Abstract:
A method for charging a rechargeable battery pack includes identifying battery capacity, determining sampling interval length according to the battery capacity, and implementing the determined sampling interval length. Also disclosed herein is a method for charging batteries comprising identifying battery capacity, determining current-on period length in duty cycle according to the battery capacity, and implementing the determined current-on period length. Further, disclosed herein is a battery charging apparatus comprising a charger for charging first and second batteries, where the first battery comprises a microprocessor. The charger further comprises at least one terminal for receiving a battery identification signal, so that the charger can distinguish between the first and second batteries. Also disclosed herein is a battery/charger combination comprising a battery comprising first, second and third terminals, at least one cell disposed between the first and second terminals and a microprocessor disposed within the battery between the first and third terminals, a charger connected to the battery via the first, second and third terminals, wherein the microprocessor controls charging of the battery by sending instructions to the charger.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/696,874, filed on Oct. 26, 2000, now U.S. Pat. No. 6,362,596, which in turn is a continuation application of U.S. patent application Ser. No. 09/292,164, filed on Apr. 15, 1999, now U.S. Pat. No. 6,175,211, which in turn derives priority under 35 USC § 119(e) from U.S. application Ser. No. 60/090,427, filed Jun. 17, 1998, now abandoned. 
     The present application is based upon and claims priority under 35 USC § 119 and 37 CFR §1.78 of copending U.S. provisional application Ser. No. 60/090,427, filed on Jun. 17, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to a method and apparatus for charging rechargeable batteries. 
     BACKGROUND OF THE INVENTION 
     The battery packs for portable power tools, outdoor tools, and certain kitchen and domestic appliances may include rechargeable batteries, such as lithium, nickel cadmium and lead-acid batteries, so that they can be recharged rather than be replaced. Thereby a substantial cost saving is achieved. Some users of battery energized equipment may have need for batteries having substantially different capacities, and to properly charge batteries, different charging rates should be used to avoid damaging the batteries. 
     A substantial cost and space saving is realized by providing a universal charging apparatus for charging the different batteries which require different charging rates. Further, it would be advantageous for the charging apparatus to optimize the different charging rates for each battery, in order to avoid overcharging of the battery and/or minimize the charging time. In addition, it would be advantageous if the charging apparatus was adaptable to charge future battery technologies for which it may not have been programmed to charge. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a method for charging a rechargeable battery pack is proposed. The charging method comprises identifing battery capacity, determining sampling interval length according to the battery capacity, and implementing the determined sampling interval length. 
     Also disclosed herein is a method for charging batteries comprising identifying battery capacity, determining current-on period length in duty cycle according to the battery capacity, and implementing the determined current-on period length. 
     Further, disclosed herein is a battery charging apparatus comprising a charger for charging first and second batteries, where the first battery comprises a microprocessor. The charger further comprises at least one terminal for receiving a battery identification signal, so that the charger can distinguish between the first and second batteries. 
     Also disclosed herein is a battery/charger combination comprising a battery comprising first, second and third terminals, at least one cell disposed between the first and second terminals and a microprocessor disposed within the battery between the first and third terminals, a charger connected to the battery via the first, second and third terminals, wherein the microprocessor controls charging of the battery by sending instructions to the charger. 
     Additional features and benefits of the present invention are described, and will be apparent from, the accompanying drawings and the detailed description below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate preferred embodiments of the invention according to the practical application of the principles thereof, and in which: 
     FIG. 1 is a circuit schematic diagram of a battery charger and a first battery according to the present invention; 
     FIG. 2 is a circuit schematic diagram of a battery charger and a second battery according to the present invention; and 
     FIG. 3 is a circuit schematic diagram of a battery charger and a third battery according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     The invention is now described with reference to the accompanying figures, wherein like numerals designate like parts. All the teachings of the Saar U.S. Pat. Nos. 4,388,582 and 4,392,101 are hereby incorporated by reference into this specification. 
     Referring to FIGS. 1-3, a battery  10  is connected to a charger control circuit  20 . Battery  10  comprises a plurality of battery cells  11  connected in series, which dictate the voltage and storage capacity for battery  10 . 
     Battery  10  preferably includes four battery contacts: first battery contact  12 , second battery contact  13 , third battery contact  14  and fourth battery contact  15 . Battery contact  12  is the B+(positive) terminal for battery  10 . Battery contact  13  is the B−or negative/common terminal. Battery contact  14  is the TC or temperature/communication terminal. Battery contact  15  is the IDP or identification terminal. Battery contacts  12  and  13  receive the charging current sent from the charger control circuit  20  (preferably from current source  22 , as discussed below) for charging the battery  10 . 
