Patent Publication Number: US-2016233555-A1

Title: Battery protection system and method

Description:
FIELD OF THE INVENTION 
     This invention relates, in one example, to a system and method for protecting against overheating, rupture, or explosion of a battery pack. 
     BACKGROUND OF THE INVENTION 
     Numerous devices, products, and systems are powered by a battery pack. A battery pack may include several cells in series. Rechargeable lithium ion batteries, in particular, are preferred because they have a high energy density. But, such batteries can overheat, rupture, or even explode if shorted or overcharged. Restrictions regarding the transportation of certain battery packs have been proposed and/or implemented as a result. 
     Recently, the United Nations created international recommendations for the design of battery packs and defined tests which must be passed by these batteries before they will be certified for public transportation. See also 49 C.F.R. §1.73.185 (shipping requirements for hazardous materials). Section 38 of the “UN Recommendations on the Transport of Dangerous Goods” is a manual of tests and criteria which batteries must meet in order to be certified for public transport on certain carriers (such as aircraft and ships). A subsection of this document applies to lithium metal and lithium ion batteries (§38.3). In that subsection, eight tests are defined which must be applied to battery products in various forms. Tests 1-4 and 6 are of a mechanical nature (Altitude, Thermal, Vibration, Shock, and Impact/Crush, respectively). Tests 5, 7, and 8 are electrical (Short, Overcharge, and Forced Discharge, respectively). 
     The test descriptions in this UN document are minimal and many details are not clarified. There is no mention of “Following the manufacturer&#39;s instructions” which might allow for individual situations to be handled differently. There have been many interpretations by vendors on how to design battery electronics to meet these requirements, some with arguable qualifications on actually meeting the intent of the document. For instance, one can set up a simple circuit that will meet the requirements using two connectors on the battery, one for charge and one for discharge. The rules are met if test 7 is applied to the charge connector but such a circuit will not pass if test 7 is applied to the discharge connector. The recommendations do not address such a situation. 
     SUMMARY OF THE INVENTION 
     In the subject invention, a battery is disabled automatically if an overcharge condition exists. At the same time, the battery protection system is low cost, small, lightweight, and functions with minimal degradation of battery performance under load and yet the preferred battery protection system is designed to pass the UN §38.3 criteria and tests without compromising the performance of the battery. Protection against short circuits is also provided. 
     Featured is a battery protection system comprising a series connection of at least a first fuse, a load/charger, and at least one cell. The cell powers the load. The charger charges the cell. A shunt switch is connected on the load/charger side of the first fuse. A control subsystem is configured to monitor the at least one cell voltage, determine when the cell voltage is above a predetermined level and close the switch causing the first fuse to blow when the cell voltage is above the predetermined level. 
     The first fuse may be connected in series with a positive or negative terminal of a connector which couples to a load or charging device. 
     The system may further include a second fuse in series with the first fuse between the shunt switch and the load. The system may further include a power storage device charged by at least one cell and configured to supply power to the control subsystem. A voltage reference circuit, if included, is configured to provide a reference voltage to the control subsystem. The control subsystem may be calibrated based on the reference voltage. The system may further include a balancing connector. 
     Also featured is a battery protection method including arranging at least a first fuse in connection between a load and at least one cell powering the load, connecting a shunt switch on the load side of the first fuse, monitoring at least one cell voltage, determining when the monitored cell voltage is above a predetermined level, and closing the switch causing the first fuse to blow when the cell voltage is above the predetermined level to disconnect the battery from an overcharging source. 
     One battery protection system includes a plurality of cells connected in series with a first connection to a first terminal of a connector through first and second fuses. A shunt switch is connected between the first and second fuses and a second terminal of the connector and a second connection to the cells. A control subsystem is programmed to monitor the cell voltages, determine when a cell voltage is above a predetermined level, and close the switch causing the first fuse to blow when a cell voltage is above the predetermined level. 
     One system for protecting a battery includes at least one cell connected to a charger/load connector. There is preferably a direct circuit from the positive side of the cell to the negative side of the cell including a fuse and a switch. One terminal of the connector is connected to the fuse. A processor is connected to the cells and monitors the cell voltages. The processor is configured to close the switch to blow the fuse when a cell voltage is above a predetermined level. 
     The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
         FIG. 1  is a block diagram showing a battery protection system incorporated on a battery pack in accordance with one example of the invention; 
         FIG. 2  is a block diagram showing, in one example, the primary components associated with the battery protection system of  FIG. 1 ; 
         FIG. 3  is a block diagram showing, in one example, the primary components associated with the control subsystem of  FIG. 2 ; and 
         FIG. 4  is a flow chart depicting the primary steps associated with the programming of the microprocessor shown in  FIG. 3  and also associated with one preferred method of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer. 
     Battery protection system  10 ,  FIG. 1  may be implemented on a printed circuit board to be attached to a battery pack, in one example, shown at  12  with individual cells A, B, and C connected in series. In other examples, there are more or less cells. The battery pack may include lithium metal, lithium ion, or other type cells. 
