Agilent HP N 250-2 Application Note free download

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Agilent AN 250-2 Lab & Industrial Power Sources Application Note Battery Charging/Discharging lead-acid cells, many manufacturers recommend that the charging current be reduced as the charge nears completion. This taper charge can be accom- Introduction: plished by inserting a small resistance in series The charging and discharging of batteries has with one of the load leads between the power sup- become an area of careful study in the aerospace ply and the battery being charged. and automotive industries as well as many others. Precise control of the charging and discharging characteristics of batteries may be necessary in Constant Current Charging: applications ranging from satellite design to bat- The automatic crossover between constant voltage tery development and evaluation. and constant current exhibited by most Agilent power supplies make them ideal for battery charg- Although sufficient for many consumer applica- ing applications. Using this feature, a battery may tions, the comparatively poor charging characteris- be charged at a constant current until the maxi- tics of readily available "battery chargers" may not mum charge voltage is reached, at which point the provide the precision necessary in many critical supply will revert to constant voltage and continue applications. To achieve a high degree of accuracy, to supply a trickle charge current sufficient to stability, and regulation, the DC power supply maintain full charge. (See Figure 1.) Thus, the approach can be utilized. Battery discharging may charging operation can be unattended after pro- be accomplished with these same DC power sup- perly setting the charging rate and the maximum plies with little or no modification to the basic unit. charge voltage, then connecting the battery to the output terminals of the power supply. Several different types of battery charging and discharging techniques using Agilent Technologies DC power supplies will be examined in this appli- cation note. Charge Methods: One of the most commonly used approaches to charging batteries is the "constant current method" sometimes referred to as a "slow charge" method. This name arises from the fact that it typically requires 14-16 hours to fully charge an Ni-Cd cell. The charge rate for this method is typically 0.1C, where C is the nominal ampere-hou