Patent Publication Number: US-9412994-B2

Title: Lithium starter battery and solid state switch therefor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority of the following applications: PCT Application PCT/US2011/001937, filed 28 Nov. 2011; U.S. Provisional Patent Application Ser. No. 61/458,657, filed 29 Nov. 2010; and U.S. Provisional Patent Application Ser. No. 61/463,736, filed 22 Feb. 2011. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for starting an internal combustion (IC) engine. More particularly, the invention is a lithium-based cell for starting such engines. The invention includes a solid state switching configuration for high powered battery systems for protecting against over-charging, over-discharging and short circuiting of batteries, especially starter batteries for internal combustion engines (ICE). 
     BACKGROUND OF THE INVENTION 
     Presently, internal combustion engines use a starter battery comprised of lead-acid to turn over an electric motor to start an IC engine. Lead-acid batteries are heavy, bulky, and have short cycle life, short calendar life, and low turn around efficiency. Lead-acid batteries also have a high internal impedance (resistance) that is greater in cold weather making it more difficult to start an IC engine in cold weather with less current available. To overcome these variables, lead-acid starter batteries are provided with oversized battery capacity in order to produce the necessary current needed for an electric starter to start an IC engine. The oversized lead-acid battery increases the weight, space requirement, and cost needed to start an IC engine. 
     In order to turn off power terminals in presently known starter batteries, expensive electronic/electrical components are required to handle the high current loads that a starter motor needs to turn over an IC engine. These embody electronic protection circuitry for upper voltage cut-off (overcharging), lower level voltage cut-off (over discharging) and temperature measurements. These circuits also induce heat losses and electrical losses that can be large, as well as taking up additional space. (Noise) spikes can trigger false voltage, temperature or current readings that can terminate the battery system&#39;s operation, when in fact all the cells are working within safe specifications. Some of these protection circuits are temperamental and difficult to reactivate once they have been triggered. For example, if an under-voltage condition happens and the cells are still in under-voltage condition with a relay approach, current can not be provided to the cells since a path has been broken thus another button needs to be pressed to activate the system for a short duration in order to allow the cells to charge. Also, in some cases such as a military application or racing application, every last bit of energy needs to be extracted, even if it damages the battery. 
     With any type of rechargeable (secondary) battery used, the battery does not operate well in a low state of charge (SOC), which in most cases is a low battery voltage. Whenever a battery is at a low voltage level, the battery can suffer internal damage permanently or the battery life can be drastically reduced. With battery chemistries such as lithium, over-charging a battery can be even more dangerous, potentially leading to an exothermal runaway reaction, which can create a fire. With a solid state switch placed in-line with the battery output power terminals, the solid state switch can be electronically controlled to open or close the current pathway leaving or entering the battery. This can prevent battery damage from happening if the battery voltage is brought too low or too high. This can be applied to any type of battery chemistry at any voltage. An example is to apply the solid state switch to a 12V car battery that starts a vehicle. A vehicle might have a voltage drain source left on, in which case the solid state switch would automatically turn off the current flow from the battery before the battery is damaged. 
     A relay or contactor could be used as well, but has the following disadvantages: 
     1) A relay or contactor continuously needs current to keep the contactor open or closed. That requires energy to do so. 
     2) A relay or contactor having a closed pathway allows current to flow in both directions and can not be controlled for a single direction. 
     3) A relay or contactor can only be ON or OFF. During a switching process for large currents large arcing can occur inside the relay or contactor, and that can cause the relay or contactor to “weld” shut. Once a relay or contactor is welded shut, no switching can occur at that point, which can be a safety issue, i.e., by not allowing switching to occur when needed. 
     4) Relays and contactors are large and bulky for larger current applications. 
     A better approach is to use a solid state switch either a FET, a MOSFET (metal-oxide-semiconductor field-effect transistor), or IGBT (insulated gate bipolar transistor) format, but not limited to these, in a unique configuration. The unique configuration involves connecting two solid state devices such as MOSFET or IGBT with the “Sources” or “Drains” tied together electrically. These solid state devices can be either N or P type. A doped semiconductor containing excess holes is called “p-type”, and when it contains excess free electrons it is known as “n-type”, where p (positive for holes) or n (negative for electrons) is the sign of the charge of the majority mobile charge carriers. This arrangement simplifies the control electronics needed and also allows current to flow in one direction but not the other with the internal diode. An FET (field-effect transistor) is a majority-charge-carrier device having an active channel through which majority charge carriers, electrons or holes, flow from the source to the drain. Source and drain terminal conductors are connected to semiconductor through ohmic contacts. The majority charge carriers enter the channel through the source and leave the channel through the drain.  FIG. 15  shows the “Drain” of each terminal being connected, and  FIG. 16  shows the “Source” of each terminal being connected. 
     The advantages of a solid state switch are: 
     1) A solid state switch needs very little energy to activate an allowed pathway to be open or close. 
     2) A solid state device can gradually increase current, controlling inrush current that might occur switching ON large power applications or providing instant short circuit protection if the current is too high. 
     3) A solid state switch can be very compact and light for higher power applications. 
     DESCRIPTION OF THE PRIOR ART 
     Applicant is aware of the following U.S. patent concerning battery packs for starting engines: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 U.S. 
                   