     As shown in FIGS. 1-3, the battery cells  11  are coupled between the battery contacts  12  and  13 . In addition, preferably coupled between battery contacts  13  and  14  is a temperature sensing device  16 , such as a negative temperature co-efficient (NTC) resistor, or thermistor, R T . The temperature sensing device  16  is preferably in close physical proximity to the cells  11  for monitoring of the battery temperature. Persons skilled in the art will recognize that other components, such as capacitors, etc., or circuits can be used to provide a signal representative of the battery temperature. 
     The charger control circuit  20  preferably comprises a controller  21 , which may be a microprocessor. Controller  21  may include positive terminal B+and negative terminal B−, which are coupled to battery  10  via battery contacts  12  and  13 , respectively. The positive terminal may also act as an input VIN, in order for the controller  21  to detect the battery voltage. In addition, the controller  21  may include an input TIN, which is coupled to the temperature sensing device  16  via the TC battery contact  14 . This allows the controller  21  to monitor the battery temperature. Controller  21  may control a current source  22  that provides current to battery  10 . This current may be a fast charging current and/or an equalization current. Current source  22  may be integrated within controller  21 . Preferably, current source  22  is designed to produce different fixed current outputs, rather than constantly variable outputs. Such current source  22  would be easy to design and inexpensive to manufacture. 
     Controller  21  may also have an input IDIN, which is coupled to the IDP terminal  15 . This input is used in part by the controller  21  to identify the type and capacity of the battery to be charged. A battery identification device  17  may be connected to the IDP terminal to provide the identification information to controller  21 . For example, in the battery  10  of FIG. 1, a battery identification device  17 , in this case a resistor R id , is connected between the IDP terminal and the negative terminal B−. The value of resistor R id  (and thus the voltage drop across the resistor) is selected to indicate the type and capacity of battery  10 . Because of the voltage drop caused by resistor R id , the controller  21  receives via IDIN input an analog signal which can be interpreted by the controller  21  to indicate the type and capacity of battery  10 . Controller  21  can then modify any and/or all charging parameters, such as charging voltage, current and time, in order to minimize charging time and/or avoid overcharging. 
     For example, the range of voltage drop, or the range of ID values representative of the voltage drop range, can be mapped out and programmed into controller  21  so that, upon input of a signal via the IDIN input, the controller  21  can access the programmed values and determine the type and capacity of the battery. Accordingly, the controller  21  may be programmed to recognize that if the ID value ranges between 50 and 106, the battery  10  contains nickel-cadmium (NiCd) cells. Similarly, ID values between 112 and 160 may indicate that the battery  10  contains nickel metal hydride (NiMH) cells. Further, ID values between 180 and 230 may indicate that battery  10  contains fixed-voltage cell technologies, such as lead acid or lithium-ion, etc., which needs to be charged under the absolute voltage termination scheme Further, the controller may be programmed to recognize that if the ID value is, for example, 56, the battery  10  is a NiCd battery with 1.3 Amps/hour capacity. The ID values and their meaning may be stored in a table T. Controller  21  need only then to access table T to determine the type and capacity of the battery. Alternatively, controller  21  may derive the type and capacity of the battery by inputing the ID value into a predetermined equation, preferably of linear form. 
     Because future battery technologies may require different charging methods than those known in the prior art, the controller  21  can be programmed to recognize batteries incorporating such technologies in order to properly charge them. Preferably, controller  21  uses the signals received via the IDIN input to identify such batteries. Again, the ID value ranges may be can be mapped out and programmed into controller  21  (and/or table T) so that, upon input of a signal via the IDIN input, the controller  21  can access the programmed values and determine the required course of action. Alternatively, controller  21  may manipulate the ID value in order to determine the required course of action. 
     For example, if the ID values range between 50 and 230, the controller  21  will recognize that it already has the charging methods for these batteries and alter the corresponding charging method according to the type and capacity of the battery. If the ID values are below 50 and/or above 230, the controller  21  then will recognize that it does not have a preprogrammned charging method for this battery. The controller  21  will then stop the charging process or receive the appropriate charging information from the battery. 
