State of charge (SOC) is a measure of the energy presently stored in a battery pack compared to a fully charged battery pack. For example, a battery pack described as one-half full has an SOC of 50%.
In the past, only a few high-end battery packs, such as those used for power tools, had SOC indicators for their battery packs. Many of the low- and medium-end power tool battery packs do not have an SOC indicator. Those battery packs that do have SOC indicators are implemented using discrete components. However, many end users find it valuable to know the battery's SOC prior to starting a project. For example, before climbing a ladder to work on the roof, it is very helpful to know how much energy is in a power tool's battery pack.
The SOC indicators are typically implemented using a set of lights such as light-emitting diodes (LEDs). The number of LEDs that are lit indicates the SOC. That is, each LED is associated with a respective SOC threshold and is lit if that threshold is reached.
There are a number of issues with conventional SOC indicators.
However, the push button may cause a fault condition that could damage the battery pack. For example, when the battery pack is stored in a tool box, the push button may accidentally be activated in a continuous manner. That is, the button may be accidentally and continuously depressed because it is pressed up against something else in the tool box. Consequently, the SOC monitor and SOC indicator are turned on, which results in a continuous current drain from the battery pack of about 10 to 20 milli-amps (mA). A typical fully charged lithium-ion (Li-ion) cell may have 1500 mA-hours of energy stored. If the battery has been used all day, it may have only about 500 mA-hours of energy remaining. In the latter case, with a current drain of 20 mA, it may take only slightly more than a day to drain all the remaining energy. Over a long weekend or if there are a few weeks between use, the battery may be completely discharged. Completely discharging a Li-ion battery can damage the battery pack and shorten its cycle life and age.
Another issue with conventional SOC indicators is that the lowest SOC is indicated by turning off all of the LEDs, which may confuse the user as to the actual SOC.
Another issue with conventional SOC indicators occurs when the SOC is almost exactly at one of the thresholds (e.g., at T1, T2, and T3). In such cases, the LEDs may flicker as the SOC changes because of electrical noise or some other reason. For example, if the battery pack voltage input to a comparator is almost exactly the same voltage as the reference threshold voltage input to the comparator, then the output may erratically alternate between a logical “1” and “0” because the battery pack voltage may experience significant noise modulation as a result of load variations or variations occurring internal to the cells. As the comparator output changes back-and-forth between “1” and “0,” the LEDs will flicker. This is distracting to the user and also does not provide a clear indication of the actual SOC.
In summary, conventional SOC indicators for the battery packs are susceptible to fault conditions that can drain the battery, and do not always provide an unambiguous indication of SOC.
An embodiment according to the present invention provides a method of operating a state-of-charge (SOC) indicator for a battery pack. The method includes: with the SOC indicator in a first state, changing operation of the SOC indicator to a second mode if a mechanism is activated; and changing operation of the SOC indicator from the second mode to a third mode if the mechanism remains activated after a timer expires. The SOC indicator consumes a first amount of power in the second mode, and consumes a second amount of power in the third mode. The second amount is less than the first amount.
Another embodiment according to the present invention provides an apparatus for indicating a state-of-charge (SOC) of a battery pack. The apparatus includes a first indicator and a second indicator. The first indicator is turned on when the SOC is greater than a first threshold and is turned off when the SOC is less than the first threshold. The second indicator is turned on when the SOC is greater than a second threshold and blinks with a regular frequency when said SOC is less than the second threshold. The second threshold is less than the first threshold.
Another embodiment according to the present invention provides a circuit for monitoring state-of-charge (SOC) of a battery pack. The circuit includes a divider, a first comparator, and data storage. The divider receives a battery pack voltage and generates a first divided signal and a second divided signal that correspond to the battery pack voltage. The first comparator compares the first divided signal and a reference signal during a first time interval, and generates a first comparing signal indicating the SOC of the battery pack based upon a result of the comparison. The data storage coupled to the first comparator stores the first comparing signal. A SOC indicator displays the SOC of the battery pack during a second time interval based upon the first comparing signal stored in the data storage. The second time interval is separated from the first time interval.
Features and advantages of embodiments of the claimed subject matter will become apparent as the following detailed description proceeds, and upon reference to the drawings, wherein like numerals depict like parts, and in which:
Reference will now be made in detail to the embodiments of the present invention. While the invention will be described in conjunction with these embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims.
Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.
Embodiments in accordance with the present invention provide methods of operating state-of-charge (SOC) indicators for battery packs, apparatuses for indicating a SOC for battery packs, and circuits for monitoring SOC of the battery pack. In one embodiment, the method includes: with the SOC indicator in a first state, changing operation of the SOC indicator to a second mode if a mechanism is activated; and changing operation of the SOC indicator from the second mode to a third mode if the mechanism remains activated after a timer expires. The SOC indicator consumes a first amount of power in the second mode, and consumes a second amount of power in the third mode. The second amount is less than the first amount. Advantageously, the low-power mode gives the battery pack a sufficient period of time to survive the discharge fault condition before becoming fully discharged, therefore mitigating the effects of a fault condition.
