3.) Battery Theory
Updated Friday 13/03/2009 3:19pm
Battery technology has advanced progressively over the past 10-15 years with the advent of a variety of lead-acid types, ranging from the multi-plate, high instantaneous current capability versions (for engine starting) to the heavy traction types having low current capabilities but high discharge levels. Low-maintenance, maintenance-free, gel-type and nickel-cadmium batteries are available for a variety of applications (see section Battery Facts & Type Comparisons).
With the exception of the nickel-cadmium type, the performance and life of most batteries is adversely affected by inadequate charging caused by poor voltage regulation, the prime causes being:
- a. sulphation, which is well known;
- b. the lesser known phenomenon occasionally referred to as 'counter voltage'
Sulphation:
This occurs as a result of batteries being left in a discharged condition for lengthy periods.
The normal chemical reaction in the battery cells becomes incomplete and an inert coating of lead sulphate forms on the active surface of the cell plates, inhibiting the charging current and reducing battery capacity. Rapid deterioration and premature failure ensues.
Counter Voltage:
This is always present during charging and is the result of a charge build-up on the surface of the battery plates, without sufficient time for the charge to percolate into the cell matrix. The result is an artificially high battery voltage which is sufficient to fool a conventional voltage regulator into believing the battery has attained a higher level of charge and the alternator output is reduced accordingly.
This is less of a problem for engine starting batteries which experience high current drain for short periods and counter-voltage is low, on recharge. The effect is considerably more marked with auxiliary or domestic batteries where there is low/medium discharge over a long period. In practice, battery capacity is never fully restored.