                   
                   
               
               
                 Pat. No. 
                 Issue Date 
                 Inventor 
                 Title 
               
               
                   
               
             
            
               
                 7,525,287 
                 Apr. 28, 2009 
                 Miyashi 
                 BATTERY PACK FOR 
               
               
                   
                   
                   
                 DRIVING ELECTRIC 
               
               
                   
                   
                   
                 MOTOR OF COMPACT 
               
               
                   
                   
                   
                 ENGINE STARTING 
               
               
                   
                   
                   
                 DEVICE, ENGINE 
               
               
                   
                   
                   
                 STARTING DEVICE DRIVEN 
               
               
                   
                   
                   
                 BY THE BATTERY 
               
               
                   
                   
                   
                 PACK, AND MANUAL 
               
               
                   
                   
                   
                 WORKING MACHINE 
               
               
                   
                   
                   
                 HAVING THE ENGINE 
               
               
                   
                   
                   
                 STARTING DEVICE 
               
               
                   
               
            
           
         
       
     
     SUMMARY OF THE INVENTION 
     The invention provides means for increasing the efficiency of a starter battery for a starter motor of an internal combustion engine. By replacing a lead-acid starter battery with a lithium base or lithium-iron-phosphate (LiFePO 4  or LiFePO) or LiFeMgPO 4  or LiFeYPO 4  cell, the needed capacity, weight and size is drastically reduced while increasing the cycle life, calendar life and turn around efficiency for a starter battery. The lithium iron phosphate (LiFePO 4 ) cell is a type of rechargeable cell, specifically a lithium ion cell, which uses LiFePO 4  as a cathode material. It may also include magnesium or yttrium in the lithium iron compound. Connecting four cylindrical cells in series, each of which has a standard industry cell format size of both 18650 (less than 3 Ah) or 26650 (less than 4 Ah), or prismatic flat or other type cells, enough current is available to penetrate to a starter motor rated for 12V system to start large IC engines that use 1, 2, 3, 4, 5, 6, 8, or 12 cylinders. Larger cells may be utilized in the invention, from 1 Ah to 5000 Ah, common sizes being 5 Ah, 10 Ah, 20 Ah, 50 Ah, 100 Ah, 400 Ah, and 500 Ah. 
     With a configuration of 4 cells in series, no protection circuit board is needed to protect the individual cells from over-voltage or undervoltage, unlike larger system using more cells which require a protection circuit board in them for safety protection. Individual cell balancing is also not needed for such a small starter battery but may be included to increase the product life. A smaller and lighter starter battery increases the performance of mobile systems that use starter batteries. The resulting increase of cycle life and calendar life reduces user costs. 
     No separate nor special charging system is needed with the invented system 
     The invention also comprises a housing for the lithium-based cells, with upper and lower mating casings, a contoured pad within the lower casing for receiving at least one lithium-based cell, and electrical connections from the at least one lithium-based batter to the exterior of the housing. Optionally, an upper battery pad may be placed in the upper casing, and, if desired, a protection circuit board, such as a balancing board or a cut-off circuit, may be placed within the upper casing for safety protection. 
     The invented solid state switch apparatus allows current to flow in one direction and not the other. A minimum of two solid state switches are arranged in a unique configuration, which allows current to flow in a controlled manner bidirectionally when needed. This is particularly useful for preventing overcharging or over-discharging an entire battery pack. A separate cell balancing circuit is used to balance out the individual cells. The solid state switch can be used on each individual cell, if desired, to prevent overcharging or over-discharging of the individual cell. It can be used with any battery application in which charging and discharging is required, and is particularly useful with lithium-based batteries. It can also be used with lead-acid batteries, nickel-cadmium (NiCd) batteries, and low self-discharge nickel metal hydride (NiMH) batteries. More sophisticated items of equipment to which a battery may be attached have programmable shut-off settings, but less sophisticated equipment does not have shut-off parameters in place. Using a battery in a starter applications (for instance, to start an IC engine) will prevent the battery from overcharging, as well as prevent the battery from being discharged to too low a level if a current drain (leakage) is present in the system, even though everything is turned off. 
     By connecting the “Sources” or the “Drains” together using a minimum of two solid state devices allows for automation and simplification to fully and partially switch the batteries power terminals ON and OFF. The two solid state devices can either be N or P type and connected either on the Positive or Negative side of the battery terminal and controlled by simple electronic circuit to control the drivers of the solid state devices. 
