Abstract:
An apparatus and method providing for detecting and responding to high voltage electrolysis within an electric vehicle battery enclosure to limit possible excessive thermal condition of the individual battery cells and modules. A microprocessor-implemented response system for high voltage electrolysis in a battery pack an evaluator to monitor, using the microprocessor, a high voltage electrolysis flag indicative of a possible high voltage electrolysis within an enclosure including a plurality of electrically-coupled battery modules storing energy for the battery pack and a coolant distribution system disposed among and electrically isolated from the plurality of battery modules; and a remediation system, coupled to the enclosure and responsive to the possible high voltage electrolysis when the evaluator detects a likelihood of the possible high voltage electrolysis, to decrease risks associated with the possible high voltage electrolysis when operated.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to U.S. patent application Ser. No.: 12/942,465 filed Nov. 9, 2010 and titled “FILL PORT FOR ELECTRIC VEHICLE BATTERY ENCLOSURE,” U.S. patent application Ser. No.: 12/942,501 filed Nov. 9, 2010 and titled “PERFORATION APPARATUS AND METHOD FOR ELECTRIC VEHICLE BATTERY ENCLOSURE,” Attorney Docket Number 20109-7056 (U.S. application Ser. No.: ______ co-filed with the present application and titled “DETECTION OF LOW VOLTAGE ELECTROLYSIS IN A BATTERY PACK,” Attorney Docket Number 20109-7057 (U.S. application Ser. No.: ______ co-filed with the present application and titled “DETECTION OF HIGH VOLTAGE ELECTROLYSIS OF COOLANT IN A BATTERY PACK,” Attorney Docket Number 20109-7058 (U.S. application Ser. No.: ______ co-filed with the present application and titled “RESPONSE TO LOW VOLTAGE ELECTROLYSIS IN A BATTERY PACK,” all the disclosures of which are hereby expressly incorporated by reference thereto in their entireties for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to detection and remediation of potentially hazardous conditions in an electric vehicle battery enclosure, and more particularly but not exclusively, to detecting and correcting high voltage electrolysis within the battery enclosure to limit possible excessive thermal conditions of the individual battery cells and modules. 
         [0003]    Battery packs used with electric vehicles store large amounts of energy in a small space, producing high energy densities. These battery packs include an external housing that is designed for more than just environmental protection and packaging efficiency. The housing also enhances safety and stability, particularly under a range of anticipated abnormal operating conditions. 
         [0004]    The battery packs are designed to provide high levels of safety and stability, yet situations can arise where a portion of a battery pack experiences a local thermal condition which generates significant heat. When the temperature is great enough and sustained, the local thermal condition can transform into a runaway thermal condition affecting wide areas of the battery pack, and sometimes the entire battery pack under certain circumstances. This runaway thermal condition can begin when the local thermal condition approaches the runaway thermal point, which can be about 200° C. 
         [0005]    Battery pack designs include an integrated and isolated cooling system that routes coolant throughout the enclosure. When in good working order, the coolant from the cooling system does not come into contact with the electric potentials protected within. It does happen that sometimes a leak occurs and coolant enters into unintended parts of the enclosure. In certain situations, the coolant may be electrically conductive and can bridge terminals having relatively large potential differences. That bridging may start an electrolysis process in which the coolant is electrolyzed and the coolant will begin to boil when enough energy is conducted into the electrolysis. This boiling can create the local thermal condition that can lead to the runaway thermal condition described above. 
         [0006]    The specific boiling point is dependent upon the characteristics of the coolant. For example, one type of coolant includes a mixture of ethylene-glycol and water which can boil at around 107° C. If enough coolant is in the enclosure and/or enough energy is used in electrolyzing the coolant, the boiling point rises due to chemical changes in the coolant from the localized boiling. In other words, the boiling of the coolant changes the boiling point. (For example, as the percentage of water is reduced in a glycol/water coolant mixture from the boiling, the boiling point increases. Pure ethylene-glycol has a boiling point of about 197° C.) As energy continues to be diverted into the electrolysis, the temperature of the local thermal condition rises and will reach close to the thermal runaway temperature if the electrolysis continues long enough under particular circumstances. Surfaces of the battery pack in contact with liquids at this temperature may initiate the runaway thermal condition. 
