Abstract:
A system and method for recharging a rechargeable battery. A battery charger includes a measuring element to measure a temperature of the rechargeable battery, the battery charger disables a charge to the rechargeable batter when the temperature is greater than a first predetermined threshold, the measuring element re-measures the temperature of the battery after a predetermined time period from the disabling of the charge and the battery charger enables the charge when the re-measured temperature is less than a second predetermined threshold, wherein the second predetermined threshold is based on the first predetermined threshold.

Description:
BACKGROUND  
       [0001]     Since the advent of batteries, there has been many different techniques employed to recharge batteries. Originally, nickel cadmium rechargeable batteries were used. In order to increase capacity and for safety of the environment, nickel metal hydride (NiMH) rechargeable batteries were introduced. Rechargeable batteries allow for the convenience of any user to reuse batteries by utilizing a charger that will convert a discharged battery into a charged battery ready for reuse. Rechargeable batteries convert electrical energy into chemical energy so that a reverse reaction occurs inside the battery thus returning the battery to its original state where there is energy ready to be used.  
       SUMMARY OF THE INVENTION  
       [0002]     A method for measuring a temperature of a battery to be recharged, disabling a battery charger when the temperature is greater than a first predetermined threshold, enabling the battery charger after a predetermined time period, re-measuring the temperature of the battery; and recharging the battery when the re-measured temperature is less than a second predetermined threshold, where the second predetermined threshold is based on the first predetermined threshold.  
         [0003]     A system having a rechargeable battery and a battery charger including a measuring element to measure a temperature of the rechargeable battery, the battery charger disabling a charge to the rechargeable batter when the temperature is greater than a first predetermined threshold, the measuring element re-measuring the temperature of the battery after a predetermined time period from the disabling of the charge and the battery charger enabling the charge when the re-measured temperature is less than a second predetermined threshold, wherein the second predetermined threshold is based on the first predetermined threshold. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  illustrates an exemplary method of recharging a rechargeable battery according to the present invention.  
         [0005]      FIG. 2  illustrates an exemplary system of a rechargeable battery and a charger with its component parts according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0006]     The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The exemplary embodiment of the present invention describes a method for charging a battery to prevent overcharging and increased battery temperature due to repeated insertion into a charger. The battery charging, overcharging, and increased battery temperature will be discussed in detail below.  
         [0007]     In the exemplary embodiments, the exemplary battery is described as a rechargeable Nickel Metal Hydride (NiMH) battery. However, those of skill in the art will understand that the use of the NiMH battery is only exemplary and that the present invention may be applied to any type of rechargeable battery. Other examples of rechargeable batteries include nickel cadmium batteries and lithium ion batteries. All these battery types exhibit a system that utilize a reverse reaction where electrons are flowed in an opposite direction of when the battery is discharged in order to recharge the battery.  
         [0008]     It should be noted that the term “battery” will be used to encompass both a battery and a cell. Technically, a cell is a single unit, potentially one cell in a battery of multiple cells or possibly the entire device. A battery is a device for creating or storing electrical energy composed of several similar cells that are connected together. However, common usage of the term “battery” encompasses both a cell and a battery and the following description will use the term “battery” interchangeably to mean both a cell and a battery.  
         [0009]     A rechargeable battery (e.g., a NiMH battery) is able to be recharged so that it may be used repeatedly. This is accomplished by providing electrical energy to the battery. The electrical energy is converted into chemical energy by the battery. When the battery is used to provide energy to a load, the chemical reaction is reversed and electrical energy is provided to the load. An inherent problem that arises when the battery is continuously charged under different levels of discharge is that the chemical reaction inside the battery may produce heat that may permanently damage the battery. Such a condition may occur when, for example, a fully charged battery is recharged or when a partially discharged battery is charged beyond its capacity. Any energy not used to recharge the battery converts to heat which raises the temperature of the battery. Consequently, the life of a rechargeable battery (i.e., the number of times the battery may effectively be recharged) is significantly shortened.  
         [0010]      FIG. 1  illustrates an exemplary method  100  to prevent overcharging and increased battery temperature from repeated charging according to the present invention. The method  100  described in  FIG. 1  acts as an intelligence system in that it uses several parameters (e.g., charging rate, timer, temperature) in order to determine when a battery is allowed to be recharged and when the system must allow the battery to reach an acceptable condition for recharging. The method  300  will be described with reference to  FIG. 2  that shows a battery charger  201 , a rechargeable battery  202 , a monitoring system  204  and its component parts (e.g., a temperature gauge  204 , a timer  205 , and a voltage gauge  206 ), and an indicator  207 .  
