Abstract:
Battery monitors are provided in association with battery stacks to monitor the health of individual batteries. This is important as damaged batteries present a fire risk. Usually the battery stack is assembled and connected to a multipin connector assembled and connected to a multipin connector which engages with a cooperating connector of a battery monitor. The connections have a tolerance so the connections make in a random and uncontrolled order. This disclosure provides ways of ensuring that the power supply connector connects first. This reduces voltage stress in the monitoring circuit and also allows steps to be taken to control inrush currents.

Description:
FIELD 
       [0001]    This disclosure relates to a way of connecting a battery monitoring system to a group of batteries, for example as might be found in a hybrid or battery powered automobile. It is desirable to avoid the battery monitoring system being electrically stressed during the process of connecting it to a battery stack. This disclosure addresses this problem. 
       BACKGROUND 
       [0002]    High voltage batteries are becoming increasingly common. An example of such a use is hybrid and electric vehicles where a plurality of lithium ion batteries are connected together to form a battery stack which looks like a high voltage battery. It is known that the charge and condition of each individual lithium ion battery within the battery stack should be monitored in order to ensure longevity of the battery system, and to take appropriate action if one of the cells get excessively hot. It is particularly important to avoid lithium ion batteries from becoming too hot because if they catch fire then they cannot be put out because combustion of the battery generates sufficient oxygen in order to continue combustion. 
         [0003]    Typically the battery stack may contain a large number of individual cells. For example, the battery pack for a Chevrolet Volt contains 288 cells. Individual cells may be monitored, or small groups of cells may be monitored in order to determine battery performance. 
         [0004]    Typically the battery pack or battery stack is at least 30% charged at the time that the stack is manufactured. Whilst this leads to a lower cell voltage, the cells cannot be further discharged without adversely affecting the lifetime of the battery. A wiring harness makes a plurality of contact points within the battery stack and is generally terminated by a suitable connector, such as a multipin socket. The battery is monitored by a monitoring system which is connected to the multipin socket by way of a multipin plug. When the plug and socket are introduced together for the first time there is no control over which one or ones of the contacts make electrical connection first. Furthermore, the operative connecting the plug and socket may introduce them at an angle, may press one end before the other and so on. Thus the components of the battery monitoring system may be exposed to the plurality of battery voltages within the battery stack in an uncontrolled and random order. This can adversely affect the durability of components in such a monitoring system, or lead to increased cost of such a monitoring system in order to provide additional protection to it to ensure that it can survive any sequence of connections being made to the battery. 
       SUMMARY 
       [0005]    According to a first aspect of this disclosure there is provided a plug and a socket for use with a battery stack and a battery monitor for monitoring batteries within the battery stack. Dimensions, positions or shapes of first and second connection elements within the plug and/or within the socket are adapted to cause the first and second connection elements to make contact with cooperating connection elements prior to the remainder of the connection elements making contact. 
         [0006]    It is thus possible to arrange for the supply rails of a battery monitoring circuit which receives its power from the battery to become energized before any other connections are made. This enables voltages within the battery monitoring circuit to become adequately established in order to prevent voltage stresses developing. 
         [0007]    In accordance with a further aspect of this disclosure there is provided a combination of a battery stack and battery monitor having a plug and socket combination arranged to cause two connections to be placed in current flow and communication before the remainder of the connections of the plug and socket combination. 
         [0008]    Advantageously the two connections are first and second connections which are made to opposing ends, or substantially opposing ends, of the battery stack such that the full stack voltage or substantially the full stack voltage or other voltage is appropriate for the design of the monitoring circuit is delivered as a power supply for the battery monitoring circuit. 
         [0009]    Even when the plug and socket combination are organized such that the power supply connections are made first when the plug and socket are connected, the high voltage across the battery stack may still lead to large initial current flows, known as inrush currents, which may adversely affect components within the battery stack, or could create sparking or arcing that may damage the contacts of the plug and socket. Advantageously inrush current limiting components may be included in the wiring or conduction paths to the first and second connection elements, or at least to one of them. 
