Method and apparatus for monitoring the condition of a battery by measuring its internal resistance

Abstract

A method comprises coupling a first power transistor as a first external load in series with the battery, coupling a second power transistor as a second external load in series with the battery, conducting each power transistor to supply a transient large current to the battery for sampling a group of sampled reference voltages and sampled load voltages in a very transient sampling time for a plurality of times and thus obtaining an internal resistance of the battery. The internal resistance of the battery can then be compared with a predetermined warning value thereof so as to determine whether the former is equal to or larger than the warning value or not, and issuing a warning through an I/O if the determination is affirmative. The invention enables a driver to correctly know the actual condition of the battery in substantially real time while consuming a minimum amount of power.

1 . A method of monitoring the electric power of a battery by measuring an internal resistance of the battery, comprising the steps of: 
 (1) coupling a first power transistor at two terminals of the battery as a first external load with a transient large current at a very transient sampling time to obtain a reference voltage;    (2) coupling second power transistor at two terminals of the battery as second external load with a transient large current at a very transient sampling time to obtain a load voltage;    (3) calculating the internal resistance of the battery by subtracting the load voltage from the reference voltage and dividing by the transient large current; and    (4) comparing the internal resistance of the battery with a predetermined warning value thereof such that a warning can be displayed if the power is lower than a predetermined level.    
     
     
         2 . The method of  claim 1 , wherein the predetermined warning value of the internal resistance of the battery to be measured is 0.001 Ω to 1.5 Ω.  
     
     
         3 . The method of  claim 1 , wherein the resistance of the external load is in a range from 25uΩ to 5000 mΩ.  
     
     
         4 . The method of  claim 1 , wherein the resistance of the external load is optionally coupled to an amplifier.  
     
     
         5 . The method of  claim 1 , wherein the external load is provided as an internal resistor of either power transistor.  
     
     
         6 . The method of  claim 1 , wherein the transient large current is in a range from 1 A to 500 A.  
     
     
         7 . The method of  claim 1 , wherein the transient sampling time is less than 0.01 second.  
     
     
         8 . The method of  claim 1 , wherein a value of the internal resistance of the battery is measured through Kelvin connections.  
     
     
         9 . A method of measuring the internal resistance of a battery, comprising the steps of: 
 (1) choosing an external load, the resistance R of which is selected in accordance with the type of the battery to be evaluated, (2) selecting a value for the nominal internal resistance of the battery in accordance with its type;    (3) choosing a first power transistor or its related circuit as a first external load to obtain a reference voltage Vr;    (4) providing the first power transistor controlled for connecting the first external load across two terminals of the battery and repetitively controlling the first power transistor to conduct so that a large transient current is drawn from the battery by the first external load at a very transient sampling time and sampling a first reference voltage V r1  between two terminals of the battery and sampling a second reference voltage V r2  between two terminals of the external load, respectively for a plurality of times, and calculating and storing average values of the voltages V r1  and V r2 ;    (5) choosing a second power transistor or its related circuit as a second external load to obtain a load voltage V L ;    (6) providing the second power transistor controlled for connecting the second external load across two terminals of the battery and repetitively controlling the second power transistor to conduct so that a large transient current is drawn from the battery by the second external load at a very transient sampling time and sampling a first load voltage V L1  between two terminals of the battery and sampling a second load voltage V L2  between two terminals of the external load, respectively for a plurality of times, and calculating and storing average values of the voltages V L1  and V L2 ;    (7) removing the second external loads for stopping supplying the transient large current;    (8) removing the first external loads for stopping supplying the transient large current;    (9) determining the large transient current I drawn by the load by subtracting V r2  from V L2  and dividing by the resistance R;    (10) calculating the internal resistance r of the battery by subtracting V L1  from V r1  and dividing by the transient large current I;    (11) comparing the obtained internal resistance of the battery to be measured with a predetermined warning value of the internal resistance of the battery to be measured so as to determine whether the former is equal to or larger than the predetermined warning value or not; and    (12) issuing a warning through an input and output (I/O) if the determination in step (9) is affirmative.    
     
     
         10 . The method of  claim 9 , wherein the predetermined warning value of the internal resistance of the battery to be measured is 0.001 Ω to 1.5 Ω.  
     
     
         11 . The method of  claim 9 , wherein the resistance of the external load is in a range from 25 uΩ to 5000 mΩ.  
     
     
         12 . The method of  claim 9 , wherein the resistance of the external load is optionally coupled to an amplifier.  
     
     
         13 . The method of  claim 9 , wherein the external load is provided as an internal resistor of either power transistor.  
     
     
         14 . The method of  claim 9 , wherein the transient large current is in a range from 1 A to 500 A.  
     
     
         15 . The method of  claim 9 , wherein the transient sampling time is less than 0.01 second.  
     
     
         16 . The method of  claim 9 , wherein the I/O is one of a display, a keyboard input, a wireless operation, net work, USB (Universal Serial Bus) connector, databus, CAN (Controller Area Network) bus, GPS (Global Positioning System), SMS (Simple Message Service), MMS (Multimedia Message Service), WAP (Wireless Application Protocol) or an access to the Internet.  
     
     
         17 . The method of  claim 9 , wherein a value of the internal resistance of the battery is measured through Kelvin connections.  
     