         [0011]     In Step  101 , the charger  201  detects the charging power supply. For example, if the device that includes the arrangement of  FIG. 2  is placed in a recharging cradle, the charger  201  may detect the charging power supply that is provided by the recharging cradle. Those of skill in the art will understand that the use of a recharging cradle is only exemplary and that there are other types of charging power supplies that may be used and detected in step  101 , e.g., directly plugging the device into a wall outlet, etc. In step  101 , the charger  201  also learns the level of charge current or the charge rate that the charger  201  is allowed to draw from the recharging power supply, e.g., the recharging cradle. For example, if the charging cradle is host or PC powered, the recharging cradle may be limited to a set charging current, e.g., 500 mA. In other situations, the charging current may not be limited to any particular value. By determining this level of charge current, the charger  201  may determine the next set of parameters in order to effectively charge the rechargeable battery  202  correctly and in the most effective manner.  
         [0012]     In Step  102 , after learning of the level of charge current in Step  101  (e.g., full current, partial current), the charger selects an appropriate charge rate. Thus, using the example of a host or PC powered charging cradle, the charger  201  may select a charge rate of 500 mA to recharge the rechargeable battery  202 . However, where the level of charge current is not limited by the recharging device, the charger  201  may use a full current charge. The charging of the rechargeable battery  202  may be commenced in step  201 .  
         [0013]     In Step  103 , the charger  201  determines if it is receiving a fast charge signal. The charger  201  will be receiving the fast charge signal if the charge is active. However, if the temperature is detected to be greater than some safety value (e.g., 55° C.), the charge will not be active and the charger  201  will not receive the fast charge signal. If Step  103  determines that the fast charge is active, then the method proceeds to Step  106 . Otherwise, if Step  103  determines that the fast charge is inactive, then Steps  104  and  105  are used to ensure that the battery  202  reaches an appropriate condition in order to recharge.  
         [0014]     In Steps  104  and  105 , the rechargeable battery  202  temperature exceeds safe limits that allow for the rechargeable battery  202  to be recharged effectively. Thus, in Step  104 , the charger  201  disables itself so that no processes take place that may increase the temperature further. In Step  105 , the temperature of the rechargeable battery  202  is allowed to drop until the appropriate temperature is reached. The charger  201  will include functionality (e.g., temperature gauge  204 ) that detects the temperature of the rechargeable battery  202  when placed in the charger  201 . The temperature gauge  204  will measure the temperature at certain time intervals (e.g., every five minutes). Steps  104  and  105  serve as safety parameters to allow the rechargeable battery  202  to recharge optimally and to prolong its life. Once Steps  104  and  105  are completed, the process returns to Step  102 , where a charge rate is selected. Once returned to Step  102 , Step  103  will determine once again if the fast charge is active and whether the temperature of the charger has reached an appropriate temperature.  
         [0015]     In Step  106 , a temperature of the rechargeable battery  202  is measured with a temperature gauge  204 . In Step  106 , the temperature of the rechargeable battery  202  with respect a threshold value is determined. The threshold value may be set at any temperature based on a variety of factors, i.e., the rechargeable battery, the device in which it is used, etc. Thus, the manufacturer of the battery, the device, the charging cradle, etc, may provide optimum threshold temperatures for use with their product. The charger  201  may include a preset temperature threshold that may not be changed by the user (e.g., the threshold may be set at the factory) or the device having the charger  201  may include a user interface for the user to set or reset the threshold temperature stored in the charger  201  (e.g., individual users may set the threshold or the owner of the device may set the threshold temperature on an enterprise level). An exemplary threshold temperature may be, for example, 45° C. However, it should be noted that the threshold temperature of 45 □C is only exemplary and that other chargers may contain a threshold temperature that is higher or lower than 45° C. Referring back to Step  106 , if the temperature of the rechargeable battery  202  is greater than or equal to the threshold temperature, then the process proceeds to Step  107 . If the temperature of the rechargeable battery  202  is less than threshold temperature, then the process proceeds to Step  111 .  
         [0016]     In Step  107 , similar to Step  105 , the charger  201  is disabled. This prevents the charger from increasing the temperature of the rechargeable battery  202  by stopping any processes that may increase an already high temperature range for recharging batteries.  
         [0017]     Once the charger  201  is disabled in Step  107 , Step  108  allows the rechargeable battery  202  an opportunity to decrease its temperature by waiting a certain time interval. In the exemplary method  100 , the time interval used before continuing the process is set at 60 seconds. However, it should be noted that the time interval of 60 seconds is only exemplary and that any other time interval may be used (e.g., 30 seconds, 2 minutes, etc.). After waiting the predetermined time interval, the charger  201  is again enabled and the process continues.  