         [0007]    The increasingly elevated temperature from the boiling coolant can therefore be great enough, depending upon many factors including the temperature and amount of coolant and location of the electrolysis, to initiate the runaway thermal condition. The chain reaction results from a heating of adjacent cells, which can cause them to overheat and fail, releasing heat that, in turn, propagates throughout the expanding affected area. 
         [0008]    Once the reaction starts, it can continue to spread throughout the battery pack or a portion thereof until overheating cells are sufficiently cooled or the entire battery pack or the portion is consumed. A typical battery pack has a high thermal mass, mostly due to the mass of the cells. A failure of an individual cell provides for a relatively low energy release. Also, surrounding battery cells must be heated to as much as 200° C. or higher before they in turn release energy. These three factors mean that a full reaction that consumes all the cells of a battery pack may take anywhere from tens of minutes to many hours. 
         [0009]    While the risk of the runaway thermal condition can be significant in cases of high-voltage electrolysis, another risk can develop as well. This risk is a consequence of the chemical reaction of electrolysis in which hydrogen gas is generated. Under some conditions, the hydrogen gas released during electrolysis can build-up inside the battery pack and become a possible hazard. 
         [0010]    A conventional solution for a problem of an initiated chain reaction is to simply permit the reaction to run its course once passengers and bystanders are clear of the vehicle. This is because it can be difficult to safely stop the thermal reaction. 
         [0011]    What is needed is an apparatus and method for detecting and responding to high voltage electrolysis within an electric vehicle battery enclosure to limit possible excessive thermal condition of the individual battery cells and modules. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    Disclosed is an apparatus and method providing for detecting and responding to high voltage electrolysis within an electric vehicle battery enclosure to limit possible excessive thermal condition of the individual battery cells and modules. The present invention includes embodiments directed towards detection algorithms and apparatus for promoting the use of voltage, current, humidity, temperature, and pressure sensors for the purpose of detecting high voltage electrolysis. Additionally, the present invention includes response processes and structures to address high-voltage electrolysis. 
         [0013]    Regarding detection, a detection system for high voltage electrolysis in a battery pack, includes an enclosure including a plurality of electrically-coupled battery modules storing energy for the battery pack and a coolant distribution system disposed among and electrically isolated from the plurality of battery modules; a sensor system, coupled to the enclosure, configured to collect a plurality of data from the enclosure; and a controller, coupled to the sensor system, configured to evaluate the plurality of data against one or more predetermined patterns associated with a possible high voltage electrolysis inside the enclosure, with the controller configured to indicate the possible high voltage electrolysis occurring within the enclosure when the plurality of data has a predetermined relationship to the one or more predetermined patterns; wherein the coolant distribution system uses a coolant solution having a mixture of a first liquid and a second liquid in a predetermined ratio to produce a first boiling point for the coolant solution, wherein boiling of the coolant solution changes the predetermined ratio to produce a second boiling point for the coolant solution higher than the first boiling point and wherein the second boiling point is about equal to a temperature sufficient to induce a thermal runaway condition for one or more battery modules of the plurality of battery modules. 
         [0014]    A method for detecting a high voltage electrolysis in a battery pack includes a) collecting a plurality of data from a sensor system measuring data from an enclosure, the enclosure including a plurality of electrically-coupled battery modules storing energy for the battery pack and a coolant distribution system disposed among and electrically isolated from the plurality of battery modules; b) evaluating, using a controller, the plurality of data against one or more predetermined patterns associated with a possible high voltage electrolysis inside the enclosure, with the controller indicating the possible high voltage electrolysis occurring within the enclosure when the plurality of data has a predetermined relationship to the one or more predetermined patterns; wherein the coolant distribution system uses a coolant solution having a mixture of a first liquid and a second liquid in a predetermined ratio to produce a first boiling point for the coolant solution, wherein boiling of the coolant solution changes the predetermined ratio to produce a second boiling point for the coolant solution higher than the first boiling point and wherein the second boiling point is about equal to a temperature sufficient to induce a thermal runaway condition for one or more battery modules of the plurality of battery modules. 
         [0015]    Regarding responding to a detected high voltage electrolysis, a microprocessor-implemented response system for high voltage electrolysis in a battery pack, includes an evaluator to monitor, using the microprocessor, a high voltage electrolysis flag indicative of a possible high voltage electrolysis within an enclosure including a plurality of electrically-coupled battery modules storing energy for the battery pack and a coolant distribution system disposed among and electrically isolated from the plurality of battery modules; and a remediation system, coupled to the enclosure and responsive to the possible high voltage electrolysis when the evaluator detects a likelihood of the possible high voltage electrolysis, to decrease risks associated with the possible high voltage electrolysis when operated. 
