The present invention relates generally to electrical storage batteries and, in particular, to battery packs having a plurality of rechargeable cells electrically coupled to each other and to a control circuit disposed within a common housing. In particular, the present invention relates to a plurality of lithium ion cells arranged according to an improved internal packing configuration. These, and additional components such as a control circuit, are disposed within a housing, such as a housing of conventional size and design.
There has been interest in the electrical power supply industry to provide rechargeable battery systems having a compact, lightweight construction made with relatively inexpensive components such as readily commercially available individual storage cells coupled together and operating under control of one or more control circuits so as to provide advanced functions such as fuel gauging, cell balancing and communication via a serial data communications bus.
In addition to battery capacity needed to drive the intended load, demands arise from the nature of the application and the intended use of the load and battery system. An example of one particularly challenging field of use is that of modern rugged mobile military applications. The military is demanding higher performance, lower weight, longer effective usage times and high reliability for mobile, handheld applications such as navigation, fire control and Multiband Inter/Intra Team Radios (MBITR). These systems rely on increasingly sophisticated battery packs for their power requirements, yet they present unique design challenges because of the extreme environments to which they are exposed. Design engineers are faced with an array of challenges in developing effective battery systems—from cell and cell pack selection to intelligent power management, from safety concerns to charging systems. For example, should the battery system undergo full or partial power failure, a command signal may change state in an unexpected and undesired manner. Armed with an understanding of these demands, however, designers can make the best choices for battery-supplied power in today's rugged military applications.
Without a simple and cost-effective charging system, coupled with reliable rechargeable battery chemistry, the significance of portable lightweight battery energy sources would drop as a practical reality and have a far less impact on today's world. Handheld radios, telemetry monitors, weather stations, test equipment, missiles, rockets and satellites and the myriad of other equipment all rely on cost-effective reliable rechargeable battery technology for their operation. Indeed, without practical rechargeable battery systems, devices would be too cumbersome in their operation for everyday use.
Arguably, the most promising widespread rechargeable battery technology in use today is lithium ion technology. Development of this battery chemistry technology is far from an overnight phenomenon, having first been discovered in 1912 and the first lithium batteries were proposed about 1970. As is true in many other disciplines, substantial advancements in the technology had to wait until new materials with unusual performance characteristics were developed. Today, lithium ion technology can take many forms. Perhaps the greatest and most promising form is that of Lithium Cobalt Oxide (Li-cobalt), but Lithium Manganese Oxide (Li-manganese), Lithium Iron Phosphate (Li-phosphate), Lithium Nickel Manganese Cobalt Oxide (NMC), Lithium Nickel Cobalt Aluminum Oxide (NCA) and Lithium Titanate (Li-titanate) also play a substantial, commercially significant role. As will be seen herein, the present invention can be readily applied to these and other battery chemistries. Lithium-ion (Li-ion) cell characteristics include a nominal voltage of 3.6 V, 1000 duty cycles per lifetime, a rate load current of less than 4° C., an average energy density of 160 Wh/kg, a charge time of less than 4 hours and a typical discharge rate of a few percent per month when in storage. Li-ion cells operate effectively between −20° C. and +60° C. With recent improvements in battery chemistry, most notably new chemical formulations, the range is extended from −30° C. to +80° C.
Principally, three primary components come together to form a lithium-ion cell. These include a positive electrode or cathode, made from a layered metal oxide such as lithium cobalt oxide, a polyanion such as lithium iron phosphate or a spinel such as lithium manganese oxide. Also included is a negative electrode or anode made, for example, from carbon, graphite, or the like. An electrolyte surrounds the electrodes and may comprise, for example, a lithium salt suspended in an organic solvent. Examples of electrolytes also include mixtures of organic carbonates such as ethylene carbonate or diethyl carbonate. Since pure lithium is highly reactive, battery designers frequently opt to use a non-aqueous electrolyte. Of importance here is the recognition that these various material types making up a lithium ion cell must be compatible one with another and when combined in a battery system, the voltage, capacity, operational life and operational safety of the resulting lithium-ion battery can take on a wide variety of values. Typically, the electrodes and electrolyte are protected by an outer container sealed to prevent the intrusion of water. Compared to other battery chemistries, lithium-ion battery systems require careful control in their operation to limit peak voltages and to prevent a wide array of damage to the battery system.
