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reducing the diameter of p1p1ng between stacks. Finally a computat1ona1 process can be used to determine the number of stacks, the number of cells per stack, and the Slze of pip1ng connecting stacks to min1m1ze the sum of 1ntra- and 1nterstack shunt losses and pumping requirements. The power requ1rement 1ndicated in table 3 for 1nstrumentat1on and con- trols is specifically needed for the meter relays and associated contactors for tr1m cell control and for several integrat1ng ampere-hour meters. The latter, be1ng research devices, should not have the1r energy needs charged to the system. The former can be replaced by solid-state sW1tch1ng devices, which will considerably reduce their power demands. F1nal1y, although not tabulated in table 3, the I2R losses could be 0 reduced 20 percent by raising the system temperature 20 degrees F, to 70 F. Note that the pump and shunt loss powers presented in table 3 are maX1- mum rates. If the pump speeds were varied cont1nuous1y 1n order to keep the flow rates at a constant multiple of the 1nstantaneous stoichiometric flow rates as the system state of charge changed, the average pump power during a complete cycle would be much less than the indicated value. Similarly, the listed shunt loss rate 1S for the case of charging at the maximum rate (l.e., when the system voltage 1S at its highest). Slnce the shunt losses tend to vary between the second and third power of the system voltage, the integrated average shunt loss dur1ng a cycle would be considerably less than represented. The final test performed w1th the 1-kW preprototype system in 1980 was the brief comb1ned operation of the Redox and photovolta1c systems. Data from a tYP1ca1 run are presented in table 4. The two systems were operating 1n configuration 1, 1n which the photovo1ta1c array 1S connected directly across the f1rst 96 cells of the Redox system. For the eXistlng test con- ditions of load, Redox state of charge, and solar 1nsolation, the array was fully act1vated (all 22 solar cell strings funct1on1ng) but was unable to reach the 120-V dc operating level. Therefore two tr1m cell packages (12 cells) were automatically brought 1nto the c1rcuit to boost the array output voltage from 111.5 Vto 120.5 Vfor the load bus. Because of the relatively low Redox system state of charge of 33 percent, the array was capable, even at 1tS 111.5-V output voltage, of provid1ng charge to the Redox system through the 96-cel1 main stack. Thus the Redox system was expend1ng 167 W through 1tS tr1m cells to boost the array power to the load by 9 V and was at the same time accept1ng 1171 Wof charge. Dur1ng these tests the pumps, instruments, and controls were st1l1 be1ng powered by separate power supp11es. All controls and sW1tchlng devices operated normally. In summary, the 1-kW Redox preprototype system, although having been operatlonal for only a short tlme ln 1980, had already provided much valuable 1nformat1on. Control concepts have been shown to be valid and trouble free. Some 1ns1ght has been ga1ned into interactions at the mutual interfaces of the Redox system, the photovo1taic array, the load, and the control dev1ces. Quant1tative measurements of loss mechanisms have glven direction for stack and system deslgn changes to minimize these losses. F1gure 12 displays the maJor mllestones associated w1th this activity. 10PDF Image | NASA Redox Storage System Development Project 1980
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