         [0010]    Additional current flow paths may be formed once the inrush current has subsided. This can be achieved by providing additional connectors on the plug which make further paths to the opposing terminals of the battery stack. Additionally or alternatively components may be provided for by bypassing the inrush current limiting components, for example by using transistor or mechanical switches to open a shunt path around the inrush current limiting component. 
         [0011]    According to a further aspect of this disclosure there is provided a method of forming a combination of a battery stack and the battery monitor for the battery stack, the method comprising forming a battery stack with a plurality of battery nodes connected to respective contacts of a first connector, and where first and second ones of the contacts are connected to battery nodes substantially at or at opposing ends of the battery stack; forming a battery monitoring circuit connected to a second connector arranged to be connectable with the first connector; and adapting conductor sizes or positions within at least one of the first and second connectors such that the first and second contacts are the first connections to be made when the first and second connectors are brought into connection with each other. 
         [0012]    Adapting the sizes or positions of the connectors may, for example, involve lengthening pins associated with the first and second contacts of a plug, lengthening a conducting sheath or cylinder or repositioning contacts associated with the first and second contacts within a socket or modifying the plug and socket that the action of coupling them together requires the contacts to be introduced in such a way that an order of connection can be guaranteed. As a further alternative, a connection inhibiting component or material may be placed adjacent or over selected conductors within, for example, a plug and socket combination. Thus, for a socket, a thin insulating film may be placed over the majority of the connectors of the socket, with apertures in the film left open for the first and second contacts. The film may be a thin insulating plastic film which is arranged to stretch during an initial phase of insertion of the plug into the socket, but to mechanically fail during the insertion process so as to allow electrical contact to be made. Thus an order of connection can be made by use of an intermediate component, such as a film, rather than modifying the plug and socket as such. 
         [0013]    As a further option a suitably shaped adapter may be used to introduce thin conducting filaments into the sockets corresponding to the first and second connectors such that these filaments reduce the gap within the plug and socket combination between cooperating connectors such that the first and second connectors naturally form the first current flow path. Furthermore, the resistance of the thin filaments can be used to limit inrush currents. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0014]    Embodiments in accordance with this disclosure will now be described, by way of non-limiting example only, with reference to the accompanying figures, in which: 
           [0015]      FIG. 1  is a circuit diagram of a battery stack in combination with a battery monitor; 
           [0016]      FIG. 2  is a cross-section through a connector suitable for connecting the battery stack to the battery monitor; 
           [0017]      FIG. 3  is a circuit diagram showing embodiment of a battery stack and monitoring circuit in accordance with this disclosure; and 
           [0018]      FIG. 4  shows a further embodiment of a battery stack and battery monitor. 
       
    
    
     DESCRIPTION 
       [0019]      FIG. 1  schematically illustrates a battery stack, generally designated  10 , in combination with a battery monitor, generally designated  14 . In order to aid manufacture, the individual cells of the battery stack may be subdivided into a plurality of battery packs designated  20 . 1 ,  20 . 2 ,  20 . 3  and so on to  20 .N, where N represents the number of individual packs within the battery stack. Each battery pack may itself contain a plurality of cells. In the example shown in  FIG. 1 , each battery pack contains six cells, the battery packs can be assumed to be the same, and therefore for brevity only the first battery pack  20 . 1  will be described in detail. 
         [0020]    The first battery pack  20 . 1  has an anode  22  and a cathode  24 . Six cells  30 ,  32 ,  34 ,  36 ,  38  and  40  are arranged in series within the battery pack  20 . 1  with the cathode of one cell connected to the anode of its neighbor. A plurality of intermediate nodes are formed. Thus an intermediate node  50  is formed between the cathode of the first cell  30  and anode of the second cell  32 . Similarly a second node  52  is formed between the cathode of the second cell  32 , and the anode of the third cell  34 . Intermediate nodes  54 ,  56  and  58  are also formed. Connections may be made to the anode and cathode of the first battery pack  20 . 1  and to each of the intermediate nodes  50 ,  52 ,  54 ,  56  and  58  between its cells  30 ,  32 ,  34 ,  36 ,  38  and  40 . Each of these connections may be taken to a respective contact or socket,  70 . 1 ,  70 . 2 ,  70 . 3  and so on within a first connector  80 . Similar connections are made for the other battery packs  20 . 2  to  20 .N. 
