Abstract:
A self-contained emergency battery charger for use in motor vehicles for charging a fully or partially discharged starter storage battery which delivers current to a starter motor of the vehicle. The batter charger contains a preconditioning circuit to preconditions a discharged battery before applying a full charging current from a charged second battery to the discharged battery. The battery charger also contains a temperature circuit which adjusts the time of charging whereby the time for providing power from the second battery is increased or decreased in relation to the second battery&#39;s temperature.

Description:
This Application claims benefit to Provisional Application No. 60/195356 filed Apr. 10, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to battery charging devices, and in particular to a self-contained emergency battery charger for use in motor vehicles for charging a fully or partially discharged starter storage battery which delivers current to a starter motor of the vehicle. 
     A motor vehicle storage battery frequently falls into a state of discharge such that it cannot deliver sufficient current to the starter motor. This is often due to lights or other accessories being accidently left on. Also, defective vehicle charging systems can result in the same problem. 
     To start a vehicle whose storage battery has been partially or completely discharged requires either by-passing the electrical starting system entirely or supplying the electrical starting system with an additional source of external electrical power. The former technique is generally accomplished by push-starting the vehicle and the latter technique by using either jumper cables connected to a fully charged external power source in another vehicle, termed “jump starting”, or a conventional battery charger. Push starting requires assistance in the form of a push vehicle or human muscle power. Additionally, only cars fitted with standard transmissions can be push started. Jump starting requires the aid of an additional vehicle. Further, cables must be available and must be externally connected, requiring the user to exit the vehicle, and be exposed to the hazards of weather or of possible battery explosion and associated mishaps as a result of a misconnection of the cables. The disadvantage of a conventional battery charger is the need to be near a source of external power such as 120 volts alternating current. 
     To overcome these problems and the limitations of prior art attempts to solve the problem, such as being useful only for one or two battery charges before the secondary battery source must be replaced, a very slow recharge cycle, a need for an external source of power, and insufficient portability or lengthy charging/recharging times, assignee developed a battery booster, subsequently patented as U.S. Pat. No. 5,637,978, issued on Jun. 10, 1997, said patent being incorporated herein by reference and hereinafter referred to as the &#39;978 battery booster. 
     Through extensive testing of lead acid batteries Applicants have learned that a fully drained automotive (lead acid) battery will not accept current and return it efficiently under certain conditions. Specifically, Applicants have found that when a lead acid battery (originally a nominal 12 volts) is discharged below 5 volts, the charge acceptance is &lt;40%. The original design parameters for the &#39;978 battery booster were to deliver 5 amps constantly from the time the charging switch is activated. During testing, limited success was achieved starting vehicles. The &#39;978 battery booster, as originally designed was successful in starting vehicles whose discharged batteries were ≧9.5 volts. Further research verified that low current return occurred when the lead acid battery was &lt;5 volts. A very high rate of current return (88% to 92%) occurred when the lead acid battery was &gt;10.5 volts. 
     During their research, Applicants also found a variation in time required to recharge a lead acid battery. Applicants found that, within operating temperature limits, during a given time period, a warm battery will provide more electrical power than cold battery. Therefore, under colder conditions the time required to fully recharge a battery is longer. The original &#39;978 battery booster had a simple resistor/capacitor circuit that took a resistor of fixed value and charged a capacitor of a fixed value giving a fixed time regardless of temperature. 
     SUMMARY OF THE INVENTION 
     The present invention “preconditions” a discharged battery before applying a full charging current from a charged second battery to the discharged battery. The invention circuitry first checks the voltage level of the discharged battery. If the voltage level is at or below a first predetermined level, a minimum charging current, which is less than half the value of a full charging current, is applied to the discharged battery from the second battery. The minimum charging current is applied to the discharged battery until the voltage of the discharged battery rises to a second predetermined level. After the voltage of the discharged battery reaches the second predetermined level, the invention applies a full charging current to until the discharged battery is fully charged. 
