System and method for monitoring a dc power system

An apparatus for testing a battery bank comprising at least one battery, the battery bank being part of a load circuit in which the battery bank, a charger, and a system load are arranged in parallel, the apparatus comprising:

• a controller;
• a main contactor located on a first leg of the load circuit between the battery bank and the charger, so that the battery bank is electrically disconnected from the charger when the main contactor is open and the battery bank is electrically connected to the charger when he main contactor is closed, the first leg of the load circuit having a battery side extending between the main contactor and the battery bank and a system load;
• a float current test circuit arranged in parallel with the main contactor, the float current test circuit comprising a shunt, a float current contactor, and a fuse arranged in series;
• a first voltage sensor having a first connection point that is in electrical contact with the first leg;
• and
• a fail-safe circuit having first and second ends electrically connected to the first leg and arranged in parallel with the main contactor, the fail-safe circuit having an active mode in which electrical current can flow in at least one direction through the fail-safe circuit and an inactive mode in which the fail-safe circuit is open, which prevents electrical current from flowing in either direction through the fail-safe circuit;
• wherein the controller is electrically connected to the main contactor, the float current contactor, the first fail-safe circuit and the controller is operationally configured to (a) close the float current contactor when the main contactor is open, (b) open the float current contactor when the main contactor is closed, and (c) cause the fail-safe circuit to enter active mode if the controller detects a failure of the main contactor.

An apparatus for testing a battery bank comprising at least one battery, the battery bank being part of a load circuit in which the battery bank, a charger, and a system load are arranged in parallel, the apparatus comprising:

• a controller;
• a main contactor located on a first leg of the load circuit between the battery bank and the charger, so that the battery bank is electrically disconnected from the charger when the main contactor is open and the battery bank is electrically connected to the charger when he main contactor is closed, the first leg of the load circuit having a battery side extending between the main contactor and the battery bank and a system load;
• a float current test circuit arranged in parallel with the main contactor;
• a first voltage sensor having a first connection point that is in electrical contact with the battery side of the first leg and a second connection point in electrical contact with the system load side of the first leg;
• a remote sense contactor in electrical contact with the first voltage sensor, the remote sense contactor operationally configured to selectively electrically connect the first voltage sensor to one of the first connection point and the second connection point;
• a fail-safe circuit having first and second ends electrically connected to the first leg and arranged in parallel with the main contactor, the fail-safe circuit having an active mode in which electrical current can flow in at least one direction through the fail-safe circuit and an inactive mode in which the fail-safe circuit is open, which prevents electrical current from flowing in either direction through the fail-safe circuit;
• and
• wherein the controller is electrically connected to the main contactor, the float current contactor, the fail-safe circuit, and the controller is operationally configured to (a) close the float current contactor, cause the remote sense contractor to connect the first voltage sensor to the first connection point when the main contactor is open and (b) open the float current contactor, cause the remote sense contractor to connect the second voltage sensor to the second connection point when the main contactor is closed.

A method of performing a float current test on a bank of batteries comprising at least one battery, the battery bank being part of a load circuit in which the battery bank, a charger, and a system load are arranged in parallel, the method comprising:

• (a) determining if all of a set of test start conditions are met;
• and
• (b) initiating a float current test when all of a set of test start conditions are determined to be met, the float current test comprising:
• (i) starting a timer;
• (ii) recording a battery start voltage when the timer reaches a first predetermined time period has elapsed;
• (iii) disconnecting the battery bank from the charger by opening a main contactor, enabling a float current circuit, and changing a location of a remote voltage sense from a first location to a second location when a second predetermined time period has elapsed, the first location being between the main contactor and the charger and the second location being between the main contactor and the battery bank;
• (iv) determining if record conditions are met;
• (v) measuring and storing a float current value for the battery bank if the record conditions are determined to have been met in step (iv);
• and
• (vi) repeating steps (iv) and (v) until a predetermined number of float current values are recorded;
• and
• (viii) providing a constant voltage to the battery bank during the performance of step (b).

A method for performing a capacity test on testing a battery bank comprising at least one battery, the battery bank being part of a load circuit in which the battery bank, a charger, and a system load are arranged in parallel, the battery bank having a nominal capacity and a set of capacity factors, the set of capacity factors including first and second capacity factors Kt1 and Kt2, the method comprising:

• (a) electrically disconnecting the battery bank from the charger and the system load;
• (b) placing the battery in electrical contact with a capacity test circuit operationally configured to apply a constant resistance across the battery bank;
• (c) maintaining the battery bank in electrical contact with the capacity test circuit until the battery bank reaches a predetermined end voltage;
• (d) measuring a time to end voltage TD2 comprising a period from the start of step (b) to the end of step (c);
• (e) measuring a temperature that is indicative of a temperature of the battery bank and calculating a temperature correction factor Tcf based on the measured temperature;
• (f) calculating an average current Iavg consisting of the mean of a first set of measurements of a current flowing through the capacity test circuit, each of the measurements of the first set of measurements being taken at first frequency during the performance of step (c);
• (g) calculating an average capacity factor Kt that is equal to the nominal capacity divided by the average current Iavg;
• (h) calculating a rated discharge time t for the capacity test performed in steps (a) through (d) as a function comprising a linear interpolation between first and second capacity factors Kt1 and Kt2;
• and
• (i) calculating a percentage C of the nominal capacity as a function of the rated discharge time t, the measured time to end of-voltage TD2, and the temperature correction factor Tcf.