Battery charger

A battery charger can include a charger controller configured to determine a total charge time that characterizes a time needed to charge a battery, the total charge time being based on a received state of charge (SOC) of the battery that characterizes a present SOC of the battery. The charger controller can also be configured to determine a charging start time for the battery based on a predetermined full charge time and the total charge time.

TECHNICAL FIELD

This disclosure relates to a battery charger. More particularly, this disclosure relates to a battery charger that includes a charger controller.

BACKGROUND

Portable electronic devices are powered by batteries that generate a voltage based on chemical reactions. As a battery provides power to the portable electronic device, the ability of the battery to provide the power becomes diminished. Many batteries that power portable electronic devices are rechargeable. However, charging such batteries can form deposits inside an electrolyte of the battery that can inhibit ion transport thereby increasing the battery's internal resistance. The increase in internal resistance reduces the cell's ability to deliver current. Thus, recharging the battery can diminish the battery's total capacity.

SUMMARY

One example relates to battery charger that includes a charger controller configured to determine a total charge time that characterizes a time needed to charge a battery. The total charge time can be based on a received state of charge (SOC) of the battery that characterizes a present SOC of the battery. The charger controller can also be configured to determine a charging start time for the battery based on a present time, a predetermined full charge time and the total charge time.

Another example relates to a non-transitory machine readable medium having instructions for performing a method. The method can include determining a total charge time of a battery based on a received SOC of the battery that characterizes a present SOC of the battery. The total charge time of the battery can also be based on a battery time constant of the battery that characterizes the product of a resistance and a capacitance of an equivalent circuit of the battery. The method can also include delaying a charging of the battery until a charging start time that is based on the total charge time and a predetermined full charge time.

Yet another example relates to a battery charging system that includes a battery pack that includes a battery. The battery charging system can also include a battery gauge configured to determine a present state of charge (SOC) of the battery. The battery charging system can further include a battery charger configured to provide a charging signal to the battery pack. The battery charger can include a charger controller configured to determine a constant current-constant voltage transition point for the battery based on a battery time constant and a full charge capacity of the battery. The battery time constant can characterize the product of a resistance and a capacitance of an equivalent circuit of the battery. The charger controller can also be configured to determine a total charge time for the battery based on the present SOC of the battery, the battery time constant and the full charge capacity of the battery. The charger controller can further be configured to determine a charging start time based on the total charge time and a predetermined full charge time. The charger controller can still further be configured to control the charging signal such that the present SOC of the battery prior to the charging start time is maintained and the present SOC of the battery is increased after the charging start time such that the present SOC of the battery is about 100% at the predetermined full charge time.

DETAILED DESCRIPTION

A battery charger can include a charger controller that can control how and when a battery is charged. In particular, upon connecting the battery charger to an external power source (e.g., a power outlet), the charger controller can delay a charging of the battery until after a charging start time is reached. The charging start time can be determined from a predetermined full charge time and a total charge time for the battery. In this manner, the time the battery is at or near a full charge state can be reduced, which can extend a life of the battery.

FIG. 1illustrates an example of a battery charging system2. The battery charging system2can include a battery gauge4that can determine a state of charge (SOC) of a rechargeable battery, which can be simply referred to as a battery6. The battery charging system2could be employed for example, in a wireless phone, a smartphone, a laptop computer, a tablet computer, an automobile (e.g., an electric automobile) or nearly any portable device that needs electrical power to operate.

In some examples, the battery gauge4can be integrated with a battery pack8that stores the battery. In other examples, the battery gauge4can be separate from the battery pack8. The SOC of the battery6can change in real time (or near real-time). To determine the SOC of the battery6, the battery gauge4can be configured to continuously sample a voltage VBATof the battery6at each of a plurality of sampling periods to provide the SOC of the battery6at each of the sampling periods based on the voltage VBAT, a temperature of the battery6, predetermined data associated with steady-state and transient behaviors of the battery6relative to a depth of discharge (DOD) of the battery6. In the example ofFIG. 1, the battery6is demonstrated as a single battery. However, it is to be understood that the battery6can represent a plurality of batteries (or battery cells) electrically connected in series, such that the voltage VBATcould represent an aggregate voltage of all of the batteries. Therefore, the SOC calculated by the battery gauge4can be an average SOC of the plurality of batteries.

