Abstract:
A jump start protection circuit having a normally open switch and a resistor positioned in parallel intermediate to a battery and a jump start post. A controller manipulates the switch between an open position and closed position, the closed position connects the jump start post to the battery and the open position disconnects the jump start post from the battery. The controller measures voltages at the battery and jump start post and is capable of receiving one or more additional inputs. The controller closes the switch when acceptable jump start conditions are detected. The controller can open the switch or maintain the switch in an open position. The jump start circuit provides protection against attempts to charge a battery with incorrect polarity connections and attempts to charge a battery from a potentially hazardous higher voltage power source.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a circuit protection apparatus that prevents a circuit from being closed when attempting to charge a battery with incorrect polarity connections or attempting to charge a battery from a potentially hazardous higher voltage power source. The apparatus is particularly useful as a motor vehicle jump start protection system and as a short circuit protection system.  
         BACKGROUND OF THE INVENTION  
         [0002]    When a battery of a first motor vehicle is flat (no power), it is known to connect a battery from a second vehicle source across the flat battery in order to start the engine of the first vehicle. Such a technique is commonly referred to as jump starting. It is also known that a flat battery may be recharged by connecting a power source such as a battery charger across the flat battery.  
           [0003]    When the battery of a motor vehicle is difficult to access or is not located in the engine compartment, but elsewhere in the vehicle, it has become common practice to provide jump start terminals in the engine compartment which can be connected to either a battery of a second vehicle or a battery charger should the battery of the first vehicle go flat. If the second battery or the battery charger is incorrectly connected (that is, the wrong polarity) to the jump start terminals, electrical components in the first vehicle (especially diodes associated with the generator of the first vehicle) may be damaged. Other conditions which cause the jump start terminal to short circuit to ground can also cause damage.  
           [0004]    Weber, U.S. Pat. No. 5,230,637, describes what can happen when sparking or a damaged battery are present when jump starting a vehicle.  
           [0005]    As the need for energy in motor vehicles increases with the addition of more electrically powered components and systems, vehicle manufacturers are contemplating higher voltage electrical architectures. The introduction of higher voltage systems increases the probability that someone will try to jump start or recharge a conventional 12 volt battery from a source that has a higher voltage. This situation can damage the battery or electrical components in the vehicle. Use of higher voltages also increases other risks resulting from sparking.  
           [0006]    The prior art includes inventions that address the problem of reverse polarity connections when jump starting a battery. Weber &#39;637 provides for jumper cables with reverse polarity protection. Another example of a jump start protection system is described in Alksnat, et al., U.S. Pat. No. 6,211,577. Alksnat &#39;577 utilizes a jump start circuit, a switch, a logic circuit, and a timer circuit. The &#39;577 patent monitors polarity differences across the jump start terminals and closes the jump start circuit switch if polarities match. A timer circuit is used to open the switch after a predetermined period of time. A manual push button is provided to enable the operator to manually close the jump start circuit switch when a second vehicle is used for jump starting.  
           [0007]    In the prior art, in order to provide jump start or reverse polarity connection protection it is necessary that either special jump start cables are used or additional operator actions are performed over and above the traditional jump start method.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention overcomes the problems noted above and satisfies the need in this field for a device that can provide protection during jump starting without the need for additional operator actions or special jump start cables.  
           [0009]    A preferred embodiment of the present invention operates by monitoring voltages at a jump start post and the positive terminal of a DC power source such as a battery. When a jump start is correctly initiated on a flat battery of a first vehicle using an appropriate battery charger or good battery from a second vehicle and correct polarity connections, a microprocessor in the jump start circuit on the first vehicle determines that the values of the two voltages fall within an allowable range of values. The microprocessor then commands that a normally open switch positioned in a circuit between the jump start post and the positive terminal of the battery be closed.  
           [0010]    The microprocessor commands the switch to open based on one or more of many possible conditions, such as receiving input from another vehicle module, detection of a condition indicating the jump start connection has been disengaged, detection of a condition precedent to jump start connection disengagement, detection of reverse polarity connections, detection of a short circuit condition or other possible conditions.  
           [0011]    When a jump start is incorrectly attempted (e.g., due to reverse polarity connections, connection to a higher voltage power source or inadvertent connection of the positive and negative terminals of the same battery (short circuit)), the switch remains open because the measured voltages fall outside an allowable range of values. Similarly, if a short circuit or other condition causes one or more functions to fall outside an allowable range of values during the course of a jump start the microprocessor commands the switch to open.  
