Abstract:
Systems and methods for a battery separator system integrating a DC contactor (solenoid) plus control electronics and all required interconnects into a single sealed enclosure for the purpose of selectively connecting and disconnecting a main and auxiliary battery under predetermined conditions. Battery monitoring and control includes programmable time delays that immunize the system from reacting to transient conditions as well as monitoring for and correcting unintended states and disabling operation when voltage conditions fall outside of prescribed limits.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a systems and methods for selectively connecting or separating a pair of batteries depending upon the state of the individual batteries and the charging system so as to maintain and preserve best condition of those batteries. 
         [0002]    There are many vehicle applications in which there is a battery (primary) used for starting the vehicle and supporting its various electrical systems. There is also a system for charging that battery whenever the vehicle engine is operating. There are furthermore many applications for an additional (auxiliary) battery or bank of batteries to be used to support auxiliary equipment. Such equipment could be living quarters equipment on a recreational vehicle, a CPAP machine in the sleeper cab of an over the road truck or any other variety of apparatus that require electrical power. The electrical loads that draw power from the auxiliary battery may operate without distinction for whether the vehicle engine and charging system are operating or not. It is common to charge the auxiliary batteries from the same charging system that charges the vehicle primary battery. It is important to prevent the electrical loads that draw power from the auxiliary battery from depleting the vehicle&#39;s primary battery to the extent that primary vehicle functions cannot be supported, such as starting the vehicle. For this reason it is necessary to have a means to selectively connect and separate the primary and auxiliary batteries depending upon the condition of those batteries and the status of the vehicles charging system. 
         [0003]    Additionally, as parts on a truck are subject to all the weather and bad roads that are experienced by the truck, damage and premature wear can be experienced by a contactor in control of joining and separating the batteries. Furthermore, contacting two direct current power sources creates a potential for a large current to spike across the contactor which could lead to premature wear of the internal components of the contactor as well. Therefore, the industry could benefit from a contactor assembly that is better protected from external influences. 
       SUMMARY OF THE INVENTION 
       [0004]    Provided is a system and methods for separating batteries. The invention being directed to providing a contactor that is better protected from outside influences such as weather and road conditions and also from potentially large current spikes. 
         [0005]    The present invention provides that the coil of the contactor is controlled by a bi-polar electronic driver with current limiting functionality. The design of the coil provides reliable latch and unlatch at voltages associated with highly discharged or damaged batteries and elevated ambient temperatures (that raise coil resistance) and furthermore with the electronic current limiting set to prevent the coil from generating Amp Turn levels sufficient to demagnetize the permanent magnet under conditions of high battery voltage and low ambient conditions (that lower coil resistance). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of a prior art contactor assembly. 
           [0007]      FIG. 2  is a perspective view of a contactor assembly according to the present invention. 
           [0008]      FIG. 3  is a cross-section view of the contactor assembly in  FIG. 1  along line  3 - 3 . 
           [0009]      FIG. 4  is a cross-section view of the contactor assembly in  FIG. 3  along line  4 - 4 . 
           [0010]      FIG. 5  is an operational flow diagram of a monitoring method according to the present invention. 
           [0011]      FIG. 6  is a diagram illustrating an intended use of a contactor assembly according to the present invention in a potential system. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structures. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 
         [0013]      FIG. 1  illustrates a prior art contactor assembly  10 . The prior art contactor assembly consists of a direct current (DC) contactor  12  electrically connected to a control circuit board (hidden) covered in electrical potting material  14  in an enclosure  16 . In other prior art embodiments (not shown) there may be no enclosure, with the control circuit board encapsulated within a block of rigid potting material such as epoxy. 
         [0014]    The prior art contactor assembly  10  is used primarily for joining and separating a Main battery  30  (see  FIG. 6 ) and an Auxiliary battery  40  (see  FIG. 6 ). The DC contactor  12  has a Main, or first, battery terminal  22  and an Auxiliary, or second, battery terminal  24 , each connected to the control circuit board (hidden) via bus bars  18  or wires (not shown). Also exposed are the DC contactor coil connections  20  between the control circuit board (hidden) within the enclosure  16  and the solenoid assembly (hidden) within the contactor  12 . 
         [0015]    Although, the control circuit board (hidden) is shielded from most environmental events including corrosive elements, moisture, and liquid ingress over the entire life of the product by the electrical potting material  14 , the bus bars  18  and the DC contactor coil connections  20  that electrically and mechanically join the control circuit board (hidden) to the DC contactor  12  are exposed to the environment and prone to corrosion or physical damage. 
