When charging a battery, it is important to use the proper charger. When the proper charger is not available for a battery, it becomes necessary to modify the charger circuitry to accommodate the battery voltage. One of the less complex ways to increase the voltage in a DC circuit is to convert the power within the circuit to AC by boosting or amplifying the current signal and then transforming the AC signal to a different voltage than the initial voltage.
Attach the black inverter clamp to the black charger battery clamp. Connect the red inverter clamp to the red battery charger clamp.
Separate the cable ends on the two-wire power cable until there is approximately four inches (10 cm) of separation between the cable ends. Strip 1/2 inch (1.27 cm) of insulation from the wire ends.
Solder one wire of the power cord to one of the transformer’s primary terminals. Solder the remainder of the electrical wire from the end of the cable to the remaining primary transformer terminal. Plug the power cord into one of the power outlets on the inverter.
Cut four pieces of wire, and strip 1/2 inch (1.27 cm) of insulation from each end of the wire. Solder one end of the first wire to one of the transformer secondary terminals. Solder one end of the second wire to the remaining transformer secondary terminal.
Twist together the cathode terminal (which is marked with a line through the diode housing) from the first diode together with the anode of the second diode with the free end of the first wire. Solder this connection.
Twist together the cathode terminal of the diode together with the anode of the fourth diode and the free end of the second wire. Solder this connection.
Slide a ring terminal over one end of the third wire and solder the wire to the terminal. Slide a ring terminal over one end of the fourth wire and solder the terminal to the wire.
Twist together the anodes from the first and third diodes, along with the free end of the third wire and solder the connection. Twist together the cathodes from the second and fourth diodes with the free end of the fourth wire and solder the connection.
Connect the ring terminal with the fourth wire to the positive terminal of the battery. Connect the ring terminal with the third wire to the negative terminal of the battery.
Plug the 12 V battery charger into the wall and switch on the charger. Turn on the inverter.