           [0012]    In accordance with the present invention a jump start circuit is provided for electrical connection between a positive battery terminal and a jump start post. The jump start circuit includes a switch configured to be coupled between the positive battery terminal and the jump start post. In a preferred embodiment, the switch is biased to a normally open position. The switch has a closed state and an open state, where the switch operates to connect the positive battery terminal to the jump start post when in the closed state and the switch also operates to disconnect the positive battery terminal from the jump start post when in an open state. The jump start circuit further includes a resistor coupled between the positive battery terminal and the jump start post in parallel with the switch. In addition, the jump start circuit also includes a microprocessor that measures voltage at the positive battery terminal and the jump start post, processes the voltage measurements, and commands the switch to close when predetermined conditions are satisfied. The microprocessor commands the switch to open when other predetermined conditions are satisfied.  
           [0013]    An advantage of the present invention is that it provides protection against incorrect polarity connection during vehicle jump starting and battery charging.  
           [0014]    It is yet another advantage of the present invention to provide protection against jump starting with an inappropriate higher voltage battery.  
           [0015]    Yet still another advantage of the present invention is that it enables jump starting with no requirements for additional operator actions over and above the traditional jump start method.  
           [0016]    Another advantage of the present invention is that it provides protection if the battery positive potential is short circuited to ground during vehicle jump starting and battery charging.  
           [0017]    Still another advantage of the present invention is that it provides short circuit protection for a circuit that connects a power source to a load by preventing a switch from closing the circuit when a short circuit condition exists in the circuit between the switch and the load.  
           [0018]    A feature of the present invention is that it can be utilized to provide a cold jump start connection and disconnection, thereby eliminating sparking while connecting and disconnecting jumper cables. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0020]    [0020]FIG. 1 is a circuit diagram of the present invention;  
         [0021]    [0021]FIG. 2 is a circuit diagram showing use of the present invention in a correctly initiated jump start;  
         [0022]    [0022]FIG. 3 is a circuit diagram showing use of the present invention in a jump start initiated with reverse polarity connections;  
         [0023]    [0023]FIG. 4 is a circuit diagram showing use of the present invention in a short circuit to ground condition; and  
         [0024]    [0024]FIG. 5 illustrates a jump start circuit in a DC power supply apparatus. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    The jump start and reverse battery protection circuit of the present invention protects against hazards associated with jump starting a motor vehicle. This is accomplished by providing a normally open switch positioned in the line that connects a jump start post to the positive terminal of a DC power source such as a battery. The switch is controlled by an algorithm stored in a microcontroller that measures, among other things, battery voltage and voltage at the jump start post.  
         [0026]    [0026]FIG. 1 illustrates a preferred embodiment of the jump start and reverse battery protection circuit (jump start circuit)  10  of the present invention. A DC power source such as a battery  12 , having a positive terminal  14  and a ground terminal  16 , normally supplies a voltage between a first line  18  and an electrical ground  20 . The battery  12  provides power to vehicle loads  22  such as lights, generator, radio, air conditioning, and ventilation systems.  
         [0027]    A first (or positive) jump start post  24  is electrically connected to the first line  18  and a second (or negative) jump start post  26  is electrically connected to the electrical ground  20 , to provide jump start posts for the battery  12  should the battery  12  go flat (lose power). Note, a negative jump start post  26  is not required for the present invention to function. A jumper cable can be connected to ground via another approach.  
         [0028]    The jump start circuit  10  in accordance with the present invention is electrically connected between the battery  12  and the positive jump start post  24 . The jump start circuit  10  includes a switch  28  positioned in the first line  18  between the positive jump start post  24  and the battery  12 . The switch  28  may be any kind of switch including an electromechanical device that is actuated by a coil  30  or an electronic switch. In the preferred embodiment, the switch  28  is biased to a normally open position. Alternatively, the switch  28  may be a latching electromechanical switch, a solid state switch, or another switch known to a person of skill in the art.  
         [0029]    The jump start circuit  10  also includes a resistor  32  that is electrically connected between the battery  12  and the first jump start post  24 . The resistor  32  is positioned in a second line  34  such that the resistor  32  is electrically in parallel with the switch  28 . The resistor  32  is sized to enable a voltage to be supplied to the positive jump start post  24 , while providing enough resistance to enable only a small or minimal amount of current to flow through it when a circuit path is provided.  
