How to Charging the Nickel Cadmium Battery(3)? How to Charging the Nickel Cadmium Battery(3)? More advanced NiCd chargers sense the rate of temperature increase, defined as dT/dt, or the change in temperature over charge time, rather than responding to an absolute temperature (dT/dt is defined as delta Temperature / delta time). This type of charger is kinder to the batteries than a fixed temperature cut-off, but the cells still need to generate heat to trigger detection. To terminate the charge, a temperature increase of 1°C (1.8°F) per minute with an absolute temperature cut-off of 60°C (140°F) works well. Because of the relatively large mass of a cell and the sluggish propagation of heat, the delta temperature, as this method is called, will also enter a brief overcharge condition before the full-charge is detected. The dT/dt method only works with fast chargers. Harmful overcharge occurs if a fully charged battery is repeatedly inserted for topping charge. Vehicular or base station chargers that require the removal of two-way radios with each use are especially hard on the batteries because each reconnection initiates a fast-charge cycle. This also applies to laptops that are momentarily disconnected and reconnected to perform a service. Likewise, a technician may briefly plug the laptop into the power source to check a repeater station or service other installations. Problems with laptop batteries have also been reported in car manufacturing plants where the workers move the laptops from car to car, checking their functions, while momentarily plugging into the external power source. Repetitive connection to power affects mostly ‘dumb’ nickel-based batteries. A ‘dumb’ battery contains no electronic circuitry to communicate with the charger. Li-ion chargers detect the SoC by voltage only and multiple reconnections will not confuse the charging regime.
More precise full charge detection of nickel-based batteries can be achieved with the use of a micro controller that monitors the battery voltage and terminates the charge when a certain voltage signature occurs. A drop in voltage signifies that the battery has reached full charge. This is known as Negative Delta V (NDV). NDV is the recommended full-charge detection method for ‘open-lead’ NiCd chargers because it offers a quick response time. The NDV charge detection also works well with a partially or fully charged battery. If a fully charged battery is inserted, the terminal voltage raises quickly, then drops sharply, triggering the ready state. Such a charge lasts only a few minutes and the cells remain cool. NiCd chargers based on the NDV full charge detection typically respond to a voltage drop of 10 to 30mV per cell. Chargers that respond to a very small voltage decrease are preferred over those that require a larger drop. more info:www.good-battery.co.uk
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