Ampere-hour relationship

FIGURE 1.30 Ampere-hour relationship of lead-acid battery. 

In the above relationship, Qg is the volumetric quantity of the metal deposited per ampere hour at a current efficiency of 100% (i.e., when p = 1) as per Faraday s law, and can be obtained from the relationship ... 

This energy is measured not only in Joules (1 J = 1 W s) but also in watt-hours (1 Wh = 3600 J.). Both the maximum ampere-hour capacity and the watt-hour energy depend on the amount of reactants in a battery at the start of discharge. As the discharge current increases, both the discharge voltage and the reactant utilization coefficient diminish. A number of attempts to find a relationship between the actual battery capacity and the discharge current were reported. An approximation found in 1897 by Peukert for lead acid batteries is sometimes used ... 

The relationship of the ampere-hour capacity (expressed as a percentage of the eapacity at 20°C on a discharge at the 0.2C rate) of the sealed niekel-metal hydride battery and the discharge temperature and current (expressed in C rate) is summarized in Fig. 29.7. 

The anode efficiency, that is the useful ampere hours per kg, increases at high current densities composition has some effect upon this, but generally maximum efficiency is obtained at current densities above 1.08A/m2 Fig. 2.13 shows this relationship. The extrapolation of these curves could suggest a certain corrosion rate even when it is not acting as sacrificial anode however, a relatively high efficiency can be maintained at low... 

Under these complex relationships, experience is crucial for selecting suitable materials. For actively corroding (consumable) materials approximate consumption rates are of the order of grams per ampere-hour (Ah), whereas for fully passive (nonconsumable) materials the corresponding consumption is on the scale of micrograms. The consumption rates for partly passive (semiconsumable) anode materials lie somewhere in between these extremes. 

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