         [0021]    Some reduction in the number of connectors can be achieved because the anode of one battery pack is often the cathode of its neighboring battery pack and hence only one rather than two connections are required at these nodes. Similarly, it is also possible if necessary to reduce the number of connections to the intermediate nodes such that rather than each individual cell  30 ,  32 ,  34 , and so on being monitored, pairs of cells or indeed small groups of cells may be monitored rather than individual cells. High current and high voltage connections are made to the battery pack by way of terminals  84  and  86 . 
         [0022]    The battery monitor  14  may comprise a plurality of monitoring integrated circuits, such as the AD7283 by Analog Devices which are able to monitor the battery voltages across a plurality of cells, and to pass this information via a daisy chained serial data bus such that cell voltages for the entire battery stack can be monitored. In the arrangement shown here, each one of the monitoring circuits  90 ,  92  and  94  can monitor the cells of two of the battery packs. Although only three monitoring circuits have been shown for simplicity more or fewer may be provided. Thus the first monitoring circuit  90  monitors the first and second battery packs  20 . 1  and  20 . 2 . The second monitoring circuit  92  can monitor the third and fourth battery packs  20 . 3  and  20 . 4  respectively, and so on. The monitoring circuits  90 ,  92  and  94  are connected to the anode and cathode of the battery pack  10  by way of connectors  70 . 1  and  70 .Q. The battery monitoring circuits  90 ,  92  and  94  are arranged in series such that when a plug  100  of the battery monitoring circuit  14  is connected to the socket  80  of the battery stack  10  the battery stack voltage is applied across the series connected monitoring circuits  90 ,  92  and  94 . The voltage across each of the circuits  90 ,  92 ,  94  is limited by a respective parallel connected Zener diode,  90   a ,  92   a ,  94   a , which is selected such that, in this example, roughly one third of the battery voltage is dropped across each one of the battery monitoring circuits  90 ,  92  and  94 . If four circuits were provided then one quarter of the battery circuit would be dropped across each circuit, if five provided then one fifth across each circuit, and so on. 
         [0023]    This voltage sharing arrangement means that the integrated circuits  90 ,  92 ,  94  are not required to be able to withstand the entirety of the battery pack voltage. This allows them to be made using less expensive semiconductor fabrication processes which are more amenable to the formation of digital logic components, such as analog to digital converters, state machines and so on provided within each one of the circuits  90 ,  92  and  94  in order to enable them to perform their measuring function, to encode the measurements in a suitable form, and then to pass those measurements along a daisy chained data bus indicated  102 . The nodes between individual ones of the battery packs can, if they are at a suitable voltage, be connected to the voltage supply node intermediate adjacent ones of the series connected measuring circuits. This enables the voltage drop across each one of the measuring circuits to be relatively well defined. 
         [0024]    In the example shown in  FIG. 1  the node  26  between the second battery pack  20 . 2  and the third battery pack  20 . 3  is connected by way of the plug and socket combination to a node  91  in the power supply chain between measuring circuits  90  and  92 . Similarly a node  28  between the fourth and fifth battery packs  20 . 4  and  20 . 5  is connected by way of the plug and socket combination to a node  93  between the second and third measuring circuits  92  and  94 . This can be continued as necessary. This ensures that once the plug and socket  100  and  80  are connected, the voltage across each one of the measuring circuits is referenced to specific nodes within the battery stack and the Zener diodes  90   a ,  92   a  and  94   a  need no longer be conducting. 
         [0025]    The plug  100  has pins  110 . 1  to  110 .Q for making connection with the sockets  70 . 1  to  70 .Q within the corresponding socket connector  80 . 