     This invented switch configuration also allows for short circuit protection across the battery power terminals, along with allowing the maximum current control when charging. 
     OBJECTS OF THE INVENTION 
     The principal object of the present invention is to provide means for increasing the performance of a starter battery for a starter motor of an internal combustion engine. 
     Another object of the invention is to provide a starter battery for an internal combustion engine that is lighter, more reliable, has less bulk, longer cycle life, longer calendar life, and higher turn around efficiency than lead-acid batteries. 
     A further object of this invention is to provide a starter battery system for an internal combustion engine that is easy to assemble, waterproof, and maintenance free. 
     Another object of the invention is to provide a starter battery for an internal combustion engine that can be used in existing vehicles. 
     Another object of the invention is to provide a starter battery for an internal combustion engine that has a wide operating temperature range with exceptional cold-weather cranking performance. 
     Another object of the invention is to provide an improved apparatus for protecting a single cell or battery from being overcharged or over-discharged. 
     Another object of the invention is to provide apparatus for charging a cell having a very low charge. 
     Another object of the invention is to provide apparatus for short circuit protection for one or more cells or batteries. 
     Another object of the invention is to provide apparatus for discharging a cell having too high a charge. 
     A further object of the invention is to provide an apparatus for short circuit protection in case a metal object causes a short circuit across the terminals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects will become more readily apparent by referring to the following detailed description and the appended drawings in which: 
         FIG. 1  is an exploded isometric view of one embodiment of the invention, in which 4 cells are arranged into a starter battery pack. 
         FIG. 2  is an exploded isometric view of another embodiment of the invention, in which 8 cells are arranged into a starter battery pack. 
         FIG. 3  is an exploded isometric view of another embodiment of the invention, in which a prismatic cell is arranged into a starter battery pack. 
         FIG. 4  is a front view of the assembled battery pack of  FIG. 3 , the rear view being identical. 
         FIG. 5  is a top view of the assembled battery pack of  FIG. 3 . 
         FIG. 6  is a right end view of the assembled battery pack of  FIG. 3 , the left end view being a mirror image thereof. 
         FIG. 7  is a schematic diagram of a block of 4 lithium prismatic cells in series connected to a balancing circuit board. 
         FIG. 8  is a schematic diagram of a block of 4 lithium prismatic cells in series connected to a balancing and cutoff circuit board 
         FIG. 9  is an isometric view of an alternative embodiment of a housing showing contacts for switches. 
         FIG. 10  is a top view of the housing of  FIG. 9  showing the contact locations. 
         FIG. 11  is a front view of the housing of  FIG. 9 , the rear view being identical. 
         FIG. 12  is an end view of the housing of  FIG. 9 , the opposite end being identical. 
         FIG. 13  is an exploded isometric view of an alternative embodiment of the invention of  FIG. 3 , in which 2 blocks of prismatic cells and a control board of cutoff switch are arranged into the housing of  FIG. 9 . 
         FIG. 14  is a schematic diagram of a Solid State Switch with “Drain” connection. 
         FIG. 15  is a schematic diagram of a Solid State Switch with “Source” connection. 
         FIG. 16  is a schematic diagram showing a preferred embodiment of the invention in which the “Drain” of each gate is connected together using N type MOSFET or IGBT with the cells being above the solid state switches. 
         FIG. 17  is a schematic diagram example of connecting the “Drain” of each gate together using N type FET, MOSFET, or IGBT with the cells being below the solid state switches. 
         FIG. 18  is a schematic diagram illustrating connecting the “Source” of each gate together using N type FET, MOSFET or IGBT with the cells being above the solid state switches. 
         FIG. 19  is a schematic diagram illustrating connecting the “Source” of each gate together using N type FET, MOSFET or IGBT with the cells being below the solid state switches. 
         FIG. 20  is a schematic diagram illustrating connecting the “Drain” of each gate together using P type FET, MOSFET or IGBT with the cells being above the solid state switches. 
         FIG. 21  is a schematic diagram illustrating connecting the “Drain” together using P type FET, MOSFET or IGBT with the cells being below the solid state switches. 
         FIG. 22  is a schematic diagram illustrating connecting the “Source” together using P type FET, MOSFET or IGBT with the cells being above the solid state switches. 
         FIG. 23  is a schematic diagram illustrating connecting the “Source” together using P type FET, MOSFET or IGBT with the cells being below the solid state switches. 
         FIG. 24  is a schematic diagram illustrating the invention utilized in engine restarting. 
         FIG. 25  is a schematic diagram illustrating short circuit protection of a battery. 
     
