Submarine batteries are the hidden power source that let a diesel-electric submarine move quietly underwater. On the surface or while snorkeling, diesel engines can run generators to recharge the battery banks. When the submarine dives, the diesel engines stop because they need air, and electric motors draw energy from the batteries.
This quiet operation is important because reducing noise helps a submarine avoid detection by sonar.
Key Facts
- Electrical energy stored in a battery can be estimated by E = VIt, where E is energy, V is voltage, I is current, and t is time.
- Battery capacity is often measured in ampere-hours, with capacity = current x time.
- Power delivered to a motor is P = VI, where P is power, V is voltage, and I is current.
- Diesel-electric submarines recharge batteries using diesel engines connected to generators when air is available.
- Lead-acid batteries are heavy and proven, while lithium-ion batteries usually store more energy per kilogram.
- Silent submerged travel depends on electric propulsion because electric motors are much quieter than running diesel engines.
Vocabulary
- Battery bank
- A battery bank is a large group of connected battery cells that stores enough electrical energy to power submarine systems and propulsion.
- Diesel-electric submarine
- A diesel-electric submarine uses diesel engines to generate electricity and batteries to power electric motors while submerged.
- Lead-acid battery
- A lead-acid battery is a rechargeable battery that uses lead plates and sulfuric acid electrolyte to store electrical energy.
- Lithium-ion battery
- A lithium-ion battery is a rechargeable battery that moves lithium ions between electrodes and can store high energy in a relatively small mass.
- Electric propulsion
- Electric propulsion is movement produced by electric motors that turn the submarine propeller or pump-jet.
Common Mistakes to Avoid
- Thinking diesel engines run normally while the submarine is deep underwater is wrong because diesel engines need a steady air supply for combustion.
- Confusing energy with power is wrong because energy is the total stored or used amount, while power is the rate at which energy is delivered.
- Assuming a larger battery voltage always means longer underwater range is wrong because range depends on total stored energy, motor power, speed, and efficiency.
- Ignoring battery safety and cooling is wrong because large battery banks can overheat, release gas, or fail if charging and discharging are not controlled.
Practice Questions
- 1 A submarine battery bank supplies 600 V at 2000 A to an electric motor for 3 hours. How much energy is delivered in kilowatt-hours?
- 2 A battery bank has a capacity of 12,000 ampere-hours. If the submarine draws a steady current of 1500 A, how long can the bank supply that current before reaching this capacity limit?
- 3 Explain why a diesel-electric submarine is usually quieter when running on batteries underwater than when operating diesel engines near the surface.