will improve your fan by allowing you to easily turn it on and off without unplugging it.
Step 4: Test Your Setup
From this point, you will need to test your setup. Your outlet should be connected directly to the transformer, which should be hooked into the rectifier. If your circuit is correct, you should now be able to probe the top and bottom of your full wave rectifier in and see around 12VDC. If this is not what you get, there is something wrong with your circuit and you can troubleshoot using the multimeter.
Step 5: Attach Your Fan
If the DC voltage is correct from the previous step, go ahead and solder the positive lead of your fan onto the top node of the rectifier and the negative lead of your fan onto the bottom node. Your fan should now be working!