AUTOSTART In The Event Of A Fault On The Power Supply From The Secondary Battery

Courtesy of VOLVO CARS CORPORATION

• The secondary battery relay (2) is activated and the contacts close.
• The secondary battery (1) does not connect. A fault in the circuit means that the secondary battery cannot supply the vehicle's other power consumers.
• The battery relay (main battery) (4) is activated and the contacts open. Only the starter motor's circuit is now connected to the battery (main battery). When the voltage difference between the battery circuit and other vehicles across the battery diode (3) increases by 0.4 V (at 20°C), the battery diode opens (lead) and supply to the vehicle's other power consumers during autostart.
• The vehicle is powered from the battery (main battery) (6).
• The starter motor relays (5) are activated and the contacts closed. The starter motor is activated. The starter motor's solenoid switches on and the starter motor starts.
• When the engine has been started, the relays return to their normal positions.

This can, for a short time (approx. 300 ms), create a large voltage drop in the electrical system and cause lamps to flash for example.