         [0016]    A method for responding to a high voltage electrolysis in a battery pack includes: a) monitoring, using a microprocessor, a high voltage electrolysis flag indicative of a possible high voltage electrolysis within an enclosure including both a plurality of electrically-coupled battery modules storing energy for the battery pack and a coolant distribution system disposed among and electrically isolated from the plurality of battery modules; and thereafter b) activating a remediation system, coupled to the enclosure and responsive to the possible high voltage electrolysis when the monitoring detects a likelihood of the possible high voltage electrolysis, to decrease risks associated with the possible high voltage electrolysis. 
         [0017]    One of the important considerations about the preferred embodiments is that all fluids do not present the same risk. Due to the phenomena of increasing boiling point vs. concentration described above, a leak of certain fluids, such as ethylene-glycol that experience increasing boiling point temperature, within a pack is potentially a much more severe and immediate threat to safety of the passengers and vehicle than ingress of another fluid, such as water accumulation due to condensation or external dirty/salty water ingress. In the event high voltage electrolysis of ethylene-glycol is detected (distinguished for example primarily by rapid boiling of the fluid), more immediate and drastic action may be appropriate than would otherwise be taken in the event a different fluid is detected within the pack. For purposes of the present invention, “high” for “high voltage” electrolysis contemplates a voltage potential and associated current just sufficient to initiate boiling of coolant within the enclosure and the particular value depends upon the material being electrolyzed. The value is most often in the range of about  100 - 150  where boiling may begin. 
         [0018]    The related and incorporated patent applications identify low voltage electrolysis (LVE) of fluid (not necessarily just coolant). While those applications are directed to different detection mechanisms, risks, and responses, low voltage electrolysis does not generate the same urgency of potential dangerous thermal conditions. However, the LVE of fluid poses different and generally viewed as lesser risks that does not require the same levels of urgency. For purposes of distinction, low voltage electrolysis of a fluid in general, coolant specifically, and 50/50 ethylene glycol/water solution most specifically, occurs at a voltage dependent upon the material. For the glycol/water solution referenced herein, LVE begins in the range of about 5 Volts. The risks are mostly associated with the generation and potential accumulation of hydrogen gas and is less urgent as described in the incorporated co-pending applications. Because of the comparative risks, the urgency is first to distinguish between HVE and LVE, and for HVE, to elevate the urgency of the response. Response to HVE should be performed as quickly as it is safe to do, with safety informed by preventing/delaying some of the potential risks associated with HVE. LVE may occur over many hours or days without major risk. 
         [0019]    The preferred embodiments include process and apparatus that are useful to detect a high voltage electrolysis reaction and include one or more of: a humidity sensor placed in the likely exhaust path(s) of the pack, or likely location(s) of high voltage electrolysis; a hydrogen sensor placed in the exhaust path of the pack or likely location(s) of HV electrolysis; one or more temperature sensors placed in locations within the pack in which coolant will likely pool and bridge two surfaces with &gt;100V potential difference; should the battery pack be sealed and equipped with relief valves, a pressure sensor within the battery pack and associated algorithm to identify electrolysis; real-time analysis of series element voltage values and histories; current sensor data from a central location in the series chain or multiple locations in addition to a current sensor at one or both terminals; real-time analysis of coolant flow rates, into and out of the battery pack; and an immersion sensor placed within the enclosure. 
         [0020]    The preferred embodiments include process and apparatus that are useful to respond to a high voltage electrolysis reaction: when an internal short spans a large portion of the series chain, the reaction can be stopped by intentionally breaking the chain; under certain circumstances, adding coolant to the pack will significantly increase the amount of time to thermal runaway by increasing the amount of water which must be boiled away; and flooding the pack with water (via an inlet port or other means through the actions of first responders) will dilute or displace the ethylene-glycol, dramatically reducing the electrolysis rate and hazard severity. 
         [0021]    Features/benefits include an ability to detect a high voltage electrolysis and/or remediate conditions or consequences of such a high-voltage electrolysis to limit a possibility of a runaway thermal condition inside a battery enclosure for a high energy battery pack, such as the type used in electric vehicles and similar applications. 