         [0016]    Corrosion of the bus bars  18  creates poor electrical sense interconnects and unpredictable voltage drops that affect the logic and control circuit&#39;s ability to accurately measure the voltages of the Main and Auxiliary batteries  30 ,  40  (see  FIG. 6 ). When the accuracy of the voltage measurements are compromised, the prior art contactor assembly  10  may react to the compromised data and actuate the DC contactor  12  to connect and disconnect the Main and Auxiliary batteries  30 ,  40  at voltage levels different than the designated voltage values. Depending on the severity of this corrosion and degradation of the electrical connection the prior art contactor assembly  10  may completely fail to open the circuit between the Main and Auxiliary batteries  30 ,  40  rendering the prior art contactor assembly  10  absolutely unable to protect the Main battery  30  from becoming discharged below a preset voltage value. Alternatively, it might fail to charge the auxiliary battery. 
         [0017]    Additionally, over the life of the product, corrosion of the bus bars  18  along with thermal aging and potting material fatigue creates voids (not shown) in the potting material  14  around the junctions  26  of the potting material  14  and the bus bars  18 . The voids (not shown) become the primary path for environmental ingress to the control circuit board (hidden) which creates unpredictable device operation, complete device failure, or even provide low voltage ignition sources from unintended ground paths. 
         [0018]    In addition to corrosion, the bus bars  18  are continuously exposed at battery potential and present a constant threat of being bridged by a conductive object to each other or chassis ground. Further, the exposed DC contactor coil connections  20  present a constant threat of being shorted to ground or disconnected. 
         [0019]      FIGS. 2 and 3  illustrate a contactor assembly  100  according to the present invention. The contactor assembly  100  preferably comprises a housing  102 , a first stud  112 , a second stud  116 , a solenoid assembly  120  (referred to occasionally as “contactor”), and a printed circuit board (PCB)  172 . 
         [0020]    The solenoid assembly  120  is preferably a bi-stable magnetic latching solenoid. The solenoid assembly  120  preferably comprises a coil assembly  122 , a plunger assembly  130 , a crossbar  144 , an end cap  146 , a pole washer  150 , and a pair of half shells  154 . The coil assembly  122  comprises a bobbin  124 , a pair of coil terminals  126  electrically connected to the bobbin  124 , and magnet wire  128  wrapped around the bobbin  124 . The bobbin  124  is at least partially positioned within the end cap  146 . The pair of half shells  154  are preferably positioned around the outside of the coil assembly  122  and in direct contact with the pole washer  150  and the end cap  146  to complete the magnetic circuit; however, this relationship is not visible in the cross-sectional view of  FIG. 3 . 
         [0021]    The plunger assembly  130  preferably comprises a first plunger part  132 , a second plunger part  134 , a magnet  138 , and a cap screw  140 . The magnet  138  is preferably a rare earth permanent ring magnet (NdFeB, Grade N42M) and is sandwiched between the first plunger part  132  and the second plunger part  134 . The first and second plunger parts  132 ,  134  preferably comprise low carbon steel and are physically joined by the cap screw  140 , which is preferably made from non-magnetic stainless steel. The plunger assembly  130  is located mostly within the bobbin  124  with the second plunger part  134  closest to the end cap  146 . 
         [0022]    A plunger shaft  136  preferably extends outward from the first plunger part  132  and through the pole washer  150  and a seal spring  156  and terminates with attachment to a head spring  158 . The crossbar  144  is mounted to the plunger shaft  136  between a retaining clip  196  and seal spring  156   
         [0023]    Contacts  160  are placed on the crossbar  144  and the triangular heads  114 ,  118  of the first and second studs  112 ,  116 , respectively. The contacts  160  preferably comprise silver cad oxide chips and are silver-brazed onto the stud heads  114 ,  118  and the crossbar  144 . The studs  112 ,  116  are rotated such that the center to center distance  162  between contacts  160  is minimized. This in turn lowers the material usage in the crossbar  144  and thereby reduces the crossbar&#39;s  144  total mass. The silver cad oxide material is able to handle high closing currents, which are expected in an application of connecting two batteries charged to different levels. However, other materials exhibiting the same characteristics are also contemplated. 
         [0024]    It should be noted that a through-hole  152  in the pole washer  150  is preferably sized large enough for the plunger shaft  136  to pass through without excessive loss of force due to non-force producing flux leakage. 
         [0025]    A coil o-ring  164  is positioned between the bobbin  124  and the pole washer  150  and is compressed as needed to take up any dimensional tolerance stack ups and also to minimize movement from vibration. The o-ring  164  also biases and maintains the bobbin  124  to its proper position in the solenoid assembly  120 . 
