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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Rectenna array measurement results

The measured performance characteristics of a rectenna array are reviewed and compared to the performance of a single element. It is shown that the performance may be extrapolated from the individual element to that of the collection of elements. Techniques for current and voltage combining were demonstrated. The array performance as a function of various operating parameters is characterized and techniques for overvoltage protection and automatic fault clearing in the array demonstrated. A method for detecting failed elements also exists. Instrumentation for deriving performance effectiveness is described. Measured harmonic radiation patterns and fundamental frequency scattered patterns for a low level illumination rectenna array are presented.

Dickinson, R. M.↗
NASA NTRS1982

Lightning protection of wind turbines

Possible damages to wind turbine components due to lightning strikes are discussed and means to prevent the damage are presented. A low resistance path to the ground is noted to be essential for any turbine system, including metal paths on nonmetal blades to conduct the strike. Surge arrestors are necessary to protect against overvoltages both from utility lines in normal operation and against lightning damage to control equipment and contactors in the generator. MOS structures are susceptible to static discharge injury, as are other semiconductor devices, and must be protected by the presence of static protection circuitry. It is recommended that the electronics be analyzed for the circuit transient response to a lightning waveform, to induced and dc current injection, that input/output leads be shielded, everything be grounded, and lightning-resistant components be chosen early in the design phase.

Dodd, C. W.↗
NASA NTRS1984

Shielding Electric Connectors From Lightning

Metallic shield for plastic-body electric power connectors, with provision for attaching cable shielding, prevents lightning-induced overvoltages from damaging sensitive electronic equipment.

Pierce, W. B.↗
NASA NTRS1981

Electromagnetic studies of redox systems for energy storage

Both chromium and iron couples were studied on various electrode surfaces in acidic perchlorate solution by using rotating ring-disk techniques. It was found that chloride which forms inner sphere coordination complexes with the redox species enhances the electrode kinetics dramatically. The effects of lead underpotential deposition and surface alloy formation on the kinetics of the chromium couple on gold were studied using both linear sweep voltammetry and potential step techniques. The lad underpotential deposition was found to slow down the kinetics of the reduction of the Cr species on gold surfaces although increase the hydrogen overvoltage. The effect on the chromium kinetics can be explained in terms of principally a double layer effect. The underpotential deposition lead species with its positive charge results in a decrease in the concentration of the Cr species at the electrode surface. Similar phenomena were also observed with bismuth underpotential deposition on gold for the iron couple.

Wu, C. D.↗
NASA NTRS1981

Analytical investigation of critical MHD phenomena

Development and analysis of schemes for suppression of the startup overvoltage transient in the AEDC High Performance Demonstration Experiment (HPDE), analysis of performance enhancement due to electrode voltage drop reduction by use of pyrolytic graphites in the HPDE, prediction of optimal loading schemes for the HPDE, prediction of PHDE performance with a diagonal electrical connection, and predictions of the likelihood and effects of axial current leakage between adjacent electrodes in the HPDE are reviewed. Simulations of tests at the AEDC/HPDE with STD Research Corporation multidimensional and time dependent computer codes provided additional validation for the computer codes and shed light on physical mechanisms which govern performance and durability of MHD power generators. The magnetoaerothermal effect was predicted by STD Research Corporation to have a significant effect on the HPDE/MHD generator performance at high interaction.

Source record↗
NASA NTRS1983

Photoelectrochemical electrodes

The surface of a moderate band gap semiconductor such as p-type molybdenum sulfide is modified to contain an adherent film of charge mediating ionene polymer containing an electroactive unit such as bipyridimium. Electron transport between the electrode and the mediator film is favorable and photocorrosion and recombination processes are suppressed. Incorporation of particles of catalyst such as platinum within the film provides a reduction in overvoltage. The polymer film is readily deposited on the electrode surface and can be rendered stable by ionic or addition crosslinking. Catalyst can be predispersed in the polymer film or a salt can be impregnated into the film and reduced therein.

Williams, R. M.↗
NASA NTRS1983

Electrical insulation design requirements and reliability goals

The solar cells in a photovoltaic module which must be electrically isolated from module exterior surfaces to satisfy a variety of safety and operating considerations are discussed. The performance and reliability of the insulation system are examined. Technical requirements involve the capability of withstanding the differential voltage from the solar cells to the module frame. The maximum system voltage includes consideration of maximum open circuit array voltages achieved under low-temperature, high-irradiance conditions, and transient overvoltages due to system feedback of lightning transients. The latter is bounded by the characteristics of incorporated voltage limiting devices such as MOVs.