         [0030]    The battery  12  provides power to the coil  30  via a third line  36 . A fourth line  38  electrically connects the positive jump start post  24  to the coil  30 . A first or battery backflow preventing diode  40  is placed in third line  36  and oriented with the anode coupled toward the battery  12  such that current can flow from the battery  12  to the coil  30 , but current cannot flow from the positive jump start post  24  to the battery  12 . A second or positive jump start post backflow preventing diode  42  is placed in the fourth line  38  and oriented with the anode coupled toward the positive jump start post  24  such that current can flow from the positive jump start post  24  to the coil  30 , but current cannot flow from the battery  12  to the positive jump start post  24 . As a result of the above described electrical connections, voltage is normally provided to the coil  30  from the battery  12 . When the battery  12  is incapable of providing sufficient voltage, voltage provided to the positive jump start post  24  is used to supply voltage to the coil  30 .  
         [0031]    The jump start circuit  10  includes a microprocessor  44  that has capability to monitor voltage levels at the positive jump start post  24  and positive battery terminal  14 , capability to process the voltage measurements, capability to command the switch  28  to close when a first predetermined condition is satisfied, and capability to command the switch  28  to open when a second predetermined condition is satisfied. In addition, the microprocessor  44  may have the capability to receive and process one or more additional inputs. These capabilities are achieved as described below.  
         [0032]    The microprocessor  44  has an output  46  that is coupled to a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) switch driver  48 . The MOSFET switch driver  48  being configured to open and close the switch  28 . It accomplishes this by controlling current flow through the coil  30  via a fifth line  50  that connects the coil  30  to the MOSFET switch driver  48 . The MOSFET switch driver  48  is connected to ground  20 . The microprocessor  44  commands the switch  28  to close by driving an output to an asserted state that turns on the MOSFET switch driver  48  which energizes the switch&#39;s control coil  30  creating sufficient force within the switch  28  to overcome a spring force that holds it open, allowing the switch  28  to close. The microprocessor  44  commands the switch  28  to open by commanding the switch control output to a non-asserted state. This turns off the MOSFET driver  48  causing an interruption in the current flowing to the coil  30 . This current interruption causes the switch  28  to open by mechanical spring force.  
         [0033]    The microprocessor  44  has a jump start post voltage sense analog to digital (A/D) input  52  that is coupled to the positive jump start post  24  to monitor the voltage level at the positive jump start post  24 .  
         [0034]    The microprocessor  44  has a battery voltage sense analog to digital (A/D) input  54  that is coupled to the positive battery terminal  14  to monitor the voltage level at the positive battery terminal  14 . Each of the voltage sense analog to digital inputs  52 , 54  converts an analog voltage to a digital value for processing by the microprocessor.  
         [0035]    The microprocessor  44  has a 5 volt DC input  56  that is coupled to a 5 volt DC voltage regulator  58 . The voltage regulator  58  receives voltage via a sixth line  60 . Voltage is supplied to the sixth line  60  from the battery  12  via the first diode  40  and the third line  36 . Voltage is also supplied to the sixth line  60  from the positive jump start post  24  via the second diode  42  and the fourth line  38 . The sixth line  60  includes a third diode  62 . The sixth line  60  between the third diode  62  and the voltage regulator  58  is connected to ground  20  via a capacitor  64 . The third diode  62  is oriented with the anode toward the battery  12  and positive jump start post  24  such that current can flow from the battery  12  and positive jump start post  24  to the voltage regulator  58  and capacitor  64 , but current cannot flow from the voltage regulator  58  or capacitor  64  to the battery  12 , positive jump start post  24 , or coil  30 . The voltage regulator  58 , capacitor  64 , and third diode  36  are arranged to provide a stable power supply to the microprocessor  44 . Voltage is provided to the voltage regulator  58  and capacitor  64  from the battery  12  and positive jump start post  24 . The arrangement of the first, second, and third diodes,  38 , 40 , 62  prevents the coil  30  from using energy stored in the capacitor  64  that is designated for use by the microprocessor  44 .  
         [0036]    The microprocessor  44  is capable of receiving at least one additional input via a vehicle input  66 . This input can include one or more signals from another vehicle module commanding the switch  28  to open or close. This input can also include a signal indicating a jumper cable (not shown) being unclamped from the jump start post  24 . This input can also include a signal indicating a step being performed preliminary to disconnection of the jump start connection.  
