Building your own DIY battery charger from spare parts can be a fun and rewarding project. With just a few basic electrical components and some tinkering, you can make a functional charger on the cheap.
What You'll Need
To build a basic battery charger, you'll need the following materials:
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Transformer - Steps down high voltage AC from the wall outlet to ~12V AC. Can salvage this from an old appliance.
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Bridge rectifier - Converts AC into DC. Can be salvaged from an old device or purchased.
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Capacitor - Smooths out the DC. Electrolytic capacitors work well.
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Regulator - Drops 12V DC down to 5V to safely charge batteries. 7805 voltage regulator is commonly used.
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Heat sink - Cools the regulator. A scrap metal plate will work.
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Charging module - Has circuitry to charge batteries and indicate charge level. Can be salvaged or bought.
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Battery holder - Holds batteries securely while charging. Can be salvaged or custom built.
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Wires - Hooks all the components together. Stranded hook up wire works well.
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Case - Houses the charger. Plastic project boxes or food containers work.
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On/off switch - Allows you to control the power. Can be salvaged from an old device.
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Fuse - Prevents current overload. Get an inline fuse holder and 1-2 amp slow blow fuse.
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Plug - Connects to AC outlet. Salvage from an old appliance cord.
In addition, you'll need basic soldering equipment, hot glue, and basic hand tools.
How a DIY Battery Charger Works
Here is a quick overview of how the various components work together in a DIY battery charger:
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The transformer converts 120V AC from the wall outlet down to 12V AC. This is a safe voltage for charging small batteries.
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The bridge rectifier converts the 12V AC into pulsing 12V DC by routing the positive sections of the AC wave in one direction, and the negative sections in the opposite direction.
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The capacitor smoothes out the pulsing DC into a steady stream of 12V DC current.
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The regulator takes the 12V DC and further reduces it to a steady 5V DC, which is a common charging voltage for many small rechargeable batteries.
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The charging module has internal circuitry to properly charge the batteries being used based on their chemistry. It indicates charging status with LEDs.
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The battery holder securely holds the batteries in connection with the charging module's terminals during charging.
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The wires carry current between all the components.
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The case neatly houses the charger, while the switch, fuse, and plug control the power safely.
Step-by-Step Building Instructions
Follow these steps to build your own battery charger:
1. Plan the Layout
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Determine an appropriate case to house your charger. Measure the internal dimensions.
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Plan out where you'll place each component and how you'll route the wiring between them.
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Decide on locations for the power switch, fuse holder, charging module, and any status LEDs.
2. Mount the Components
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Transformer - Securely mount it to the case, ensuring no loose wires touch the metal core.
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Bridge rectifier - Attach it to a heat sink, such as a scrap aluminum plate. This cools the rectifier.
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Capacitor - Glue or tie it securely, ensuring it won't touch other components.
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Regulator - Attach to a heat sink and mount it securely.
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Charging module - Screw or glue it in place, ensuring terminals are accessible.
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Battery holder - Mount it securely near the charging module's terminals.
3. Wire the Components
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Refer to a wiring diagram for proper connections. Solder for secure connections.
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Transformer - Connect the AC wires to the bridge rectifier input.
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Rectifier - Connect the positive and negative DC outputs to the capacitor and regulator inputs.
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Regulator - Connect the 5V DC output to the charging module's power terminals.
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Charging module - Connect the battery holder terminals to its charge terminals.
4. Install Controls and Finish
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Connect the AC plug to the transformer's input wires. Add the inline fuse.
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Connect the power switch to the AC wires between the plug and fuse.
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Tidy all the wiring using wire loom and strain relief. Double check connections.
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Close up the case and screw it shut. Your charger is complete!
Charging Batteries
To use your new DIY battery charger:
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Ensure you are charging batteries of the correct size, voltage, and chemistry for your charging module.
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Insert the batteries into the battery holder, ensuring correct polarity.
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Plug in the charger and flip on the power switch. The status LEDs will indicate charging.
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Allow the batteries to fully charge, then disconnect them when finished.
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Always supervise charging batteries. Do not leave charging unattended.
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Avoid shorting the battery terminals together outside of the charger.
With some thriftiness and ingenuity, you can build your own capable battery charger for pennies on the dollar compared to commercial versions. Plus you'll learn useful electronics skills in the process! Just be sure to follow safe wiring methods and double check your work.