         [0022]    Other features, benefits, and advantages of the present invention will be apparent upon a review of the present disclosure, including the specification, drawings, and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the present invention and, together with the detailed description of the invention, serve to explain the principles of the present invention. 
           [0024]      FIG. 1  illustrates a system of an electric vehicle that includes a propulsion battery that is cooled using a coolant recirculating through an enclosure that houses individual battery modules of the propulsion battery; 
           [0025]      FIG. 2  illustrates a flow diagram for a detection process; and 
           [0026]      FIG. 3  illustrates a flow diagram for a remediation response process. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Embodiments of the present invention provide an apparatus and method providing for detecting and responding to high voltage electrolysis within an electric vehicle battery enclosure to limit possible excessive thermal condition of the individual battery cells and modules. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. 
         [0028]    Various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein. 
         [0029]    In the discussion herein regarding the preferred embodiments, a particular coolant mixture is contemplated to be used—namely a ethylene glycol/water mixture. More generically, the preferred embodiments are configured to detect and respond to a coolant distribution system that uses a coolant solution having a mixture of a first liquid and a second liquid in a predetermined ratio to produce a first boiling point for said coolant solution, wherein boiling of said coolant solution changes said predetermined ratio to produce a second boiling point for said coolant solution higher than said first boiling point and wherein said second boiling point is about equal to a temperature sufficient to induce a thermal runaway condition for one or more battery modules of said plurality of battery modules. 
         [0030]      FIG. 1  illustrates a system  100  of an electric vehicle that includes a propulsion battery  105  that is cooled using a coolant recirculating through an enclosure  110  that houses a plurality of battery modules  115  of propulsion battery  105 . There are many ways that a cooling system is implemented but will typically include a fluid reservoir  120 . The cooling system is monitored and controlled by a controller  125 . In the preferred embodiments, a particular sensing arrangement is implemented as more detailed below. One or more sensors of a sensor system  130  are used to monitor specifically for parameters indicating that the high voltage electrolysis is occurring or that it is likely occurring. 
         [0031]    In general, detection of a high voltage electrolysis reaction includes proper selection, placement, and implementation of the one or more sensors of sensor system  130 . Controller  125  monitors sensor system  130  and applies the proper detection logic based upon the detection mechanism. Upon detection of actual or possible high voltage electrolysis, controller  125  initiates operation of a remediation system  135  to respond appropriately to the detected actual or possible high voltage electrolysis. These are two independent, though related, aspects of the present invention. The first is detection of a high voltage electrolysis event and the second is remediation of such an event. The remediation options, including those available beyond those shown and described herein, do not require detection of the high voltage electrolysis using one of the disclosed systems or processes. Similarly, detection options, including those available beyond those shown and described herein, do not require remediation of the high voltage electrolysis using one of the disclosed systems or processes. 
         [0032]      FIG. 2  and  FIG. 3  further illustrate this independence and relationship.  FIG. 2  illustrates a flow diagram for a detection process  200 . Process  200  includes a high voltage electrolysis (HVE) monitoring step  205 , an HVE test step  210 , and an HVE flag step  215  when the test at step  210  is true. 
         [0033]    Step  205  monitors one or more sensors of sensor system  130  shown in  FIG. 1 . The sensors are implemented to examine specific conditions, parameters, and operational characteristics of system  100  appropriate for the methodology used to detect an HVE of coolant inside a battery enclosure. An result of monitoring data from the sensors is tested at step  210  to determine whether HVE is underway. In some cases it may be an indication of likely HVE or possible HVE. 
         [0034]    Depending upon the nature of the test and the threshold set for initiation of remediation, there may be different responses and urgency levels for initiation of the remediation. In some implementations, there are combinations of sensors providing different indications, not all of which may have the same urgency. There may also be different remediation responses appropriate for different types of sensor indications. Thus the test at step  210  may be binary type indication (e.g., YES or NO as shown), or it may indicate varying probabilities for different possible risks. 
         [0035]    When the test at step  210  is positive to indicate existence, or possible existence, of HVE in system  100 , process  200  sets a flagging mechanism or other status mechanism appropriate for the test performed at step  210 . Some other system or process may monitor the flag and initiate an appropriate response. Flagging a possible HVE condition within enclosure  110  identified in step  215  refers to those general concepts of acknowledging and initiating further action. This is not limited to polling/testing a state of a data flag, but may include interrupt processing and other evaluative systems for responding to a state, variable, signal, or other “flag” that indicates an affirmative test/evaluation at step  210 . The results of step  215  are made available to a response initiation process, such as the process shown in  FIG. 3 . 