     The cells A, B, and C are connected to power/charger connector  14  with a positive  16   a  terminal and a negative  16   b  terminal as shown in  FIG. 2  to be connected to a load  18 ,  FIG. 1  powered by the battery pack. In but one example, the load  18  is a robot or unmanned aerial vehicle. Connector  14  can also be connected to charger  20  for charging battery pack  12 . In some designs, a balancing connector  22  is also included and connected to charger  20  during charging of the battery pack. 
     Protection system  10 ,  FIG. 2  includes at least first fuse F 1  arranged in series between a load/charger and at least one cell. In one example, F 1  is disposed in line  30   a  ultimately connected to the positive terminal  16   a  of the connector  14 ,  FIG. 1  to be connected to load  18  and charger  20 . Line  30   a  is also connected to the cell A as shown in  FIG. 1 . Fuse F 1  could instead be disposed in the common or negative line  30   d ,  FIG. 2 . Fuse F 1  may be replaceable in some versions. 
     Shunt switch  34  (shown here as a power FET) is connected on the load or connector side of fuse F 1  as shown in  FIG. 2  between lines  31   a  and  30   d . Other switching devices may be employed. Fuse F 2 , if included, is connected in series with fuse F 1  between lines  31   a  and  32   a . Line  31   a  connects to fuse F 1  and line  32   a  connects to positive terminal  16   a  of connection  14 ,  FIG. 1 . The operation of fuse F 2  is discussed below. 
     Control subsystem  40  is configured to control switch  34  and to automatically turn it on when certain conditions are met. When switch  34  is turned on, fuse F 1  blows. With fuse F 1  blown, there is an open circuit between charger  20 ,  FIG. 1  connected to connector  14  and cells A, B, and C. Preferably, switch  34  is closed automatically when an overcharge condition is detected. Thus, the cells are protected from further overcharging. 
     Control subsystem  40  may include a microprocessor, field programmable gate array, application specific integrated circuit, a controller, or similar circuitry preferably running computer instructions as described below. Equivalent analog circuitry may also be used. In the version shown in  FIG. 3 , microprocessor  50  inputs  1 ,  2 , and  3  are used to monitor the cell voltages, step  70 .  FIG. 4 . In this particular example there are three cells connected in series in order to obtain a higher voltage and the individual connections of the cells are brought to microprocessor  50 . The terminal on line  30   c  is the top or positive side of the first cell in the series connected to the microprocessor input  3  and to the bottom (negative) of the second cell. The negative of this first cell is connected to a circuit common point usually referred to as the return or common or ground point of a circuit shown here as  30   d . This common is connected to all the devices of the circuitry even though those connections are not depicted in  FIG. 3 . The second microprocessor connection connects to the top (positive) side of the second cell and the bottom (negative) side of third cell. Likewise the other microprocessor connection is to the top of the third cell which is also the main positive output connection point of the battery going to the main connector  14 ,  FIG. 2  through fuse F 1  and optional fuse F 2 . 
     In this way, the voltage levels of the individual cells can be monitored by microprocessor  50 . Averaging techniques may be used to account for transient voltages on the battery. Each voltage level, for example, may be read several times before a comparison is made to a predetermined voltage level, step  72 ,  FIG. 4 . This predetermined voltage level may be stored in memory. In one example, if a cell voltage is normally 4.2 volts at full charge, the stored threshold may be 4.4 volts which, if reached, indicates in an overcharge condition, step  74 ,  FIG. 4 . When an overcharge condition is detected for any cell, microprocessor  50 ,  FIG. 3  functions to output a signal which closes (turns on) switch  34 ,  FIG. 2 , step  76 ,  FIG. 4 . Fuse F 1 ,  FIG. 2  then blows and the battery is disconnected from the overcharging source preventing overheating, rupture, and/or an explosion. 
     Turning switch  34  on allows electric current to flow from the positive side of the cells through fuse F 1 , through switch  34 , and then back to the negative side of the cells. This direct path across the cells of the battery produces a very high current which will quickly blow fuse F 1 . Then, the cells are disconnected from the terminals  16   a  and  16   b  of the power/charger connector  14 ,  FIG. 1  which will prevent overcharging damage to the battery cells. In one example, fuse F 1  may be rated at 30 amps and the current capability of the cells is over 100 amps so that fuse F 1  would quickly blow when switch  34  is activated. 
     An optional indicator (e.g., a lamp) may be provided and activated (e.g., illuminated), step  78 ,  FIG. 4  to provide an indication that fuse F 1 ,  FIG. 2  is blown and requires replacing. In other embodiments, fuse F 1  is resettable via control subsystem  40 . 
