DC load method

FIGURE 8.8 DC load method. Simplistic, but the true integrity of the Randles model cannot be seen. R1 and R2 appear as one ohmic value. 

Today s rapid-test methods range from the traditional DC load to AC conductance to advanced electrochemical impedance spectroscopy (EIS). Each has its advantages and limitations—and none fully satisfies all requirements. No single device can assess all battery characteristics on the fly. Much like a doctor examining a patient, or a weatherman forecasting the weather, several methods are needed to assess the overall condition. 

FIGURE 8.9 The two-tier DC load test method adheres to the lEC 61951-1 2005 standard. The load test is the preferred method for batteries powering DC loads. 

The DC load has limitations in that it blends R1 and R2 of the Randles model into a combined resistor and ignores the capacitor C (see Figure 8.8). Capacitor C is an important component of a battery and represents 1.5 farads (F) per 100-Ah capacity. In essence, the DC method sees the battery as a resistor, providing only ohmic references. Capacity estimation is not possible. 

The two-tier DC load test method applies two sequential discharge loads of different currents and time durations. lEC 61951-1 2005 specifies that the battery be first discharged at a low current for 10 sec, followed by a higher current for 3 sec (see Figure 8.9). This test protocol provides lifelike test conditions for many battery applications. The differences between the two load conditions provide additional battery information, but the values are strictly resistive and do not reveal capacity. 

B01 L.M. Barker and R.E. Hollenbach, J. Appl. Phys. 41, 4208-4226 (1970). 70B02 R.R. Boade, Experimental Shock Loading Properties of Porous Materials and Analytical Methods to Describe these Properties, Sandia Laboratories Report No. SC-DC-70-5052, August, 1970. 

Comparisons of the accuracy and efficiency for three numerical procedures, the direct summation, DC-FFT-based method and MLMI, are made in this section. The three methods were applied to calculating normal surface deformations at different levels of grids, under the load of a uniform pressure on a rectangle area 2a X 2fo, or a Hertzian pressure on a circle area in radius a. The calculations were performed on the same personal computer, the computational domain was set as -1.5a=Sx 1.5a and -1.5a=Sy 1.5a, and covered... 

As of this writing (ca 1993) there are eight methods of erythrocyte entrapment. Six methods depend on loading via hypotonic exchange, one method dc icnds on chlurpromazine-induced endocytosis. and one depends on voltage-step induced transitory permeation,... 

S.P. Howell J.E. Tiffany, "Methods for Routine Work in the Explosives Physical Laboratory of the Bureau of Mines , USBurMines Technical Paper 186, Wash, DC (1918), 14-15 (Detn of apparent specific gravity by sand method) 4) C.E. Munroe J.E. Tiffany, "Physical Testing of Explosives , USBurMines Bull 346, Wash, DC (1931), 22-3 (Detn of apparent sp gr by sand test) 24 (Detn of shaking density) 5) Vennin, Burlot Lecorche" (1932), 154 (Gravimetric apparent density) 6) Pepin Lehalleur (1935), 41, 54 62 (Densite de enlargement) 99-100 (Densimeters of Bianchi and of Bode) 7) Hayes (1938), 50 (Loading density)... 

Specimens were strained in a push-pull mode by an Instron machine, Model TF-DM, which has cross head speeds from 0.05 to 0,5 cm/min and a load capability up to 10" kg. Details of the apparatus for the mechanical and electrical tests are reported elsewhere Only a brief description of the electrical portion is given here. The resistivity was measured by the typical four-probe dc method. A set of voltage leads were soft-soldered across the gauge length of the specimen surface. 

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