         [0026]    The cap screw  140  has a cap screw head  142  which extends outward from the first plunger part  132 . When a positive coil pulse is applied, the plunger assembly  130  will move towards the pole washer  150  (contacts closed). When a negative coil pulse is applied, the plunger assembly  130  will move towards the end cap  146  (contacts open) until the cap screw head  142  makes contact with the end cap  146  and defines a gap  166  between the second plunger part  134  and the end cap  146 . The size of the gap  166  between the cap screw head  142  and the end cap  146  determines the force required to open the solenoid assembly  120  and also affects the coil current required to close the solenoid assembly  120 . 
         [0027]    During the closing operation, the coil assembly  122  and the magnet  138  work together to overcome the head spring  158  and the seal spring  156 . Inversely, during the opening operation, the coil assembly  122  must cancel out the magnet  138  enough for the head spring  158  and the seal spring  156  to overcome the magnet  138 . 
         [0028]    The solenoid assembly  120  is secured inside the housing  102  with a solenoid retainer  168 . An o-ring  170  is positioned between the end cap  146  and the solenoid retainer  168 ; however, this relationship is not visible in the cross-sectional view provided in  FIG. 3 . The o-ring  170  takes up any dimensional tolerance stack ups and may also act as a shock absorber when the end cap  146  is impacted by the plunger assembly  130  at each opening of the solenoid assembly  120 . The o-ring  170  also encourages an intimate contact between the end cap  146  and the edges of the half shells  154  so as to minimize the magnetic reluctance at those interfaces. The solenoid retainer  168  may also assist in providing proper alignment of the electrical connections of a first stud-to-PCB terminal  174  and a second stud-to-PCB terminal (hidden) between the first and second studs  112 ,  116  and the printed circuit board  172  as well as the coil terminals  126  to the PCB  172  (discussed below). 
         [0029]    The PCB  172  is preferably located inside the housing  102  and below the solenoid assembly  120  as oriented in  FIG. 3 . The PCB  172  is preferably conformal coated or over-molded and secured by a plurality of screws  198 , preferably PLASTITE® screws. 
         [0030]    The first stud-to-PCB terminal  174  and the second stud-to-PCB terminal (hidden) electrically connect the first stud  112  and the second stud  116  to the PCB  172 , respectively. The first stud-to-PCB terminal  174  and the second stud-to-PCB terminal (hidden) are voltage sense lines linking the high current first and second studs  112 ,  116  to the PCB  172 . Both the first stud-to-PCB terminal  174  and the second stud-to-PCB terminal (hidden) may comprise a bend  176  therein. The bend  176  allows for thermal expansion and contraction, without stressing the solder joint connecting the first stud-to-PCB terminal  174  and the second stud-To-PCB terminal (hidden) to the PCB  172 . 
         [0031]    The PCB  172  is also preferably electrically connected to the solenoid assembly  120  through the pair of coil terminals  126 . 
         [0032]    The location of the PCB  172  inside the housing  102  allows the PCB  172  to monitor battery voltage (batteries are connected to the high current studs  112 ,  116 ) without requiring any additional connections. Limiting the number of connections to the batteries  30 ,  40  also limits the opportunities for failure, short circuits, etc. 
         [0033]    The housing  102  comprises a base  104  with a sealing lip  108  around a perimeter  106 . A mounting plate gasket  186  is compressed between the sealing lip  108  and a mounting plate  182 . The mounting plate  182  is preferably affixed to the housing  102  by rivets  188  and is of a thickness to provide adequate stiffness between the rivets  188 . The mounting plate  182  may include machined counter bored recesses  184  for the rivets  188  to be recessed within. 
         [0034]    Additionally or alternatively, any number of LED indicators  190  and lead wires for I/O ports (not shown) and the ground  192  may be connected to the PCB  172  inside the housing  102  but visible or accessible outside the housing  102 , shown here in the base  104 . For example, an LED  190  may signal whether the solenoid assembly  120  is closed by remaining “on-solid” and the LED  190  may be “on-blinking” when the solenoid assembly  120  is open. Additionally or alternatively, LEDs  190  may be used to signal other operational conditions and/or error message. Furthermore, additional leads (not shown) may be used for data transfer (e.g., updates or uploading operational data) or real-time system health monitoring. Multiple configurations of the contactor assembly  100  are possible. The prescribed number of lead wires (not shown) and/or LEDs  190  can be determined at the time of order and may be punched or drilled into the base  104  of the housing  102  at that time. Molded pockets  110  in the base  104  are preferably sized to accept standard cable seals  194  (see  FIG. 4 ). 