         [0036]      FIG. 3  illustrates a flow diagram for a response process  300 . Process  300  includes a monitoring step  305 , a test step  310 , and a remediation initiation step  315 . Step  305  includes an appropriate evaluative process for monitoring a status of an HVE flag, such as may have happened at step  215  of  FIG. 2 . Step  310  tests whether the HVE flag meets a predetermined pattern indicating that HVE is, or may be, occurring. The pattern may be a bit value, a threshold, or other parameter that can be used to selectively test for the HVE condition. 
         [0037]    When the test at step  310  is affirmative that HVE is, or may be, occurring, process  300  executes step  315  to initiate remediation of the detected HVE condition. The initiation response varies but is appropriate for the detected condition and other implementation details. Further details of the sensor(s) and possible remediation response(s) are detailed below. 
         [0038]    I. HVE Detection 
         [0039]    Regarding specifics of representative sensors for sensor system  130 . The preferred embodiments include process and apparatus that are useful to detect HVE within enclosure  110 . 
         [0040]    HUMIDITY—Sensor system  130  may include one or more humidity sensors. Enclosure  110  may be hermetically sealed but will often provide for one or more one-way exhaust ports to allow gas to escape. HVE boils the coolant and results in an increase in humidity. The humidity sensors are placed in the likely exhaust path(s) of enclosure  110 , or likely location(s) of HVE. Analyses of the orientation and arrangement of enclosure  110 , battery modules  115 , and coolant circulation paths, including possible failure modes, provides an indication of these likely locations. In some cases, the design of one or more of these systems is adapted to improve detection using humidity sensors, or to enable fewer sensors to be used. 
         [0041]    One way that humidity sensors may be used to detect HVE is to monitor for a particular pattern indicative of HVE in the particular implementation. For example, should the humidity sensors detect a sustained rise in humidity to  100 % within a short period of time (e.g.,  120  seconds). Other patterns may be appropriate in this or other contexts. 
         [0042]    HYDROGEN GAS—Sensor system  130  may include one or more hydrogen gas sensors. Enclosure  110  may be hermetically sealed but will often provide for one or more one-way exhaust ports to allow gas to escape. Hydrogen gas is produced during HVE. The hydrogen gas sensors are placed in the likely exhaust path(s) of enclosure  110 , or likely location(s) of HVE. Analyses of the orientation and arrangement of enclosure  110 , battery modules  115 , and coolant circulation paths, including possible failure modes, provides an indication of these likely locations. In some cases, the design of one or more of these systems is adapted to improve detection using hydrogen gas sensors, or to enable fewer sensors to be used. 
         [0043]    One way that hydrogen sensors may be used to detect HVE is to monitor for a particular pattern indicative of HVE in the particular implementation. For example, should the hydrogen gas sensors detect any increase in concentration of hydrogen above zero. Other patterns may be appropriate in this or other contexts. 
         [0044]    TEMPERATURE—Sensor system  130  may include one or more temperature sensors. While the circulating coolant within enclosure  110  is isolated from the modules and high-potential voltage surfaces of propulsion battery  105 , sometimes coolant may leak from the coolant system into enclosure  110 . Enclosure  110  may be hermetically sealed and the leaking coolant may begin to pool. When such a pool bridges two potential surfaces having a large potential difference (e.g., &gt;100V), HVE may begin. Initially the pooled and electrolyzing coolant has a boiling point of about 107° C. As the HVE continues, the composition of the pooled electrolyzing coolant changes, and the boiling point rises and can approach 197° C. The temperature sensors are placed within enclosure  110  at any locations where such pooling and bridging may occur. Analyses of the orientation and arrangement of enclosure  110 , battery modules  115 , and coolant circulation paths, including possible failure modes, provides an indication of these likely locations. In some cases, the design of one or more of these systems is adapted to improve detection using temperature sensors, or to enable fewer sensors to be used. 