     To save power, microprocessor  50 ,  FIG. 3  may be programmed to sleep periodically, step  80 ,  FIG. 4  and then wake at shown at step  82 , based on timer  83 . For example, the microprocessor  50 ,  FIG. 3  could read the voltages and carry out steps  70 - 74 ,  FIG. 4  which consumes less than 1 second and then sleep for a longer time such as 15 seconds to reduce energy consumption. This duty cycle results in greatly reduced average power consumption by the monitoring system. 
     Second fuse F 2 ,  FIG. 2  may be provided in series with first fuse F 1  between shunt switch  34  and the load/charger. Fuse F 2 , while optional, provides further improvement in some unusual circumstances which might occur in use of a battery pack. As described above, the basic action of switch  34  is to provide a controlled high current path from the battery through fuse F 1  to intentionally blow fuse F 1 . When switch  34  is activated, there is also the possibility of a high current path between the connections  16   a ,  16   b  and switch  34  if terminals  16   a  and  16   b  are connected to a high current source. F 2  is inside this path. If a user connects the battery pack to a high current power source (e.g., a car battery) externally through the power/charge connector  14 ,  FIG. 1 , such a high current source might over-power switch  34  and prevent it from working properly. With fuse F 2  included, switch  34  will serve the function of blowing fuse F 1  from energy from the included battery cells. Fuse F 2  blows with energy supplied by an external high current source. Thus, no matter what is connected externally, switch  34  will still effectively serve its purpose to blow fuse F 1 . 
     Note too the connection from the cells to the power connector is direct not going through any electronic switches which could introduce losses but only going through both fuses F 1  and F 2 . One advantage of this design is that no other electronic components are in the path between the battery cells and the connection to the product load. Fuses are very low resistance devices that have little impact on the power going through them unless the current is too high. Fuses do not present any significant reduction of performance compared to a battery with electronic series switches. 
     The balancing connector  22 ,  FIG. 1 , may be used by the charger  20  to assure that all the cells of the battery are equally charged. Using connections to each cell, as shown, the charger  20  can check individual cell voltage and charge any cells that are below a predetermined voltage and discharge any cells that are above the predetermined voltage. This connector is connected directly to the battery cells through fuses F 1 , F 3 , and F 4 ,  FIG. 2 . These fuses are meant to protect the battery should a short occur on any of the terminals of this connector  22  to other terminals, or to the terminals of power connector  14 . Some safety testing includes overcurrent tests on the balancing connector  22 , and these fuses serve to meet the requirements of these tests. 
     Microprocessor  50 ,  FIG. 3  is preferably chosen to have the capability to execute software which is permanently programmed into the part as well as the capability to read voltages and preferably includes an Analog-To-Digital Converter (ADC) for this purpose. In  FIG. 3 , the microprocessor chip is shown with four voltage inputs on the left side, labeled  1 ,  2 ,  3 , and  4 . This provides a way to measure the voltage on each of the battery cells as well as an optional voltage reference device  54  which provides a precise voltage level to processor  50 . The microprocessor with an ADC is capable of measuring the voltages on its pins to some degree of accuracy as specified by the manufacturer of the chip. The accuracy should be high enough to make a positive determination of the overvoltage state of the cells. In one example, a lower cost system can be produced if a microprocessor chip with low accuracy voltage measurement capability is used and an external highly accurate voltage reference IC  54  is included in the design. In this case, the microprocessor measures the three cell voltages and uses the reference voltage for calibration thus maintaining the accuracy needed to determine an overcharge state. 
     In one example, the reference voltage is V ref  and the processor  50  reads on pin  4  V ref1 . The logic of the processor thus adjusts its reading of the voltage levels read from the cells by a correction factor based on the difference between V ref  and V ref1 . It would be equally effective to use a microprocessor with an internal voltage reference of high accuracy. Also, there are several other possible implementations whereby a voltage can be read accurately. 
     In one example, a small amount of energy is taken from the cells of the battery pack to power the control or microprocessor system. Other possible implementations could power the microprocessor system from a different battery or other external power source. The optional power hold-up device  56  serves to regulate power and to also maintain power during a fuse blow event when the microprocessor is powered by the cells of the battery being protected. Though it is convenient to use the power from one of the battery cells of the pack to power microprocessor system  50 , there is a disadvantage which becomes evident in some modes of operation. During the very short time when the fuse is being blown, the voltage on the battery can be reduced due to the high energy required to blow the fuse. If the cells of the battery pack are near the end of their discharge life (near the point where recharge is required) the voltage on the cells may fall to a point where the microprocessor  50  may not be able to function properly. The power hold-up circuit  56  solves this problem through use of a storage device such as capacitor  58  shown in  FIG. 3 . This capacitor can be charged with energy from the cells for use at a later time when the microprocessor system runs to determine the overcharge state of the cells and possibly blows fuse, F 1 ,  FIG. 2 . The power hold-up circuit  56  is therefore an improvement in operation of the invention but the invention can be implemented without it. 
     Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. 
     In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended. 
     Other embodiments will occur to those skilled in the art and are within the following claims.