A lead-acid battery is an accumulating whole of S with lead-acid connected in series and joined together in the same case.

This storage systems of electricity is largely used in the Industrie like in the equipment of the vehicles Automobile S.

History

The lead accumulator was invented in 1859 by French Gaston Planté. It was the first refillable accumulator.

At the origin, the accumulators were located in tanks out of glass. Thereafter, one systematized the use of the plastic tanks.

Nowadays, the batteries without maintenance spread: treated thimbles antisulfatage, plates with lead-calcium, removing the need to remake the level of liquid, and thus allowing sealing.

Features

A lead-acid battery is characterized primarily by:
  • the nominal voltage which depends on the number of elements, the nominal voltage U is equal to the number of elements multiplied by 2,1 V
  • the storage capacity , noted C , which is expressed in amp S during 1 hour: corresponding theoretical electrical energy is C X U , expressed in Wh. (Let us note that the value in Ah has value only for one tension or rather a beach of tension. Generally it is considered that a lead accumulator is discharged when it reaches the tension of 1.8 V , therefore a battery from 6 elements or 12 V is discharged, when it reaches the tension of 10.8 V ).
  • the maximum current which it can provide during a few moments, or peak current in amps CCA .

These maximum values are given by the manufacturer for a battery new and charged at 100%, they appreciably vary according to the state of load, are degraded according to time thus, that use which is made battery.

  • the electrochemical reactions to the electrodes are the following ones:

Anode (oxidation):

\ mbox {Pb} (S) + \ mbox {SO} _ {4} ^ {2} (aq) \ leftrightarrow \ mbox {PbSO} _ {4} (S) +2e^- \ quad \ epsilon^o = -0.356 \ \ mathrm {V}

Cathode (reduction):

\ mbox {PbO} _ {2} (S) + \ mbox {SO} _ {4} ^ {2} (aq) +4 \ mbox {H} ^++2e^- \ leftrightarrow \ mbox {PbSO} _ {4} (S) +2 \ mbox {H} _2 \ mbox {O} (L) \ quad \ epsilon^o = 1.685 \ \ mathrm {V}

Performances

The lead-acid battery is that which with worst the specific Power 35 Wh/kg , after the Nickel-Fer battery. But as it is able to provide a current of great intensity, useful for the electric starting of the internal combustion engines, it still is very much used in particular in the motor vehicles.

Use

This battery is used to feed the electric components of the motor vehicles with explosion, particularly the electric starter, supplied with a Dynamo or a Alternateur.

Historically, the batteries of cars or motor cycles generally made 6 volts (3 elements). At the time modern, the batteries with 12 volts (6 elements) are generalized on the cars and motor cycles, whereas the heavy or military vehicles use the 24 volts.

The lead-acid batteries are also used to feed all kinds of electric machines. The electric cars still were not essential because of the bad report/ratio masses/energy of the batteries although the output of an electrical motor is exceptional.

These batteries can be used to store energy produced intermittently, like solar energy or wind mill.

Causes of degradation

The leading causes of degradation of the batteries are:
  • sulphating
  • the discharge supplements
  • cycling
  • the oxidation of the electrode S
  • the oxidation of the terminals

Sulphating

Sulphating represents the accumulation of Sulfate of lead on the electrodes. This phenomenon appears naturally with each discharge of the battery, and disappears at the time of a refill. However under certain conditions (prolonged or too major discharge, important temperature, gasification of the electrolyte), of lead the stable sulfate small islands appear and are not dissolved any more at the time of the load. The lead sulfate thus generated decreases the capacity of the battery by preventing the reactions on the electrode and from its low electric conductivity.

The process of sulphating is stopped as soon as the battery is given in load.

Exemple: A sulphated battery of 1000 CCA in a new state, but controlled with 12  V and with a power of 500 CCA, will take again after refill a higher tension or equalizes with 12,6  V but the measured power of 500 CCA will evolve/move little.

A battery in this state will not allow several consecutive startings of a motor vehicle and will be able to cause, for example, a breakdown immobilizing as of the cold first. In a general way, its battery should be reloaded regularly to make it last.

Désulfatation

There exists a means of reversing the process of sulphating of a battery. That consists of the sending of electric impulses at the frequency of resonance of the battery (between 2 and 6 MHz). During this process, the ions of suffers enter in collision with the plates, which causes to dissolve lead sulfate which recovers them.

Complete discharge

For a motor vehicle, the complete discharge of the battery generally intervenes by low fuel consumption for one prolonged length of time (ex ceiling lights) or by an important consumption (ex headlights dipped, ventilation), engine with the stop. The tension is then very weak at the boundaries of the battery, lower than 10 volts for a battery whose nominal voltage is of 12  V.

A starting battery discharges also all alone in time. It is thus likely to reach its complete discharge if it is not reloaded regularly. For this reason, there exist the chargers " of maintenance " batteries.

The batteries in a state of complete discharge must be reloaded within a 48 hours maximum delay: beyond, the damage is irreversible (except by desulfatation).

Cycling

The manufacturers of batteries indicate their lifespan in the form of a number of standardized cycles of discharge/refill.

At the conclusion of a certain operating time depend on the number and amplitude of the cycles, the battery is worn: the electrolyte presents an aspect noirâtre.

Exemple: The repeated use of a driving lifting forage ladder to the stop accelerates the wear of the battery by cycling.

Oxidation of the electrodes

Oxidation is a cause of dysfunction of the batteries. When the level of electrolyte is too low, the plates enter in contact with the air and oxidize. The power with starting is cut down, even if the level of electrolyte is supplemented. The lack of electrolyte can come from an intensive use (ex: auxiliary equipments…), of an important outside temperature (higher or equalizes with 30  °C) or of a too high charging voltage.

Oxidation of the terminals

It happens that a battery whose thimbles are not tightened enough, or who is only useful very little, way its terminals to oxidize, which will prevent the current from passing and thus, in the long term, a complete discharge.

See too

Random links:Emile Mompart | Rollo (department) | Elias James Corey | Frassem | Strake