The SOC of the battery6can be provided to a battery charger10. In some examples, the battery charger10can be implemented, for example, as hardware (e.g., an integrated circuit (IC) chip) coupled to discrete circuit components. In some examples, the battery charger10(or some components thereof) can be implemented as machine readable instructions stored in a non-transitory computer readable medium, such as a memory12wherein a processing unit (e.g., a processor core) can access the memory12and execute the machine readable instructions. In still other examples, the battery charger10can be implemented as a combination of hardware and software, such as firmware.

Upon connecting (e.g., “plugging in”) the battery charging system2to a power source (e.g., an external power source), the battery charger10can receive a power signal (labeled inFIG. 1as “POWER SIGNAL”). As one example, the power source could be a 110 Volt (V) power source or a 220 V power source (e.g., an electrical outlet). In another example, the power source could be a 5 V direct current (DC) power source (e.g., a universal serial bus (USB) connection). The power signal can be a signal that corresponds to a signal provided at the power source. For instance, in some examples, the power signal can be a stepped down and rectified version of the signal provided by the power source (e.g., a 12 V DC signal). In other examples, the power signal could be a pass through of the signal at the power source (e.g., a 5 V DC signal). At or near time a of connecting the battery charger10to the external power source, an initial SOC of the battery6can be received (labeled inFIG. 1as “SOC”). Such an initial SOC can represent a present SOC of the battery (SOCp) at the time of the connection.

The battery charger10can provide and control a charge signal (labeled inFIG. 1as “CHARGE SIGNAL”) to the battery6via the battery pack8. In response to the charge signal, the battery6can be charged at a predetermined rate. Moreover, the battery gauge4can provide the SOC of the battery6as feedback for the charge signal. As explained herein, by controlling the charge signal, the SOC of the battery6can be increased up to about 100%. At an SOC of about 100%, the battery6can be considered to be in a fully charged state. Moreover, the battery6can have a full charge capacity (FCC) of the battery6that can initially be approximately equal to an SOC of about 100% for the battery6. However, as the capacity of the battery6degrades over time (due to repeated charging), the difference between an SOC of about 100% for the battery6and the FCC of the battery6can increase. The FCC of the battery6can be a predetermined, measured value in milliamps per hour (mA/h).

The battery6charge signal can be controlled by a charger controller14of the battery charger10. In some examples, the charger controller14can be implemented, for example, as an IC chip, such as an application specific integrated circuit (ASIC) chip. In other examples, the charger controller14could be implemented as a microcontroller with embedded instructions (e.g., firmware). In still other examples, the charger controller14can include a processing unit (e.g., a processor core) and a non-transitory machine readable medium such as the memory12that stores machine executable instructions. In such a situation, the memory12could be implemented as volatile memory (e.g., random access memory (RAM)), non-volatile memory (e.g., a solid state drive, flash memory, a hard disk drive, etc.) or a combination thereof. Moreover, in such an example, the processing unit can access the memory12and execute the machine readable instructions.

For many batteries, such as a lithium ion battery, the more time that the battery6is at an SOC of about 100% (e.g., at or near FCC of the battery6), the total capacity of the battery6degrades. For instance, if the battery6is kept at or near an SOC of about 100%, the battery's6charging capacity will degrade faster than if the battery6is kept at an SOC of about 50%. Thus, the battery charger10can be configured to limit a percentage of time that the battery6is kept at or near an SOC of about 100%, thereby extending the life (e.g., reducing the degradation rate of the battery6).

