Abstract:
A method of charging a battery at multiple charges rates includes determining a type of power source connected to a charging circuit and determining a voltage of a battery to be charged by the power source. A desired charging voltage is determined in response to the power source type and the battery voltage. A difference between the desired charging voltage and the battery voltage is determined. A digital potentiometer is selectively commanded to adjust the desired charging voltage to vary the difference and alter a charging rate of the battery, such that the difference is increased to increase the charging rate or is decreased to decrease the charging rate.

Description:
BACKGROUND 
       [0001]    This application relates to battery charging, and more particularly to a control circuit operable to charge a battery at multiple charge rates. 
         [0002]    If an electric generator is used to charge a battery, it may be difficult to predict the output of the generator, since the generator output may rely on environmental conditions such as an amount of available light if the generator includes photovoltaic cells, a flow of fluid if the generator is a hydroelectric generator, or an amount of wind if the generator includes a wind turbine. 
       SUMMARY 
       [0003]    A method of charging a battery at multiple charge rates includes determining a type of power source connected to a charging circuit and determining a voltage of a battery to be charged by the power source. A desired charging voltage is determined in response to the power source type and the battery voltage. A difference between the desired charging voltage and the battery voltage is determined. A digital potentiometer is selectively commanded to adjust the desired charging voltage to vary the difference and alter a charging rate of the battery, such that the difference is increased to increase the charging rate or is decreased to decrease the charging rate. 
         [0004]    A control circuit operable to charge a battery at multiple charge rates includes a power source having a power source voltage and a voltage regulator. The voltage regulator produces a charging voltage in response to the power source voltage exceeding a voltage threshold. A digital potentiometer provides a feedback voltage to the voltage regulator such that the digital potentiometer is operable to dynamically adjust the charging voltage and a corresponding charging rate of the charging voltage. A charge enable circuit is operable to enable or disable a charging current of the charging voltage from charging a battery. A microcontroller is operable to control the charge enable circuit and the digital potentiometer. The microcontroller determines a type of power source, determines the charging voltage and corresponding charging rate in response to the type of power source and a voltage of the battery, and commands the digital potentiometer to adjust the charging voltage such that a difference between the charging voltage and a voltage of the battery may be varied to alter a charging rate of the battery. 
         [0005]    A method of charging a battery at multiple charge rates determines a difference between a desired charging voltage from a power source and a voltage of a battery to be charged. The desired charging voltage is selectively adjusted to vary the difference and alter a charging rate of the battery, such that the difference is increased to increase the charging rate or is decreased to decrease the charging rate. A check is performed to verify that the charging rate does not cause the power source to exceed its maximum power output. 
         [0006]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  schematically illustrates a circuit operable to charge a battery at multiple charge rates. 
           [0008]      FIGS. 2-3  schematically illustrate a method of operating the circuit of  FIG. 1  to charge a battery at multiple charge rates. 
           [0009]      FIG. 4  schematically illustrates the circuit of  FIG. 1  in greater detail. 
           [0010]      FIG. 5  schematically illustrates an example controller of the circuit of  FIG. 1 . 
           [0011]      FIG. 6  schematically illustrates a DC/DC converter of the circuit of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  schematically illustrates a circuit  10  operable to charge a battery at multiple charge rates. The circuit includes an alternating current (“AC”) power source  12  that is operable to charge a battery  14  which powers a load  16 . In one example the power source  12  is a hydroelectric generator operable to harvest energy from a flow of fluid, such as water, and the load  16  is an electric faucet operable to control a flow of water. Of course, these are only examples and other power sources and loads would be possible. 
         [0013]    An AC/DC converter  18  converts an AC current from the power source into a direct current (“DC”) voltage and DC current. A DC/DC converter  20 , which includes a digital potentiometer  22 , adjusts the DC voltage to be a desired charging voltage. A charge enable circuit  24  enables or disables the power source  12  from charging the battery  14 . A switch  26  is operable to disconnect the battery  14  from the load  16 . In one example the switch  26  is an air gap switch such that no leakage current may flow to the load when the switch  26  is OFF. A voltage booster  28  is operable to increase the voltage output by battery  14  to the load  16 . A controller  30  is operable to control the DC/DC converter  20  and the charge enable circuit  24 . The controller includes an AC threshold circuit  32  and a microcontroller  34 . 
         [0014]      FIGS. 2-3  schematically illustrate a method  100  of operating the circuit  10  of  FIG. 1  to charge the battery  14  at multiple charge rates. A waveform frequency of AC current from the power source  12  is obtained (step  102 ). To perform step  102 , the controller  30  receives inputs AC 1 , AC 2  from the power source  12  (see  FIGS. 4-5 ). The inputs AC 1 , AC 2  are received into AC threshold circuit  32  which includes a zener diode  36  and an optocoupler  38 . The optocoupler  38  electrically isolates the microcontroller  34  from the AC input voltage from the power source  12 . 
         [0015]    Referring to  FIG. 5 , the zener diode  36  implements a voltage threshold in the circuit  10 . The zener diode  36  is oriented to prevent a flow of current from the input AC 1  through the optocoupler  38  unless a voltage of the input AC 1  exceeds a breakdown voltage of the zener diode  36 . If the voltage of input AC 1  is less than the threshold, the zener diode  36  blocks a flow of current, and a frequency of the power source  12  is interpreted as being zero (step  104 ) and the charge enable circuit  24  is disabled (step  106 ) so that the battery will not be charged. This feature may be useful if the power source  12  is a generator, and if one wishes to not draw any current from the generator until the generator is outputting at least a minimum voltage. 
         [0016]    If the voltage of input AC 1  exceeds the breakdown voltage of zener diode  36 , then current flows from optocoupler to the microcontroller  34 , and the microcontroller  34  determines a frequency of the current (step  104 ). A voltage of the battery  14  is measured (step  108 ). A comparison is performed to determine if the frequency of the current is representative of a generator (step  110 ). In one example step  110  defines the power source  12  to be a generator in response to the frequency being within a first range (e.g. on the order of 60 Hz) and defines the power source  12  to be a constant output power source (e.g. 24 VAC plug in power source) in response to the frequency being within a second range (e.g. on the order of 300 Hz) that is higher than the first range. Of course, these are only examples and other ranges and power sources could be used. 
         [0017]    If the power source  12  is determined to be a generator, then a desired charging voltage of the circuit  10  is defined as shown in equation #1 below (step  112 ) such that a charging rate of the charging voltage varies depending on a frequency of current from the power source  12  at a given voltage of battery  14 . 
         [0000]        CV=BV +( m *Frequency+ b )  equation #1
 
