How to Build Your Own 9 Volt Battery Charger

Written by william kinsey
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How to Build Your Own 9 Volt Battery Charger
Transformers are a key component in battery chargers. (power supply image by pmphoto from

A 9-volt battery is typically used for certain small devices such as toys and other devices that require a small compact power source. Because of their high usage in the toy industry, rechargeable 9-volt batteries have become the common choice. In fact, many hobbyists choose to build their own 9-volt battery charger, allowing them to customise it to their own particular needs.

Skill level:

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Things you need

  • 120-Volt to 12-volt power transformer with a 9-volt tap
  • 12-Volt bridge rectifier
  • Wire cutters
  • Wire Strippers
  • 12 Gauge electrical wire
  • 6-Foot power cord

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  1. 1

    Review the transformer schematic that came with the transformer. Identify the two primary terminals. Strip 1/2 of an inch of insulation off of the two wires of the power cord. Take one of these two wires and connect it to the first primary terminal. Connect the second wire to the second primary terminal.

  2. 2

    Identify the two 9-volt transformer terminals on the secondary side of the transformer. Then identify the two 120-volt AC terminals on the bridge rectifier. Connect one of the 9-volt terminals to one of the two AC terminals of the rectifier using the 12 gauge wire. Then connect the second 9-volt terminal to the second AC terminal.

  3. 3

    Connect a 6-foot wire to the positive terminal of the rectifier. Attach an alligator style clamp to the opposite end of that wire and label it "Positive."

  4. 4

    Repeat step 3 for the negative terminal of the rectifier, but label the alligator clamp "Negative." Voltage regulation circuitry can be added after the rectifier if needed.

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