This invention relates, in one example, to a system and method for protecting against overheating, rupture, or explosion of a battery pack.
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'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.
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.
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:
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,
The cells A, B, and C are connected to power/charger connector 14 with a positive 16a terminal and a negative 16b terminal as shown in
Protection system 10,
Shunt switch 34 (shown here as a power FET) is connected on the load or connector side of fuse F1 as shown in
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 F1 blows. With fuse F1 blown, there is an open circuit between charger 20,
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
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,
Turning switch 34 on allows electric current to flow from the positive side of the cells through fuse F1, 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 F1. Then, the cells are disconnected from the terminals 16a and 16b of the power/charger connector 14,
An optional indicator (e.g., a lamp) may be provided and activated (e.g., illuminated), step 78,
To save power, microprocessor 50,
Second fuse F2,
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 F1 and F2. 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,
Microprocessor 50,
In one example, the reference voltage is Vref and the processor 50 reads on pin 4 Vref1. 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 Vref and Vref1. 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
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.