Starting and Charging: Fundamentals and Basics

This article explains some of the terms and expressions used by Volvo.

Armature
The rotating part of an electric motor.

Bimetallic spring
Two joined Strips of different metals with different rates of expansion, shaped as a plate spring. As temperature increases the spring bends in one direction, as temperature decreases it bends in the opposite direction.

Buffer
A buffer reduces the effect of a strong variation of force, current, load etc.

Commutator
The segmented ring mounted on the armature shaft.

De-ionized water
Water with reduced chemical energy; can be used instead of distilled water in car batteries.

Density
Weight per unit volume, measured in kg/I.

Diode
A device which allows electric current to pass in one direction only.

Distilled water
Purified water. The impurities have been removed by heating up and vaporizing water. The vapor is then cooled and water, called distilled water, is collected. It is used in car batteries to dilute the sulphuric acid in the electrolyte.

Deionized water can also be used.

Electrolyte
Sometimes called battery water. A substance which will conduct electricity and undergoes a chemical decomposition when an electric current is passed through it.

Exciter current-winding
Responsible for the magnetic field in which the armature turns.

Field winding
See exciter winding.

Half wave rectification
Only one half of the alternator current passes through the rectifier so that only half of the electrical energy is available.

Reactive coil
Often called choke coil. Usually the coil is wrapped around an iron core. Suppresses electromagnetic waves; acts as an anti-interference device. A reactive coil has a small resistance against low frequencies and a high resistance against high frequencies.

Specific gravity
The ratio of the density of an electrolyte to the density of water at a specific temperature.

Voltage drop
The loss in voltage resulting from electrical resistances in cables and connections.

Thermistor
A resistor whose resistance is greatly dependent on temperature. An abbreviation for "Thermally Sensitive Resistor".

Torque
The force developed at a certain distance from the centre of a body.