The battery charger10can include battery data16that can characterize information about the battery6. The battery data16can be stored, for example, in the memory12. The battery data16can include a full charge time18for the battery6. The full charge time18can be a time of day that the battery6is to be at or near a SOC of about 100%. In some examples, the full charge time18can be set, for example, in response to user input (labeled inFIG. 1as “USER INPUT”). For instance, in examples where the battery charger10is implemented on a smartphone, the user can set a full charge time18via a graphical user interface (GUI). In a given example, the full charge time18of the battery6can be set to 7:00 A.M. Moreover, in the given example, the full charge time18can be representative of a time in the morning that a portable electronic device (e.g., a wireless phone) would typically need to be at a fully charged state (e.g., the start of a work day). In some examples, the user input can set the full charge time18to a setting that indicates that the battery6is to be charged immediately.

The battery6can have an equivalent circuit that can be modeled as a resistor in series with a capacitor. The battery data16can also include a battery time constant (τ)20that can characterize the product of the resistance and the capacitance of the equivalent circuit (e.g., an RC time constant for the battery6). In some examples, the battery time constant (τ)20can be derived from experimental data employed to generate the equivalent circuit of the battery6. In some examples, the battery time constant (τ)20can be a fixed value that can be based on physical properties of the battery6. In other examples, the battery time constant (τ)20can vary as a function of a temperature of the battery6.

The charge signal provided to the battery charger10can have three different states. In a first state, the charge signal can maintain the SOC of the battery6at the present SOC (SOCp). Thus, in the first state, the charge signal is provided with a current that can maintain the SOC of the battery6, but does not significantly increase the SOC of the battery6. As an example, in the first state, the charge signal can be provided intermittently, such that the SOC of the battery6increases by a relatively small amount (e.g., about 2% or less), and then the charge signal is terminated until the SOC of the battery6returns to the previous SOC. In this manner, the battery6charging system2can ensure that the SOC of the battery6does not decrease when the battery charger10is connected to a power source.

Additionally, in a second state, the charge signal can be provided at a constant current. Moreover, at some point in time, the charge signal can switch to a third state that provides a constant voltage. The switch between the second state and the third state of the charge signal can be referred to as a constant current-constant voltage (CC/CV) transition point22, which can be a specific SOC of the battery6. To determine the CC/CV transition point22, the charger controller14can employ Equation 1.

wherein:τ is the battery time constant20for the battery6;SOCCVis the SOC of the battery6at the CC/CV transition point22;Istis the constant current provided during the second state of the charge signal;Itapis a taper current provided after termination of a charging of the battery6; andFCC is the full charge capacity of the battery6.

In some examples, the values of the constant current the second state (Ist) and the taper current (Itap) can be fixed parameters of the battery charger10. The charger controller14can store the CC/CV transition point22in the battery data16. Additionally, Equation 2 can characterize an amount of time to provide the charge signal (at a constant current) in the second state until the CC/CV transition point22is reached.

wherein:tccis the time remaining (in seconds) for providing the charge signal at the second state (e.g., at a constant current) before the CC/CV transition point22is reached; andSOCpis a present value of the SOC of the battery6.

Further, Equation 3 can characterize an amount of time to provide the charge signal at the third state (e.g., at a constant voltage) after the CC/CV transition point22is reached.

wherein:tcvis the time remaining (in seconds) for providing the charge signal the third state before the SOC of the battery6is about 100%.

FIG. 2illustrates an example of a graph50that plots a time to full charge (e.g., an amount of time needed to reach about 100% SOC of the battery6) as a function of an SOC of the battery6illustrated inFIG. 1. Moreover, a point52on the graph can represent the CC/CV transition point of the battery6. That is, in the present example, the CC/CV transition point52can occur when the SOC of the battery6reaches about 68%, which can correspond to a time to full charge of about 3.3×103seconds (about 55 minutes). Moreover, at an SOC before the CC/CV transition point52, the charge signal can be provided in the second state (e.g., at a constant current), and the SOC of the battery6and the time to full charge of the battery6have a substantially linear relationship. After the CC/CV transition point52, the charge signal can be provided in the third state (e.g., at a constant voltage) and the SOC of the battery6and the time to full charge of the battery have a substantially non-linear relationship (e.g., a logarithmic relationship).