After construction, a lithium-ion cell must be charged in order to acquire energy which is stored in the battery for later use. When the battery is being charged, lithium ions are liberated from the positive electrode, and move through the electrolyte to the negative electrode where they remain. During discharge, the lithium ions move in a reverse direction across the electrolyte toward the positive electrode, producing energy to an external device through electron flow through the device, a process interconnected that to that of ion flow within the cell.
As will be seen herein, the present invention has found immediate application with lithium-ion cells having a cylindrical form. However, as will be appreciated from studying the materials herein, the present invention also finds immediate practical application to other shapes or formats of lithium-ion cells, including those having a soft flat body or pouch, as well as larger cylindrical shapes which include terminals affording ready mechanical connection to external devices.
As mentioned, the present invention finds application for use with rechargeable battery systems. However, in the field of lithium ion technology, at least, these types of systems all have a limited thermal operating range. At times, it is necessary to provide portable lightweight electrical power in environments having extreme temperature ranges. A classic solution overcoming this type of problem has been to use non-rechargeable battery systems typically referred to as primary lithium battery systems. The present invention also has relevance to non-rechargeable or primary battery systems. In extreme applications, rechargeable battery chemistries may not be able to perform in a reliable manner. In this instance, disposable, one-time-use lithium cells (known as lithium-primary cells) may be considered. These lithium-primary cells feature a nominal voltage of 3.6 V, an optimal load current of less than 5° C., an average energy density of 160 Wh/kg and a negligible self-discharge rate supporting years of storage.
The range of anticipated operating temperatures often lies at the heart of extreme applications. By way of example, lithium-primary cells have been known to operate in temperatures ranging from −40° C. to +80° C. Examples of lithium-primary chemistries include lithium thionyl chloride (Li/SOCl2), lithium sulfur dioxide (Li/SO2) and lithium manganese dioxide (Li/MnO2).
Although the present invention is discussed with regard to a wide array of lithium-ion technologies, the present invention applies equally well to different types of battery chemistries, employing materials unrelated to those of lithium-ion systems. As will be seen herein, in one aspect, the present invention is directed to systems of battery packs, which employ a plurality of individual cells physically associated together and electrically coupled together to operate as a single entity. Thus, the present invention is concerned with balancing their compatibilities among all of the components employed within the systems, despite the precise nature of any particular system. Such considerations will come to the fore when considering the development of control circuitry designed to protect the system as a whole as well as to provide balance among its various components so as to optimize overall system performance.
One ongoing challenge has been to offer greater battery capacities in ever smaller sized packages. A special example of this industry goal is to provide increases in energy capacity for conventional, standardized packages that are well defined in the industry. Battery systems are not readily miniaturized using photolithographic and other popular techniques, as may be possible with other electronics components. Rather, reductions in battery size are more usually accompanied by improvements in battery materials themselves to pack greater energy storage in a smaller sized package. This of course may be attended by changes in battery chemistry. The present invention is concerned with advantages in increasing the capacity of battery packs, regardless of any particular chemistry employed, or whether the battery cells are rechargeable, or not.
Approaching the problem from a different perspective, there is a need to adapt and improve upon known commercial products so as to reduce overall operating expenses by eliminating the need for additional training of end-users and maintenance technicians. A special example of this is in the realm of military applications, where familiarity with new, improved products is vital to mission success, where lives are placed at risk in the interest of national defense. As is well known to those employed in the battlefield, it is surprising how quickly even very small changes can spin out of control in a critical life-threatening situation. The more the details and familiarity with systems is reduced, greater attention can be paid to the task at hand.
Apart from using known systems in a known way, it is frequently necessary to adapt or customize a system to meet changing conditions. By reducing the need to pay attention to changes in standardized systems, a user can devote greater energy to adapting a given system to meet unusual, unforeseen requirements. As a related benefit, by keeping improvements in existing equipment transparent to the user, greater use can be made of related accessories. As those responsible for systems operation will attest, oftentimes the array of accessories can outweigh the system they support.
As with other types of electronic components, battery systems are becoming more sophisticated, and have a tendency to use newer materials that exhibit sensitivities and requirements not previously encountered. With the ability to apply increasingly complex electronic controls, materials and component arrangements that are more inherently unstable may be made reliable in a practical environment. Nonetheless, the overall package must, as always, be rugged and capable of withstanding harsh environmental conditions. Controls needed to maintain a high standard of systems reliability must however not be prohibitively expensive or unusually difficult to deploy in practical real-world products. As will be seen herein, the present invention provides these desired types of improvements, thus delivering advantages without unnecessary downside risk.
