What are Front terminal batteries?

General information about front terminal batteries, Discharging, determining the state of Battery Banks.

Here is the content list:

How Lead-Acid Batteries Work?

Discharging

Battery Banks

How Lead-Acid Batteries Work?

Most front terminal batteries are constructed with the positive electrode (the anode) made from a lead-antimony alloy with lead (IV) oxide pressed into it, although front terminal batteries designed for maximum life use a lead-calcium alloy. The negative electrode (the cathode) is made from pure lead and both electrodes are immersed in sulphonic acid.

When the battery is discharged water is produced, diluting the acid and reducing its specific gravity. On charging sulphonic acid is produced and the specific gravity of the electrolyte increases. The specific gravity can be measured using a hydrometer and will have a value of about 1.250 for a charged cell and 1.17 for a discharged cell, although these values will vary depending on the make of the battery. The specific gravity also depends on the battery temperature and the above values or for a battery at 15°C.

If front terminal batteries are over-discharged or left standing in the discharged state for prolonged periods hardened lead sulfate coats the electrodes and will not be removed during recharging. Such build-ups reduce the efficiency and life of front terminal batteries. Overcharging can cause the electrolyte to escape as gases.

Discharging

Front terminal batteries transfer energy to electrons so that they 'flow' around a circuit, the Electro-Motive Force (EMF) is the total amount of energy per coulomb of charge that a battery can supply and is measured in volts. The EMF of a front terminal battery is provided by the chemical reactions described above and can be seen as the maximum possible voltage across the cell's terminals (the open-circuit voltage). The path taken when the current passes through the front terminal batteries will have resistance. This internal resistance depends on the cell's design, construction, age, and condition. On discharge, this internal resistance (Rc) causes the voltage measured across the cell's terminals to be less than the EMF of the cell.

Note that if a high resistance voltage meter is used to measure the voltage across a battery’s terminals it will register the front terminal battery’s EMF; as long as there is no current flowing through a load from the battery. If the terminal voltage is measure when a current is flowing through a load from the battery, the meter will register the EMF minus the voltage drop across the internal resistance.

Battery Banks

Battery banks in small power systems normally have nominal voltages of either 12V or 24V however, lead-acid front terminal batteries are available from 4V up to 24V. Front terminal batteries can be combined in series so that their voltages are added together: two 12V front terminal batteries in series will provide 24V. Although voltages are adding the same current will flow through each battery, so that two identical front terminal batteries 12V in series supplying 5A to a load each supply 5A: therefore, the Ah capacity of two identical front terminal batteries in series is the same as one battery on its own. The total internal resistance (RC) of front terminal batteries in series will equal the internal resistances of the individual front terminal batteries added together.

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