         [0035]    In operation a microprocessor (not shown) on the PCB  172  will preferably be continuously monitoring voltage values of the main and auxiliary batteries  30 ,  40  and the current state of the solenoid assembly  120  (i.e., open or closed). The voltage values are preferably taken at the studs  112 ,  116 . The voltage at the studs  112 ,  116  will differ from the voltage at each battery  30 ,  40  by a factor that is the product of current flow between batteries  30 ,  40  in amps multiplied by the resistance of the respective cable (not shown) connecting the batteries  30 ,  40  to their respective stud  112 ,  116 . In all but the first minute or two after the contactor closes, the inter-battery current is normally of a magnitude such that the voltage drop across the cables connecting the batteries  30 ,  40  to the studs  112 ,  116  is not of great significance in determining the correct state for the solenoid assembly  120 . To limit the need for a second “Vsense” connection at each battery  30 ,  40  and to avoid reacting to high cable voltage drop during the first seconds to minute or so after contactor operation, time delays are preferably introduced in the cycle of operation. 
         [0036]    The ability to sense the independent voltages of the Main and Auxiliary batteries  30 ,  40  at the studs  112 ,  116  when the solenoid assembly  120  is open and millivolt difference between the Main and Auxiliary batteries  30 ,  40  at the studs  112 ,  116  when the solenoid assembly  120  is closed allows the microprocessor to use logic to verify if the solenoid assembly  120  is in the correct open or closed state. By nature, a bi-stable magnetic contactor does not require any power to stay in the contacts open or contacts closed state; the microprocessor provides a pulse of energy to actuate the solenoid assembly  10  and toggles the solenoid assembly  120  open or closed depending on voltage inputs measured at the studs  112 ,  116 . The contactor assembly  100  is preferably designed to open and close the solenoid assembly  120  under specified maximum ambient and minimum voltage conditions. Without further intervention, permanent degradation of the magnet  138  could occur under certain anticipated combinations of voltage and temperature. To protect against this, the microprocessor (not shown) incorporates current limiting procedures. 
         [0037]    It is possible that external influence such as shock or internal solenoid malfunction could create a situation in which the voltage values indicate to the microprocessor that the solenoid assembly  120  should be in one of an open or a closed state when in actuality the solenoid assembly  120  is in the opposite state. This failure will continue to cause unintended operation until corrected. 
         [0038]    If the microprocessor determines the solenoid assembly  120  is in the incorrect state, the solenoid assembly  120  will be pulsed a predetermined number of times, preferably up to three times, in an attempt to restore the proper state. If the pulsing does not restore the solenoid assembly  120  to the proper state, the microprocessor will set an error condition. Once in the error condition the microprocessor will recheck the state of the solenoid assembly  120  at predetermined intervals, preferably about every two minutes. 
         [0039]    It is preferable that the solenoid assembly  120  be open and remains open if the Main battery  30  is below a first voltage limit. If the solenoid assembly  120  is closed and voltage of the Main battery  30  falls below the first voltage limit, the solenoid assembly  120  is opened, given that other requirements are met, so that the loads on the auxiliary side of the system cannot draw down the Main battery  30 . 
         [0040]    The solenoid assembly  120  will be closed and remain closed if the voltage of the Main battery  30  is at or above a predetermined voltage limit sufficient to charge both batteries, barring the contactor assembly  100  experiencing any of the limitations set forth herein which would prevent the changing of state from open to closed. 
         [0041]    Additionally or alternatively, instead of immediately toggling the solenoid assembly  120  “on” (contacts closed) and “off” (contacts open) upon reaching the contacts close voltage “V CON ” and the contacts open voltage “V DCON ” thresholds, the microprocessor will wait a predetermined duration of time (the duration of time could be set or changed according to operational demands and requirements. 
         [0042]    If the measured Main battery voltage does not satisfy the requirements at any time during the “ON Delay/OFF Delay,” the time delay will restart. This ensures that the solenoid assembly  120  will not respond to transient conditions. For field diagnosis this means the appropriate V CON  and V DCON  voltage levels must be maintained constantly for a minimum of the predetermined “On Delay/OFF Delay” duration to induce a change of state. 