         [0026]    A problem with this multipin plug and socket configuration is that necessarily some tolerance on pin and socket position must be provided in order to ensure that all of the connections can make contact when the plug and socket are fully engaged. This positional tolerance, coupled with limited flexibility of the material making the plug and socket, means that the order in which the connections are made when the plug and socket are connected together is ill defined, and any one of the voltages at any one of the nodes in the battery pack may be the first voltage applied to the monitoring circuit. A close to worst case scenario would be if the first connection to be made is that of connection  70 . 2  corresponding to just one cell short of the high voltage terminal of the battery stack and the next connection is an input pin close the bottom of the battery stack. If, as might be reasonable, all of the measuring circuits  90 ,  92  and  94  are at a ground voltage, then the potential difference at one of the input pins of the measuring circuit  90  could be substantially the entire voltage of the battery stack. This may cause damage to the signal handling components within the circuit  90 . Such a voltage might, for example, punch through the insulation of a field effect transistor used as a sampling switch as part of an analog to digital converter or as a switch within a multiplexor. The circuit can partially be protected by including a low pass filter  150  formed of a resistor and capacitor combination at the input to the circuit  90 , in the hope that this delays the voltage rise at the input whilst other ones of the connections become connected and the power supply connections  70 . 1  and  70 .Q become connected. Whilst provision of such a low pass filter arrangement  150  can protect the integrated circuits, it can bring its own problems because all this extra capacitance takes space, and also needs to be charged when connections are made. The filter  150  in  FIG. 1  is associated with node  50  of the battery stack. Further filters (not shown) are provided in association with nodes  52 ,  54 ,  56  and so on. 
         [0027]    Investigations show that elapsed time from the first contact being made to the last contact being made is normally in the range of 10-20 milliseconds. Whilst this is not long, this should be compared with the Latchup testing performed on automotive parts which generally requires them to survive a current of 100 milliamps for around 5 milliseconds. Thus the connection stress may be in excess of the rated Latchup tolerance of the components. 
         [0028]    The inventor noted that it would be desirable to be able to ensure that the power rail for the monitoring circuits  90 ,  92  and  94  became established before connections were made to the various intermediate nodes  24 ,  26 ,  28 ,  50 ,  52 ,  54 ,  56  and so on. This is because each one of the monitoring circuits  90 ,  92  and  94  can rapidly move to a respective voltage domain where the voltage at its input pins is much closer to voltage at the intermediate nodes, such that surge currents are reduced as these monitoring connections are made. 
         [0029]    This feature, namely establishing the power supply for the monitoring apparatus  14  can be achieved by modifying either one or both of the plug  100  and socket  80  such that the pin and corresponding connector  100 . 1  and  70 . 1  and pin and corresponding connector  110 .Q and  70 .Q interengage with each other before any other of the pin and connector combinations  70 . 2 ,  100 . 2 , to  70 .Q−1,  100 .Q−1. This can be achieved, as shown in  FIG. 2 , by lengthening pins  100 . 1  and  100 .Q compared to any of the other pins, and/or extending the length of the conductive piece of the socket  70 . 1  and  70 .Q compared to any other ones of the sockets. In an alternative approach, the pin and socket lengths may be kept roughly the same, but small additional contact elements could be inserted into socket  70 . 1  and  70 .Q, for example by way of a jig allowing small spring like or filamentous conductors to be inserted into the appropriate sockets. 
         [0030]    Whilst ensuring that the supply rails for the measuring circuit become established first is advantageous in many aspects, it does mean that a large inrush current can flow into the integrated circuits, and to any capacitors associated with them for power supply smoothing. Thus, if the series resistor  120  connecting pin  110 . 1  to the positive supply terminal of the monitoring circuit  90  has a value of, say, 20 ohms and the battery stack comprises 96 cells with a nominal voltage of 3 volts each, then the initial surge current through the 20 ohm resistor  120  could be in the order of 14.4 amps. Thus this requires the use of a surge rated resistor in order to avoid damage, thereby incurring additional cost. It is therefore beneficial to increase the value of the resistor  120  in order to limit the inrush current. Thus if the resistors  120  had a value of 10 kilo-ohm each then the inrush current would be limited to 14.4 milliamps. If the resistors were 1 kilo-ohm then the inrush current would be limited to 144 milliamps. While these larger values of resistances limit the inrush current, they may fail to provide the current flow acquired to power the monitoring circuit correctly. 
