Fault detector for a plurality of batteries in battery backup systems

• US 5,254,930 A
• Filed: 06/10/1992
• Issued: 10/19/1993
• Est. Priority Date: 06/10/1992
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Digital Equipment Corporation (HP Inc.)
• Inventors: Daly, James A.
• Primary Examiner(s): Peckman, Kristine L.
• Application Number:
  US07/896,713
• Time in Patent Office: 496 Days
• Field of Search: 320/31, 320/32, 320/43, 320/44, 320/48, 320/39, 320/40, 320/6, 320/14, 320/15, 320/16, 320/17
• US Class Current: 320/119
• CPC Class Codes: H02J 7/00304 Overcurrent protection
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: Y10S 320/13 Fault detection
• CPC Class Codes: Y10S 320/29 Transformer having plural secondaries

Abstract

According to the invention a battery charger for charging a plurality of batteries includes a voltage supply connected by a pair of switches to a power converter including a transformer having a primary winding and a plurality of secondary windings. Each secondary winding is coupled to a battery. Voltage is transferred from the voltage supply to the primary winding when the switches are closed and current is transferred from the secondary windings to the batteries when the switches are open. Charge control circuitry monitors the voltage of each battery and the total battery voltage and determines the amount of current to supply to the batteries. Supervisory logic monitors the current received from the secondary windings by each of the batteries and the voltage of each of the batteries to determine the charge status of each battery and the operating status of the power converter. If one battery continues drawing a greater proportion of the maximum current relative to the remaining batteries after the predetermined voltage limit has been reached, this indicates that there is a short circuited cell causing one battery to draw a greater proportion of current or that there is a cell with high impedance causing one battery to draw a smaller proportion of current. For both fault conditions, the supervisory circuit detects the current imbalance and generates a shutdown signal. The shutdown signal is also asserted when the supervisory circuit detects an over voltage condition in any of the batteries, or an over current in the primary winding. The shutdown signal subsequently precludes further operation of the charge control circuit for a predetermined time period, alerting the system operator of a problem within the battery backup system, and avoiding the loss of vital information and expensive computing time by allowing for correction of the fault condition before damage results.

Claims

1. A battery charger for charging a plurality of batteries, comprising:

a transformer, comprising a primary winding and a plurality of secondary windings;

each of said secondary windings connected to a corresponding one of said plurality of batteries;

a charge supply controller operable to repetitively switch a d.c. supply across said primary winding to cause a charging current to be supplied by each of said secondary windings to each corresponding battery of said plurality of batteries to charge each of said batteries to a voltage;

said charge supply controller responsive to said charging current supplied to said plurality of batteries and responsive to said voltage of each battery of said plurality of batteries to control the rate of switching of said d.c. supply and said charging current supplied to said batteries; and

supervisory means responsive to said voltage of each of said batteries and to said charging current of each of said secondary windings, for detecting when said voltage of any of said plurality of batteries rises above a predetermined voltage level or for detecting when said charging current to any of said batteries rises above a predetermined current level for discontinuing supply of charging current to said batteries.

2. A battery charger according to claim 1, wherein said supervisory means is separately responsive to the voltage of any battery of said plurality of batteries exceeding an overvoltage level greater than said predetermined voltage level for discontinuing supply of said charging current to said plurality of batteries.

3. A battery charger according to claim 1, wherein said supervisory means is further responsive to a current flow through said primary winding exceeding a predetermined level to discontinue supply of said charging current to said plurality of batteries.

4. A battery charger according to claim 1, wherein said primary winding is connected at each end to respective switches operable to connect and disconnect said primary winding to and from said d.c. supply, said battery charger including a pulse width modulator connected to operate said switches according to an adjustable duty cycle, and wherein said charge controller is connected to said pulse width modulator to adjust said duty cycle.

5. A battery charger for charging a plurality of batteries, comprising:

a transformer, comprising a primary winding and a plurality of secondary windings, wherein each battery of said plurality of batteries is coupled to a corresponding one of said plurality of secondary windings;

a plurality of switches for coupling a charging voltage supply to said transformer, said switches to allow delivery of a voltage to said primary winding of said transformer when in a closed position, and to allow each of said batteries to receive a current from said corresponding secondary winding of said transformer when said switches are in an open position;

voltage measurement means for monitoring a voltage of each battery of said plurality of batteries, including means for determining a voltage offset between said voltage of each battery and a predetermined voltage;

current measurement means for measuring said current from said secondary windings of said transformer;

limiting means responsive to said voltage offset and said current measurement means for limiting said current from said secondary windings of said transformer to predetermined current;

charge control logic responsive to said limiting means, for controlling said plurality of switches, said charge control logic to operate in a current mode and in a voltage mode; and

supervisory means for detecting a plurality of fault conditions responsive to said current measurement means and said voltage measurement means, said supervisory means including shutdown means for disabling said charge control logic in the event one of said plurality of fault conditions is detected.

6. A battery charger comprising:

a transformer coupled to a DC charging voltage supply source, said transformer having a primary winding, and a plurality of secondary windings each having an equal number of turns;

a plurality of switches having an open position and a closed position coupled to said transformer and to said voltage source to control the application of voltage across said primary winding to create a primary winding current;

a plurality of capacitor and battery parallel pairs, each pair coupled to a corresponding one of said plurality of secondary windings to receive a charging current from said corresponding secondary winding when said switches are in said open position;

voltage measurement means for generating a first control voltage representing the sum of voltages of each battery of said plurality of batteries;

first current measurement means for providing a second control voltage representing a total charging current supplied by said plurality of secondary windings to said plurality of batteries;

second current measurement means for providing a plurality of individual voltages corresponding to said plurality of secondary windings representing the corresponding charging current supplied to said corresponding battery and capacitor pair by said corresponding secondary winding;

control means responsive to said first and second control voltages for controlling the operation of said switches between said open and closed positions;

overvoltage detection means responsive to said voltage measurement means for providing a first shutdown signal when the voltage of any battery of said plurality of batteries exceeds a first voltage limit;

overcurrent detection means responsive to said primary winding current to provide a second shutdown signal when said primary winding current exceeds a predetermined value;

imbalance detection means responsive to said voltage measurement means and said second current measurement means to provide a third shutdown signal when said first control voltage exceeds a first threshold voltage and any one of said plurality of individual voltages exceeds a second threshold voltage; and

supervisory means separately responsive to each of said first, second and third shutdown signals for allowing said control means to disable operation of said switches.

7. The apparatus of claim 6, wherein said control means includes a pulse width modulator responsive to said first and second control voltages to adjust a duty cycle of said switches.