         [0037]    The microprocessor  44  provides an output to turn on the MOSFET switch driver  48  commanding the switch  28  to close when a first predetermined condition is detected by the microprocessor  44 . If another similar voltage battery of either higher or lower charge state or an appropriate battery charger is connected to the jump start posts  24 ,  26  with correct polarity, for a predetermined period of time, such as 2 seconds, a first set of predetermined conditions is satisfied, causing switch  28  to close and initiate a jump start. In this case, the voltage at the positive battery terminal  14  does not equal the voltage at the positive jump start post  24 , the voltage at the positive jump start post  24  is within a predefined range, and the voltage at the positive jump start post  24  is stable for 2 seconds. Although 2 seconds is a preferred period of time to allow for the voltage to stabilize, the time to allow for stabilization can range from 0 to 15 seconds.  
         [0038]    The microprocessor  44  commands the switch  28  to open by commanding the switch control output to a non-asserted state when a second predetermined condition is detected. This turns off the MOSFET switch driver  48 , preventing the voltage from the first jump start post  24  from reaching the battery  12  and vehicle loads  22  via the switch  28 . It also prevents voltage from the battery  12  from reaching the first jump start post  24  via the switch  28 .  
         [0039]    There are many conditions that will cause the switch  28  to open. These conditions include the following conditions from the second set of predetermined conditions that cause the switch  28  to open: the voltage at the positive jump start post  24  or the voltage at the positive battery terminal  14  exceeding a predefined range for a predefined period of time such as 50 milliseconds; a signal being received from another vehicle module indicating the vehicle is moving; or there is insufficient voltage to the coil  30  to hold the switch  28  closed.  
         [0040]    In addition or in the alternative, one or more of the following may also be included in the second set of predetermined conditions that cause the switch  28  to open: the absolute value of the voltage at the positive battery terminal  14  minus the voltage at the positive jump start post  24  exceeding a threshold amount (indicating unacceptable switch contact resistance or excessive current); a signal being received commanding the switch  28  to open; a signal being received indicating that a step being performed preliminary to disconnection of the jump start connection; a signal being received indicating an automatic transmission selector being placed into reverse or drive gear; or a signal being received indicating a manual transmission being placed into gear. Other conditions may also be added as they occur to one of ordinary skill in the art.  
         [0041]    Any suitable electronic circuitry for voltage monitoring and processing may be used in the microprocessor  44 . An exemplary microprocessor  44  is the PIC16F73B microcontroller made by Microchip Corporation. Alternatively, the microprocessor  44  in the jump start circuit of the present invention can be replaced by a logic circuit, state machine or discrete logic gates and voltage comparators that incorporate the same logic algorithm to control the switch  28  actuation through any type of switch driver  48  such as a MOSFET or Bipolar driver.  
         [0042]    A vehicle equipped with a preferred embodiment as shown in FIG. 1 will accept or provide charging current in a jump start with another vehicle not equipped with this invention or with another vehicle equipped with this invention. A vehicle equipped with this invention can also accept charging current from a battery charger.  
         [0043]    [0043]FIG. 2 illustrates one vehicle correctly connected to another vehicle for jump starting, each vehicle having the embodiment of the present invention as depicted in FIG. 1. FIG. 2 depicts a battery  12 , positive battery terminal  14 , ground battery terminal  16 , first (or positive) jump start post  24 , switch  28 , resistor  32 , and second line  34  as described in FIG. 1 on a vehicle  1  with a flat battery. FIG. 2 also depicts a battery  12 ′, positive battery terminal  14 ′, ground battery terminal  16 ′, first (or positive) jump start post  24 ′, switch  28 ′, resistor  32 ′, and second line  34 ′ as described in FIG. 1 on vehicle  2  with a good battery. In addition to the items shown in FIG. 1, FIG. 2 also depicts an internal resistance  100 ,  100 ′ in each battery  12 ,  12 ′. A first jumper cable  102  having an electrical resistance  104  is shown connecting the positive jump start post  24  on vehicle  1  to the positive jump start post  24 ′ on vehicle  2 . A second jumper cable  106  having an electrical resistance  108  is shown connecting the ground battery terminal  16  on vehicle  1  to the ground battery terminal  16 ′ on vehicle  2 . FIG. 2 depicts the switches  28 ,  28 ′ as open. The switches  28 ,  28 ′ would typically be open before the respective microprocessor (not shown) of the present invention on each vehicle determines that predetermined conditions are satisfied for the respective switch  28 ,  28 ′ on each vehicle to close.  