In one embodiment, the apparatus includes a first indicator and a second indicator. The first indicator is turned on when the SOC is greater than a first threshold and is turned off when the SOC is less than the first threshold. The second indicator is turned on when the SOC is greater than a second threshold and blinks with a regular frequency when said SOC is less than the second threshold. The second threshold is less than the first threshold. Advantageously, a positive and unambiguous indication is provided when the lowest SOC is reached.
In one embodiment, the circuit includes a divider, a first comparator, and data storage. The divider receives a battery pack voltage and generates a first divided signal and a second divided signal that correspond to the battery pack voltage. The first comparator compares the first divided signal and a reference signal during a first time interval, and generates a first comparing signal indicating the SOC of the battery pack based upon a result of the comparison. The data storage coupled to the first comparator stores the first comparing signal. A SOC indicator displays the SOC of the battery pack during a second time interval based upon the first comparing signal stored in the data storage. The second time interval is separated from the first time interval. Advantageously, the user will see a stable SOC indication each time the push button is activated.
In one embodiment, the mode detector 302 includes a push button (not shown) and determines a mode for the monitoring circuit 304 and the SOC indicator 306.
When operating in the standby mode, the monitoring circuit 304 and the SOC indicator 306 are inactive and consume a first amount of power. When operating in the normal mode, the monitoring circuit 304 and the SOC indicator 306 are active and operate with a second amount of power which is much higher than the first amount. When operating in the low-power mode, the monitoring circuit 304 and the SOC indicator 306 may consume a third amount of power which is higher than the first amount but still much lower, e.g., 1000 times lower, than the second amount of power. For example, the low-power mode may operate at a current of about 10 micro-amps, while the standby mode operates at a current of about 0.25 micro-amps (about 250 nano-amps). How the mode detector 302 selects a mode from the standby mode, the normal mode, and the low-power mode is further described in
In one embodiment, when the normal mode is detected by the mode detector 302, the monitoring circuit 304 monitors the SOC of the battery 308, and generates a control signal 310 indicating the SOC to the SOC indicator 306. Accordingly, the SOC indicator 306 displays the SOC of the battery 308 by turning on or turning off the LEDs 306_1, 306_2 and 306_3.
In block 502, in one embodiment, the monitoring circuit 304 and the SOC indicator 306 operate in the standby mode.
In block 504, the mode detector 302 determines whether a mechanism is activated, for example, the mode detector 302 determines whether a push button has been pressed (e.g., pushed by a user). In general, the mechanism is not limited to the push button; another mechanism can also be used depending on the requirements of particular applications. If the push button has not been pressed, the monitoring circuit 304 and the SOC indicator 306 remain in the standby mode. If the push button has been pressed, in response, the monitoring circuit 304 and the SOC indicator 306 are activated and transform from the standby mode to the normal mode, as shown in block 506.
When operating in the normal mode in block 506, the monitoring circuit 304 and the SOC indicator 306 are activated and a delay timer (not shown) is started. Because a delay timer is used, a microcontroller is not necessary, thus reducing cost.
In block 508, the monitoring circuit 304 monitors the delay timer to track the moment when the delay timer has expired, and a determination is made with regard to whether the delay timer has been expired. Until the time delay has terminated, the delay timer will continue to measure time. In one embodiment, the delay timer has a period of 4 seconds. Generally speaking, the delay timer has a period that is long enough to detect the SOC of the battery pack but short enough to avoid unnecessarily consuming the battery charge. If the delay timer expires, the flowchart 500 proceeds to block 510.
In block 510, the mode detector 302 determines whether the mechanism is deactivated. For example, the mode detector 302 determines if the push button has been released. If the push button has been released (that is, it is no longer depressed), the battery system 300 is operating normally, and the monitoring circuit 304 and the SOC indicator 306 are transformed to the standby mode in block 502 to wait for the next depression of the push button.
However, in block 510, if the mode detector 302 determines that the push button has not been released (remains depressed), then the monitoring circuit 304 and the SOC indicator 306 are transformed to the low-power mode in block 512. The monitoring circuit 304 and the SOC indicator 306 remain in the low-power mode until the push button is released. In one embodiment, the power consumed in the low-power mode is less than the power consumed in the normal mode, e.g., the power consumed in the low-power mode is 1000 times lower than power consumed in the normal mode. After the push button is released, the monitoring circuit 304 and the SOC indicator 306 will transform to the standby mode to wait for the next depression of the push button.