       High Voltage Lockout: 
       [0043]    There is a considerable lack of general understanding across the overall battery separator market as to what actually happens with respect to inrush current when two batteries at different potential are connected suddenly by an electromechanical device. The contacts  160  of the contactor assembly  100  are subject to a short duration but extremely high magnitude current spike that is only limited by the inherent impedance produced by the cable and other components in the circuit. Typical battery separators provide warnings that the device may be damaged at higher than rated operational voltages but do not provide safeguards to prevent this from happening. Higher than rated system voltage does not only risk damaging electronic components; these high voltage conditions may be passed through the logic and control circuit to the coil of the DC contactor where the coil windings and solenoid rare earth permanent magnet may be damaged. Higher than rated system voltages on only the Main battery stud  112  creates a greater potential differential between the Main and Auxiliary batteries studs  112 ,  116  that directly creates higher magnitude inrush currents that are likely to damage, weld, or prematurely age the contacts  160 . 
         [0044]    According to the present invention, the potential for damage from higher than rated system voltages may be reduced by continuously monitoring the voltage values at the studs  112 ,  116  and applying logic to determine if the system voltage has exceeded a predetermined upper limit programmed in the microprocessor (for example, 17 VDC). If voltage exceeds the predetermined limit on the Main battery stud  112  the contactor assembly  100  will remain in its current contacts open or contacts closed state and continue to monitor conditions until measurements indicate the voltage is within the predetermined limits. This circumstance will also set an error condition (for example, turning the LED  190  to “off-solid”) to notify the operator that there is a potentially hazardous system fault. 
       Low Voltage Lockout: 
       [0045]    Similar to the High voltage lockout discussed above; low voltage measured at the Main battery stud  112  will create conditions that endanger proper operation of the contactor assembly  100  as well. Lower than rated system voltage may be passed through the logic and control circuit to the coil assembly  122  and the coil assembly  122  will not be given enough power to properly change the state of the solenoid assembly  122 . 
         [0046]    Lower than rated system voltage on only the Main battery stud  112  also likely indicates a damaged Main battery  30  and creates a greater potential differential between the Main and Auxiliary batteries  30 ,  40 . The greater potential between batteries  30 ,  40  directly creates higher magnitude inrush currents that are likely to damage, weld, or prematurely age the contacts  160 . 
         [0047]    According to the present invention, the potential for damage from lower than rated system voltages may be reduced by continuously monitoring the Main and Auxiliary battery studs  112 ,  116  and applying logic to determine if the system voltage has dropped below a predetermined lower limit programmed in the microprocessor (for example, 9.8 VDC). If voltage is at or below the predetermined limit on the Main battery stud  112 , the contactor assembly  100  will remain in its current contacts open or contacts closed state and continue to monitor conditions until measurements indicate the voltage is within the predetermined limits. This circumstance will set an error condition (for example, turning the LED  190  to “off-solid”) to notify the operator that there is a potentially hazardous system fault. 
         [0048]      FIG. 5  illustrates an example of the monitoring process and situationally switching the contactor  120  under certain conditions. As shown, the Main and Auxiliary batteries are continually monitored  1000 . The state of the contactor is determined  1002 . If the contractor is in the correct state, continue to monitor  1004 . If the contactor is in the incorrect state, it is determined whether the voltages of the Main and Auxiliary batteries are in a safe range to pulse the contactor  1006 . If so, the contactor is pulsed up to a predetermined amount of times until the state is corrected  1008 . If after pulsing the contactor is still in the incorrect state an error condition is set and the contactor continues to be monitored  1010 . If, after a predetermined amount of time has passed, the state is still incorrect, the pulsing procedure may be repeated  1012 . If initially the Main and Auxiliary batteries are not in a safe range for pulsing the contactor, an error condition is set and monitoring of the state condition and the voltages of the Main and Auxiliary batteries is continued  1014 . 
         [0049]    Additionally or alternatively, it is determined whether the voltage measurements require the opening or closing of the contactor  1016 . If not, continue to monitor the voltage values  1018 . If so, it is determined whether the voltages of the main and auxiliary battery are in a safe voltage range to open or close the contactor  1020 . If the voltages are in the safe range, continue to monitor for a predetermined amount of time  1022 . If the measurements remain consistent with switching the contactor, switch the state of the contactor  1024 . If the voltages are not within the safe range, an error condition is set and monitoring continues  1026 . 
         [0050]      FIG. 6  illustrates a potential intended use of the contactor assembly  100  according to the present invention. As shown here, the contactor assembly  100  is placed between the Main battery  30  and the Auxiliary battery  40 , whereby the Auxiliary battery  40  is also directly electrically connected to a Continuous Positive Airway Pressure (CPAP) machine  50 . 
         [0051]    The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.