    
    
     DETAILED DESCRIPTION 
     Lithium containing LiFePO, LiFePO 4 , LiFeMgPO 4 , and LiFeYPO 4  cells have a low nominal cell voltage (3.2V-3.3V) that match directly with existing 12V lead-acid equivalent systems. Four LiFePO cells in series have a nominal voltage of 13.2V. Thus they can directly replace existing 12V lead-acid equivalent systems without requiring any electrical modification. 
     Other lithium chemistries have a higher nominal voltage, such as: lithium-cobalt (3.6V), lithium-manganese (3.7V-3.8V), lithium-nickel-cobalt-manganese (3.7V). Each of these thus have a higher system voltage when 4 cells are used in series. With the higher cell voltages, most existing 12V direct replacement systems will not be able to charge other lithium cell chemistries above 60% of their capacity. Other lithium-based cells that can be utilized in this invention are lithium-cobalt-oxide (LiCoO 2 ), lithium-manganese-oxide (LiMn 2 O 4 ), lithium-nickel-cobalt-manganese-oxide (LiNiCoAlO 2 ), lithium-nickel-manganese-cobalt-oxide (LiNiMnCoO 2 ), and lithium-titanate (Li 4 Ti 5 O 12 ). 
     LiFePO, LiFePO 4 , LiFeMgPO 4 , and LiFeYPO 4  cells also have a higher thermal runaway condition than lead-acid cells. For a thermal runaway to occur, the cell temperature must be extremely hot (over 200° C.). When a cell reaches a certain temperature, mostly caused by overcharging, then the cell will start producing more heat by an internal reaction that fuels itself in most cases with a fire, which phenomenon is known as “thermal runaway”. All other Lithium cell chemistries have a lower thermal runaway temperature making those cells more prone to catch on fire. 
     A thermal venting cap is usually placed inside each individual cylindrical cell casing to minimize the chances of explosion. The venting cap allows the electrolyte of a cell to leak out before an internal fire can occur. 
     Although it is advantageous to use protective circuitry, it is possible to operate the present invention without protective circuitry, which simplifies the system to allow charging or discharging. Omitting all of the electronic protection circuitry for upper voltage cut-off (overcharging), lower level voltage cut-off (over discharging) and temperature measurements reduces the overall manufacturing cost of the starter battery. This also simplifies the system to allow charging or discharging in all conditions and not be restricted by any suggested or specified operating range. 
     By using lithium cells, a battery housing structure is both smaller and lighter than with lead-acid cells. Any time less internal mass is involved the housing structure size can be reduced, which also results in reducing cost. 
     The housing structure of the embodiment of  FIGS. 1 and 2  may vary in depth to accommodate varying numbers of cells which provides for different capacity. The lid structure of the housing (or casing) for cylindrical cells is the same for most battery packs, as shown. Such cells can be stacked in parallel to allow for larger capacity for different battery packs to be assembled. The lid of the housing also incorporates a threaded bushing made from aluminum to minimize weight, but that has similar electrical properties to aluminum, copper or brass, or an internally threaded hole to receive an electrical connector screw. 
