How to Build Automotive Battery Charger / Booster

Having an automotive battery charger can be very useful on days when you leave your lights on. Battery chargers are used to replenish the energy a battery loses during abnormal use. In some instances, a low battery only needs to be recharged to bring it back up to a usable level. In other cases, the battery may need to be replaced if it cannot be recharged. Not much cost is saved by building a battery charger yourself, but it is a fun project for learning about electricity.

 

Bolt the transformer to the mounting block. Identify the primary and secondary side of the transformer. The power cord should have a plug on one end and two wires on the other end. Strip 1/2 inch of insulation off of the two wires and connect these two wires to the two terminals on the primary side of the transformer. This will provide power to the transformer. Do not plug the cord in yet.

 

Check the documentation that came with the transformer to identify the two 12-volt terminals on the secondary side of the transformer. Connect a 12-gauge wire from one 12-volt terminal to one of the two AC terminals on the bridge rectifier. Connect the second 12 -volt terminal to the second AC terminal on the bridge rectifier. Secure the bridge rectifier to the mounting block.

 

Connect an 8 gauge red cable to the positive terminal of the bridge rectifier. Connect an 8 gauge black cable to the negative terminal of the bridge rectifier. Strip 1/2 inch of insulation off the end of the red and black wires. Connect one large alligator clamp to each wire.

 

Clip the red cable alligator clip onto the red positive test probe of the digital multimeter. Clip the black cable alligator clip onto the black positive test probe of the digital multimeter. Turn the digital multimeter on and set it to measure DC voltage. Plug in the transformer and check the digital multimeter reading. The reading should be between 11 and 13 volts.