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At least 73 records · Page 4

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NASA NTRS2013

Are Soft Short Tests Good Indicators of Internal Li-ion Cell Defects?

The self discharge test at full state of charge, may not be a good one to detect subtle defects since the li-ion chemistry has the highest self discharge at full state of charge. One should characterize self discharge versus storage time for each cell manufacturer/design to differentiate between normal self discharge and that due to a subtle manufacturing defect. The various soft short test methods indicate that if this test is carried out at full discharge (0% SOC) with all capacity removed (by lowering the current load in a stepwise manner to the same end of discharge voltage), then the cells need to be placed in storage for more than 72 hours to get a good analysis on the presence of subtle defects since it takes more than 72 hours to achieve voltage stabilization. If the cells are to be charged up even to a small percentage (ex. 1%), 72 hours are sufficient to determine issues. However, the pass/fail criteria should be based on a valid OCV decline. Less than 10 mV voltage decline is not a good method to detect subtle defects. As mentioned in the first bullet, self discharge is a competing reaction when a charge is introduced and hence a characterization of the self discharge versus storage time is required to fully correlate voltage decline to a failure due to a subtle defect. Soft short test method cannot be relied on for defect detection because cells with and without voltage decline seemed to have similar defects and characteristics. Screening methods such as internal resistance and capacity as well as a 3-sigma range for OCV, mass and dimensions should be used to screen out outliers. A very critical aspect in the understanding of subtle defects is to carry out destructive analysis of cells from every lot to confirm the quality of production and screen all cells and batteries in a stringent manner to have a high quality set of flight cells. Self Discharge Test: Fully charged cells shall be placed in Open circuit stand for 72 hours (OCV measurement twice a day); continue for total of 14 days with 1 reading per day 2. Soft Short Test 1: Fully charge; cells discharged to manufacturer's end of disch. Voltage (EODV) cutoff at C/5 rate; stand for 30 minutes; discharge with C/500 to the same EODV. stand for another 30 minutes; discharge the cells again using C/1000 current to the same EODV. OCV measurements twice a day for 72 hours and then for total of 14 days (data collection same as in 1.) 3. Soft Short Test 2: Fully charge; cells discharged to the manuf. EODV with a C/13 constant current; provide a 10 hour rest, discharge again to the same EODV with a current of C/250, provide a 10 hour rest, discharge again using a C/250 rate, provide a 24 hour rest, charge using C/250 to 3.15 V (for ~12 hours). OCV measurements twice a day for at 72 hours. (data collection same as in 1.) 4. Soft Short Test 3: Fully charge; cells shall be discharged using C/10 current to manuf. EODV. Allow the cell to remain at Open circuit for 10 seconds. Discharge the cell at C/20 rate to the same EODV, hold open circuit for 24 hours. Discharge the cells at C/200 rate to the same end of voltage cutoff and hold open circuit for 24 hours. Discharge the cells one more time at C/200 rate to the same EODV and hold open circuit for 36 hours. Charge at C/200 rate to 3.15 V and hold for 3 days. Record OCV during the open circuit stand periods every 12 hours and at the beginning and end of the 3 day hold (include the 12 hour OCV recording during this time also). Capacity Cycling: Cells with declining voltages - one cell from each manufacturer chosen for cycling Destructive Physical Analysis (DPA): Cells with and without decline chosen from each lot for DPA.

Jeevarajan, J.↗

NASA NTRS1975

A study of short test and charge retention test methods for nickel-cadmium spacecraft cells

Methods for testing nickel-cadmium cells for internal shorts and charge retention were studied. Included were (a) open circuit voltage decay after a brief charge, (b) open circuit voltage recovery after shorting, and (c) open circuit voltage decay and capacity loss after a full charge. The investigation included consideration of the effects of prior history, of conditioning cells prior to testing, and of various test method variables on the results of the tests. Sensitivity of the tests was calibrated in terms of equivalent external resistance. The results were correlated. It was shown that a large number of variables may affect the results of these tests. It is concluded that the voltage decay after a brief charge and the voltage recovery methods are more sensitive than the charged stand method, and can detect an internal short equivalent to a resistance of about (10,000/C)ohms where "C' is the numerical value of the capacity of the cell in ampere hours.