     Referring now to the drawings, and particularly to  FIG. 1 , the invented battery pack  10  comprises a housing  12 , having a lower receptacle  14  and a mating top  16 , at least one lithium-based rechargeable battery  18 , or cell, within the housing, with appropriate electrical connections. The total discharging amount of each lithium-based cell in the battery pack is one (1) to 5000 Ah, and charging voltage per one cell is 3.0 to 4.2 V. 
     The lower portion of the housing  16  can be provided with bottom padding  20  which fits therein, receives the cell or cells, and mates with the lower receptacle  14 . A top pad  22  can be provided in the top  16  of the housing, as desired. 
     Electrical connections  24  are provided between the cells, as shown, positive to negative, with screws  26  connecting the cells through holes  28  the bottom of the housing to electrical leads, not shown, but which leads connect to bottom screws  30 . Alternatively, a welded connection can be used instead of screws. 
     Optionally, a protection circuit board  32  may be placed within the upper casing or top  14  for safety protection. Such a protection circuit board may be a cutoff board or a cell-balancing circuit board. A cell-balancing circuit board may include a cutoff function. A lithium iron battery having two or more cells in series has a battery voltage equal to the sum of the individual cell voltages. Over the life of the battery, it may be charged and discharged for hundreds or thousands of cycles. The individual cells may age differently. Some cells may become mismatched with respect to the others. This phenomenon is corrected, by balancing. Balancing is the process of forcing all of the cells to have identical voltages. This is accomplished by a balancing circuit. 
     Starter battery systems can utilize a greater number of lithium cells as desired for greater capacity. 
     Lithium cells have substantially less weight than a lead-acid cell, and are 80% smaller. A lithium cell will last about 3 times as long as a lead-acid cell with 100% full discharge cycles. Lithium cells are maintenance free, whereas lead-acid cells need to be refilled with distilled water to maintain the acid level above the plates. Lithium cells do not freeze. They have a discharge power 8 times that of lead-acid. Their charging time is less than 2 hours. 
     Lithium cell self discharge rate is less than 2% monthly, whereas the self discharge rate for a lead-acid cell is 10% monthly. 
     Lithium cells can operate at very high temperature, up to 70° C. without major degradation. They can also operate at very low temperature, down to −30° C. with slight capacity degrade at that temperature, but power is available. 
     Lithium cells are 98% energy efficient (energy going in and out of the cell), whereas lead-acid cells are only 90% energy efficient. 
     For each 12 volt increment, four LiFePO 4  cells are required in series, and some cases fewer cells with other lithium chemistries. The following Table compares the lead-acid battery voltages to the LiFePO 4  cell requirements and for other lithium-based battery cells: 
     