         [0018]    where
       CV is a charging voltage of the circuit  10 ;   BV is a voltage of the battery  14 ;   m is a slope of the charge voltage CV; and   b is an offset of the slope.       
 
         [0023]    If the power source  12  is determined to not be a generator, then a desired charging voltage of the circuit  10  is defined as shown in equation #2 below (step  114 ) such that the charging rate is constant and does not depend on frequency. 
         [0000]        CV=BV+z   equation #2
 
         [0024]    where z is a constant. 
         [0025]    A check is performed to determine whether a voltage of the battery  14  exceeds a maximum permissible battery charge (step  116 ). In one example the maximum permissible charge is determined by a manufacturer of the battery and is stored in the microcontroller  34 . If the maximum permissible charge is exceeded then the charge enable circuit  24  is disabled (step  106 ). If the maximum permissible charge is not exceeded, the charge enable circuit is enabled, or if already enabled is maintained in its enabled state (step  118 ). 
         [0026]      FIG. 3  illustrates step  118  in greater detail. A check is performed to determine if the charge enable circuit  24  is enabled (step  120 ). If the charge enable circuit  24  is already enabled then it is maintained in its enabled state (step  122 ), and if the charge enable circuit  24  is disabled then it is enabled (step  124 ). Step  124  is performed using the “Charge Enable” signal  60  (see  FIGS. 4-6 ). The microcontroller  34  commands the digital potentiometer  22  to adjust a charge voltage to the desired charge voltage of steps  114 - 114  (step  126 ). 
         [0027]    A rate at which the circuit  10  charges the battery  14 , or “charging rate” is directly proportional to a difference between the charging voltage and the voltage of battery  14 . As this difference increases the charging rate increases, and as this difference decreases the charging rate decreases. However, as charging rate increases a power draw on the power source  12  also increases. Therefore, a check is performed to determine whether a charge rate of the circuit  10  causes the power source  12  to exceed is maximum power output (step  128 ). 
         [0028]    If the power source is exceeding its maximum power output then the charging rate is reduced by reducing a difference between the charging voltage and the battery voltage (step  130 ). Step  130  is performed by transmitting information about the power source  12  in a signal “PS Info”  62  to the digital potentiometer  22  (see  FIGS. 4 ,  6 ). Although “PS Info” is shown as a single signal  62 , it is understood that the signal  62  could include multiple signals (e.g. a power source type signal, a frequency signal, and a battery voltage signal). If the power source is not exceeding its maximum power output then the battery  14  is permitted to continue charging at the charge rate (step  132 ). The method  100  is then repeated (step  134 ). 
         [0029]    Additional details of the circuit  10  will now be described. Referring to  FIG. 4 , a light-emitting diode (“LED”) D 2  may be used to indicate whether the battery is connected or disconnected from the circuit  10 . Input connector  40  and output connector  42  may be used to connect the power source  12  and the load  16  to the circuit  10 . In one example the connectors  40 ,  42  are 9-volt battery style connectors. Of course, other connectors could be used. 
         [0030]    Referring to  FIG. 5 , LED D 7  may be used to indicate a charging status of the battery  14 . In one example, the LED D 7  provides a first notification if the battery  14  is charging (e.g. flashing ON and OFF) and may provide a second notification if the battery  14  is fully charged (e.g. remaining ON). Of course, other notifications would be possible. 
         [0031]    Referring to  FIG. 6 , a voltage control circuit  64  receives a feedback signal from the digital potentiometer  22  so that the voltage control circuit  64  can implement a desired charging voltage. 
         [0032]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.