Ross, R. G., Jr.↗
NASA NTRS1988

Electrochemical processing of solid waste

The investigation into electrolysis as a means of waste treatment and recycling on manned space missions is described. The electrochemical reactions of an artificial fecal waste mixture was examined. Waste electrolysis experiments were performed in a single compartment reactor, on platinum electrodes, to determine conditions likely to maximize the efficiency of oxidation of fecal waste material to CO2. The maximum current efficiencies for artificial fecal waste electrolysis to CO2 was found to be around 50 percent in the test apparatus. Experiments involving fecal waste oxidation on platinum indicates that electrodes with a higher overvoltage for oxygen evolution such as lead dioxide will give a larger effective potential range for organic oxidation reactions. An electrochemical packed column reactor was constructed with lead dioxide as electrode material. Preliminary experiments were performed using a packed-bed reactor and continuous flow techniques showing this system may be effective in complete oxidation of fecal material. The addition of redox mediator Ce(3+)/Ce(4+) enhances the oxidation process of biomass components. Scientific literature relevant to biomass and fecal waste electrolysis were reviewed.

Bockris, J. OM.↗
NASA NTRS1989

Output-Isolation And Protection Circuit

Output-isolation circuit couples precise analog signals (-10 to +10 V, 0 to 20 kHz) from computer or from other electronic equipment to external electronic equipment that may be at different ground potential. Circuit functions in presence of common-mode voltages up to 2,500 Vac or 3,500 Vdc. To prevent damage from accidental connection of output leads to powerlines or other sources of high voltage, circuit includes features that protect input and output signal lines against normal-mode overvoltages up to 120 V ac or dc.

Wagner, Charles A.↗
NASA NTRS1989

Choosing Compositions Of Electrocatalysts

Simple theory predicts compositions of alloys that exhibit maximum catalytic activities in presence of certain reactants. Method used to select best catalysts for electrochemical batteries and fuel cells. Oxygen-electrode overvoltage plotted against solubility parameter of lead/platinum electrode in acidic and basic solutions. Electrode formed by plating mixtures of lead and platinum, corresponding to various solubility parameters. Method based on one used to analyze activities of nonelectrical catalysts in reactions involving hydrogen or oxygen. Rate of such reaction increases when solubility parameter of catalyst matches reactant.

Lawson, Daniel D.↗
NASA NTRS1992

Profile of a cell test database and a corresponding reliability database

The development of computerized control, and data retrieval for aerospace cell testing affords an excellent opportunity to incorporate three specific concepts to both manage the test area and to track product performance on a real-time basis. The adoption and incorporation of precepts fostered by this total quality management (TQM) initiative are critical to us for retaining control of our business while substantially reducing the separate quality control inspection activity. Test discrepancies are all 'equally bad' in cell acceptance testing because, for example, we presently do not discriminate between 1 or 25 mV for an overvoltage condition. We must take leadership in classifying such discrepancies in order to expedite their clearance and redirect our resources for prevention activities. The development and use of engineering alerts (or guardbanding) which more closely match our product capabilities and are toleranced tighter than the required customer specification are paramount to managing the test unit in order to remain both quality and cost effective.

Brearley, George R.↗
NASA NTRS1999

Response of NiMH Cells to Burp Charging

Performance cycling and calorimetric analysis of nickel metal hydride (NNH) calls have revealed that reverse pulse ("burp") charging improves performance over other charging techniques. Burp charging periodically applies a short-duration, high-rate discharge pulse followed by short rest during an otherwise galvanostatic charge as shown in Fig. 1. Results show improved charge input and output, lower heat generation during charge, lower charge overvoltage, and no loss of cycle life [I]. The burp charge method has been improved over the years purely by trial and error. Several hypotheses have been put forward (see articles cited in (1) to explain why burp charging improves performance For example, it has been suggested that the discharge pulses dislodge gas bubbles that would otherwise mask the active elect-ode surfaces. However, no evidence was found in the literature to support this or other hypotheses. Overall, a better understanding of the phenomenon is needed to help guide further improvements in the burp-charging method, and this is the objective of our investigation.