Advantageously, the low-power mode gives the battery pack a sufficient period of time to survive a discharge fault condition before becoming fully discharged, therefore mitigating the effects of a fault condition when, for example, the push button is continuously depressed, by accident or otherwise. The length of battery survival time is dependent upon the SOC of the battery prior to entering the fault condition.
In one embodiment, the SOC of the battery pack has a first threshold T1, a second threshold T2, and a third threshold T3, wherein T1 is greater than T2, which is greater than T3, that is, T1>T2>T3. The SOC indicator 306 displays the SOC with LEDs 306_1, 306_2, and 306_3 according to a comparison result of the SOC of the battery back and the thresholds (e.g., T1, T2, and T3). In one embodiment, the LED 306_1 is turned on when SOC is greater than T1, and is turned off when SOC is less than T1. The LED 306_2 is turned on when SOC is greater than T2, and is turned off when SOC is less than T2. The LED 306_3 is turned on when SOC is greater than T3, and blinks when SOC is less than T3.
Therefore, the SOC indicator 306 can operate in state 602, 604, 606, or 608, for example. Specifically, as shown in
In one embodiment, the indicating circuit 700 includes the monitoring circuit 304 coupled to the LED 306_3. A resistor R1, the LED 306_3, and a transistor Q1 are coupled in series. The monitoring circuit 304 includes a voltage comparator 702, a pulse generator 712, and a logic circuit 720, in one embodiment. The voltage comparator 702 compares a battery pack voltage VB and a third predetermined reference voltage VT3 indicative of the third threshold T3, and generates a comparison signal 714 based upon a result of the comparison. The pulse generator 712 generates a pulse signal PUL. The logic circuit 720 receives the comparison signal 714 and the pulse signal PUL, and accordingly provides a switching signal SW to the transistor Q1. The transistor Q1 is turned on or off according to the switching signal SW, so as to conduct or not conduct a current through the LED 306_3.
In one embodiment, the logic circuit 720 includes an inverter gate 708, an AND gate 710, and an OR gate 704. The AND gate 710 receives the comparison signal 714 via the inverter gate 708 and receives the pulse signal PUL generated by the pulse generator 712. Accordingly, the AND gate 710 generates a signal 718. The OR gate 704 receives the signals 714 and 718, and outputs the switching signal SW to the transistor Q1. In one embodiment, the signals 714, PUL, 718, and SW are digital signals. In one embodiment, the transistor Q1 can be an N-type metal-oxide-semiconductor-field-effect transistor (MOSFET), which is, for example, conducted on when the switching signal SW has a first level (e.g., represented by logic “1”), and cut off when the switching signal SW has a second level (e.g., represented by logic “0”).
More specifically, if the battery pack voltage VB is greater than the third predetermined reference voltage VT3, then the voltage comparator 702 outputs the comparison signal 714 in a first state, for example, logic “1” state. The comparison signal 714 in logic “1” state is presented to the input of the OR gate 704, and accordingly the switching signal SW has a first value, e.g., logic “1”, to turn on the transistor Q1. Thus, a current is conducted through the resistor R1, the LED 306_3, and the transistor Q1, to ground. As such, the LED 306_3 is turned on. In one embodiment, the LED current is limited by the resistor R1.
If the battery pack voltage VB is less than the third predetermined reference voltage VT3, then the voltage comparator 702 outputs the comparison signal 714 in a second state, for example, logic “0” state. The inverter 708 receives the comparison signal 714 in logic “0” and presents a signal 716 in logic “1” to the AND gate 710. The signal 716 in logic “1” enables the AND gate 710 to pass the pulse signal PUL from the pulse generator 712 to the OR gate 704. Accordingly, the switching signal SW will switch between a first value (e.g., logic “1”) and a second value (e.g., logic “0”) as the pulse signal PUL does, and toggle the transistor Q1 with the frequency of the pulse signal PUL. Accordingly, the current through LED 306_3 is conducted on and off alternately. Therefore, the LED 306_3 blinks at a rate equal to the frequency of the pulse signal PUL. In one embodiment, the pulse signal PUL has a frequency of 2 Hz. The resultant current in the transistor Q1 will modulate the LED 306_3, which will blink and thus provide a visual alert to the user.