       
         
           
               
               
               
             
               
                 TABLE I 
               
               
                   
               
               
                   
                   
                 (LiCoO 2 ), (LiMn 2 O 4 ), 
               
               
                 Nominal 
                   
                 (LiNiCoAlO 2 ), (LiNiMnCoO 2 ), or 
               
               
                 Lead-Acid 
                 LiFePO 4   
                 (Li 4 Ti 5 O 12 ) 
               
               
                 Voltage 
                 (3.3 V nominal) 
                 (3.7 V nominal) 
               
               
                   
               
             
            
               
                 12 V 
                  3 to 4 cells in series 
                  2 to 4 cells in series 
               
               
                 24 V 
                  5 to 9 cells in series 
                  5 to 8 cells in series 
               
               
                 36 V 
                  8 to 13 cells in series 
                  7 to 12 cells in series 
               
               
                 48 V 
                 11 to 17 cells in series 
                 10 to 16 cells in series 
               
               
                 60 V 
                 14 to 22 cells in series 
                 12 to 19 cells in series 
               
               
                 72 V 
                 16 to 26 cells in series 
                 15 to 23 cells in series 
               
               
                 84 V 
                 19 to 31 cells in series 
                 17 to 27 cells in series 
               
               
                 96 V 
                 22 to 35 cells in series 
                 19 to 31 cells in series 
               
               
                 108 V  
                 25 to 39 cells in series 
                 22 to 35 cells in series 
               
               
                 120 V  
                 27 to 44 cells in series 
                 24 to 39 cells in series 
               
               
                   
               
            
           
         
       
     