     In providing the charge to the discharged battery from the charged second battery, the present invention adjusts the time of charging whereby the time for providing power from the second battery is increased or decreased in relation to the second battery&#39;s temperature. 
     These together with other objects of the invention, along with various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed hereto and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the invention. 
     FIG. 2 is a schematic circuit diagram of the prior art. 
     FIG. 3 illustrates the diagram of FIG. 2 modified according to the present invention. 
     FIG. 4 is a schematic circuit diagram according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is an improvement in providing a charge to a discharged battery from a charged second battery as identified in the &#39;978 patent. Specifically, the present invention adds a preconditioning step to the charging process as well as temperature compensation. 
     The invention has a generally box-like, rectangularly shaped housing  1 , having a front  2 , back  3 , two sides  4 , a top  5  and a bottom  6 . The housing front  2  has a panel  10  attached covering the entire housing front  2 . Visible horizontally across the panel  10  from the left side  4  to the right side  4 ′ are an auxiliary power tap  11  which allows power to be drawn from the invention power source  30  , i.e., charging battery, for non-vehicle battery-charging purposes. Immediately to the right of the tap  11  is an opening  12  through which a power cord  16  passes, said power cord  16  terminating in a male receptacle  17  adapted for insertion into a vehicle&#39;s cigarette lighter receptacle  27 . The male receptacle  17  has a positive lead  18  terminating centrally along its central longitudinal axis and a cylindrical housing  19  connected to the invention common ground  38 . Immediately to the right of said opening  12  is a first switch  13  which is a three-way switch. The switch  13  provides a “Charge” setting  13 A, an “Off” setting  13 B and a “Recharge” setting  13 C. To the right of the switch  13  are two light indicators  14 ,  15 . The light indicator  14  immediately to the right of the switch  13  is yellow and indicates various vehicle storage battery  20  charging modes. The next light indicator  15  is green and indicates various invention charging, recharging and test modes. 
     FIG. 2 illustrates the circuit diagram of the &#39;978 patent. Referring to FIG. 2, there is shown a vehicle storage battery  20 . A vehicle storage battery is typically a 12 volt, 40 Ampere-Hour, lead acid battery. A vehicle storage battery  20  and vehicle cigarette lighter  25  electrical circuit is shown. The lighter  25  is formed of a female receptacle  27  terminating centrally along its central longitudinal axis in a positive lead  26 . There is a fuse  23  between the positive terminal  21  of the vehicle storage battery  20  and the lighter positive lead  26 . The lighter receptacle  27  is electrically connected to the battery negative terminal  26 . 
     The invention has a charging battery  30 . The nominal voltage output from the charging battery  30  is represented by the symbol Vc. The charging battery  30  in this embodiment of the invention is a 12 volt, 7 Ampere-Hour, sealed, lead acid battery. This type of battery is rated at 12 volt nominal output. The charging battery  30  has a positive terminal  31  and a negative terminal  32 . 
     An optional auxiliary circuit is formed with the charging battery  30  to the auxiliary power tap  11 . The tap  11  is comprised of a female receptacle  35  terminating centrally along its central longitudinal axis in a positive lead  36 . The tap positive lead  36  is electrically connected by means of electrical line  37  to the charging battery positive terminal  31 . The tap receptacle  35  is electrically connected to a common ground  38  terminating in the charging battery negative terminal  32 . This embodiment of the invention contains a positive temperature coefficient resistor, P 1 , between the charging battery negative terminal  32  and the common ground  38 . The resistor, P 1 , is variable and non-linear. P 1  has a low resistance value at relative low temperatures, but has substantially higher resistance at high temperatures. P 1  acts as a current limiting fuse. P 1  will exhibit low resistance characteristics at less that 6 amps and very high resistance at greater than 6 amps. 
