Cell Voltage Under Load

Charge/discharge cycle characteristics for a cell operating at room temperature are shown in Fig. 6.21. The high cell voltage under load (> 1.5 V even at a rate of 2 C) is noteworthy. 

Cell voltage under load eurrent (A/cm) is expressed as (Hirschenhofer et al, 1998) ... 

The cell voltage under load, the closed circuit voltage (CCV), depends on the current, the state of charge, and on the cell s history, like its hfetime or storage period. 

Figure 3.12 Fuel cell voltages and current levels as a function of various parameters involved. (AS reaction entropy T temperature electrolyte resistance ff- thermal cell voltage P thermodynamic cell voltage f cell voltage under load i load current tj overvoltage at the electrodes n number of cells f configuration factor.)...

To predict the local polarisation in a full-scale cell or stack at any point, its dependence on composition, pressure, and temperature of the gas flowing in the gas channel contacting the electrode must be known. In a large cell, these bulk gas properties vary from one point to the next. Electrode polarisation or overpotential - the difference between the local potential of the electrode under load and the potential at open circuit (equilibrium potential) - is also a local quantity because it depends not only on the bulk gas composition but also on the current density. In a large cell the current is usually distributed nonuniformly, as discussed in Sections 11.2-11.5. Similar to Eq. 7, one can express the local cell voltage under load, i.e., when current is passed, as the thermodynamic cell potential minus three loss terms the ohmic loss, the cathode polarisation, and the anode polarisation ... 

The photogenerated current is in the same direction as /, but is always less than because the battier potential under load conditions is always less than F, which results in a larger flow of majority carriers than that in a short-circuited cell. Thus, when a solar cell is under load, the current and voltage are always less than and lU, respectively this condition is the curve-factor loss. Depending on the characteristics of the particularp—n junction and on the cell operating conditions, there is an optimal load resistance that maximizes the power output of the cell, ie, the product of its current and voltage. 

We perform work whenever we connect the two poles of the battery across a load. The Toad in this respect might be a torch, calculator, car, phone or watch - anything which causes a current to pass. And this flow of current causes the voltage across the battery or cell to decrease see Figure 7.4. We call this voltage the voltage under load . 

Catalyst deterioration due to gas poisoning is only avoided by careful gas cleaning. Anodic oxidation followed by dissolution of Pt and transfer to the cathode is a serious cause for Pt loss. It is potential dependent and accelerates as the cathode potential increases, for instance under partial load or in off-time, when the cathode potential drifts toward the oxygen equilibrium potential. Therefore it is of utmost importance that whenever the fuel cell is switched off, the oxygen in the cathode lumen is rapidly exchanged by inert nitrogen and that the cell voltage under operation does not surmount 0.8 V. 

Figure 1. SoC-error matrices for voltage under load (1st row), open circuit voltage (2nd row) and 100 mHz fixed frequency impedance (3rd row). Results for the LFP cell are displayed in the left, NCM in the right column. Scales show the absolute deviation between calculated SoC and that determined by...

FIGURE 19.6 Drop in a cell voltage under constant load of EFCs implanted in the tissue of a clam (solid line) and rat brain (dashed line) [125,130]. At the times marked with arrows, (1) the load was switched off or (2) a slight manipulation of the position of the electrodes was performed, returning the voltage to initial values. (Reprinted with permission from Ref. [130]. Copyright 2012, Royal Society of Chemistry.)... 

Honeywell have recently developed a high-integrity erimp-sealed lithium-vanadium pentoxide button cell. This has an open-circuit voltage of 3.42 V and a voltage under load of more than 3V. The G3093 model has a rated eapacity of 300mA h and the G3094... 

Final voltage (voltage under load after 20mA h have been removed I.IOV from a fully charged cell)... 

Table 36.1 Typical applications, load, voltage under load and amperage reading for testing cf the most widely used carbon-zinc Leclanche cells and batteries...

ANSI designation Application Load ( ) Voltage under load (% of applied voltage shown on cell or battery label Amperage (A) for usable cell or battery (test for an instant only)... 

Figure 56.21 Projected performance of Catalyst Research Corporation Lithiode TM lithium-iodine cells based on 5 years test data, (a) Voltage under 190kn load, (b) voltage under load (Courtesyof Catalyst Research Corporation)...

As can be seen from Eigure 11b, the output voltage of a fuel cell decreases as the electrical load is increased. The theoretical polarization voltage of 1.23 V/cell (at no load) is not actually realized owing to various losses. Typically, soHd polymer electrolyte fuel cells operate at 0.75 V/cell under peak load conditions or at about a 60% efficiency. The efficiency of a fuel cell is a function of such variables as catalyst material, operating temperature, reactant pressure, and current density. At low current densities efficiencies as high as 75% are achievable. 

It is well known that the working voltage of a practical cell under load usually rises with an increase in temperature. However, this is almost entirely due to a reduction in the internal resistance of the cell caused by an increase in the conductivity of the electrolytic phase and in the diffusion rates of the eleclroactive species. 

Discharge curves show either the open circuit voltage of a cell or halfcell as a function of the fraction of discharge completed, or, much more commonly, the cell voltage during a deep discharge, usually under a fixed load or at constant current. The abscissa may be calibrated in terms of the quantity of electricity passed (Ah) or as a percentage of the theoretical capacity,... 

Single Celt. Under load, the voltage of one individual fuel cell element is less than one volt, Therefore, the assembly ol many cells, connected in senes as a stack, is required. Each individual cell contains the elements needed for feeding reactants to the electrode surface, and removal of water front the cell, as shown in Fig. 1 for a hydrogen air-cell with acid electrolyte. 

Here, an array of one-dimensional models are used for both the cathode and anode. The initial conditions for the model are a steady state load applied to achieve an operating cell voltage of 0.70 V Under these conditions a temperature rise across the cell exists due to the heat generated within the cell (see Section 9.5.2). At timet = 0,... 

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