Scott, W. R.↗

NASA NTRS1978

Results of module electrical measurement of the DOE 46-kilowatt procurement

Current-voltage measurements have been made on terrestrial solar cell modules of the DOE/JPL Low Cost Silicon Solar Array procurement. Data on short circuit current, open circuit voltage, and maximum power for the four types of modules are presented in normalized form, showing distribution of the measured values. Standard deviations from the mean values are also given. Tests of the statistical significance of the data are discussed.

Curtis, H. B.↗

NASA NTRS1976

High altitude calibration of thirty-three silicon and gallium arsenide solar cells on a sounding rocket

Twenty-nine n/p silicon and four p/n gallium arsenide solar cells were calibrated on board a high-altitude sounding rocket which provided a stable platform outside the earth's atmosphere. Approximately 75 characteristic current-voltage curves were obtained for each of thirty-two of the cells; the calibration accuracy for both current and voltage was 0.1%. For comparison, the short circuit current, open circuit voltage, and maximum power of the solar cells were also measured under solar simulators (air mass = 0) and on the ground (air mass = 1.2).

Thomas, N. L.↗

NASA NTRS1979

Investigation of reliability attributes and accelerated stress factors on terrestrial solar cells

The results of accelerated stress testing of four different types of silicon terrestrial solar cells are discussed. The accelerated stress tests used included bias-temperature tests, bias-temperature-humidity tests, thermal cycle and thermal shock tests, and power cycle tests. Characterization of the cells was performed before stress testing and at periodic down-times, using electrical measurement, visual inspection, and metal adherence pull tests. Electrical parameters measured included short-circuit current, open circuit voltage, and output power, voltage, and current at the maximum power point. Incorporated in the report are the distributions of the prestress electrical data for all cell types. Data were also obtained on cell series and shunt resistance.

Prince, J. L.↗

NASA NTRS1980

Driver for solar cell I-V characteristic plots

A bipolar voltage ramp generator which applies a linear voltage through a resistor to a solar cell for plotting its current versus voltage (I-V) characteristic between short circuit and open circuit conditions is disclosed. The generator has automatic stops at the end points. The resistor serves the multiple purpose of providing a current sensing resistor, setting the full-scale current value, and providing a load line with a slope approximately equal to one, such that it will pass through the origin and the approximate center of the I-V curve with about equal distance from that center to each of the end points.

Turner, G. B.↗

NASA NTRS1980

Radiation damage in high voltage silicon solar cells

Three high open-circuit voltage cell designs based on 0.1 ohm-cm p-type silicon were irradiated with 1 MeV electrons and their performance determined to fluences as high as 10 to the 15th power/sq cm. Of the three cell designs, radiation induced degradation was greatest in the high-low emitter (HLE cell). The diffused and ion implanted cells degraded approximately equally but less than the HLE cell. Degradation was greatest in an HLE cell exposed to X-rays before electron irradiation. The cell regions controlling both short-circuit current and open-circuit voltage degradation were defined in all three cell types. An increase in front surface recombination velocity accompanied time dependent degradation of an HLE cell after X-irradiation. It was speculated that this was indirectly due to a decrease in positive charge at the silicon-oxide interface. Modifications aimed at reducing radiation induced degradation are proposed for all three cell types.

Weinberg, I.↗

NASA NTRS1980

Radiation damage in high voltage silicon solar cells

Three high open-circuit voltage cell designs based on 0.1 ohm-cm p-type silicon were irradiated with 1 MeV electrons and their performance determined to fluences as high as 10 to the 15th/sq cm. Of the three cell designs, radiation induced degradation was greatest in the high-low emitter (HLE) cell. The diffused and ion implanted cells degraded approximately equally but less than the HLE cell. Degradation was greatest in an HLE cell exposed to X-rays before electron irradiation. The cell regions controlling both short-circuit current and open-circuit voltage degradation were defined in all three cell types. An increase in front surface recombination velocity accompanied time dependent degradation of a HLE cell after X-irradiation. It was speculated that this was indirectly due to a decrease in positive charge at the silicon-oxide interface. Modifications aimed at reducing radiation induced degradation are proposed for all three cell types.