     Also shown is a depiction of the three-way switch  13  mentioned above. The switch  13  may be termed a first switching means and is adapted to electrically connect the battery positive terminal  31  to one of three nodes  13 A,  13 B or  13 C. The switch  13  provides a “Charge” setting when the battery positive terminal  31  is connected to node  13 A; an “Off” setting when connected to node  13 B; and a “Recharge” setting when connected to node  13 C. The switch  13  is shown in its “Charge” setting  13 A. The “Charge” setting establishes a circuit whereby the charging battery  30  and other invention circuitry charge the vehicle storage battery  20  through the cigarette lighter  25 . The “Recharge” setting establishes a circuit whereby the invention charging battery  30  is recharged from the vehicle storage battery  20  through the cigarette lighter  25 . 
     The “Charge” circuit established by the switch  13  places a capacitor C 2  in parallel to the charging battery  30  wherein the capacitor C 2  positive terminal  61  is electrically connected to the switch node  13 A. A resistance network comprised of two resistors R 6 , R 8 , in series, is also electrically connected in parallel with the capacitor C 2 . An RC (resistance-capacitance) network comprised of a resistor R 11  and capacitor C 3 , in series, is also electrically connected in parallel with the resistance network R 6 , R 8 . An inductance L 1  and diode D 1  are electrically connected in series with the charging battery positive terminal  31  wherein the inductance L 1  input terminal  40  is electrically connected to the capacitor C 2  positive terminal  61 , the resistance network R 6 , R 8  positive node  60 , and the RC network R 11 , C 3  positive node  62 . The inductance L 1  output terminal  41  is connected to the diode D 1  positive terminal  42 . The diode D 1  negative terminal  43  is connected to the positive lead  18  of the power cord male receptacle  17 . A second switch U 1 , having a primary terminal  55  and two secondary terminals, one  56  of said secondary terminals being positive and the other  57  being negative, said secondary terminals  56 ,  57  being adapted to jointly connect to said primary terminal  55  or being jointly disconnected from said primary terminal  55 , said positive secondary terminal  56  being connected to said inductance L 1  output terminal  41  and said negative secondary terminal  57  being connected to said common ground  38 , thereby interconnecting the inductance L 1  output terminal  41  to ground  38  when the switch U 1  is closed. A diode D 3  interconnects the positive terminal  52  of the switch U 1  with the junction  73  of R 11  and C 3 . A U 1  switch control  50  interconnects the inductance L 1  input terminal  40  to ground  38 . The switch control  50  is electrically connected to the switch U 1  and also is connected to a resistance network comprised of two resistors R 1 , R 2 , in series. The resistance network R 1 , R 2  interconnects the diode D 1  negative terminal  43  to ground  38 . The switch control  50  is connected to the junction  51  of R 1  and R 2 . A capacitor C 1  is connected in parallel to the resistance network R 1 , R 2  wherein the capacitor C 1  positive terminal  45  is electrically connected to the resistance network R 1 , R 2  positive node  63 . The diode D 1  negative terminal  43 , resistance network R 1 , R 2  positive node  63 , and capacitor C 1  positive terminal  45  are electrically connected to the positive lead  18  of the power cord male receptacle  17 . 