As systems managers will immediately appreciate, substantial cost advantages can be achieved whenever a system can be constructed from a smaller variety of different types of components. For example, inventory costs are reduced, critical components are easier to stock and are more readily obtained in the available marketplace. In addition, training costs are reduced, and it is more likely that peripheral knowledge and skills developed for similar but not identical products can be brought to bear for products being designed and deployed. As a result, design times for new products can be greatly reduced. The present invention provides such advantages and allows construction of the battery packs and other battery systems to be simplified.
Despite advances, relatively simple, durable devices are needed for providing portable and lightweight electrical energy sources.
With the advent of portable lightweight electronics devices, the need for reliable cost effective portable lightweight energy sources has increased dramatically. A popular format for battery storage energy sources is the so-called “battery pack.” Battery pack systems typically include a plurality of energy storage cells, coupled together and disposed within an outer container. Electrical terminals are provided to connect the internal energy cells to external load devices. It has become increasingly popular to provide some manner of visual gauge to provide a ready estimate of the remaining battery life, and perhaps to indicate critical operating parameters such as output voltage and temperature conditions within the battery pack.
As mentioned, the present invention is not intended to be limited to any particular battery chemistry or type. However, initial attention has been focused on lithium-ion battery technology arranged in an industry standard “2590 battery pack” type. In this type of arrangement, pluralities of lithium ion cells are disposed, along with one or more control circuits, within an outer surrounding housing. The individual cells are electrically coupled together according to a defined configuration, by electrically conductive interconnects, which in turn are coupled to battery pack terminals for communication with external load devices.
Although a number of different configurations may be theoretically possible in the abstract sense for standardized battery types, industry standard 2590 battery packs have been provided with 24 lithium-ion cells, thus setting the overall energy capacity of the battery pack, typically estimated as 24 times the energy capacity of each individual cell. Because the 2590 battery packs have been well defined in the commercial marketplace, it is not possible to improve battery capacity by enlarging the standardized size of the outer battery pack container. Rather, as will be seen herein, additional energy cells are disposed within the standardized size container according to the present invention. In addition, it has become accepted practice to divide the total number of cells in two to form two packs or sections. The packs are then coupled to one another in series or parallel to provide two different operating voltages, with the higher voltage usually being double that of the lower output voltage.
According to one aspect of the present invention, the cells are arranged in a combined series/parallel arrangement, sufficient to provide the lower operating voltage expected by an end-user. The present invention then employs a voltage regulator circuit to boost the lower voltage to an upper voltage level expected by the end user. In this manner, a battery pack is provided meeting a user's customary expectations. In addition to the voltage regulator circuit, other control functions are provided by an internal control circuit disposed within the outer housing. With the present invention, a user enjoys an immediate increase in battery power.
An example embodiment is directed to a battery pack for electronics devices and the like. The pack includes an outer housing supporting an electronic control module and a battery terminal block connected to the control module. A plurality of individual energy cells are disposed within the housing and are coupled to each other, the control module and the terminal block. Also included is a plurality of sense wires coupling the energy cells to the control module.
Another example embodiment is directed to an internal component arrangement within a battery pack. The pack includes a housing and a housing cover. The arrangement includes a plurality of energy cells assembled beforehand, for later insertion in the housing,
In one example embodiment, a battery pack for a cordless power device comprises a housing defining a hollow cavity, and a plurality of rechargeable energy cells disposed within the hollow cavity of the housing. The number of energy cells is divisible by a number other than 8, and the energy cells are coupled together to provide a lower maximum voltage than that required by the user. A plurality of interconnecting links electrically couple the energy cells together and provide a convenient internal component arrangement that can be fabricated prior to insertion within the outer housing. A control circuit is electrically coupled to the energy cells for controlling the operation of the energy cells during charging and discharging of the energy cells, and to perform other protective and power management functions. The control circuit also includes a voltage boost function that raises the output voltage of the energy cells to a maximum voltage required by the user.
The present invention finds immediate application in the field of smart battery packs which are capable of self-monitoring, wherein the voltage of each energy cell is individually monitored by a controller in the pack, such as a microprocessor, microcontroller, etc. This requires that each energy cell be wired up to the controller.
In the drawings:
The invention disclosed herein is, of course, susceptible of embodiment in many forms. Shown in the drawings, and described herein in detail, are preferred embodiments of the invention. It is understood, however, that the present disclosure is an exemplification of the principles of the invention and does not limit the invention to the illustrated embodiments.
