So after spending some time relaxing back home, I have decided to involve myself into a small project. I thought why not use one of the many old power supplies that my father stores in his office and make my own lab bench power supply to provide 5V, 12V, -5V and -12V. I believe I will find it helpful and convenient to have a portable lab bench power supply, in terms of my final project; that's why I am posting a small guide into what I have done. The guide I have used to do this one is a really nice video on YouTube, feel free to check it out. Click here to watch the video
So let's begin,
As you may know a PC power supply will take the 230V - 240V AC from the mains supply and convert it into 5V, 12V, -5V and -12V DC in order to power the PC motherboard and the peripherals. New power supplies also provide 3.3V as well, but since this a very old PSU no 3.3V is available and also I don't believe I will really need it anyway.
WARNING: The big capacitors inside will still hold a large charge after disconnecting the PSU from the mains, therefore be really careful when the lid is open. You can leave the PSU's capacitors to discharge for some hours or even a day if you are too worried about an electric shock.
Firstly I purchase a new switch to replace the old one, in order to switch on the PSU. I have also bought a green LED, a current limiting resistor of 680 ohms for the LED and a small resistor of 5 ohms at 5W to be used as a dummy load parallel to the 5V output. I have also bought one black and four red binding posts. For the LED current limiting resistor you may use a resistor with a smaller value to increase the brightness, but remember that a resistor is necessary to avoid blowing up the LED.
After purchasing the above mentioned components I continued with cutting the holes to the case of the power supply, in order to mount the binding posts, green LED and power switch.
Next I have separated all the wires into colour groups and solder them together. The various colours on the wires means different voltage levels. Remember to leave behind two ground wires, one red wire (+5V) and of course the orange wire (see the diagram below to see their use).
BLACK = 0V (Ground)
RED = +5V
WHITE = -5V
YELLOW = +12v
BLUE = -12V
ORANGE = POWER ON (This just means when the power supply is working, the orange wire will be at 5V and 0V when is not)
I also tried to keep everything as tidy and safe as possible using heat shrink tubing. The final product looks like this:
So this is the simple diagram I used to connect the wires:
To demonstrate how the LED and the switch operate see the following pictures:
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| The PSU is connected to the mains, but not turned on, therefore only the switch LED is illuminated. Green LED is off. |
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| The PSU switch is turned on, thereby the green LED turns on as well indicating that the front voltage supply rail is ready for operation. |
After connecting everything up and closing the case, the end result looks really good:
Deliberately, I did not go into much detail into what I have done, since there are numerous detailed guides out on the web. I hope you enjoyed this small guide and hopefully you will try it yourself since the above project is really easy and very useful in many applications.
Until next time !!=)
