Abstract: A method of operating a fuel cell stack that powers a vehicle includes determining when the vehicle is in a non-moving state, calculating an O2 concentration over time of an assumed enclosed space while the vehicle is in the non-moving state, establishing a set of O2 concentration concern levels that includes a first O2 concentration concern level being less than a standard atmospheric O2 concentration and a second O2 concentration concern level being less than the first O2 concentration concern level, comparing the O2 concentration of the assumed enclosed space over time with the set of O2 concentration concern levels, and operating the fuel cell stack without restriction when the vehicle is in the non-moving state so long as the O2 concentration of the assumed enclosed space remains greater than the first O2 concentration concern level.

Abstract: A method of operating a fuel cell stack that powers a vehicle includes determining when the vehicle is in a non-moving state, calculating an O2 concentration over time of an assumed enclosed space while the vehicle is in the non-moving state, establishing a set of O2 concentration concern levels that includes a first O2 concentration concern level being less than a standard atmospheric O2 concentration and a second O2 concentration concern level being less than the first O2 concentration concern level, comparing the O2 concentration of the assumed enclosed space over time with the set of O2 concentration concern levels, and operating the fuel cell stack without restriction when the vehicle is in the non-moving state so long as the O2 concentration of the assumed enclosed space remains greater than the first O2 concentration concern level.

Abstract: A system and method for monitoring the conductivity of a cooling fluid flowing in a fuel cell system on a vehicle including a chassis. The fuel cell system includes a fuel cell stack electrically coupled to a stack bus and a battery electrically coupled to a propulsion bus. The method includes operating the fuel cell system, measuring a first isolation resistance at the first power level, measuring a first stack voltage, and measuring a first battery voltage. The method also includes operating the fuel cell system at a second power level, and measuring a second isolation resistance, measuring a second stack voltage, and measuring a second battery voltage. The method calculates a stack coolant resistance using the first and second isolation resistances, the first and second stack voltages, and the first and second battery voltages, which is then used to calculate the cooling fluid conductivity.

Abstract: A system and method for monitoring the conductivity of a cooling fluid flowing in a fuel cell system on a vehicle including a chassis. The fuel cell system includes a fuel cell stack electrically coupled to a stack bus and a battery electrically coupled to a propulsion bus. The method includes operating the fuel cell system, measuring a first isolation resistance at the first power level, measuring a first stack voltage, and measuring a first battery voltage. The method also includes operating the fuel cell system at a second power level, and measuring a second isolation resistance, measuring a second stack voltage, and measuring a second battery voltage. The method calculates a stack coolant resistance using the first and second isolation resistances, the first and second stack voltages, and the first and second battery voltages, which is then used to calculate the cooling fluid conductivity.

Abstract: A power converter includes positive and negative input lines and an input capacitor coupled across the input lines. The power converter also includes a switch coupled across the input lines that includes a control contact and an additional contact. The power converter also includes switch controller coupled to the control contact and that includes positive and negative input connections. The power converter also includes a contactor diagnostic supply interface coupled between the positive input connection and the additional contact.

Abstract: A coolant conductivity method and apparatus used to determine when a coolant, circulating through a vehicle's coolant system, starts to conduct electrical current and loses its electrical isolation properties. The system includes a battery monitor controller senses one or more isolation resistances placed throughout a fuel cell system and is programmed to run an isolation algorithm. The isolation algorithm opens and closes contactors in a specific order, measures the resistance of the one or more isolation resistances and calculates a coolant conductivity value. The system will indicate when the coolant needs to be replaced.

Abstract: An apparatus and method to detect a short circuit event in a fuel cell system of a vehicle. The detection relies on three existing sensors within the fuel cell system, two current sensors and a voltage sensor. A controller executes an algorithm with a set of thresholds stored in a computer readable medium to monitor the sensors to sense if any of the threshold values are crossed. If crossed, the controller may take remedial action to stop the short circuit and/or prevent damage to the fuel cell system. A mode manager may work with the controller to determine when the operating conditions of the fuel cell system are ideal for sensing for a low voltage condition indicative of a short circuit event. A pair of integrators may be electrically coupled to an alternating current sensor to differentiate a short circuit event from a high frequency resistance current.

Abstract: System and methods relating to a configuration for a fuel cell system having lower coolant path isolation resistances are disclosed. In certain embodiments, the fuel cell system may include a first fuel cell substack comprising a first plurality of cells. The fuel cell system may further include a second fuel cell substack comprising a second plurality of cells. The first and second fuel cell substacks may share at least one terminal and/or share a common wet end. A coolant system may be coupled to the first fuel cell substack and the second fuel cell substack and be configured to remove heat generated by the first fuel cell substack and the second fuel cell stack during operation of the fuel cell system using a coolant.

Abstract: A coolant conductivity method and apparatus used to determine when a coolant, circulating through a vehicle's coolant system, starts to conduct electrical current and loses its electrical isolation properties. The system includes a battery monitor controller senses one or more isolation resistances placed throughout a fuel cell system and is programmed to run an isolation algorithm. The isolation algorithm opens and closes contactors in a specific order, measures the resistance of the one or more isolation resistances and calculates a coolant conductivity value. The system will indicate when the coolant needs to be replaced.

Abstract: A fuel cell system that employs a technique for reducing or significantly eliminating the MEA degradation that occurs as a result of the hydrogen-air front in the anode flow channels at system start-up. After system shut-down, any hydrogen remaining within the anode flow channels will be quickly reacted or diffused. At the next start-up, a switch is closed to provide a dead short across the positive and negative terminals of the fuel cell stack as hydrogen is being introduced into the anode flow channels. The existing air in the cathode flow channels reacts with the hydrogen being introduced across the membrane in the normal fuel cell reaction. However, the short prevents a voltage potential across the membrane.