         [0031]    The inventor realized that this problem could be solved, as shown in  FIG. 3 , by the inclusion of additional pins within the connector and socket combination such that the initial connection could be made via a relatively high resistance path in order to limit the inrush current, but as the plug and socket were brought fully into engagement, a second power supply path having a lower resistance is opened thereby ensuring that the monitoring circuit is properly powered. 
         [0032]    The arrangement shown in  FIG. 3  is similar to that of  FIG. 1 . Thus six battery packs  20 . 1  to  20 . 6  are connected in series. Only the batteries within the first battery pack have been illustrated, but the other battery packs are to be understood to be like the first battery pack  20 . 1 . The monitoring circuits  90 ,  92  and  94  are provided in series connection as described herein before with respect to  FIG. 1 . 
         [0033]    For diagrammatic simplicity the connections made by the plug  80  and socket  100  combination of  FIG. 1  are designated by nodes  200 . 1  to  200 .Q. 
         [0034]    However now at least one, and preferably two extra connections are provided. These are designated  200 . 0  and  200 .Q+1. 
         [0035]    These extra connections may be provided on the multipin connectors  80  and  100 , and if so these connections are provided with the elongated pins/sockets or other adaptations to ensure that these two connections are the ones that make first. Thus these would be allocated to the endmost connections of the plug and socket shown in  FIG. 2 . 
         [0036]    As an alternative, they could be allocated to an additional two pin connector that is to be connected prior to the multipin connector that carries to connections  200 . 1  to  200 .Q. 
         [0037]    The additional current flow paths via the connections/nodes  200 . 0  and  200 .Q+1 are associated with resistors  210  and  212  which connect to the positive supply of the first measurement circuit  90  and to the negative supply of the last measurement circuit  94 . The resistors are selected to limit the inrush current. Thus rather than being, say around  20  ohm as described with respect to  FIG. 1 , the resistors  210  and  212  may be larger, say 1K, 2K, 5K 10K and so on. 
         [0038]    Using 10K resistors would provide a series resistance of 20K and limit the inrush current to 288/20000=14.4 mA. 
         [0039]    The inrush current limiting resistors  210  and  212  still allow the internal voltages to become established before the measurement connections  200 . 1  to  200 .Q are made. It can also be seen that the current limiting resistors get bypassed when the connections  200 . 1  and  200 .Q are made. 
         [0040]    As a further alternative, and returning to the circuit configuration of  FIG. 1 , the resistors  120  and  122  in series with the supply terminals of the series connected measurement circuits may be placed in series with a further component such as an additional resistor and transistor or switch that can short the additional resistor out; or with a series connected FET that can act as a controllable resistance. Thus the effective resistance could start high, and then be controlled to reduce. This may be used to avoid forming extra connections at the connectors (i.e. the plug and socket). Such an arrangement is shown in  FIG. 4 . 
         [0041]    Here resistor  120  is replaced by resistors  120 a and  120   b . Resistor  120   a  has a low value, say in the order of 10 to 50 ohms whereas resistor  120   b  is significantly larger, possibly several kilo-ohms. 
         [0042]    A transistor  250  is provided in parallel with resistor  120   b , and may initially be in a high impedance state and become switched to a low impedance state in response to a control signal applied to its gate G. The control signal may be generated by a RC timer. The transistor may be P-type or N-type depending on the circuit designer&#39;s preference. 
         [0043]    Additionally or alternatively inductors may be included in the power supply path to limit inrush currents. 
         [0044]    An alternative approach to extending the metal connective part of the contacts within, for example, the socket is to have all the contacts substantially the same length, but introduce an insulator which prevents contact being made during an initial stage of insertion of the plug into the socket for selected ones of the contacts. This may be achieved by placing a thin non-conducting film over the majority of the surface of the socket, leaving only selected apertures of the socket uncovered, such as those corresponding to connectors  70 . 1  and  70 .Q. Thus the film inhibits connection for most of the connectors during the insertion process, until such time as the pins of the plug overstretch the film and rupture it, thereby allowing the pins to make contact with the metallic portions of the socket. 
         [0045]    It is thus possible to protect the monitoring circuit from damage due to the possibility of any make order connection by the plug and socket combination used to connect the monitoring circuit to the battery stack. 
         [0046]    Several embodiments of the invention are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations of the invention are covered by the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.