Study of the Battery
A battery is any element capable of storing electrical energy for later use. The elements that form a battery are shown in the figure above. The liquid inside the battery is called the electrolyte, which is composed of a mixture of distilled water and sulfuric acid with a ratio of 34% sulfuric acid and the rest distilled water. The electrolyte level must be one inch above the plates.
Coupling Batteries
To achieve higher voltages (V) or battery capacity (Amp-hours Ah) than those available with standard batteries in the market, a joining technique is used. This binding can be through:
- Series Coupling
- Parallel Coupling
- Mixed Coupling
Series Coupling: The main feature of series coupling is that the battery voltage is added, and the capacity remains the same. A point to take into account with this coupling is that the battery capacity (Ah) must be the same for all batteries. If one of them has less capacity during the charging of the batteries, this battery would reach full charge before the others, which would be subjected to an overload. The effects can damage the battery. Also, during the discharge process, the battery with less capacity is discharged before the others, and its plates can be sulfated.
Parallel Coupling: The main feature of parallel coupling is that the capacities of the batteries are added, while the voltage remains invariable. A point to take into account with this coupling is that all batteries must have equal voltage (V) at their terminals. If not, the battery with the highest terminal voltage will discharge through the one with the lower voltage.
Mixed Coupling: Mixed coupling involves joining batteries in series and in parallel to achieve the sum of the benefits of each coupling type.
Checking the Charge of a Battery
To check the status of a battery’s charge, a hydrometer or weigh-acids (figure below) is used. This consists of a graduated glass cylinder with an open extension for the liquid to enter. The liquid is absorbed by the internal vacuum created by a bulb located at the top of the device. Inside, there is a sealed glass ampoule filled with air and balanced with lead shot. The ampoule is graduated densimetrically from 1 to 1.30.
Method of Measurement: The open end is inserted through the mouth of each battery cell, as shown in the figure above right, aspirating enough liquid to raise the ampoule and read the density corresponding to each cell directly on the graduated scale. After reading, the liquid must be returned to the cell. Some hydrometers use a color scale instead of numbers.
The hydrometer test should not be performed immediately after filling the cell with distilled water but must wait until it is thoroughly mixed with the acid.
A good battery performance is obtained when the gravity of the electrolyte is between 1.24 and 1.26. For a full charge, it has to give us 1.28. If we have a value of 1.19, the battery is discharged.
You can also check the charge of a battery with a voltmeter specifically designed for this type of measurement, which has a resistance between the test tips. This voltmeter is unique because the measurement causes a discharge of the battery through the resistance. The measurement should be done as quickly as possible to avoid causing a significant discharge of the battery.
Values read on the voltmeter are:
- If the battery has not been used in the last 15 minutes, we will have a voltage of 2.2 V per cell if the battery is fully charged, 2 V if it is at half charge, and 1.5 V if it is discharged.
- If the battery has just been discharged, we will have a voltage of 1.7 V per cell if the battery is fully charged, 1.5 V if it is at half charge, and 1.2 V if it is discharged.
Example: 2.2 V x 6 cells = 13.2 V. This would be the measured voltage when the battery has not been used for more than 15 minutes and is fully charged.
Battery Charging
Before charging a battery, it must be checked and cleaned superficially. The electrolyte should be at its proper level. The cell caps must be uncovered and kept open during charging, and polarity must be respected when connecting the battery to the charger.
The battery charger (seen in the figure) should be regulated to a charging current of 10% of the nominal battery capacity, which is expressed in ampere-hours (Ah) by the manufacturer. For example, for a 55 Ah battery, the charging intensity will be 5.5 A. The internal temperature of the electrolyte should be checked and should not exceed 25 to 30°C. The charging should be interrupted when the temperature of one of the central cells reaches 45°C and resumed again when it has cooled down.
Whenever a battery cable is to be disconnected, the ground or negative cable is removed first, and then the positive cable. To connect the battery, the positive cable is connected first, and then the ground cable.