     The ID value ranges can then be used to identify what kind of information the controller  21  will receive. For example, if the ID values are between 231 and 240, the controller  21  will recognize that the battery will send a list of commands for the controller  21  to execute and that, once the list is transmitted, the battery will not receive any further information from and/or send any further commands to controller  21 . Preferably, such list of commands is sent through the TC contact  14 . Similarly, if the ID values are below 50, the controller  21  will recognize that the battery is a “smart power-up” battery, as discussed below. Further, if the ID values are above 240, the controller  21  will recognize that the battery is a “fill smart” battery, as discussed below. 
     Accordingly, the controller  21  is able to distinguish between a battery having a charging method pre-programmed in the controller  21  and a battery that will provide controller  21  with charging instructions. Preferably, the controller  21  is able to make this distinction through the use of a single input line (IDIN). Also, the controller  21  preferably detects the battery type and capacity through the use of the same input line. 
     FIGS. 2 and 3 illustrate two different types of smart batteries. In FIG. 2, in addition to the resistor R id , battery  10  has an on-board controller  30  (preferably comprising a microprocessor  31 ). The controller  30  is preferably not normally powered-up and is dormant until the battery  10  is connected to charger  20 . When controller  21  detects that battery  10  is a power-up smart battery (because of the ID value obtained via the IDIN input), controller  21  preferably provides enough current and voltage through the IDP terminal to drive controller  30 . Once controller  30  is powered, controller  21  relinquishes control of the charging process to controller  30 . Controllers  21  and  30  preferably communicate via the TC terminal. Controller  30  can then control the charging of battery  10  by providing charger  20  with the steps required to charge the battery. Preferably, controller  30  actively controls the charging process. In other words, controller  30  issues commands to controller  21  to enable/disable current feed, etc. Controller  30  may also request information from controller  21 , such as charger status, battery voltage and/or temperature, etc., which controller  30  can then use to carry out the charging process. 
     Similarly, in FIG. 3, battery  10  has an on-board controller  40  (preferably comprising a microprocessor  41 ). Unlike the controller  30 , controller  40  is preferably normally powered-up at all times. Such controller  40  can then provide to or receive from the charger and/or device data, such as state-of-charge information. By being normally powered, controller  40  can also log and/or store any data as required. When controller  21  detects that battery  10  is a power-up smart battery (because of the ID value obtained via the IDIN input), controller  21  relinquishes control of the charging process to controller  40 . Preferably, controllers  21  and  40  preferably communicate via the TC terminal. Controller  40  can then control the charging of battery  10  by providing charger  20  with the steps required to charge the battery. Preferably, controller  40  actively controls the charging process. In other words, controller  40  issues commands to controller  21  to enable/disable current feed, etc. Controller  40  may also request information from controller  21 , such as charger status, battery voltage and/or temperature, etc., which controller  40  can then use to carry out the charging process. 
     As mentioned above, the preferred current source  22  provides fixed current outputs. Accordingly, battery packs of varying capacities may be charged with this fixed-current output power supply. Thus, it is preferable that the charging method is adaptable to properly charge the different batteries. 
     In particular, because overcharging may cause damage to the batteries, it is preferable to terminate the charging process based on voltage change rates or temperature change rates. These change rates however are dependent upon the length of sampling time interval. Usually, sampling time intervals are selected as a compromises between having a long time interval, accelerating the processing time but risking missing important events between samples, and a short time interval, slowing the processing time to process unimportant events or noise. In other words, if the sample time interval is too long, an event between samples may be missed and the battery may be overcharged. Conversely, if the sample time interval is too long, the charging process may be terminated prematurely without fully charging the battery. 
     It is thus proposed that sample time intervals be preferably C-rate-specific, otherwise the battery may be overcharged or undercharged. The C-rate is equal to the charger current output divided by the battery capacity. Accordingly, the C-rate when a four amp/hour battery is charged by a two amp charger is 0.5C. It has been found that a two amp charger may be used to charge a two amp/hour battery (at a 1C rate), the battery should reach full charge in one hour. The termination algorithm used to terminate the charging process may have, for example, a sample time interval of one minute. If a one amp/hour battery is placed in the same two amp charger (at a 2C rate), the battery should reach full charge in 0.5 hours. However, if the termination algorithm uses the same sample time interval of one minute, the sampling will be too slow and may cause overcharging of the battery. Similarly, if a four amp/hour battery is placed in the same two amp charger (at a 0.5C rate), the battery should reach full charge in two hours. However, if the termination algorithm uses the same sample time interval of one minute, the sampling will be too fast, causing early termination of the charging process and thus undercharging of the battery. 
