Charging constant-voltage, current limited

With this background, we can estimate and design the battery performance in terms of the power and the actual capacity. To understand the power performance, we illustrate how to calculate the maximum power in Figure 5.6. If we can know the battery s internal resistance and assume that it is a certain constant value, the power characteristics can be estimated and is related to the state of charge, an upper current limit, and a lower voltage limit. 

Constant-voltage charging characteristics with current limitations are shown in Fig. 26.12. The current is often limited to 0.1 to 0.4C A, and charging is normally carried out in the voltage range of 1.50 to 1.65 V per cell. The charging time may vary from 5 to more 25 h, depending on current limitation value and cell type. 

We saw previously that concentration polarization results in the decrease of solute concentration near the permselective interface (right at the interface in the electro-neutral version) where most of the system s resistance thus concentrates, and where the space charge develops. The system is expected to be sensitive to the minimum concentration value, and because of nonlinearity nontrivial effects, could be anticipated in response to unsteady disturbances of this value (e.g., provided by harmonic modulation superimposed upon a constant voltage applied to the system). Since it is easier to increase the minimal concentration (close to zero at the limiting current) than to decrease it, we might expect a positive rectification effect for the direct current component, counterintuitive ( anomalous ) in the present system with a convex stationary VC curve. Thus the topic of this section is the rectification effects that arise in the stationary concentration polarization in response to a harmonic voltage modulation. 

Fig. 9.3. Example of current-limited constant-voltage (CV or lU) charging for a 200-Ah VRLA battery at 2.23 VPC (solid line) and 2.40 VPC (dotted line). Larger Ah charge returns are for 2.40 VPC charge. (From Ref. [3], p. 84.)...

Constant voltage-constant current combinations. It is also possible to combine the CV and CC approaches in fact, one of the most eflbctive methods for charging VRLA batteries is the so-called lUI algorithm. This is simply a current-limited, CV charge with a CC finishing step at some low current level an example is shown in Fig. 9.6. In this example, a CV charge at 2.45 VPC is first applied with a... 

Constant potential charging is not recorrunended as the system has a tendency to go into thermal runaway. A modified constant voltage with a current limit is... 

The limit values for the charging currents above gassing voltage are listed in Table 12.3. During the constant-voltage charging period (2.4 V/ cell) an allowed tolerance of 1% may not be exceeded (5). 

The lUIa characteristics (Figure 13.6) is composed of an lU characteristic with an attached charging phase. Upon reaching a certain lower current limit, charging is continued at slightly increased voltage with constant current (I-charging phase). 

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