     
         18 . A method of evaluating the condition of a battery, comprising the steps of: 
 (1) beginning by setting an interrupt vector address as an initial address of a program;    (2) initializing a register and I/O pins for setting an initial value of the register, activating the interrupt vector and a timer, and defining a state and an initial value of each I/O pin;    (3) choosing an external load, a resistance R of which is based on a type of the battery to be evaluated;    (4) selecting a value for a nominal internal resistance of the battery in accordance with its type;    (5) choosing a first power transistors as first external load and conducting the first power transistors for providing the transient large current;    (6) transiently sampling between two terminals of the battery with a transient large current supplied from the conducted first power transistor for K 1  times, where K 1 ≧1 and for L 1  times, where L 1 ≧1, respectively so as to obtain an average of each group of a first sampled reference voltage V r1  between two terminals of the battery and a second sampled reference voltage V r2  between two terminals of the external load;    (7) choosing a second power transistor as second external loads and conducting the second power transistors for providing the transient large current;    (8) transiently sampling at two terminals of the battery with a transient large current supplied from the conducted second power transistor for K 2  times, where K 2  ≧1 and for L 2  times, where L 2 ≧1, respectively so as to obtain an average of each group of a first sampled load voltage V L2  between two terminals of the battery and a second sampled load voltage V L1  between two terminals of the external load;    (9) removing the second external load for stopping supplying the transient large current;    (10) removing the first external load for stopping supplying the transient large current;    (11) determining whether the number of samplings is equal to N or not, where N ≧1 and if the determination is negative then loops back to step (6);    (12) determining the large transient current I drawn by the load by subtracting V r2  from V L2  and dividing by R;    (13) calculating the internal resistance (r) of the battery by subtracting V L1  from V r1  and dividing by the transient large current I of the battery; and    (14) comparing the obtained internal resistance (r) of the battery to be measured with the selected nominal value thereof to determine the condition of the battery to be measured.    
     
     
         19 . The method of  claim 18 , wherein the transient sampling time is less than 0.01 second.  
     
     
         20 . The method of  claim 18 , wherein the I/O is one of a display, a keyboard input, a wireless operation, net work, USB (Universal Serial Bus) connector, databus, CAN (Controller Area Network) bus, GPS (Global Positioning System), SMS (Simple Message Service), MMS (Multimedia Message Service), WAP (Wireless Application Protocol) or an access to the Internet.  
     
     
         21 . The method of  claim 18 , wherein a value of the internal resistance of the battery is measured through Kelvin connections.  
     
     
         22 . An apparatus for monitoring the condition of a battery by coupling a first power transistor as a first external load to obtain a first sampled reference voltage and a second sampled reference voltage and coupling a second power transistor as a second external load to obtain a first sampled load voltage and a second sampled load voltage, comprising: 
 a controller for controlling the apparatus so as to sample a voltage across the battery in predetermined periods of time responsive to imposition of a known external load chosen responsive to the type of the battery, calculate an internal resistance of the battery to be measured, and compare the internal resistance of the battery to be measured with a predetermined warning value therefor;    an external load being a load element and having a predetermined resistance, the external load comprising the first and second external loads both coupled in series with the battery, respectively;    a voltage-sampling circuit responsible for sampling voltages across two terminals of the battery;    a transient current control circuit including the first power transistor and the second power transistor, when the transient current control circuit is connected across two terminals of the battery so as to be controlled by the controller for being served as a switch of the apparatus so that a large transient current of the first and second power transistors is drawn by the first and second external loads from the battery and sampling the above voltages of the battery at a very transient sampling time for a plurality of times; and dividing a difference between the second sampled load voltage and the second sampled reference voltage by the resistance of the external load to obtain a large transient current of the battery; and dividing a difference between the average first sampled reference voltage and the average first sampled load voltage by the large transient current of the battery so as to obtain the internal resistance of the battery to be measured; and    an input/output(I/O) means responsive to the controller for issuing a warning responsive to comparison of the calculated value of the internal resistance of the battery with the predetermined value thereof.    
     
     
         23 . The apparatus of  claim 22 , wherein the apparatus further comprises an amplifier optionally coupled to the parallel first and second transistors taken as load.  
     
     
         24 . The apparatus of  claim 22 , wherein the load element is an internal resistance of the power transistor.  
     
     
         25 . The apparatus of  claim 22 , wherein the transient current control circuit comprises two or more parallel power transistors.  
     
     
         26 . The apparatus of  claim 22 , wherein the resistance of each of the first and second power transistors is in a range from 25 uΩ to 5000 mΩ.  
     
     
         27 . The apparatus of  claim 22  wherein the predetermined warning value of the internal resistance of the battery to be measured is 0.001 Ω to 1.5 Ω.  
     
     
         28 . The apparatus of  claim 22 , wherein the transient large current is in a range from 1 A to 500 A.  
     
     
         29 . The apparatus of  claim 22 , wherein the voltage sampling time is less than 0.01 second.  
     
     
         30 . The apparatus of  claim 22 , wherein the I/O is one of a display, a keyboard input, a wireless operation, net work, USB (Universal Serial Bus) connector, databus, CAN (Controller Area Network) bus, GPS (Global Positioning System), SMS (Simple Message Service), MMS (Multimedia Message Service), WAP (Wireless Application Protocol) or an access to the Internet.  
     
     
         31 . The apparatus of  claim 22 , wherein a value of the internal resistance of the battery is measured through Kelvin connections.