Abstract: An apparatus and method to detect a short circuit event in a fuel cell system of a vehicle. The detection relies on three existing sensors within the fuel cell system, two current sensors and a voltage sensor. A controller executes an algorithm with a set of thresholds stored in a computer readable medium to monitor the sensors to sense if any of the threshold values are crossed. If crossed, the controller may take remedial action to stop the short circuit and/or prevent damage to the fuel cell system. A mode manager may work with the controller to determine when the operating conditions of the fuel cell system are ideal for sensing for a low voltage condition indicative of a short circuit event. A pair of integrators may be electrically coupled to an alternating current sensor to differentiate a short circuit event from a high frequency resistance current.

Abstract: A system for oxidizing contaminants on both the cathode and anode electrodes in a fuel cell stack by applying a suitable voltage potential across the electrodes that causes the oxidation. The system includes a battery and an electrical converter electrically coupled to the battery. The electrical converter is configured to assist in providing an oxidation potential to the fuel cell stack by converting electrical power from the battery at a time effective to oxidize contaminants on the cathode or anode electrodes in the stack. The electrical converter provides a positive potential to the fuel cell stack to oxidize contaminants on the cathode electrodes and provides a negative potential to the fuel cell stack to oxidize contaminants on the anode electrodes. If the battery is a high voltage battery, then the converter is a power converter and if the battery is a low voltage battery, then the converter is boost converter.

Abstract: A system that monitors fuel cells in a fuel cell group. The system includes a plurality of voltage sensors coupled to the fuel cells in the fuel cell group, where each sensor monitors a different voltage of the fuel cells and where lower priority voltage sensors monitor higher voltages and higher priority sensors monitor lower voltages. The system also includes a plurality of oscillators where a separate oscillator is coupled to each of the sensors. Each oscillator operates at a different frequency where higher frequency oscillators are coupled to lower priority sensors and lower frequency oscillators are coupled to higher priority sensors. A light source that receives frequency signals from the oscillators and switches on and off in response to the frequency signals. A light pipe receives the switched light signals from the light source and provides light signals at a certain frequency at an end of the light pipe.

Abstract: A fuel cell system that includes a cell voltage monitoring sub-system that measures the cell voltage of each cell in a fuel cell stack and provides an indication of a low performing or failed cell. The fuel cell system uses the cell voltage monitoring sub-system to determine if one of the wires connected to a bipolar plate in the stack is broken or has otherwise failed. The cell voltage monitoring sub-system uses differential amplifiers to compare the positive side voltage and the negative side voltage of a cell to determine if the cell voltage is low or the cell is failing. By looking at the outputs of two differential amplifiers in the cell voltage monitoring sub-system, it can be determined whether adjacent cells provide an indication of both cells failing, which would indicate that a connection wire has failed.

Abstract: A system that monitors fuel cells in a fuel cell group. The system includes a plurality of voltage sensors coupled to the fuel cells in the fuel cell group, where each sensor monitors a different voltage of the fuel cells and where lower priority voltage sensors monitor higher voltages and higher priority sensors monitor lower voltages. The system also includes a plurality of oscillators where a separate oscillator is coupled to each of the sensors. Each oscillator operates at a different frequency where higher frequency oscillators are coupled to lower priority sensors and lower frequency oscillators are coupled to higher priority sensors. A light source that receives frequency signals from the oscillators and switches on and off in response to the frequency signals. A light pipe receives the switched light signals from the light source and provides light signals at a certain frequency at an end of the light pipe.

Abstract: A fuel cell system is provided that includes a fuel cell stack with a plurality of fuel cells and a power converter in electrical communication with the fuel cell stack. The power converter is configured to selectively regulate a power of the fuel cell stack and short circuit the fuel cell stack, as desired. A method for starting the fuel cell stack is also described, including the steps of causing a short circuit of the fuel cell stack by placing the power converter in a short circuit mode; introducing a hydrogen to the anodes of the fuel cell stack to displace a quantity of air on the anodes; and placing the power converter in a power regulation mode. A degradation of the fuel cell stack during start-up is thereby militated against.

Abstract: At least one positive temperature coefficient element is used to efficiently control fuel cell voltage at startup and shutdown making the fuel cell more efficient and protecting the electro catalyst layer.

Abstract: A fuel cell system that employs a technique for reducing or significantly eliminating the MEA degradation that occurs as a result of the hydrogen-air front in the anode flow channels at system start-up. After system shut-down, any hydrogen remaining within the anode flow channels will be quickly reacted or diffused. At the next start-up, a switch is closed to provide a dead short across the positive and negative terminals of the fuel cell stack as hydrogen is being introduced into the anode flow channels. The existing air in the cathode flow channels reacts with the hydrogen being introduced across the membrane in the normal fuel cell reaction. However, the short prevents a voltage potential across the membrane.

Abstract: A voltage monitoring system for measuring the voltage of the fuel cells in a fuel cell stack that employs optical devices for providing an optical signal of the measured voltages, where one or more of the fuel cells power the optical devices. A surface mount device is electrically coupled to opposing plates in the stack, or opposing plates over a plurality of cells in the stack. The surface mount device includes a bonded contact and a spring contact to provide the electrical connection. A detector is positioned remote from the stack that receives the optical signals and converts them back to electrical signals indicative of the voltage.

Abstract: A fuel cell system that includes a single enclosure for all of a fuel cell stack and other stack critical electronics and components, such as power distribution components, voltage monitoring and detecting components, electrical isolation components, etc. The single enclosure offers a number of advantages, such as reduced weight and reduced complexity for service and safety.