         [0045]    One way that temperature sensors may be used to detect HVE is to monitor for a particular pattern indicative of HVE in the particular implementation. For example, should the temperature sensors detect a sustained rise in local battery temperature of propulsion battery  105  within a specified period (e.g., 120 seconds) in an area likely to experience HVE to within ±5° C. of the nominal boiling point of the coolant ratio used in the liquid cooling system, followed possibly by a steady increase in temperature in these locations. Other patterns may be appropriate in this or other contexts. 
         [0046]    PRESSURE—Sensor system  130  may include one or more pressure sensors. When enclosure  110  is hermetically sealed to prevent/inhibit ingress/egress of gas, many designs include pressure relief valves. The pressure sensors are placed inside such an enclosure. A particular pattern of gas build-up may indicate HVE. In some cases, the design of one or more of the enclosure, battery modules, and coolant system is adapted to improve detection using pressure sensors, or to enable fewer sensors to be used. 
         [0047]    One way that pressure sensors may be used to detect HVE is to monitor for a particular pattern indicative of HVE in the particular implementation. For example, should the pressure sensors detect a sustained increase in pressure of propulsion battery  105  to the nominal relief pressure within a specified period (e.g., 120 seconds) due to rapid boiling of coolant. Other patterns may be appropriate in this or other contexts. 
         [0048]    VOLTAGE—Sensor system  130  may include one or more voltage sensors. battery modules  115  are coupled in series to store and produce the energy of propulsion battery  105 . Additionally, it is common for the modules themselves to include series-connected batteries or other battery unit. The voltage sensors are placed in enclosure  110  to measure real-time series voltage values of propulsion battery  105 , battery modules  115 , and batteries/battery units as necessary or desired. 
         [0049]    One way that voltage sensors may be used to detect possible HVE is to monitor for a particular pattern indicative of HVE in the particular implementation and may make use of historical voltage levels stored by controller  125 . For example, should the voltage sensors detect a voltage drop of contiguous series elements relative to unaffected series elements and relative to expected voltage drop. This voltage drop is indicative of an internal current loop. Depending on pack geometry, certain series elements are much more likely to be the terminal elements of an electrolysis short circuit than others. For example, in a pack configuration having a plurality of series-connected modules (each module including series connected cells) where every x th  module (e.g., every fifth module) is proximate to other modules at high relative potential, the electrolysis reaction will bridge between these modules. A detection process can be particularly sensitive to contiguous voltage drops bookended by these series elements to more positively identify an internal short as an electrolysis phenomenon. Other patterns may be appropriate in this or other contexts. 
         [0050]    CURRENT—Sensor system  130  may include one or more current sensors. battery modules  115  are coupled in series to store and produce the energy of propulsion battery  105 . Additionally, it is common for the modules themselves to include series-connected batteries or other battery unit. The current sensors are placed in enclosure  110  to measure real-time series current values of propulsion battery  105 , battery modules  115 , and batteries/battery units as necessary or desired. 
         [0051]    One way that current sensors may be used to detect possible HVE is to monitor for a particular pattern indicative of HVE in the particular implementation. For example, should the current sensors detect a reading higher than a reading at the pack terminals it may indicate an internal current loop possibly caused by electrolysis. Other patterns may be appropriate in this or other contexts. 
         [0052]    COOLANT FLOW RATE—Sensor system  130  may include one or more coolant flow rate sensors. The cooling system recirculates coolant through enclosure  110  while isolating the coolant from coming into contact with the energy surfaces of propulsion battery  105 . The coolant flow rate sensors are placed in a coolant flow path into, through, and out of enclosure  110  to measure an entering coolant flow rate and an exiting coolant flow rate. 
         [0053]    One way that coolant flow rate sensors may be used to detect possible HVE is to monitor for a particular pattern indicative of HVE in the particular implementation. For example, should the coolant flow rate sensors detect that more coolant is flowing into enclosure  110  than is flowing out, it may indicate a leak of coolant into enclosure  110  that increases a risk of electrolysis. Other patterns may be appropriate in this or other contexts. 
         [0054]    IMMERSION—Sensor system  130  may include one or more immersion sensors. When enclosure  110  is sealed to prevent/inhibit ingress/egress of fluid, strategically positioned immersion sensors are placed inside such an enclosure. A particular pattern of fluid accumulation may indicate HVE or a condition where HVE may occur. In some cases, the design of one or more of the enclosure, battery modules, and coolant system is adapted to improve detection using immersion sensors, or to enable fewer sensors to be used. 