Darcy, Eric C.↗
NASA NTRS2000

Temperature Distribution Within a Defect-Free Silicon Carbide Diode Predicted by a Computational Model

Most solid-state electronic devices diodes, transistors, and integrated circuits are based on silicon. Although this material works well for many applications, its properties limit its ability to function under extreme high-temperature or high-power operating conditions. Silicon carbide (SiC), with its desirable physical properties, could someday replace silicon for these types of applications. A major roadblock to realizing this potential is the quality of SiC material that can currently be produced. Semiconductors require very uniform, high-quality material, and commercially available SiC tends to suffer from defects in the crystalline structure that have largely been eliminated in silicon. In some power circuits, these defects can focus energy into an extremely small area, leading to overheating that can damage the device. In an effort to better understand the way that these defects affect the electrical performance and reliability of an SiC device in a power circuit, the NASA Glenn Research Center at Lewis Field began an in-house three-dimensional computational modeling effort. The goal is to predict the temperature distributions within a SiC diode structure subjected to the various transient overvoltage breakdown stresses that occur in power management circuits. A commercial computational fluid dynamics computer program (FLUENT-Fluent, Inc., Lebanon, New Hampshire) was used to build a model of a defect-free SiC diode and generate a computational mesh. A typical breakdown power density was applied over 0.5 msec in a heated layer at the junction between the p-type SiC and n-type SiC, and the temperature distribution throughout the diode was then calculated. The peak temperature extracted from the computational model agreed well (within 6 percent) with previous first-order calculations of the maximum expected temperature at the end of the breakdown pulse. This level of agreement is excellent for a model of this type and indicates that three-dimensional computational modeling can provide useful predictions for this class of problem. The model is now being extended to include the effects of crystal defects. The model will provide unique insights into how high the temperature rises in the vicinity of the defects in a diode at various power densities and pulse durations. This information also will help researchers in understanding and designing SiC devices for safe and reliable operation in high-power circuits.

Kuczmarski, Maria A.↗
NASA NTRS2006

Single Event Transients in Voltage Regulators for FPGA Power Supply Applications

As with other bipolar analog devices, voltage regulators are known to be sensitive to single event transients (SET). In typical applications, large output capacitors are used to provide noise immunity. Therefore, since SET amplitude and duration are generally small, they are often of secondary importance due to this capacitance filtering. In low voltage applications, however, even small SET are a concern. Over-voltages may cause destructive conditions. Under-voltages may cause functional interrupts and may also trigger electrical latchup conditions. In addition, internal protection circuits which are affected by load as well as internal thermal effects can also be triggered from heavy ions, causing dropouts or shutdown ranging from milliseconds to seconds. In the case of FPGA power supplies applications, SETS are critical. For example, in the case of Actel FPGA RTAX family, core power supply voltage is 1.5V. Manufacturer specifies an absolute maximum rating of 1.6V and recommended operating conditions between 1.425V and 1.575V. Therefore, according to the manufacturer, any transient of amplitude greater than 75 mV can disrupt normal circuit functions, and overvoltages greater than 100 mV may damage the FPGA. We tested five low dropout voltage regulators for SET sensitivity under a large range of circuit application conditions.

Poivey, Christian↗
NASA NTRS2009

Performance and Safety Testing of Varta Li-Ion Polymer Cells

Varta Cell Characteristics: Voltage : 3.7 V Capacity : 1.21 Ah Dimensions : 5mm X 37mm X 38.5 mm MOSFET switches for Overvoltage and Undervoltage. Initial Screening Results 29 Cells delivered: Statistics on Ph ysical Screening: Thickness (mm): Average- 5.08; Weight(g)- 22.8938; OCV (V)- 3.787; CCV (V)- 3.491.

Patel, Pranav↗
NASA NTRS2010

Hazards Due to Overdischarge in Lithium-ion Cylindrical Cells in Multi-cell Configurations

Lithium-ion cells in the cylindrical Commercial-off-the-shelf 18650 design format were used to study the hazards associated with overdischarge. The cells in series or in parallel configurations were subjected to different conditions of overdischarge. The cells in parallel configurations were all overdischarged to 2.0 V for 75 cycles with one cell removed at 25 cycles to study the health of the cell. The cells in series were designed to be in an unbalanced configuration by discharging one cell in each series configuration before the start of test. The discharge consisted of removing a pre-determined capacity from the cell. This ranged from 50 to 150 mAh removal. The cells were discharged down to a predetermined end-of-discharge voltage cutoff which allowed the cell with lower capacity to go into an overdischarge mode. The cell modules that survived the 75 cycles were subjected to one overvoltage test to 4.4 V/cell.