Referring back toFIG. 1, Equation 2 can be employed to determine a total time that the charge signal is provided in the second state (e.g., at constant current) when the SOC of the battery6is initially at 0%, which can result in Equation 5. Additionally, Equation 3 can be employed to determine a total time that the charge signal is provided in the third state (e.g., at constant voltage) when the SOC of the battery6is at or near the CC/CV transition point22, which can result in Equation 6.

wherein:ttapis the remaining charge time from the CC/CV transition point22to an SOC for the battery6of about 100%.

By solving Equation 3 for the battery time constant (τ)20, Equation 7 can be derived.

τ=FCC⁡(1-SOCst)-Ist*tlastIst-Itap+Ist*ln⁡(ItapIst)Equation⁢⁢7
wherein:tlastis a measured charging time for charging the battery6from a starting SOC of the battery6(SOCst) to an SOC of about 100%; and SOCstis less than SOCCV.

Accordingly, by measuring the total charge time (ttot)24and employing Equation 7, in some examples, the charger controller14can determine the battery time constant (τ)20, which can be stored in the battery data16. In some examples, the battery time constant (τ)20can be an average of multiple battery time constants (τ) derived from Equation 7. Additionally, in some examples, the battery time constant (τ)20can be updated in the battery data16by the charger controller14after completing a full charging of the battery6by employing Equation 7.

Furthermore, Equations 1, 2 and 3 can be combined to derive Equation 8, such that a total charge time (ttot)24can be calculated (e.g., by the charger controller14) from the present SOC of the battery6(SOCp).

ttotis the total charge time24from the present SOC of the battery6(SOCp) to a SOC for the battery6of about 100%.

By employing substitution, Equation 8 can be expanded to derive Equation 9.

Accordingly, the charger controller14can calculate the total charge time (tot)24by employing Equation 9 in response to receiving the present SOC for the battery6(SOCp). The charger controller14can store the total charge time (ttot)24in the battery data16. Additionally, in some examples, the charger controller14can output a total charge time signal (labeled inFIG. 1as “TOTAL CHARGE TIME”) to an external system (e.g., a host system). The total charge time signal can include data that characterizes the total charge time (ttot)24such that the external system can implement further processing of the total charge time (ttot)24. In such a situation, the total charge time signal can be provided to the external system over a bus, such as the Inter-Integrated Circuit (I2C) bus coupled to the battery charger10.

The charger controller14can determine a charging start time26based on the total charge time (ttot)24and the full charge time18. To determine the charging start time26, the charger controller14can subtract the total charge time (ttot)24from the full charge time18. For instance, in the given example where the full charge time18is 7:00 A.M., and the total charge time (ttot)24is determined to be about 1.5 hours, the charging start time26can be set to about 5:30 A.M. The charging start time26can be stored, for example, in the battery data16.

Additionally, the battery charger10can receive a present time signal (labeled inFIG. 1as “PRESENT TIME”) that characterizes a present time. In some examples, the present time signal could be provided from an external source (e.g., a telecommunications tower or a network server). In other examples, the present time signal could be provided from an internal component (e.g., an internal clock). The charger controller14can cause the battery charger10to provide the charge signal in the first state to maintain the present SOC (SOCP) of the battery6from the present time until the present time is the same (or nearly the same) as the charging start time26. Accordingly, the charger controller14can cause the battery charger10to delay charging the battery6until the charging start time26. At (or after) the charging start time26, the charger controller14can cause the battery charger10to charge the battery6in a manner described herein.