Weinberg, I.↗

NASA NTRS1982

High speed computerized data acquisition of photovoltaic V-I characteristics

The voltage current (V-I) characteristics of the photovoltaic array were studied under actual environmental conditions. A method of data acquisition was devised that uses a capacitor charge technique to obtain the V-I characteristic and a computerized data system to display, record and process the data. The capacitor charge technique uses an array shorting transistor and a capacitor bank to sweep the array operating voltage and current from short circuit to open circuit in a specified time (approximately 125 ms). The computerized data system is synchronized with this transition and repetitively samples the array voltage and current during the transition and records the ambient conditions. This data is then normalized by the computer to standard conditions (100 mW/sq cm, 28 C) and is available in tabular and graphic form for both the voltage current and voltage power characteristics. The capacitor charge technique is described.

Delombard, R.↗

NASA NTRS1984

Radiation effects in silicon and gallium arsenide solar cells using isotropic and normally incident radiation

Several types of silicon and gallium arsenide solar cells were irradiated with protons with energies between 50 keV and 10 MeV at both normal and isotropic incidence. Damage coefficients for maximum power relative to 10 MeV were derived for these cells for both cases of omni-directional and normal incidence. The damage coefficients for the silicon cells were found to be somewhat lower than those quoted in the Solar Cell Radiation Handbook. These values were used to compute omni-directional damage coefficients suitable for solar cells protected by coverglasses of practical thickness, which in turn were used to compute solar cell degradation in two proton-dominated orbits. In spite of the difference in the low energy proton damage coefficients, the difference between the handbook prediction and the prediction using the newly derived values was negligible. Damage coefficients for GaAs solar cells for short circuit current, open circuit voltage, and maximum power were also computed relative to 10 MeV protons. They were used to predict cell degradation in the same two orbits and in a 5600 nmi orbit. Results show the performance of the GaAs solar cells in these orbits to be superior to that of the Si cells.

Anspaugh, B. E.↗

NASA NTRS1984

Radiation effects in silicon and gallium arsenide solar cells using isotropic and normally incident radiation

Anspaugh, B. E.↗

NASA NTRS1985

Thermal stress cycling of GaAs solar cells

A thermal cycling experiment was performed on GaAs solar cells to establish the electrical and structural integrity of these cells under the temperature conditions of a simulated low-Earth orbit of 3-year duration. Thirty single junction GaAs cells were obtained and tests were performed to establish the beginning-of-life characteristics of these cells. The tests consisted of cell I-V power output curves, from which were obtained short-circuit current, open circuit voltage, fill factor, and cell efficiency, and optical micrographs, spectral response, and ion microprobe mass analysis (IMMA) depth profiles on both the front surfaces and the front metallic contacts of the cells. Following 5,000 thermal cycles, the performance of the cells was reexamined in addition to any factors which might contribute to performance degradation. It is established that, after 5,000 thermal cycles, the cells retain their power output with no loss of structural integrity or change in physical appearance.

Janousek, B. K.↗

NASA NTRS1986

An IBM PC-based math model for space station solar array simulation

This report discusses and documents the design, development, and verification of a microcomputer-based solar cell math model for simulating the Space Station's solar array Initial Operational Capability (IOC) reference configuration. The array model is developed utilizing a linear solar cell dc math model requiring only five input parameters: short circuit current, open circuit voltage, maximum power voltage, maximum power current, and orbit inclination. The accuracy of this model is investigated using actual solar array on orbit electrical data derived from the Solar Array Flight Experiment/Dynamic Augmentation Experiment (SAFE/DAE), conducted during the STS-41D mission. This simulator provides real-time simulated performance data during the steady state portion of the Space Station orbit (i.e., array fully exposed to sunlight). Eclipse to sunlight transients and shadowing effects are not included in the analysis, but are discussed briefly. Integrating the Solar Array Simulator (SAS) into the Power Management and Distribution (PMAD) subsystem is also discussed.

Emanuel, E. M.↗

NASA NTRS1988

Molecular-Beam-Epitaxy Program

Molecular Beam Epitaxy (MBE) computer program developed to aid in design of single- and double-junction cascade cells made of silicon. Cascade cell has efficiency 1 or 2 percent higher than single cell, with twice the open-circuit voltage. Input parameters include doping density, diffusion lengths, thicknesses of regions, solar spectrum, absorption coefficients of silicon (data included for 101 wavelengths), and surface recombination velocities. Results include maximum power, short-circuit current, and open-circuit voltage. Program written in FORTRAN IV.