Jeevarajan, Judith↗
NASA NTRS2012

Safety and Long-Term Performance of Lithium-ion Pouch Cells

Lithium-ion batteries have the highest energy density of the batteries available in the commercial market today. Although most lithium-ion cell designs use a metal can design, this has changed significantly in recent years. Cell designs are offered in the pouch format as they offer better volumetric and gravimetric energy densities and in some cases, higher tolerance to abuse or off-nominal conditions. In the past decade, several state-of-the-art lithium-ion pouch cell designs have been tested. The pouch cell designs have become more robust in the past two years but there are still a few issues that need to be looked into for optimization. The pouch cells seem to have a tendency to swell when left in storage under ambient conditions. The cells also swell under overvoltage and undervoltage conditions. A significant issue that has been observed is the swelling of the cells under a vacuum condition which could lead to deformation of the cell pouch after this exposure. This last factor would be very critical in the use of these cell designs for space applications as vacuum exposure is used to check for cell and battery leaks before it is flown into space. In rare cases, corrosion of the aluminum layer of the pouches has been observed in stored cells. Pouch material analysis has been carried out in an effort to understand the strength of the pouches and determine if this is a factor in the corrosion as well as unsafe condition of the cells as deformation of the inner layers of the pouch could occur when the cells swell under the various conditions described above. Pouch materials are typically aluminized plastic, made up of a layer of Al sandwiched between one or more layers of polymeric material. Deformations or cell manufacturing processes could lead to a compromise of the inner polymeric layer/s of the pouch leading to the corrosion of the Al layer in the aluminized pouch material. The safety of the pouch cell designs has been determined for cells from various manufacturers. The results are varied and in some cases, unexpected. This paper presents a summary of the tests carried out on a few li-ion pouch cell designs from various cell manufacturers. The data will include performance under different conditions specifically cycling under vacuum conditions with and without restraints as well as safety test data. The presentation will also include detailed analysis of the pouch material for the cells studied.

Jeevarajan, Judith↗
NASA NTRS2018

Advanced Stirling Convertor Control Unit Testing at NASA Glenn Research Center in the Radioisotope Power Systems System Integration Laboratory

Future NASA missions could include long-duration flyby, orbital, lander, or rover applications where generating power from sunlight may be limited. Radioisotope power systems (RPSs) provide a dependable power source for missions where inadequate sunlight or operational requirements make other power systems impractical. Over the past 16 years, NASA Glenn Research Center has been supporting the development of RPSs. The advanced Stirling radioisotope generator (ASRG) utilized a pair of advanced Stirling convertors (ASCs). Although flight development of the ASRG has been canceled, much of the technology and hardware continued development and testing to guide future activities. Specifically, a controller for the convertor(s) is an integral part of a Stirling-based RPS. For the ASRG design, the controller maintains stable operation of the convertors, regulates the alternating current produced by the linear alternator of the convertor, provides a specified direct-current output voltage for the spacecraft, and synchronizes the piston motion of the two convertors to minimize vibration as well as manage and maintain operation with a stable piston amplitude and hot-end temperature. It not only provides power to the spacecraft but also must regulate convertor operation to avoid damage to internal components and maintain safe thermal conditions after fueling. Lockheed Martin Coherent Technologies, Inc., has designed, developed, and tested an ASC control unit engineering development unit (ACU EDU) to support this effort. GRC used the ACU EDU as part of its nonnuclear representation of a RPS that also consists of a Dual advanced Stirling convertor simulator (DASCS), and associated support equipment to perform a test in the Radioisotope Power Systems System Integration Laboratory (RSIL). The RSIL was designed and built with flexibility to evaluate hardware utilizing RPS technology. The RSIL provides insight into the electrical interactions between as many as three radioisotope power generators, associated control strategies, and typical electric system loads. The first phase of testing included a DASCS that was developed by Johns Hopkins University Applied Physics Laboratory and simulates the operation and electrical behavior of a pair of ASCs in real time via a combination of hardware and software. Testing included the following spacecraft electrical energy storage configurations: capacitor, battery, and supercapacitor. Testing of the DASCS and ACU in each energy storage configuration included simulation of a typical mission profile and transient voltage and current data during load turnon and turnoff. Testing for these devices also included the initiation of several system faults such as short circuits, electrical bus overvoltage, undervoltage, and a "dead bus" recovery to restore normal power operations. The goal of this testing was to verify operation of the ACU(s) when connected to a spacecraft electrical bus. The results of these tests are presented here.

General↗