05 November, 2009

Electrical unit of Hybrid Vehicle

Hybrid vehicles are part electrical and part mechanical. The electrical definitions apply to the electrical part of the hybrid vehicle. Batteries are classified as primary batteries or secondary batteries. A primary battery cannot be recharged, and, therefore, is of little use in a hybrid. The chemical reactions providing the electrical energy are irreversible. A secondary battery, which has reversible reactions, can be charged and discharged. The basic unit of a battery is the voltaic cell, or just cell. Appendix 6.1 discusses the cell and gives the component parts, anode, cathode, and electrolyte, that form the basic unit. Batteries are composed of collections of cells. Typically, cells have a voltage of less than 4 V. Each cell has a voltage depending on the electrochemical potential of the chemicals. Nickel metal hydride (NiMH) has cell potential of 1.2 V. Lead acid has a cell potential of 2 V. To increase voltage, cells are placed in series end-to-end. A 12 V lead acid battery has six cells in series. Nominally the lithium-ion (Li-ion) battery has a cell voltage of 3.6–4.3 V. Four features are used quantitatively to describe the battery: current, voltage, energy, and power. These features can be described by analogy or defined by precise scientific definitions that can be found in any physics textbook. A water hose is useful as an analogy. The amount of water fl owing through the hose is analogous to electrical current. The unit for electrical current is ampere. The water hose analogy for voltage is pressure. High pressure water in the hose has lots of voltage. An appropriate analogy for a storage battery is a water dam. When the water depth behind the dam is zero, the battery is dead. When the dam is full of water, the battery is charged.


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