Charging Batteries and Keeping Them Healthy
Operating aircraft batteries outside their ambient temperature or charging voltage limits can result in excessive cell temperatures, leading to electrolyte boiling, rapid deterioration of the cells, and battery failure. The relationship between maximum charging voltage and the number of cells is also important, as this determines the rate at which energy is absorbed as heat within the battery. For lead-acid batteries, the voltage per cell must not exceed 2.35 volts, while NiCd batteries usually have 1.4 and 1.5 volts.
The battery charging system in an airplane is a constant-voltage type. An engine-driven generator, capable of supplying the required voltage, is connected through the aircraft’s electrical system directly to the battery. A battery switch is incorporated in the system so that the battery may be disconnected when the airplane is not in operation.
The voltage of the generator is controlled by means of a voltage regulator connected in the field circuit of the generator. For a 12-volt system, the voltage of the generator is adjusted to approximately 14.25 volts, and on a 24-volt system, the adjustment is between 28 and 28.5 volts. When these conditions exist, the initial charging current through the battery is high. As the state of charge increases, the battery voltage also increases, causing the current to taper down. When the battery is fully charged, its voltage is almost equal to the generator voltage, and very little current flows into the battery. When the charging current is low, the battery may remain connected to the generator without damage.
When using a constant-voltage system in a battery shop, a voltage regulator that automatically maintains a constant voltage is incorporated into the system. A higher capacity battery has a lower resistance than a lower capacity battery. Therefore, a high capacity battery draws a higher charging current than a low capacity battery when both are in the same state of charging. The constant voltage method is the preferred charging method for lead-acid batteries.
Constant current charging is the most convenient for charging batteries outside the airplane, as it lets several batteries of varying voltages to be charged at the same time on the same system. A constant charging system usually consists of a rectifier to change the normal AC supply to DC, while a transformer is used to reduce the available 110-volt or 220-volt AC supply to the desired level before it is passed through the rectifier. If a constant charging system is used, multiple batteries may be connected in series, provided that the charging current is kept at such a level that the battery does not overheat or gas excessively.
Battery inspection and maintenance will vary depending on chemical technology and construction type, as well as the manufacturer’s approved procedures.
- To determine the life and age of a battery, record the install date of the battery and document this age in the aircraft’s maintenance logs.
- Lead-acid battery state of health may be determined by duration of service interval, environmental factors, and observed electrolyte leakage. If the battery needs to be refilled often, with no evidence of leakage, this could indicate a poor state of the battery, the charging system, or an overcharge condition.
At Accelerating RFQs, owned and operated by ASAP Semiconductor, we can help you find all the battery systems and parts for the aerospace, civil aviation, and defense industries. We’re always available and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, email us at sales@acceleratingrfqs.com or call us at 1-780-851-3631.
