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Maintaining Nickel-Cadmium Batteries


Compared with lead batteries, nickel-cadmium batteries require more complex maintenance because they have discharging and recharging cycles requiring that the batteries be attended by an operative during this lengthy process; in addition they need to be handled in a shop equipped with an air suction device.


“It is in order to ensure that nickel-cadmium batteries maintain their charge level constant over time and exploit their full potential that it is necessary to go through a series of steps in the maintenance process, whereby the batteries are brought to the maintenance shop to be fully discharged and then fully recharged. The charge of the battery is brought to zero in order to make sure that it has no power at all,” Segrè says. “The battery is then fully charged to the nominal value, an energy charge is consequently applied, and a measurement is then taken as to how much voltage is lost in time due to energy absorption. This measurement provides an assessment of the battery’s ‘health’ condition. Once it is ascertained that the battery is fine, a second discharge cycle is performed. The battery is then fully recharged and reinstalled on board. This type of maintenance is more demanding – even in terms of manpower – and requires specific tooling.”


Every battery model has its own maintenance manual and kit for accomplishing charge and discharge tasks. The health of nickel-cadmium batteries is ensured by how accurately the charge and discharge tasks are performed. “When maintenance is being initiated it is of fundamental importance to properly predict the discharge time of the cells, which have to be fully discharged, and proceed to recharge them. In fact, it is possible to experience the so-called ‘memory effect’ when a battery is not fully discharged and has a residual charge. When it is recharged, the available charge is not the full charge but rather the full charge net of the residual charge. If a battery is not fully discharged the residual charge actually has a negative effect in the recharge process. This consideration is important because it affects the usable life of a battery. Oftentimes you have to change the batteries - or replace their cells - because prior discharge and recharge maintenance cycles have not been properly performed,” Segrè says.


To conclude, lead, nickel-cadmium, and gel batteries are the types that can be most commonly found on helicopters. Turbine- powered helicopters tend to be equipped with nickel-cadmium batteries and these require relatively complex maintenance because of the discharging and recharging cycles that have to be performed and that are key to ensuring their health and functionality.


76 Nov/Dec 2017


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