At the charging start time26, if the present SOC (SOCP) of the battery6is less than the CC/CV transition point22, the charger controller14can cause the battery charger10to provide the charge signal in the second state (e.g., at a constant current) until the CC/CV transition point22is reached. Moreover, upon reaching the CC/CV transition point22, the charger controller14can cause the battery charger10to change the charge signal from the second state (e.g., at a constant current) to the third state (e.g., at a constant voltage). If the present SOC (SOCP) of the battery6is greater than or equal to the CC/CV transition point22, the charger controller14can cause the battery charger10to provide the charge signal in the third state until the SOC of the battery6reaches a fully charged state of about 100%. Upon reaching the fully charged state, the charger controller14can cause a battery charger10to provide the charge signal in the first state to maintain charge of the battery6at the fully charged state of about 100% until the power signal is ceased, which can indicate that the battery charger10has been disconnected from the power source (e.g., unplugged).

By employing the battery charging system2, the time at which the battery6is at or near the fully charged state of about 100% can be reduced. Such a reduction can slow a degradation of the charging capacity of the battery6. In this manner, the benefits of having a fully charged battery can be achieved at a desired full charge time18that can be specified without the consequences (e.g. battery capacity degradation) of having the battery6at the fully charged state for an excessive amount of time. Furthermore, prior to the charging start time26, the SOC of the battery6is maintained, but not significantly increased. Accordingly, upon connecting the battery charger10to the power source, the SOC of the battery6does not decrease such that a user could, in some examples, employ the portable device associated with the battery6while the battery charger10is connected to the power source.

Moreover, the derived Equations 1-9 are relatively simple and the variables (e.g., parameters) for the Equations 1-9 are easily obtained such that the battery charger2can be implemented relatively easily and without advanced mathematical techniques (e.g., curve fitting). Furthermore, since the battery charger10switches from the charging signal from the second state (e.g., a constant current) to the third state (e.g., a constant voltage) at the transition point, the battery6can be charged at an optimal rate, which can be referred to as a “healthy rate” that does not damage or degrade the battery6. In comparison, some conventional battery chargers simply charge batteries at a fastest possible rate (e.g., not the optimal rate) thereby degrading a charge capacity of the battery.

FIGS. 3-8depict experimental data derived from observation of charging a battery. In particular,FIGS. 3, 5 and 7illustrate graphs100,110and120that depict experimental data that plots a time to full charge as a function of an SOC of a battery (e.g., the battery6illustrated inFIG. 1). InFIGS. 3, 5 and 7, two plots are illustrated, a first plot depicts a time to full charge (labeled inFIGS. 3, 5 and 7as “MEASURED TIME”) that characterizes an experimentally measured amount of time to charge the battery. A second plot depicts an estimated time to full charge (labeled inFIGS. 3, 5 and 7as “ESTIMATED TIME”) that characterizes a time to full charge estimated for the battery with an SOC of about 0%, wherein the estimated time to full charge is based on Equation 9. Moreover, in Equation 9, a battery time constant for the battery is calculated using Equation 7. InFIG. 3, to charge the battery, a constant current is applied to the battery at a rate to fully charge the battery in one hour, which can be referred to as a rate of about 1 C. InFIG. 5, to charge the battery, a constant current is applied to the battery at a rate of about 1.2 C, which would be about 20% more current than the charge rate of 1 C. InFIG. 7, to the charge the battery, a constant current is applied to the battery at a rate of about 1.8 C, which would be about 80% more current than the charge rate of 1 C.

FIGS. 4, 6 and 8illustrate graphs102,112and122that illustrate an error percentage (%) plotted as a function of the SOC of the battery. InFIG. 4, the error percentage corresponds to the difference between the first and second plots inFIG. 3. InFIG. 6, the error percentage corresponds to the difference between the first and second plots inFIG. 5. InFIG. 8, the error percentage corresponds to the difference between the first and second plots inFIG. 7. As illustrated inFIGS. 3-8, by employing Equations 7 and 9, the estimated time for charging the battery can have a high degree of accuracy (less than 0.5% error). Moreover, as illustrated inFIGS. 4, 6 and 8, the error percentage tends toward 0% at as the SOC of the battery approaches 100%.