     The controller  21  may calculate the desired sampling rate by identifying the battery type and capacity, using a prior scheme or the schemes proposed above, calculating the C-rate, and dividing a constant X by the C-rate to determine the length of sampling interval. Constant X preferably represents the length of a preferred sampling interval, which may be about 30 or 60 seconds. Persons skilled in the art will recognize that the selected length of the preferred sampling interval involves weighing different considerations, as discussed above. 
     The ID value may also be used to provide the proper sampling interval. For example, the controller  21  may access a table of stored values representative of different sampling intervals related to different batteries and use the ID value to select the value related to the proper sampling interval from the table. Alternatively, the controller  21  may input the ID value into an equation that would provide the proper sampling interval. This equation is preferably linear in nature, i.e., follows the form m(ID value)+b, where m and b are constants selected to provide proper one-to-one correspondence between the range of ID values and the range of sampling intervals. 
     Once the proper sampling interval is selected, it is preferable that the controller  21  implement the proper sampling interval automatically. The controller  21  can then properly calculate meaningful voltage and/or temperature change rates, and terminate according to methods well known in the art. 
     In addition, controller  21  may terminate charging after a predetermined number of sampling intervals has elapsed. The predetermined number of sampling intervals may range between 30 and 140, where the preferred number of sampling intervals is 120. 
     Once the controller  21  terminates charging, the current source  22  may provide a maintenance and/or equalization current to the battery. 
     Such scheme is especially useful for cell chemistries, such as NiCd, that allow the battery to be charged over wide range of charge rates, allowing the battery to be charged as quickly as possible. This scheme may also simplify the code for controller  21 , if the different voltage curves for the different capacities vary only along the x-axis, i.e., time, rather than on the y-axis, i.e., voltage or temperature. This scheme may also be used for cell chemistries, such as NiMH, that cannot accept charging current beyond capacity. 
     Another scheme may be used for cell chemistries, such as NiMH, that cannot accept charging current beyond capacity. In other words, if a battery can only accept one amp, such battery could be damaged if it was inserted into a two amp charger. Such a problem may be avoided if the controller  21  repeatedly switches on and off the current source  22 , preferably creating a duty cycle where the current is on for a specific period of time and off for a specific period of time. 
     Assuming that the length of the duty cycle is fixed, the controller  21  need only calculate the length of the “current-on” period, as the length of the “current-off” period will be equal to the length of the duty cycle minus the length of the current-on period. The controller  21  may calculate the desired sampling rate by identifying the battery type and capacity, using a prior scheme or the schemes proposed above, calculating the C-rate, and multiplying a constant Y by the C-rate to determine the current-on period length. Constant Y preferably represents the length of a duty cycle, which may be about 30 or 60 seconds. Persons skilled in the art will recognize that the selected length of the duty cycle involves weighing different considerations, as known in the art. The ID value may also be used to provide the proper current-on period length. For example, the controller  21  may access a table of stored values representative of different current sampling intervals related to different batteries and use the ID value to select the value related to the proper current-on period length from the table. Alternatively, the controller  21  may input the ID value into an equation that would provide the proper current-on period length. This equation is preferably linear in nature, i.e., follows the form n(ID value)+c, where n and c are constants selected to provide proper one-to-one correspondence between the range of ID values and the range of current-on period lengths. 
     Once the proper current-on period length is selected, it is preferable that the controller  21  implement the proper current-on period length automatically. The controller  21  can then properly calculate meaningful voltage and/or temperature change rates, and terminate according to methods well known in the art. 
     In addition, controller  21  may terminate charging after a predetermined number of sampling intervals has elapsed. The predetermined number of sampling intervals may range between 30 and 140, where the preferred number of sampling intervals is 120. 
     Once the controller  21  terminates charging, the current source  22  may provide a maintenance and/or equalization current to the battery. 
     Preferably the sampling interval length coincides with the duty cycle length. It is also preferable that the instant when the battery conditions are sampled be coincident or near coincident with the end of the duty cycle. 
     If the battery capacity is larger than the current output of the charger, it is preferable to increase the sampling interval, while continuously sending current to the battery. Preferably the sampling interval is selected according to the method described above. 
     Persons skilled in the art may recognize other alternatives or additions to the means or steps disclosed herein. However, all these additions and/or alterations are considered to be equivalents of the present invention.