How to Build a Battery Isolator

High power (20 ampere or greater) diodes are required for this project.
••• diodes image by Albert Lozano from Fotolia.com

Automotive battery charging circuits are designed to recharge and maintain a single battery. However, automobiles with custom audio systems, electric winches or other high-drain devices may require a second battery to power these devices.

One of the problems with connecting two batteries directly to an automotive charging system is that if one battery is weaker (provides less electrical current at the same voltage) than the other, the charging system may be taxed beyond its design parameters for providing power. This also has the undesirable consequence of draining the “good” battery to equalize the charge in both batteries.

One way to charge both batteries without overtaxing the charging system is by using a battery isolator. A battery isolator is constructed using two diodes, which act as one-way electrical check valves for the charging system.

    Cut three, 2-foot-long pieces of wire and strip one-half inch of insulation from each wire end.

    Solder a lug terminal to one end of the first wire, and mark the side of the lug terminal with the letter “A.” Solder the free end of the first wire to the anode leads on both diodes.

    Solder a lug terminal to one end of the second wire, and mark the side of the lug terminal with the number “1.” Solder the free end of this wire to the cathode lead on the first diode.

    Solder a lug terminal to one end of the third wire, and mark the side of the lug terminal with the number “2.” Solder the free end of this wire to the cathode lead on the second diode.

    Things You'll Need

    • Solder-type lug terminals (3)
    • High-current diodes (two; RF1501TF3S or equivalent – See “Resources”)
    • Soldering iron
    • Electronic solder
    • Electrical wire (insulated copper, minimum 8 AWG thickness)
    • Electrical pliers
    • Permanent marker

    Tips

    • When attaching this battery isolator to the charging system, connect the “A” lug terminal to the charging system (typically the “BAT” terminal on an automotive alternator). Attach the “1” lug terminal to the positive terminal on the first battery, and attach the “2” lug terminal to the positive terminal on the second battery.

    Warnings

    • The battery isolator will become very hot during use.

Related Articles

How to Get 12 Volts From a 48 Volt Golf Cart
How to Build DC to AC Power Inverters
How to Convert 12 Volt Alternator to 120 Volts
How to Reduce 12 Volt to 6 Volt
How to Convert 12 Volt to 6 Volt
How to Use a Resistor for 12 Volt to 5 Volt
How to Wire a Battery in Series
How to Get 12 Volts From a 48 Volt Golf Cart
How to Reduce Voltage on 12 Volt System to 4 Volt
How to Build You Own Battery Pack AA 9 Volt
How to Convert a John Deere 4020 From Two Batteries...
How to Turn a 12-volt DC Into a 5- or 6-volt DC
How to Convert a 9V Battery to 3.3V DC
How to Calculate KVA to MVA
How to Calculate Ohms
How to Build a 120V AC to 12V DC Power Converter
How to Convert Ohms to Kilowatts
Batteries Rely on What to Separate Positive & Negative...
How to Regulate DC Power With Resistors
How to Convert Megawatts to Amps