     To charge the vehicle battery the switch  13  is set to “Charge” mode. The power cord male receptacle  17  is inserted into the cigarette lighter  25  thereby establishing an electrical connection among the Cl positive terminal  45 , the diode D 1  negative terminal  43  and the resistance network R 1 , R 2  positive node  63 , and the vehicle battery positive terminal  21 , and thereby establishing an electrical connection between the vehicle battery negative terminal  22  and the invention common ground  38 . The C 1  negative terminal  46  is also attached to the common ground  38 . In the “Charge” mode the invention must be capable of stepping up the voltage from the loaded terminal voltage Vc of the charging battery  30  to the terminal voltage required to charge the vehicle storage battery  20 , i.e., from approximately 12 volts to approximately 14 volts. In the present invention this is done by means of a “boost converter” which is that portion of the circuit comprised of the elements L 1  (inductance), D 1  (diode), and U 1  (switch). The switch U 1  is controlled by a switch control unit  50 . The switch control unit  50  is self-oscillating with a switching rate based upon output voltage feedback across the resistance network R 1  and R 2 . The voltage between the inductance L 1  positive terminal  40  and ground  38  supplies power to the switch control unit  50  circuitry. In the switch “Charge” setting, an electrical connection is made across terminal  13 A thereby electrically connecting an input filter capacitance, C 2 , from the charging battery positive terminal  31  to the common ground  38 . C 2  provides a filtering function and a low impedance input to U 1 . C 1  provides a load for the booster converter to discharge into in case the fuse  23  is blown or some other similar situation arises. The Charging setting also connects the charging battery positive terminal  31  in electrical series connection with the input terminal  40  of the inductance L 1 . In the Charging mode, when the switch U 1  closes, the inductance L 1  is in series with the charging battery  30 . Current in the inductance L 1  increases slowly rising to 5 amps. Because of the nature of an inductance, when the switch U 1  opens, current will still flow in L 1  and the voltage across L 1  will adjust to maintain current flow. Since the voltage at the L 1  input terminal  40  must equal Vc, there will be a polarity change wherein the voltage at the L 1  output terminal  41  will become greater than Vc at the L 1  input terminal  40  thereby maintaining current flow in L 1 . With the power cord male receptacle  17  connected to the cigarette lighter  25 , the positive terminal  21  in the vehicle storage battery  20  will feel the greater voltage at the L 1  output terminal  41 . The effect of this greater voltage will cause the L 1  5 amp current to flow into the vehicle storage battery  20 . The inductance L 1  in effect acts as a current fly wheel. D 1  prevents the vehicle storage battery  20  from discharging back into L 1 . The switch U 1  will then close again and the process will repeat. 
     The “Recharge” circuit established by the switch node  13 C interconnects a positive temperature coefficient resistor, P 2 , with the charging battery positive terminal  31  and the vehicle battery positive terminal  21 . By connecting the power cord male receptacle  17  with the vehicle cigarette lighter  25 , an electrical connection between the vehicle battery negative terminal  22  and the invention common ground  38  is established. Like P 1 , the resistor, P 2 , is variable and non-linear. P 2  has a low resistance value at relative low temperatures, but has substantially higher resistance at high temperatures. Initially, the resistance of P 2  rises very slowly as temperature rises. After the temperature reaches a designated value, the resistance of P 2  rises exponentially. P 2  is also current limiting and acts as a self-repairing fuse. Unlike prior art devices, P 2  allows the charging battery  30  to recharge without exceeding the safe recharging current, i.e., approximately 2 amps. The Recharge circuit is basic and permits a simple and efficient method of recharging the invention charging battery  30  after use. 
     The light indicators  14 ,  15  indicate to the user what is happening and in this embodiment of the invention are light emitting diodes (LEDs). A resistance network comprised of two resistors R 9 , R 10 , in series, is electrically connected between the switch node  13 C and ground  38 . An LED control unit  70  is connected to the junction  71  of R 9  and R 10 . The LED control unit  70  is also connected to the junction  72  of R 6  and R 8 , and also to the junction  73  of R 11  and C 3 . The positive terminal  74  of the yellow LED  14  is electrically connected to the switch node  13 A and the positive terminal  76  of the green LED  15  is electrically connected to the switch node  13 C. The negative terminal  75  of the yellow LED  14  and the negative terminal  77  of the green LED  15  are both connected to the LED control unit  70 . In operation, the green LED  15  lights when the switch  13  is in the “Charge” position at switch node  13 A and Vc is below 9.5 volts thereby indicating that no charge is left in the charging battery  30 . Power to light the green LED  15  and operate the LED control unit  70  comes from the vehicle storage battery  20 . The green LED  15  also lights when the switch  13  is connected to the “Recharge” position  13 C and Vc is above 12.5 volts thereby indicating that the charging battery  30  is fully charged. Voltage feedback signals for these two conditions are provided by the resistance networks comprised of R 6  and R 8 , and R 9  and R 10 , respectively. The yellow LED  14  operates as follows. If the voltage across C 3  is less than a designated reference voltage, the yellow LED  14  will be turned on. If the voltage across C 3  is greater than a designated reference voltage, the yellow LED  14  will be turned off. When switch U 1  closes, C 3  is discharged via D 3 . When U 1  opens, C 3  slowly recharges via R 11 . If U 1  is being switched at high frequency then the average charging voltage on C 3  will be low and usually below a reference voltage, resulting in the yellow LED  14  being brightly illuminated thereby indicating that current is being transferred from the charging battery  30  to the vehicle storage battery  20 . If vehicle battery  20  is not connected via the cigarette lighter  25  and plug  17 , the voltage across C 1  will rise and the switch U 1  will operate at a low frequency. This results in a greater charging voltage across C 3 , usually greater than the reference voltage, and consequently an apparently dimmer yellow LED  14  because of the greater amount of time the LED  14  is turned off. 
