Subject: Automobile Engineering

Topic: Electrical System, Starting Systems & Alternator

Difficulty: Medium

The battery rating are recommended by society of Automotive Engineers (SAE):
i) 20 hour rating - It indicates the lighting ability of a full charge battery. It is obtained by discharging the battery at a current rate equal to 1/20 of the manufacturer’s ampere hour rating. The current rate that battery deliver continuously for 20 hour after which cell voltage should not drop below 1.75 & battery temperature is 80 degree Fahrenheit

ii) Coil rating:- It gives an indication of cold weather starting ability of the battery. The number of minutes of a 6 volt battery can deliver 300 ampere at 0 degree F before cell voltage drops below 1 volt.
iii) 25-ampere rating It measures the battery performance at a moderate constant current output at 80 F to a final limiting voltage 1.75 volt/cell. It is the ability of battery to carry electrical operating load when generator is not working.
iv) 90 minute rating:- It is the amount of current that can be delivered by battery continuously during 20 minute. Without dropping a cell voltage below 1.5 A temperature of 27 degree celsius is maintained at the start of test.