Battery Charging Knowledges from battery-center.net

May 16, 2012 - PRLog -- What happens to a battery when it is charged and discharged?

   The chemical reactions on discharge convert lead, lead oxides, and acid into free electrons (good stuff), water (also good stuff), and lead sulfates (bad stuff). The chemical reactions on recharge reverse the process. The tricky part is to recharge the battery in such a manner so that the sulfates are eliminated by recombining with water to re-form into acid without loosing the hydrogen and oxygen gasses that make up the water. Oxygen and hydrogen gas will be released at recharge voltages between 13.8 V (2.30 volts per cell) and 14.2 V (2.37 vpc). You will see later that virtually all battery chargers have output voltages during some portion of the charge algorithm that are higher than the gassing voltage. Battery construction plays a very large part in determining what happens to the oxygen and hydrogen gas after it is released as a by-product of the recharge chemical reaction.

What is a charge algorithm?

   The battery charger controls the voltage that is applied to the battery, the amount of charge current that is supplied to the battery, and depending on the level of sophistication in the charger technology, the timing associated with what may be multiple voltage and current levels. The following paragraphs provide an overview with some significant detail of the different charging modes, or stages that may be included in a charging algorithm. Basically, a charge algorithm is a collection of all of the software controls over electrical parameters and timing that are applied sequentially to the charging system hardware for the express purpose of recharging a discharged battery. Stated a little more directly, the charging algorithm is what controls the battery charger behavior as measured at its electrical output terminals.

Battery Charging Algorithm Fundamentals:

   There are 4 distinct charging modes, or stages, within a battery charging cycle. Not all of these modes are essential in every battery application. The software that controls the charge cycle modes is often referred to as an algorithm.

   The General 4 Step Charging graph shows the 4 distinct charging stages or modes that will be described in detail later. The alpha indicators on the axes indicate general values for time, charging voltage, or charging current.

General 4 Step Charging Algorithm


   Figure 1: General 4 Step Charging Algorithm

   For the voltages: “A” is the voltage value held constant by the charger during the Absorption stage. “B” is the voltage value held constant by the charger during the Equalization stage. “C” is the voltage value held constant by the charger during the Storage or Float stage.

   For the currents: “D” is the regulated current limit or the current value held constant by the charger during the Bulk Charge stage. “E” is the regulated current limit or the current value held constant by the charger during the Equalization stage. “F” is the maintenance current value provided by the charger during the Storage of Float stage.

   For timing: “W” is the elapsed time for the Bulk Charge stage and is the starting time for the Absorption stage. “X” is the total elapsed time for both the Bulk Charge and Absorption stages. The duration of the Absorption stage is numerically equal to (X – W). “Y” is the total elapsed time from the start to the end of the current limit phase of the equalization stage. “Z” is the total elapsed time from the start to the beginning of the Storage or Float, Maintenance stage. The duration of the Storage or Float, Maintenance stage is indefinite. The duration of the Equalization stage is numerically equal to (Z-W-X).

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   The charger will remain in float as long as power is applied to the charger, or until some monitored circumstance occurs which resets the charge cycle, or until power is removed from the charger. A typical monitored circumstance that would trigger a charger reset would be if the battery voltage dropped below a certain value. This would indicate that a parasitic load is attached to the battery while it is being charged and that the amplitude of the parasitic load current is greater than the current being supplied by the charger. In that case, the battery is being discharged even while the charger is attempting to maintain its charge level. This circumstance is not at uncommon in industrial applications.

   Virtually every battery manufacturer has developed different charging algorithms to optimize the recharge characteristics of a given style of battery in a given application. Sometimes the differences between these charging algorithms seems to be fairly insignificant, but depending upon the battery application, even seemingly slight differences in the charging algorithm can have a significant impact on the cycle life of the battery.

General 3 Step Charging Algorithm


   Figure 2: General 3 Step Charging Algorithm

   The General 3 Step Charging graph above shows the 3 charging stages. The descriptions are identical to the General 4 Step Charging Algorithm, except that there is no equalization charge stage. The alpha indicators on the axes indicate general values for time, charging voltage, or charging current.

   For the voltages: “A” is the voltage value held constant by the charger during the Absorption stage. “C” is the voltage value held constant by the charger during the Storage or Float stage. For the currents: “D” is the regulated current limit or the current value held constant by the charger during the Bulk Charge stage. “F” is the maintenance current value provided by the charger during the Storage or Float, Maintenance stage.

   For timing: “W” is the elapsed time for the Bulk Charge stage and is the starting time for the Absorption stage. “Z” is the total elapsed time for both the Bulk Charge and Absorption stages. The duration of the Absorption stage is numerically equal to (Z – W). “Z” is the total elapsed time from the start to the beginning of the Storage or Float, Maintenance stage. The duration of the Storage or Float stage is indefinite.

Adaptive 4 Step AGM Charging Algorithm

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   Figure 3: General 4 Step Charging Algorithm

   For illustration purposes, each time interval corresponding to each charging mode will be highlighted on the above graph immediately preceding the description of the charging mode.

   The previous graph shows voltage and charge current time profile for the most sophisticated charging algorithm available in Deltran chargers. This charging profile was developed by Deltran engineers in conjunction with manufacturers of Sealed, AGM (Absorbed Glass Matte), Lead Acid batteries. This particular algorithm, the Adaptive 4 Step AGM Charging Algorithm is only available on the higher-powered Battery Tender? products: the 300 and 600-Watt SuperSmart® High Frequency (Golf Cart style) chargers, and the High Powered, DVD and DVS dual and single output portable chargers.

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