Dual Battery System for ’91-’97 Land Cruisers • by: Christo Slee
Click on the picture above to get a PDF document of the schematic
Adding a winch, auxiliary lighting or an other power hungry accessories might put too much strain on your stock battery and a need for a seconds battery soon arises. In addition to reserve capacity, a second battery is an excellent way to ensure that you can get out of the boonies when your main battery fails, or is killed by winching or leaving the stereo on for too long.
After contemplating different systems and our own considerations we came up with the following list of requirements:
- Charge both batteries when the car is running but disconnect the batteries when not.
- Override the default connection behavior from inside the truck.
- Winch should draw power from either battery or both.
- Winch power should be disabled when not in use.
- Self jump self mode in case main battery goes dead
The system we decided upon consist of the following:
- Factory battery tray hold down bar from 1991 FJ 80.
- Sleeoffroad.com modified windshield washer bottle relocating kit
- Dual input /one output 300 amp marine battery switch.
- 200 amp continuous duty solenoid.
- Lots of 1ga welding cable.
- Interior switches, relays and other wiring.
200 Amp Continuous duty solenoid that keeps both batteries connected when engine is running. The solenoid is activated from the charge circuit of the alternator.
After relocating the washer bottle and installing the battery tray, the solenoid was installed on the fender, between the air filter housing and battery tray.
The solenoid is activated from the charge circuit of the alternator. The circuit can be turned off via a dash switch, thus overriding the default connection of the batteries when the vehicle is running.
The ground side circuit of the solenoid is run through a normally closed relay. This activation side of this relay is powered from the output side of the marine battery switch. A small circuit was installed from the output side of the marine switch to trip a normally closed relay on the ground side of the solenoid. This effectively takes the solenoid out of the circuit when the winch is activated.
After this, the marine battery switch was installed on ‘legs’ welded to the windshield washer relocate kit bracket. 1 ga welding cables were run from each battery to the switch. Then the solenoid was connected in parallel to the switch.
The switch has the following settings:
1 – Power to the winch is supplied from main battery
2 – Power to the winch is supplied from second battery
BOTH – Power is supplied to winch from both batteries. The BOTH position of the switch also serves as a SELF JUMP START position.
Since we added interior winch controls using the stock a stock antenna switch, it was decided to add a warning light to indicate when the winch was “live”.