Cooling system for secondary battery

A cooling system for a secondary battery, the secondary battery being installed on an electric vehicle for driving the electric vehicle, the cooling system comprising:

• a cooling fan configured to send cooling air to the secondary battery, the cooling fan being configured to be driven based on a command value, the command value being a parameter that determines a rotational speed of the cooling fan;
• a temperature sensor configured to detect a temperature of the secondary battery;
• and
• a controller configured to:
• drive the cooling fan at a fixed command value for a predetermined period when the temperature of the secondary battery becomes equal to or higher than a first predetermined temperature after the electric vehicle is started,
• detect a presence or absence of an abnormality in the cooling fan based on an actual rotational speed of the cooling fan during the predetermined period, and
• inhibit fixing the cooling fan at any fixed command value when the temperature of the secondary battery is equal to or higher than a second predetermined temperature that is higher than the first predetermined temperature, and drive the cooling fan at a variable command value.