         [0044]    In the example depicted in FIG. 2, the internal battery resistance  100 ,  100 ′ on each vehicle is small or negligible, the resistance  104 ,  108  of each jumper cable is small or negligible, and assuming the resistance values of the resistors  32 ,  32 ′ on each vehicle are approximately equal, then where the voltage V 1  at the positive battery terminal  14  on vehicle 1 equals 10 V and the voltage V 1 ′ at the positive battery terminal  14 ′ on vehicle  2  equals 12 V, then the voltage V 2  at the positive jump start post  24  on vehicle  1  and the voltage V 2 ′ at the positive jump start post  24 ′ on vehicle  2  would each equal approximately 11V. This voltage falls in a range that would typically partially or fully satisfy the set of predetermined conditions necessary to close the switch  28 ,  28 ′ on each vehicle. Note that it is not necessary for the resistance values of the resistors  32 ,  32 ′ to be approximately equal for the present invention to function. Further, there is no need for an additional button to initiate a jump start between two vehicles similarly equipped with this invention.  
         [0045]    [0045]FIG. 3 illustrates one vehicle connected to another vehicle for jump starting with incorrect polarity, each vehicle having the embodiment of the present invention as depicted in FIGS. 1 and 2. FIG. 3 depicts the same items as shown in FIG. 2 except that a first jumper cable  102  having an electrical resistance  104  is shown connecting the positive jump start post  24  on vehicle  1  to the ground battery terminal  16 ′ on vehicle  2 . A second jumper cable  106  having an electrical resistance  108  is shown connecting the ground battery terminal  16  on vehicle  1  to the positive jump start post  24 ′ on vehicle  2 . FIG. 3 depicts switches  28  and  28 ′ as open. Using the same assumption as described above in FIG. 2, then where the voltage V 1  at the positive battery terminal  14  on vehicle  1  equals 10 V and the voltage V 1 ′ at the positive battery terminal  14 ′ on vehicle  2  equals 12 V, then the voltage V 2  at the positive jump start post  24  on vehicle  1  would equal approximately −1V and the voltage V 2 ′ at the positive jump start post  24 ′ on vehicle  2  would equal approximately +1V. Each of these voltages being outside of a range that would satisfy a predetermined condition necessary for the switches  28 ,  28 ′ to close. Further, in the example depicted in FIG. 3, if the resistor  32  is sized at 1000 Ohms, the amount of current flowing through each jumper cable is approximately 0.01 Amp. This is an insufficient amount of current to cause significant electrical arcing. In an unprotected jump start with reverse polarity connections, the amount of current flowing through one or both jumper cables could be several hundred amps for an uncontrolled amount of time. This event can cause significant electrical arcing.  
         [0046]    [0046]FIG. 4 illustrates one vehicle having the embodiment of the present invention as depicted in FIG. 1 in a situation where a short circuit to ground path  120  exists between the positive jump start post  24  and the ground battery terminal  16 . FIG. 4 also depicts the battery  12 , the positive battery terminal  14 , the ground battery terminal  16 , the first (or positive) jump start post  24 , the switch  28 , the resistor  32 , and the second line  34  as depicted in FIG. 1. In this situation, the present invention provides protection because when the short circuit to a ground path  120  exists the voltage V 2  at the positive jump start post  24  is close to zero. This value does not satisfy a predetermined condition that causes the microprocessor (not shown) to command the switch  28  to close.  
         [0047]    Note further, if the incorrect polarity and/or short circuit condition as depicted in FIGS. 3 and 4 respectively occurs after successfully initiating a jump start as shown in FIG. 2, the resulting voltages at the positive battery terminals  14 ,  14 ′ and the positive jump start posts  24 ,  24 ′ satisfy conditions that cause the switches  28 ,  28 ′ to open. This safely limits duration of any large current flow resulting from the reverse battery connection and/or short circuit to a period of time much less than one second, thereby minimizing the likelihood of damage to the vehicle electrical system and possible injury to the operator.  
         [0048]    Note that FIGS.  1 - 4  depict circuit diagrams comprising the jump start circuit  10  and the battery  12 . Physical embodiments of the jump start circuit  10  can be packaged separately from the battery  12 . The jump start circuit can also be entirely or partially packaged in the battery  12  or as part of an integral unit with items such as the battery  12 , positive jump start post  24 , and/or negative jump start post  26 .  
         [0049]    [0049]FIG. 5 illustrates a DC power supply apparatus  200  having a chargeable battery  12  and a jump start circuit  10  electrically connected between the positive end of the battery  12  and the positive jump start post  24 .  
         [0050]    Other ways to package the jump start circuit  10  may also occur to a person of skill in the art.  
         [0051]    This invention has been described with reference to the preferred embodiment and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the invention. For example, one skilled in the art would realize that where signal generating, sending, or receiving is described herein, the intended purpose can also be accomplished by modifying or terminating an existing signal.