For ease of description, a battery pack device embodying the present invention provides electrical power for a variety of different electrical devices. The battery pack device is described herein in its usual assembled position as shown in the accompanying drawings and terms such as upstream, downstream, inner, outer, upper, lower, horizontal, longitudinal, etc., may be used herein with reference to this usual position. However, the device may be manufactured, transported, sold or used in orientations other than that described and shown herein.
Referring now to the drawings, and initially to
According to one aspect of the present invention, the cells are arranged in an internal component arrangement, preferably before being inserted within a housing 24. The arrangement is held in place by a plurality of interconnect straps which are welded, soldered or otherwise secured to the terminals of the energy cells, in a manner known in the art. One example of a preassembled internal component arrangement will be described below with respect to
Principles of the present invention can be applied to a wide variety of battery packs and other battery products. The present invention will be described herein with regard to an industry standard “2590 battery pack” type. This type of battery pack has demonstrated high rate capability, is lightweight, has high energy density and provides long operating life and long shelf life while operating in a wide range of temperatures. Such a conventional battery is typically rated at about 206-215 Wh (watt-hours) and is suitable for use in communications, medical, military and instrumentation applications where extended battery life is critical. In this type of arrangement, a plurality of lithium-ion cells are disposed, along with one or more control circuits within an outer surrounding housing.
The cells serve as the primary energy source of the battery pack. Cells include a positive terminal adjacent its cathode electrode, and a negative terminal adjacent its anode electrode. The cathode and anode terminals are separated by a thin plastic film or separator. All three elements are maintained in an electrolyte medium to promote charge transfer between the electrodes that releases stored battery power. For example, a polymer battery uses a gel polymer as its electrolyte.
A large number of 18650 type cells have been placed in wide spread commercial use. This type of cell has its components contained in an outer cylindrical metal enclosure employed as a negative terminal. The cylindrical 18650 cells are efficient at distributing heat generated from the center of the cell to the cell exterior. Heretofore, 2590 type battery packs have been provided with 24 energy cells arranged in two packs or sections, to provide either a nominal 15 V output (as when the two sections are coupled in parallel) or a 30 V output, when the energy cells are all connected in series with one another. As a result, overall battery capacity is bounded by the precise type of energy cell employed and the output voltage desired.
As mentioned, it is generally preferred to use rechargeable lithium-ion 18650-type energy cells, available from a variety of different sources. Accordingly, it is to be expected that the battery capacity of the individual energy cells might vary from one source to another, thus providing a designer of battery packs with a range of choices for the makeup of the internal energy cells components disposed within the housing 24. Assuming, for example, that 18650 type cells having a battery capacity of 3.0 Ah are considered, the overall capacity of battery pack 10 would yield (3.7V/cell) (24 cells) (3.0 Ah) or 266.4 Wh. While the overall battery capacity can vary somewhat depending upon the commercial source of the energy cells, the capacity is generally observed to fall within a relatively narrow range of values due to practical, commercially available choices. According to principles of the present invention, the internal component arrangements of energy cells within housing 24 can be improved to allow additional standard-sized readily commercially available energy cells, thus substantially increasing the capacity of the battery pack.
The control circuit must perform a number of different functions. For example, in addition to minimizing thermal effects due to discharge under load, the control circuit must also control the charge rates of the energy cells. Consider, for example, a 18650 Li-cobalt cell. Even though this type of battery gives a high specific energy, it cannot be charged and discharged at a current higher than its rating. For example, an 18650 cell with a 2,000 mAh rating can only be charged and discharged at 2,000 mA. Forcing a fast charge or applying a load higher than 2,000 mA causes overheating and undue stress. One manufacturer recommends a charge-rate of 0.8 C at a level less than 2,000 mA for an optimal fast charge. The control circuit limits the charge and discharge rate to a safe level of about 1 C.
The control circuit controls safety and power management. The circuit may be packaged in the form of a printed circuit board having not only protection circuitry and thermal sensors, but which also provides the system intelligence for advanced functions such as fuel-gauge calculations on remaining cell capacity, cell balancing, managing thermal sensors such as thermistors to monitor internal pack temperature and to register not only operating temperature at the core, but also at the edge of the pack, as well as outside the enclosure. The control circuit also provides other advanced functions, such as LEDs that indicate pack or cell status, and a serial data communications bus that communicates with the host device.