     As shown in  FIGS. 3 through 6 , a block  40  formed of one or more flat prismatic cells connected in series is fitted into a housing  12 , each block of cells having a common set of electrical connections  42 A and  42 B. A protection circuit board  30  is provided within the housing, and is electrically connected to the block.  FIGS. 4 through 6  show the assembled housing with the electrical connections  24 A and  24 B in the top thereof. 
       FIG. 7  shows a block of 4 flat lithium based prismatic cells connected to a balancing circuit board  46 , which has a balancing controller or microprocessor  60 .  FIG. 8  shows a block of 4 flat prismatic cells connected to a balancing and cutoff circuit board  48 , which includes a controller  60  and a solid state cutoff switch  62 , such as an FET.  FIGS. 9 through 12  show the housing  12  for the battery pack  10  with positive terminal  34  and negative terminal  36 . 
       FIG. 13  shows multiple blocks  40  of flat cells along with bottom padding, packing, or spacers  50 , flat packing  52 , and large packing blocks  54 , all of which packing is optional. The upper portion or top section  56  of the housing is advantageously provided with three contacts on each end thereof, as shown. 
     An auto-detect restart feature is especially useful for a motorcycle: “IQ Restart technology” protects the battery from a deep cycle discharge by monitoring battery voltage level and shutting the battery power off prior to a full discharge, such as in the case of leaving a headlight or electrical component on for an extended period of time while the engine is off. Enough reserve power is left in the battery, to automatically detect (by measuring a change in resistivity) a starting effort and allow the user to start the engine again. This avoids the cyclist being stranded or the headache of replacing a battery. The auto-detect apparatus has at least one lithium-based cell, a voltage detector, an associated switch such as a cutoff board, or a micro-controller in a balancing circuit connected to a solid state switch, such as an FET. One function turns off an FET in the circuit when the voltage drops to a preselected level, leaving sufficient reserve capacity for starting the engine. A second function detects a “keying cycle” or the resistance change upon attempting to start the engine, which turns on the FET. This resistance change is a reaction to a key turn, push button, or remote activator. 
     To control the solid state switches, electronic controls are needed for the different voltages, currents and/or temperature with specified parameters in which cells work to prevent damage. The control electronics used in battery systems are often referred to a Battery Management System (BMS) or Battery Management Unit (BMU). The BMS or BMU can individual monitor all the cell or battery voltages, and/or temperatures. To protect a single cell or battery from being over charged, that might lead to an exothermal runaway reaction creating a fire and/or to prevent the cell from damaging when discharging them too low, the solid state switch would close or open the current pathway to prevent cell damage from occurring. 
     The arrangement of devices shown in  FIGS. 15 and 16  are examples of how solid state switches can be configured to connect the “Drains” or “Sources” together which is an unconventional approach. The solid state switches in parallel are examples to increase the current capabilities. 
     Referring particularly to  FIG. 17 , under normal operations both T 1  and T 2  are ON allowing power pathway to go in both directions: discharge and charge. Should a cell be outside of its specified working specification (cell voltage), both D 1  and D 2  can be turned off but current can still flow through the internal diode to allow for added functionality. 
     In the event that the cell voltage drops too low, below the set voltage configuration, from a drain on the battery, T 1  will turn off, preventing further discharge from occurring. However, with the internal diode in place of T 1 , and T 2  still on, the circuit will allow charging to occur. 
     If the cell voltage goes too high, above the set voltage configuration, T 2  will turn off, preventing further over charging from occurring. However, with the internal diode in place of T 2 , and T 1  still on, the circuit will allow discharging to occur. 
     Using solid state switching in the configuration shown in  FIG. 17  allows for user friendly reactivation of the circuit without any pushbuttons or reset buttons. Both Charge and Discharge current can go through the internal MOSFET or IGBT diode to bring the cell back to the specified operating voltage. 
     Alternative switch and gate arrangements are set forth in  FIGS. 18 through 23 . Each such arrangement works in a similar manner as that describing the  FIG. 17  operation. 
     The invention&#39;s restart function is illustrated by  FIG. 24 . Controller  60  is connected to a battery pack having a block of cells  64  and to MOSFETs Q 1  and Q 2 . After a low voltage cutoff, the controller periodically tests the load to detect a change in the load impedance. When an abrupt change in the load impedance is detected, for example connecting or disconnecting a load such as the headlight(s), the ignition switch, or the starter switch, the controller  60  turns on power MOSFETs Q 1  and Q 2 , which reconnects the battery to the vehicle and allows the vehicle to be restarted. 