         [0055]    One way that immersion sensors may be used to detect possible HVE is to monitor for a particular pattern indicative of HVE in the particular implementation. For example, should the immersion sensors detect coolant accumulation within enclosure  110 , a risk of electrolysis is increased. Other patterns may be appropriate in this or other contexts. 
         [0056]    As noted herein, some implementations may use one or more of the sensors disclosed herein. Some of the implementations detect HVE with a high probability of accuracy while others detect possible HVE. Proper selection and use of one or more different types of sensors increases the data from which highly accurate predictions are made. 
         [0057]    II. Remediation Response 
         [0058]    The preferred embodiments include process and apparatus that are useful to respond to a detected or possible high voltage electrolysis reaction. The preferred responses include one or both of stopping the energy driving the HVE and lowering the boiling point of the electrolyzing coolant. 
         [0059]    Open Circuit Response 
         [0060]    Remediation system  135  includes a mechanism to open a short circuit caused by the conducting pool of coolant bridging two surfaces having a large potential difference. When such an internal short spans a large portion of the series chain, the HVE reaction can be stopped by intentionally breaking the chain and stopping the flow of energy into the pooled coolant, for example using overcurrent protection devices, and most preferably using sacrificial overcurrent protection devices such as fuses and the like. While it is unlikely that HVE will itself generate currents large enough to activate internal electrical safety mechanisms such as fuses, controller  125  can interrupt the series chain in one or more locations by opening relays or contactors or intentionally blowing fuses. Once an internal short has been identified, controller  125  intentionally blows one or more internal fuses, such as by activating a “crowbar” device at the pack terminals. 
         [0061]    Coolant Addition 
         [0062]    Remediation system  135  includes a mechanism to add coolant into enclosure  110 . Under certain circumstances, adding coolant to the pack will significantly increase the amount of time to thermal runaway by increasing the amount of water which must be boiled away. Controller  125  activates pumps of the cooling system to push additional coolant through the leak and maintain a low ethylene-glycol/water ratio as the temperature at the HVE location rises. 
         [0063]    Water Addition 
         [0064]    Remediation system  135  includes a mechanism to add water into enclosure  110 . Flooding the pack with water (via an inlet port or other means through the actions of first responders) dilutes and/or displaces the ethylene-glycol, dramatically reducing the electrolysis rate and hazard severity. 
         [0065]    The systems and methods are preferably implemented using a microprocessor executing program instructions from a memory, the instructions causing the apparatus to perform as described herein. 
         [0066]    The system and methods above has been described in general terms as an aid to understanding details of preferred embodiments of the present invention. In the description herein, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of embodiments of the present invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus, systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, or operations are not specifically shown or described in detail to avoid obscuring aspects of embodiments of the present invention. 
         [0067]    Reference throughout this specification to “one embodiment”, “an embodiment”, or “a specific embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention and not necessarily in all embodiments. Thus, respective appearances of the phrases “in one embodiment”, “in an embodiment”, or “in a specific embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics of any specific embodiment of the present invention may be combined in any suitable manner with one or more other embodiments. It is to be understood that other variations and modifications of the embodiments of the present invention described and illustrated herein are possible in light of the teachings herein and are to be considered as part of the spirit and scope of the present invention. 
         [0068]    It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application. 
         [0069]    Additionally, any signal arrows in the drawings/Figures should be considered only as exemplary, and not limiting, unless otherwise specifically noted. Furthermore, the term “or” as used herein is generally intended to mean “and/or” unless otherwise indicated. Combinations of components or steps will also be considered as being noted, where terminology is foreseen as rendering the ability to separate or combine is unclear. 
         [0070]    As used in the description herein and throughout the claims that follow, “a”, “an”, and “the” includes plural references unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
         [0071]    The foregoing description of illustrated embodiments of the present invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the present invention, as those skilled in the relevant art will recognize and appreciate. As indicated, these modifications may be made to the present invention in light of the foregoing description of illustrated embodiments of the present invention and are to be included within the spirit and scope of the present invention. 
         [0072]    Thus, while the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of embodiments of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. Therefore, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the present invention. It is intended that the invention not be limited to the particular terms used in following claims and/or to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include any and all embodiments and equivalents falling within the scope of the appended claims. Thus, the scope of the invention is to be determined solely by the appended claims.