Introduction: 4Pin Molex Power Supply / Power 2 HDD With One Adapter

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This will show

  1. How to make a Molex 4 Pin Power Supply from a Conventional 12V Adapter?
  2. Run 2 External Hard drives with one Power Adapter.

Step 1: Parts Needed

Most of the parts from scrap which is shown.

  1. 12V 2A Adaptor
  2. Male Power Connector (which suits the External HDD)
  3. Female Power Connector (which suits the Power Adapter 12V 2A)
  4. LM7805 IC
  5. 100 uF 25V Electrolytic Capacitor
  6. 0.1 uF Capacitor, Code - 104
  7. 3.3K Ohms Resistor
  8. 3mm Green or Blue LED
  9. Male 4 pin Molex Connector
  10. 7805 PCB or just use a scrap Terminal Connector as used for testing only
  11. Heat sink (HIGHLY RECOMMENDED)


It is highly preferable to mount the circuit in a proper PCB. Since 7805 dissipates large amount of heat even for a short time. It is highly recommended to add a powerful Heat Sink for a long run.

Step 2: Circuiting

Mostly pictures and self explanatory

Make LM7805 Circuit in a PCB and provide a Heatsink

  1. 12V 2A Output to Female Connector

  2. Female Connector for Molex 12V and GND

  3. Female Connector to Male Connector for Pwr supply other HDD

  4. Circuit the LM7805 IC as shown and take GND and +5V to Molex

  5. Connect +12V GND GND +5V as per the pinouts shown

Step 3: Testing

Totally self explanatory check the attached picture.

Check quoted notes in the picture.

Step 4: Output

Picture showing both HDD powered with a single 12V adaptor.

Finish the tested circuit in a PCB and a proper Enclosure.