Assembled battery system and assembled battery protection device

A protection device for an assembled battery including a plurality of electric cell blocks connected in series, the electric cell blocks each including at least one nonaqueous electrolyte secondary battery provided with a negative electrode current collector formed of aluminum or an aluminum alloy, the device comprising:

• a voltage measuring unit configured to measure a plurality of voltages of the electric cell blocks;
• a controller which controls charge/discharge of the assembled battery in accordance with the measured voltages;
• and
• bypass circuits connected in parallel to the electric cell blocks, the bypass circuits each bypassing a current that flows from a negative electrode of one of the electric cell blocks to a positive electrode of the one of electric cell blocks when the measured voltage of the one of electric cell blocks is a negative value not greater than a threshold value,
• wherein the bypass circuits each include a MOSFET and a bias voltage source, the MOSFET storing a threshold voltage and having a source terminal connected to the positive electrode of a first corresponding one of the electric cell blocks, a gate terminal and a drain terminal, a drain terminal connected to the negative electrode of the first corresponding electric cell block and a gate terminal, the bias voltage source applying a bias voltage between the gate terminal and the drain terminal.

An assembled battery system comprising:

• an assembled battery including a plurality of electric cell blocks connected in series, the electric cell blocks each including at least one nonaqueous electrolyte secondary battery;
• a voltage measuring unit configured to measure a plurality of voltages of the electric cell blocks;
• a controller which controls charge/discharge of the assembled battery in accordance with the measured voltages;
• and
• bypass circuits connected in parallel to the electric cell blocks, the bypass circuits each bypassing a current that flows from a negative electrode of one of the electric cell blocks to a positive electrode of the one of electric cell blocks when the measured voltage of the one of electric cell blocks is a negative value not greater than a threshold value,
• wherein the bypass circuits each include a MOSFET and a bias voltage source, the MOSFET storing a threshold voltage and having a source terminal connected to the positive electrode of a first corresponding one of the electric cell blocks, a gate terminal and a drain terminal, a drain terminal connected to the negative electrode of the first corresponding electric cell block and a gate terminal, the bias voltage source applying a bias voltage between the gate terminal and the drain terminal.