As mentioned, battery protection functions are often included to limit the charge and discharge rates to safe levels. Since the cells are most critically affected by extreme temperatures, many of the advanced functions are employed for temperature control in one way or another. For example, forcing a fast charge or applying a load higher than recommended causes overheating and undue stress. Also, the battery's chemical reaction at high discharge rates generates a substantial amount of heat, and the effects of this heat must be factored into a practical battery-pack design. The effect of the generated heat is compounded in a multicell pack. Accordingly, the control circuit is employed to limit the charge and discharge rates to safe levels in this regard, as well. Active safety circuits have been required for some time now to ensure that commercially important battery chemistries are kept in a stable condition.
Each rechargeable battery chemistry has its own set of risks that must be managed on an ongoing basis. Li-ion batteries require the greatest degree of protection, including a thermal shutdown separator and exhaust vents (within each cell) to vent internal pressure. Typically, vent holes are unobstructed openings that expel potential gas vented from cells (when the cells are stressed under load or subject to high temperature environmental conditions). In some applications, high-pressure vent holes are also provided to moderate internal pressures by exhausting warm air within a pack only after a specific pressure has been reached within the pack. As long as the pressure is not increased to a dangerous level within the pack, high-pressure vent holes can control heat generated within the pack.
An external safety circuit that prevents overvoltage during charge and undervoltage during discharge must often be provided, along with one or more thermal sensors to prevent thermal runaway. Adequate battery protection must be provided to afford an appropriate level of safety and must be incorporated into the battery pack design. This attention to detail is warranted, however, since Li-ion battery packs have the potential of offering the most attractive method of portable battery power. As a result, many of the portable devices using the older chemistries have migrated to Li-ion in recent years.
In addition to these and other functions, a control circuit according to principles of the present invention also has a voltage boost capability, allowing the energy cells of the battery pack to be coupled together for a lower voltage than would otherwise be required. With voltage boost provided by the control circuit, this lower voltage can be increased as desired to a maximum level.
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As mentioned above, the prior art 2590-type lithium ion rechargeable battery 30 includes two independent 15-volt sections or packs, each with twelve cells and separate control and protection circuitry and battery capacity gauges for each pack, that allow operation of the battery in either 15-volt or 30-volt modes. As opposed to battery packs according to principles of the present invention, the prior art conventional 2590-type battery includes a pair of battery packs (pack A and pack B) that operate in combination. The combination operates in parallel or in series depending on how the connector on the battery engages the end device. Both packs A and B have their own protection, balancing and fuel gauging circuitry. Each individual pack (A or B) has twelve cells (18650 type) connected in a 4 series, 3 parallel connection (known as 4S3P). This can then result in a 4S6P or 8S3P configuration when the connector is engaged with the end device. For example, a pack assembled in a 4S6P configuration (four cells in series, six strings in parallel) Li-ion pack using 18650 cells (18-mm diameter, 65-mm length, 2.4-Ah), provides 14.4 V and 14.4 Ah of capacity. Thus, a conventional 2590 battery is limited to a total of twenty-four energy cells and a total watt-hour capacity of (3.7V/cell) (number of energy cells) (Ah rating of the energy cell). For example, the use of 3.0 Ah 18650 energy cells would yield a capacity of (3.7V/cell) (24 energy cells) (3.0 Ah) or 266.4 Wh. A significant advantage of the battery pack of the present invention is the use of a homogenous design that eliminates the use of two packs (pack A and pack B) so as to eliminate the possibility of an imbalance between (non-existent multiple) packs A and B as in a conventional 2590-type battery pack design. Out of balance packs result in a truncated run time on the 8S discharge due to one of the packs (either A or B) striking its low voltage cutoff first.
Relying on the existing draft angles of the conventional plastic housing of a conventional 2590 battery pack, along with a novel packing configuration, 28 cells can be positioned within the standard plastic housing of a conventional 2590-type battery. A representative diagram of the battery configuration of the present invention is shown in
A table of representative values for a typical 2590-type battery pack is as follows:
These nominal specifications pertain to military batteries and other products manufactured by Ultralife Corporation, headquartered in Newark, N.Y.
As mentioned above, battery packs according to principles of the present invention have a resulting cell count (28 cells) that is not divisible by eight and, if used in a standard dual pack 2590-type configuration, would result in two separate packs of 4S3.5P with which it is not possible to achieve an 8S3.5P configuration. Instead, a battery design according to the present invention utilizing one pack (pack A or B only) is employed to provide a 4S7P configuration.