Advantageously, the LED 306_3 blinks at a regular frequency (e.g., 2 Hz) when the lowest SOC (the state 608 in
SOC Indicator without Flicker
In one embodiment, the monitoring circuit 800 includes a divider 818, a multiplexing module 812, a reference generator 820, a comparator 802, and a storage module 816. In one embodiment, the divider 818 includes four resistors R8
In one embodiment, the multiplexing module 812 includes a multiplexer 806 and a control circuit 808. The multiplexer 806 receives the divided voltages VD1 to VD3, and selects a signal VMUX from VD1 to VD3 in sequence according to a control signal CTR1 generated by the control circuit 808. In one embodiment, the control signal CTR1 includes three digital signals CTR1
In one embodiment, the reference generator 820 generates a reference signal VR. The comparator 802 then compares the signal VMUX and the reference signal VR to generate a comparing signal 814 based upon a result of the comparison. In other words, the comparator 802 compares the divided voltages VD1, VD2, VD3 with the reference signal VR in sequence.
In one embodiment, the ratio between the resistors R8
R
T
/R
8
4
=V
T1
/V
R. (1)
In one embodiment, a ratio between the total resistance RT and a sum of the resistances of the resistor R8
R
T/(R8
In one embodiment, a ratio between the total resistance RT and a sum of the resistances of the resistor R8
R
T/(R8
Therefore, when the divided voltages VD1 to VD3 are selected and compared with the reference signal VR in sequence and are all greater than the reference signal VR, the battery pack voltage VB is indicated to be greater than the first predetermined reference voltage VT1, which further indicates that the SOC of the battery pack is above 80%, for example. When the voltages VD1 and VD2 are greater than the reference signal VR and the voltage VD3 is less than VR, it indicates the battery pack voltage VB is greater than the second predetermined reference voltage VT2 but less than the first predetermined reference level VT1. As such, the SOC of the battery pack is above 40% but below 80%, for example. When only the voltage VD1 is greater than VR, and the voltages VD2 and VD3 are both less than VR, it indicates the battery pack voltage VB is greater than the third predetermined reference voltage VT3 but less than the second predetermined reference level VT2. As such, the SOC of the battery pack is above 25% but below 40%, for example. When the voltages VD1 to VD3 are all less than VR, it indicates the battery pack voltage VB is less than the third predetermined reference voltage VT3. As such, the SOC of the battery pack is below 25%, for example. Consequently, by comparing the divides voltages with the reference signal VR, the SOC of the battery pack can be monitored.
In one embodiment, the storage module 816 includes a data storage 804 and a control circuit 810 coupled together. The data storage 804 can be implemented using latches or a register, for example. The data storage 804 receives the comparing signal 814 and stores the comparing signal 814 according to a control signal CTR2 generated by the control circuit 810. In other words, the data storage 804 sequentially stores the comparison results between the reference voltage VR and each of the divides voltages VD1 to VD3.
As shown in
After a delay, the control signals CTR1
After a delay from time t8 when the signal CTR1
Advantageously, results of the comparisons between the battery pack voltage VB and the reference signal VR are stored; thus, the results of the comparisons are invariant prior to activating the SOC indicators 306, which ensures there will not be any flickering. The user will see a stable SOC indication each time the push button is activated. The SOC indication may include, for example, one, two, or three lit LEDs or one blinking LED.
In one embodiment, the monitoring circuit 1000 includes a divider 818, a reference generator 820, multiple comparators 1002, 1004, and 1006, and a storage module 1016. In one embodiment, the divider 818 includes four resistors couple in series, a ratio among which is the same as the description in
As shown in
Thus, advantageously, similar to the description in
In one embodiment, first the SOC of the battery pack is determined by one or more comparison results and then the results are stored in data storage. The SOC of the battery pack can be determined via a polling method that uses a single comparator, in which the battery pack voltage is compared to each threshold one-by-one, or via another method in which the battery pack voltage is compared to each threshold contemporaneously using multiple comparators. After the comparison results have been stored, a current is applied to the SOC indicator 306, so that the SOC indicator 306 indicates the SOC of the battery pack.
Essentially, three stages are implemented: measure stage (making a decision on what the SOC is), store stage (storing the decision), and display stage (displaying the decision). Thus, the measurement time interval (during which the SOC is determined) is separated from the indication time (at which the SOC is displayed to the user). This type of approach ensures there is a single SOC displayed on the LEDs per push button depression. In this manner, an unambiguous indication of SOC is provided to the user.
The various features described above can be implemented independently of one another or in combination. That is, the protection against faults feature, the positive indicator of SOC feature, and the non-flickering SOC indicator feature can each be implemented without the other features, or in any combination.
While the foregoing description and drawings represent embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope of the principles of the present invention as defined in the accompanying claims. One skilled in the art will appreciate that the invention may be used with many modifications of form, structure, arrangement, proportions, materials, elements, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims and their legal equivalents, and not limited to the foregoing description.
This application claims priority to the U.S. provisional application Ser. No. 61/648,971, titled “Battery Pack State of Charge Indicators,” filed on May 18, 2012, which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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61648971 | May 2012 | US |