     The performance of the invention on a particular vehicle may be calculated as follows. To determine the energy transfer to the “dead” vehicle storage battery  20 , multiply the time (in hours) by the charge current (typically  5  Amperes) and factor the “charge-discharge” efficiency of the vehicle storage battery  20  (assume 50%). Since the battery charger will be a “constant current” device, the energy transferred to the vehicle storage battery  20  will be linear with time. On the assumption that it will take about 0.56 Ampere-Hours to start a typical, but cold, functioning vehicle engine (200 Amperes×10 seconds×3600 seconds/hour), it will take about 15 minutes to transfer enough energy to start the vehicle. If the vehicle storage battery  20  is not discharged as much, less charging time will be required. The above performance figures are stated at 32° F. (0° C.). 
     Referring to FIGS. 3 and 4, the present embodiment of the invention, provides a 2 ohm, 10 watt, block resistor R- 7  in parallel with a power MOSFET on the negative side of the unit. The block resistor has a resistance in the range of 1 to 4 ohms, and a watt rating of from 8 to 12 watts. When the unit is turned on, the preconditioning step prevents excessive current levels when the voltage differential between the vehicle battery and the charging battery is high. This step provides preconditioning to the depleted battery. The resistor limits the charging current to 7 amps. The preconditioning charge of 7 amps is maintained until the discharged battery voltage reaches 10.5 volts or when the voltage differential across the resistor is less than 2 volts. This generally takes from 30 to 35 seconds. When this point is reached, an operational amplifier is activated turning on the FET that completes the negative path. In this embodiment of the invention this is the most efficient charge point. At this point of activation a DC-to-DC “up” converter is engaged to boost the DC level of the charging battery to 15-17 amps. The invention will run in the fully charging mode from 10 to 15 minutes. The invention uses a current mode PMW controller device that provides cycle-by-cycle current limitation that prevents over-current conditions from occurring. A timer is also incorporated into the invention that activates the second green light at a predetermined time. 
     The original circuitry in the &#39;978 patent (see FIG. 2) had a simple resistor/capacitor circuit that took a resistor of fixed value and a charge capacitor of fixed value giving a fixed time regardless of temperature. For temperature control, a thermistor th- 1  is placed in series with the resistor R- 11  to vary the time it takes to charge the capacitor depending on the unit&#39;s temperature. In this embodiment of the invention the thermistor is a negative type where a decrease in temperature results in an increase in resistance resulting in longer time to charge the capacitor. The temperature of both the discharged battery and the second battery is dependent upon the ambient temperature and time of either battery to reach that temperature if, before use, either is at a temperature different than the ambient temperature. For example is the situation where the second battery is brought to a cold garage holding the vehicle with the discharged battery. 
     It is understood that the above-described embodiment is merely illustrative of the application. Other embodiments may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.