Introduction

Salvaging parts from computers can be very useful especially the ATX power supply as it can be converted to a lab bench power supply giving us +3.3V  +5V   +12V -12V -5V outputs with lots of power ,mine a 300W unit gives up to 30A on the 5V output which can be very handy when powering big DC motors and other stuff so let’s gather the parts and start making our power supply , forgetting about batteries and cellphone chargers to power our circuits :

The video explains it all about the making watch it :


About The Circuitry

What we need?

  • 5x Binding posts (red)
  • 1x Binding post (black)
  • 1x Toggle Switch
  • 1x 3mm Green LED
  •  1x 3mm Red LED
  • 2x 220Ω Resistor for the led’s
  • Dummy Load

Hers an image explaining the color code of the wires of a power supply :

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We have to put a dummy load on the supply to keep it stable even when we only draw small amounts of current. Old power supply’s use the most amount of power on the 5v rail so we am going to be connecting the dummy load on the 5v if you have a newer power supply you’ll need to put them on the 12v rail

Assuming the dummy load should draw at least 0.5A.

  1. Here is the calculation if you have most of your power on 5V/3,3V rail:

R=U/I=5V/0,5A=10Ω

P=U*I=5V*0,5A=2,5W

2. Here is the calculation if you have most of your power on 12V rail:

R=U/I=12V/0,5A=24Ω

P=U*I=12V*0,5A=6W

Conclusion :

  • 5v     10Ω  2.5W
  • 12V   24  6W

The Connections image assuming you have an old Power Supply :

power-supply-schematics

If you have most of your power on the 12V rail then you need to connect a 24Ω resistor to 12V instead of 10Ω to 5V.

My Power Supply Finished

DIY Power Supply
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