Cell voltage monitor for a fuel cell stack
First Claim
1. A voltage monitoring unit comprising:
- at least one cell in a fuel cell stack;
a heating resistor;
a rectifier in series with said heating resistor;
said heating resistor and rectifier in series being connectable across said fuel cell, wherein the polarity of said rectifier is such that current is prevented from flowing through said rectifier when said fuel cell is in voltage reversal; and
a sensing thermistor, said sensing thermistor being electrically isolated from and in thermal communication with said heating resistor, wherein the resistance of the sensing thermistor is indicative of the voltage of at least one fuel cell.
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Abstract
Voltage reversal in fuel cell stacks may be detected and/or prevented by monitoring each cell or small groups of cells in the stack for low voltage conditions. An improved cell voltage monitor is constructed using a plurality of voltage monitoring units in which each unit comprises a heating resistor, a rectifier in series therewith, and a sensing thermistor in thermal communication with the heating resistor. The heating resistor is electrically-connected across a cell or cells and heats the associated sensing thermistor in accordance with the voltage of the cell(s). Since the resistance of the sensing thermistor is indicative of its temperature and hence also of voltage of the cell(s), the sensing thermistor resistance can be used to signal a low voltage condition.
68 Citations
29 Claims
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1. A voltage monitoring unit comprising:
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at least one cell in a fuel cell stack;
a heating resistor;
a rectifier in series with said heating resistor;
said heating resistor and rectifier in series being connectable across said fuel cell, wherein the polarity of said rectifier is such that current is prevented from flowing through said rectifier when said fuel cell is in voltage reversal; and
a sensing thermistor, said sensing thermistor being electrically isolated from and in thermal communication with said heating resistor, wherein the resistance of the sensing thermistor is indicative of the voltage of at least one fuel cell. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A method for detecting a low voltage in a fuel cell in a fuel cell stack comprising:
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connecting a heating resistor and a rectifier in series across said fuel cell wherein the polarity of said rectifier is such that current is prevented from flowing through said rectifier when said fuel cell is in voltage reversal;
positioning a sensing thermistor in thermal communication with and electrically isolated from said heating resistor such that said sensing thermistor is heated when current flows through said heating resistor; and
obtaining a signal indicative of the resistance of said sensing thermistor, said signal detecting a low voltage in at least one fuel cell. - View Dependent Claims (26, 27, 28, 29)
connecting a reference thermistor in series with and thermally isolated from said sensing thermistor;
applying a reference voltage across the series-connected sensing and reference thermistors; and
measuring the voltage across said sensing thermistor.
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27. The method of claim 25 wherein said sensing thermistor is a resettable thermal switch and said signal indicates whether said resettable thermal switch is open or closed.
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28. The method of claim 25 comprising thermally isolating said sensing thermistor from said fuel cell stack.
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29. A method of monitoring for voltage reversal in a fuel cell stack comprising using the method of claim 25 to detect for any low voltage fuel cell in said fuel cell stack.
Specification