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How to Build a 9V Rechargeable Battery Into Existing Electronics

Modern battery powered devices, such as portable radios and pocket torches, can cost a great deal more when replacing their disposable primary batteries. One possible solution is to replace the manufacturer's original power supply with a longer lasting and more environmentally-friendly, 9V PP9-type rechargeable battery. It is unlikely that your particular portable device operates at 9V, so it is necessary to convert the PP9 battery voltage to the operating voltage of your device. This can be done using an LM 317 voltage regulator, integrated circuit.

Things You'll Need

  • LM 317 datasheet
  • Strip board
  • Side cutters
  • Thin gauge wire
  • LM 317 voltage regulator
  • 240 Ohm resistor
  • Hobbyist's resistor kit
  • Soldering iron
  • PP9 snap on connector
  • Heat shrink tubing
  • Hot air gun
  • PP9 battery
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Instructions

  1. Create the Circuit Using Strip Board

    • 1

      Download and print the LM 317 data sheet from the National Semiconductor website. The link is provided in the Resources section. You will need this document to be able to build the voltage converter circuit.

    • 2

      Cut a piece of strip board using side cutters. The grid size will need to be 20 by 20 holes.

    • 3

      Assemble the circuit by placing the components in the strip board holes, according to the LM 317 datasheet. Use thin gauge wire to make the connections, but do not connect the resistor, "R2."

    • 4

      Solder the components in place using a soldering iron. Be careful not to bridge any connections unnecessarily with excess solder.

    Calculate the Value of "R2"

    • 5

      Use the online LM 317 calculator to calculate the required value of '"R2." Use trial and error to change the value of "R2" until you obtain the desired output voltage. The output voltage should match the operating voltage of the appliance you are modifying.

    • 6

      Select a matching resistor from your hobbyist's resistor kit. Position this resistor in the space you left for "R2" on your strip board.

    • 7

      Solder the resistor in place on your circuit strip board.

    • 8

      Solder the negative side of your PP9 battery connection to the ground side of the stripboard. Solder the positive side of your PP9 battery connection to pin three of the LM 317 voltage regulator.

    • 9

      Connect the positive side of the appliance's battery connector to pin two of the LM 317 battery connector. Connect the negative side of the appliance's battery connector to the ground side of the strip board.

    Insulate and Test the Circuit

    • 10

      Insert the strip board into a length of heat shrink tubing. Heat this with a hot air gun until it tightly wraps around the board.

    • 11

      Conduct a final visual inspection of the circuit before connecting power. Do not connect the battery if you have any doubts as to the safety of your circuit.

    • 12

      Connect the PP9 battery and turn the appliance on. The strip board will now be converting a 9V battery to the operating voltage of your appliance.

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