As mentioned, the present battery pack also includes but a single set of protection, balancing and fuel gauge circuitry. Moreover, due to the increased parallel connections, an additional ptc (positive temperature coefficient) parallel break is provided to account for any cell failures along the parallel string. The circuit is then regulated at the 29V end (using various methods) to simulate the eight cell series connection, thus resulting in an effective 8S3.5P output. This results in a higher intrinsic watt-hour capacity than a conventional 2590 battery pack. For example, an arrangement of the same 3.0 Ah 18650 cells according to the present invention would yield a capacity of (3.7V/cell) (28 cells) (3.0 Ah) or 310.8 Wh. This represents an increase in capacity by 16.7% from the same 18650 cells used in a conventional 2590 battery versus the improved 2590 battery design of the present invention with the present new battery configuration.
Run test data relating to a conventional 2590 battery pack and a battery pack according to the present invention are shown in Appendices A and B, respectively. As indicated in Appendix A, over a run time of about 5.5 hours, the conventional battery pack (in a single pack configuration) exhibited a capacity of about 95.6 Wh (corrected)—which translates to about 191.2 Wh as a double pack configuration. As indicated in Appendix B, over a run time of about 5.4 hours, the battery pack of the present invention exhibited a capacity of about 299.2 Wh (corrected).
A range of anticipated operating temperatures often lies at the heart of extreme applications. A battery pack must be continuously monitored to manage its thermal loading. Oftentimes, the primary temperature-related concern arises from temperature changes that are dependent on the amount of current drawn from the pack (i.e., greater current results in greater heat generation). These temperature increases, both within and outside the pack, must be factored into the design of the battery pack and portable device. Thermal monitoring and heat dissipation within the battery pack is critical for high-temperature operation.
Temperature-related concerns are not limited to high temperature levels. The performance of rechargeable Li-ion batteries starts to suffer as the temperature drops below 0° C., causing the internal impedance of the battery to increase. Cell capacity is also reduced at lower temperatures. If these cells are used or stored at or below −50° C., irreparable damage may occur under certain conditions to internal separators within the cells, making the cells a safety hazard.
A table of physical, electrical and environmental requirements of a battery pack according to the present invention is included below:
With the features described herein, the heat of the energy cells of battery pack 10 upon discharge is reduced since the heat on discharge follows a close relationship to a resistive heating function. The R (internal resistance of the energy cell) in the 4S6P configuration is R/6. The R in the 4S7P configuration (utilizing the same energy cell in both designs) is R/7. This results in a 14% drop in heat due to energy cell discharge since the parallel string has a lower parallel resistance.
The present invention provides an improved high watt-hour lithium ion rechargeable battery pack including a plurality of cells (not comprising a multiple of eight) and an electrical circuit to provide a battery pack that mimics eight cells in series. As will be seen herein, the 28 energy cells are coupled together to achieve a maximum voltage which is substantially less than that of 28 energy cells coupled in series. Accordingly, the electrical control circuit includes a regulator with output voltage boosting circuitry to provide both of the desired 14.8V and 29.6V outputs. For example, the voltage boost circuitry can employ conventional switched-mode power supply techniques. In particular, the present invention relates to a battery pack comprising a non-multiple of eight cells (of the type typically used in a 2590 battery pack) and a corresponding mechanical packing assembly. The improved electromechanical design provides an increased capacity of about 16% watt-hours more than a standard 2590 battery pack due to the increase in cell count (as a non-multiple of eight cells).
There are other substantial advantages of present battery pack designs according to principles of the present invention, in addition to the substantial increase in capacity mentioned above. These advantages include reduced heat of the cells upon discharge, and avoidance of an imbalance in multiple internal battery packs. In a conventional 2590-type battery pack design, two 4S protection circuits (each including overvoltage, undervoltage, overcurrent and short circuit) must be employed, along with two 4S fuel gauge circuits. Both control circuits are necessary to accomplish an 8S voltage. By way of contrast, with the present invention, only one control circuit is required to provide voltage regulation (boost) as well as the protection, balancing and fuel gauge circuit functions for all of the energy cells employed in battery pack 10. Since only a single control circuit is used in the present invention, a substantial reduction in internal control components is achieved. Thus, both the complexity and cost of the battery pack are reduced.
The foregoing description and the accompanying drawings are illustrative of the present invention. Still other variations and arrangements are possible without departing from the spirit and scope of this invention. For example, although the battery pack and method according to the principles of the present invention have been explained above with regard to a particular commercial application, it will be readily appreciated that the present battery pack and method can be advantageously employed to provide improved measured dispensing of a variety of materials.
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