Sparks, Patricia D.↗

NASA NTRS1991

Thermocouple-Signal-Conditioning Circuit

Thermocouple-signal-conditioning circuit acting in conjunction with thermocouple, exhibits electrical behavior of voltage in series with resistance. Combination part of input bridge circuit of controller. Circuit configured for either of two specific applications by selection of alternative resistances and supply voltages. Includes alarm circuit detecting open circuit in thermocouple and provides off-scale output to signal malfunctions.

Simon, Richard A.↗

NASA NTRS1979

Voltage-current-power meter for photovoltaic solar arrays

A meter is disclosed for measuring the voltage, current, and power (VIP) parameters of a photovoltaic solar array, or array module, under sunlight operating conditions utilizing a variable load connected across the array and controlled by a voltage regulator which responds to the difference between the output voltage of the array and a programmed test voltage from a source which generates a single ramp voltage for measuring and recording current as a function of voltage, repeated ramp voltages at a high rate for peak output measurements or a DC voltage for VIP measurements at selected points on the I-V characteristic curve of the array. The voltage signal from a current sensing element, such as a shunt resistor in series with the variable load, is compared with the output current of a reference solar cell to provide a normalizing signal to be added to the signal from the current-sensing element in order to provide a record of array current as a function of array voltage, i.e., for all load conditions from short circuit to open circuit. As the normalized current is thus measured, an analog multiplier multiplies the array voltage and normalized current to provide a measurement of power. Switches are provided to selectively connect the power, P, current, I, or voltage, V, to a meter, directly or through a peak detector. At the same time any one of the parameters V, I and P may be recorded as a function of any other parameter.

Ross, Ronald G.↗

NASA NTRS2013

Detectors Ensure Function, Safety of Aircraft Wiring

Pedro Medelius waited patiently in his lab at Kennedy Space Center. He had just received word that a colleague was bringing over a cable from a Space Shuttle solid rocket booster to test Medelius new invention. Medelius was calm until his colleague arrived, with about 30 other people. "Talk about testing under pressure," says Medelius. "There were people there from the Navy, the Air Force, and the Federal Aviation Administration." After the group s arrival, Medelius took a deep breath and connected his Standing Wave Reflectometer (SWR) to the cable. He wiggled the cable around, and the display showed a fault (a short or open circuit in wire) about an inch and a half inside the connector on the cable. His colleague questioned the results, because he had already checked that area on the cable. Medelius used the SWR to check again but got the same result. "That is when we took the cable apart and looked inside," Medelius says. "Lo and behold, that was exactly where the fault was." The impetus for Medelius new wire inspection technology came about in 1999 when one of the space shuttles lost power due to a fault somewhere in its more than 200 miles of electrical wiring. "The backup circuit was activated and prevented a major dysfunction, but nevertheless, there was a problem with the wiring," Medelius describes. Even though technicians used a device called a multimeter to measure the electrical current to find which wire had a fault, it could not pinpoint exactly where on the wire the fault was located. For that, technicians had to visually inspect the wire. "Sometimes they would have to remove the whole wire assembly and visually inspect every single wire. It was a very tedious operation because the wires are behind cabinets. They go all over the place in the shuttle," says Medelius. "NASA needed an instrument capable of telling them exactly where the faults were occurring." To meet NASA s needs for a highly precise device to inspect electrical power bundles, wires, and connectors, Medelius devised the SWR. "It came down to what was affected when a wire is short circuited or opened," he says. "We worked out a few equations based on physical principles." The SWR proved very sensitive, and the technology was patented.

Source record↗

NASA NTRS1981

Multijunction high voltage concentrator solar cells

The standard integrated circuit technology has been developed to design and fabricate new innovative planar multi-junction solar cell chips for concentrated sunlight applications. This 1 cm x 1 cm cell consisted of several voltage generating regions called unit cells which were internally connected in series within a single chip resulting in high open circuit voltages. Typical open-circuit voltages of 3.6 V and short-circuit currents of 90 ma were obtained at 80 AM1 suns. A dramatic increase in both short circuit current and open circuit voltage with increased light levels was observed.

Valco, G. J.↗