         [0018]     In Step  110 , the temperature of the rechargeable battery  202  is again tested. Step  110  serves as a failsafe so that the process does not automatically continue despite the temperature of the rechargeable battery  202  still being above a threshold temperature. However, in Step  110 , the threshold temperature may be changed from the first threshold value used in Step  106 . For example, the threshold temperature used in Step  110  may be lowered by 2° C. from the threshold temperature used in Step  106 , e.g., Threshold  1  =45° C. and Threshold  2  =43° C. This allows for more definiteness in terms of whether the rechargeable battery  202  has reached an appropriate temperature for it to be recharged. Again, it should be noted that the lowering of the threshold temperature in Step  110  by 2° C. is only exemplary and that other options for a second threshold temperature are available such as lowering the original threshold temperature by 3, 4, or 5° C. It may also be considered that the threshold temperature in Step  110  may be the same (or even higher) than that in Step  106 . While the preferred embodiment is for the second temperature threshold to be decreased, there may be situations where an increase is allowable.  
         [0019]     If Step  110  determines that the temperature of the rechargeable battery  202  is still greater than or equal to the second threshold temperature, then the process returns to Step  107  so that the charger  201  may be disabled again to attempt to lower the temperature of the rechargeable battery  202 . This cycle will continue until the rechargeable battery  202  has reached an appropriate temperature for recharging. Once the rechargeable battery  202  reaches a temperature that is lower than the second threshold temperature, then the process continues to Step  111 .  
         [0020]     In Step  111 , the rechargeable battery  202  is recharged. The system will include functionality to allow a user to know when the charger  201  is recharging the rechargeable battery  202  by utilizing an indicator  207 . The indicator  207  may include, for example, blinking a light emitting diode (LED) and playing evenly spaced sounds. In addition to allowing the user know when the charger  201  is recharging the rechargeable battery  202 , the charger  201  will include functionality that allows the system to monitor the fast charge with a monitoring system  203 . The monitoring system  203  serves as an assurance that the rechargeable battery  202  will be fully charged rather than charging for a set period of time thereby running a risk of only partial recharging.  
         [0021]     The monitoring system  203  may determine different parameters to decide if the charging is complete or if another cycle must be run in order to fully recharge the rechargeable battery  202 . Such parameters include, for example, temperature, time, and voltage by utilizing the temperature gauge  204 , a timer  205 , and a voltage gauge  206 , respectively. In order for the process to terminate at Step  112 , a combination of the parameters for voltage and time will be used as will be discussed below.  
         [0022]     If the temperature gauge  204  of the monitoring system  203  concludes that the temperature has increased beyond the threshold temperature used in Step  106  during the recharging process, then the process proceeds to Step  107 . At Step  107 , the cycle process beings in order to lower the temperature of the rechargeable battery  202  until the second threshold temperature of Step  110  is reached.  
         [0023]     If the timer  205  of the monitoring system  203  concludes that a time of a cycle has expired, then the process proceeds to Step  107  as well. The system will include the timer  205  so that recharging is done in time intervals. Such a time interval may be, for example, 133% of a normal fast charge time. A normal fast charge time may be, for example, 120 minutes. Thus, an exemplary time interval for recharging would be 160 minutes. Due to the possibility of the rechargeable battery  202  reaching an increase in temperature that is lower than the threshold temperature of Step  106  but higher than the second threshold temperature of Step  110 , Step  111  would serve as a failsafe for temperature by using time. As such, an unnecessary increase in temperature will not result.  
         [0024]      1  If the voltage gauge  206  of the monitoring system  203  concludes that the voltage of the rechargeable battery  202  has not reached its optimal (i.e., maximum) capacity, then the process proceeds to Step  107 . After a temperature determination that it may continue to recharge, the charger  201  will continue to recharge the rechargeable battery  202  until the optimal capacity is reached.  
         [0025]     In Step  111 , if the monitoring system  203  concludes that the rechargeable battery  202  has reached the optimal capacity using the voltage gauge  206  and does so within a pre-determined time interval using the timer  205 , then the process ends at Step  112 . Upon completion of the recharging, the charger  201  will also include functionality to indicate to a user that the process has terminated and that the rechargeable battery  202  is fully recharged by utilizing the indicator  207 . The indicator may include, for example, emitting a steady light from a LED and playing a constant sound. It should be noted that there may be two independent indicators to display when the charger  201  is charging the rechargeable battery  202  and when the charger  201  has charged the rechargeable battery  202 .  
         [0026]     It will be apparent to those skilled in the art that various modifications may be made in the present invention, without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.