     When the controller drives the base of Q 3  high through R 1 , Q 3  and Q 4  turn on. When Q 4  turns on, it connects the battery to the load through R 4  and D 1 . R 4  and the load impedance form a voltage divider, and the resulting voltage at node A will depend on the load impedance. D 2  steers the node A voltage to the R 5 /R 6  voltage divider which scales down the voltage at node B to a level that the controller can read using an analog-to-digital converter (ADC). The ADC may be of the type commonly included as a built-in peripheral in a micro-controller or a digital signal processor; alternatively the ADC may be a standalone device. After turning on Q 4 , the controller may make one or more ADC readings after one or more fixed or variable delay periods. By reading the ADC at different times after turn-on, the controller can infer not only the resistive, but also the inductive and/or capacitive components of the load impedance. By tracking the periodic ADC readings and applying the appropriate digital filtering, abrupt changes in the load impedance can be determined. Gradual changes in the ADC readings, which may be caused for example by temperature changes or battery charge depletion, are disregarded (i.e., filtered out). Immediately after making the required ADC reading(s) the Controller turns off Q 3  and Q 4  to minimize battery drain. It should be noted that while Q 3  and Q 4  are shown here as bipolar junction transistors, a number of other types of electronic devices could be used to accomplish the switching function of Q 4 , including but not limited to one or more MOSFETs or a relay. 
     In order to conserve battery charge as long as possible in low voltage cutoff mode, the controller tests the load impedance only as often as necessary. The testing period is determined by the application, and is approximately 1 to 5 seconds. In a vehicle application, this period represents the maximum time that a user would have to hold a starter switch in the start position in order to effect a restart after a low voltage cutoff. To further reduce drain on the battery, the testing period may be extended if the battery remains in low voltage shutdown mode for a long time, or if the battery voltage (in one or more cells) continues to drop. 
     The invention is useful for short circuit protection as shown in  FIG. 25 . Cross-coupled NAND gates E and F form a set-reset (SR) latch that controls the gate drive of power MOSFET Q 2 . The latch is set when the controller  60  drives Q 2  ENABLE low. When Q 2  ENABLE is driven high again, the output of NAND gate G is low and NAND gate H turns on Q 3 , which turns on Q 4 , which supplies the boosted gate drive voltage to turn on Q 2 . C 3  and C 4  help ensure fast turn-on of Q 2  even with the relatively high value resistors for R 4 , R 5 , and R 8  required to satisfy the application&#39;s low power requirements. 
     Current monitor A monitors the voltage drop across the drain-source ON resistance (R DS(on) ) of power MOSFET Q 1  and sources a current into node B that is proportional to the MOSFET current. R 1  converts this current to a voltage that is compared to VREF at comparator D. When a short circuit occurs, the voltage at node B will exceed VREF (at least momentarily) and cause the output of D to go low, resetting the S-R latch. When the S-R latch is reset the output of G will go high, and C 2  will differentiate a positive going pulse into the base of Q 5 , causing Q 5  to turn on for a few microseconds and rapidly discharge the gate of Q 2 . Rapid turn-off of Q 2  is essential to limiting the energy associated with a short circuit event. By monitoring the status of the S-R latch, the controller  60  can determine when a short circuit cut-off event has occurred. C 1  low pass filters the signal at node B so that extremely short duration overcurrent conditions can be tolerated if desired. The controller  60  may adjust VREF to compensate for Q 2 &#39;s R DS(on)  variation with temperature if desired, or to adjust the over current trip threshold. 
     The solid state switches can be transistors, FET (field-effect transistors), JFET or JUGFET (junction gate field-effect transistors), BJT bipolar junction transistors, CMOS (complementary metal-oxide-semiconductors), VMOS (Vertical Metal Oxide Silicon), TMOS transistors, vertical DMOS (Double-Diffused MOS), or HEXFET. (hexagonal shape MOSFET). 
     It should be noted that the invented solid state switch apparatus can also be used in any battery system that requires charging and discharging in order to extend the battery life, and for safety. This is extremely useful and is a first for starter batteries. 
     The solid state devices all need to be the same (N) or (P) type used in the same circuit, as illustrated. 
     SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION 
     From the foregoing, it is readily apparent that I have invented an improved means for increasing the performance of a starter battery for a starter motor of an internal combustion engine, and a starter battery for an internal combustion engine that is lighter, more reliable, has less bulk, longer cycle life, longer calendar life, and higher turn around efficiency than lead-acid batteries. The starter battery system for an internal combustion engine is easy to assemble, waterproof, and maintenance free, can be used in existing vehicles, and has a wide operating temperature range with exceptional cold-weather cranking performance. The invention also apparatus for protecting a single cell or battery from being over charged, as well as providing apparatus for charging a cell having a very low charge, more effectively, and more economically than heretofore has been possible. 
     It is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof, and that various modifications and additions may be made to the apparatus by those skilled in the art, without departing from the spirit and scope of this invention, which is therefore understood to be limited only by the scope of the appended claims.