Controller for battery charger

• US 4,746,852 A
• Filed: 09/03/1985
• Issued: 05/24/1988
• Est. Priority Date: 10/29/1984
• Status: Expired due to Term

• Current Assignee: Christie Electric Corp. (Transdigm Group Incorporated)
• Original Assignee: Christie Electric Corp. (Transdigm Group Incorporated)
• Inventors: Martin, Ray J.
• Primary Examiner(s): Hickey, R. J.
• Application Number:
  US06/771,824
• Time in Patent Office: 994 Days
• Field of Search: 320/20, 320/21, 320/39, 320/40, 320/14, 320/31, 328/132
• US Class Current: 320/106
• CPC Class Codes: H02J 7/00711 with introduction of pulses during the charging process
• CPC Class Codes: H02J 7/007184 in response to battery voltage gradient

Abstract

A controller for a battery charger terminates battery charging operation as a function of a time derivative of measured battery voltage. The controller has analog and digital embodiments. A controller with means for determining a time derivative of the measured battery voltage, determining a change in slope of the time derivative, and using said change in slope as a control function for the battery charger.

Claims

1. A controller for a battery charger, including in combination:

a differential amplifier having first and second inputs and an output;

a first sample and hold circuit having the battery voltage connected as an input and providing an output as one input to said differential amplifier;

a second sample and hold circuit having the output of said first sample and hold circuit as an input and providing an output as the other input to said differential amplifier;

an AND gate having first and second inputs and an output, with the AND gate output controlling the battery charger;

a first slope detector having the output of said differential amplifier as an input and providing an output when a slope of a first sign is detected;

a second slope detector having the output of said differential amplifier as an input and providing an output when a slope of the opposite sign is detected, with said second slope detector output connected as one input to said AND gate; and

a latch circuit having the output of said first slope detector connected as input and providing an output as the other input to said AND gate.

2. A controller for a battery charger, including in combination:

means for measuring the voltage of the battery to provide a measured voltage;

an analog to digital converter for converting the measured voltage from an analog voltage to a digital voltage;

means for computing a time derivative of said digital voltage and determining a change in slope of said time derivative; and

means for shutting off the charger as a function of said change in slope;

said analog to digital converter including

a comparator having first and second inputs,

a summing circuit having first and second inputs, and an output connected as one input to said comparator,

a first digital to analog converter having an output connected as one input to said summing circuit,

a second digital to analog converter,

a divider circuit having as an input, the output of said second digital to analog converter, with the divider circuit output connected as the other input to said summing circuit, and

a sample and hold circuit having the battery voltage connected as an input and having an output connected as the other input to said comparator.

3. A controller as defined in claim 2 for use with a battery having an identification resistor, including:

means for providing an electrical current of known value in said resistor;

means for measuring the voltage developed across said resistor by said current; and

means for relating the measured voltage to a predetermined battery identification.

4. A controller for a battery charger for use with a battery having an identification resistor, wherein the battery charger operates in a three step sequence consisting of a charging pulse for a first time period, a discharging pulse for a second time period, and no pulse for a third time period, including in combination:

means for measuring the voltage of the battery during said third time period to provide a measured voltage;

an analog to digital converter for converting the measured voltage from an analog voltage to a digital voltage;

means for computing a time derivative of said digital voltage and determining a change in slope of said time derivative;

means for shutting off the charger as a function of said change in slope;

means for providing an electrical current of known value in said resistor;

means for measuring the voltage developed across said resistor by said current; and

means for relating the measured voltage to a predetermined battery identification, said means for relating including;

a memory;

means for converting the measured voltage to a number; and

means for looking up in said memory a battery identification corresponding to said number.

5. A controller for a battery charger wherein the battery charger operates in a three step sequence consisting of a charging pulse for a first time period, a discharging pulse for a second time period, and no pulse for a third time period, including in combination:

means for measuring the voltage of the battery during said third time period to provide a measured voltage;

an analog to digital converter for converting the measured voltage from an analog voltage to a digital voltage;

means for computing a time derivative of said digital voltage and determining a change in slope of said time derivative;

means for shutting off the charger as a function of said change in slope;

a first battery identification resistor;

a current source of known value;

first circuit means for connecting said current source across said first resistor to provide a first voltage across said first resistor;

a set of parameter tables stored in memory;

an index table stored in memory, said index table including an index relating voltage numbers and parameter tables; and

means for selecting a parameter table as a function of said first voltage across said first resistor.

6. A controller for a battery charger for use with a battery discharge booster having a current source, wherein the battery charger operates in a three step sequence consisting of a charging pulse for a first time period, a discharging pulse for a second time period, and no pulse for a third time period, including in combination:

means for measuring the voltage of the battery during said third time period to provide a measured voltage;

an analog to digital converter for converting the measured voltage from an analog voltage to a digital voltage;

means for computing a time derivative of said digital voltage and determining a change in slope of said time derivative;

means for shutting off the charger as a function of said change in slope;

a discharge current resistor; and

circuit means for connecting said resistor to the current source of the battery discharge booster.

7. A method for controlling a battery charger and identifying a battery to be charged prior to initiating the charging, including the steps of:

measuring the voltage produced across a resistor by a known current, which resistor is associated with a specific battery;

converting the measured voltage to a number;

looking up the number in a table in a charger memory to relate the measured voltage with the specific battery;

operating the charger in a continuously repeating three step sequence consisting of a charging pulse for a first time period, a discharging pulse for a second time period, and no pulse for a third time period;

measuring the voltage of the battery during said third time period to provide a measured voltage;

determining a time derivative of said measured voltage to provide a voltage derivative;

determining a change in slope of said voltage derivative; and

shutting off the charger as a function of said change in slope.