In view of the foregoing structural and functional features described above, example methods will be better appreciated with reference toFIGS. 9 and 11. While, for purposes of simplicity of explanation, the example methods ofFIGS. 9 and 11are shown and described as executing serially, it is to be understood and appreciated that the present examples are not limited by the illustrated order, as some actions could in other examples occur in different orders and/or concurrently from that shown and described herein. Moreover, it is not necessary that all described actions be performed to implement a method. The example methods ofFIGS. 9 and 11can be implemented as instructions stored in a non-transitory machine-readable medium. The instructions can be accessed by a processing resource and executed to perform the methods disclosed herein.

FIG. 9illustrates a flow chart of an example method200for charging a battery. The method200could be implemented, for example, by the battery charging system2illustrated inFIG. 1. At210, upon detecting a power signal, a battery charger (e.g., the battery charger10illustrated inFIG. 1) can receive an initial SOC for a battery (e.g., the battery6illustrated inFIG. 1) from a battery gauge (e.g., the battery4illustrated inFIG. 1). The initial SOC for the battery can be referred to as the present SOC for the battery (SOCp). At220, a charger controller (e.g., the charger controller14illustrated inFIG. 1) of the battery charger can determine a battery time constant (τ) for the battery. The battery time constant (τ) can be determined, for example, by employment of Equation 7.

At230, the charger controller can determine a CC/CV transition point (SOCCV) for the battery. To determine the CC/CV transition point (SOCCV), the charger controller can employ, for example, Equation 1. At240, the charger controller can determine a total charge time (ttot) for the battery. To determine the total charge time (ttot), the charger controller can employ, for example, Equation 9.

At250, the charger controller can determine a charging start time. To determine the charging start time, the charger controller can examine a stored full charge time and subtract the total charge time from the full charge time. For instance, if the full charge time is 9:30 A.M. and the total charge time is about 2 hours and 20 minutes, the charging start time can be about 7:10 A.M.

At260, the charger controller can make a determination as to whether a present time is at (or past) the charging start time. If the determination at260is negative (e.g., NO), the method200can proceed to270. If the determination at260is positive (e.g., YES), the method200can proceed to280. At270, the charger controller can control a charge signal provided by the battery charger to the battery and causes the battery charger to provide the charge signal in a first state, such that the present SOC (SOCp) of the battery is maintained, but not significantly increased. At280, the charger controller can cause the battery charger to provide the charge signal in a second state (e.g., a constant current) or third state (e.g., a constant voltage) to charge the battery until the SOC of the battery reaches about 100%. By employment of this method, the amount of time that the battery is at or near an SOC of about 100% is reduced, since the charging of the battery is delayed until the charging start time is reached.

FIG. 10illustrates an example of a battery charger300. The battery charger300could be employed to implement the battery charger10illustrated inFIG. 1. The battery charger300can include a charger controller302that can be configured to determine a total charge time (ttot) that characterizes a time needed to charge a battery. The total charge time can be based on a received SOC (labeled inFIG. 10as “SOC”) of the battery that characterizes a present SOC of the battery. The battery charger can also determine a charging start time for the battery based on a predetermined full charge time and the total charge time.

FIG. 11illustrates an example of a method400for charging a battery. The method400could be implemented, for example, by the charger controller14illustrated inFIG. 1. At410, a total charge time (ttot) of a battery can be determined (e.g., by the charger controller) based on a received state of charge (SOC) of the battery that characterizes a present SOC of the battery and the total charge time (ttot) of the battery can also be based on a battery time constant (τ) of the battery that characterizes the product of a resistance and a capacitance of an equivalent circuit of the battery. At420, a charging of the battery can be delayed (e.g., by the charger controller) until a charging start time that is based on the total charge time (ttot) and a predetermined full charge time.