Abstract:
An alternator testing method and system that provides high resolution signals and stable loads during alternator tests. The method according to the present invention comprises the steps of: coupling a load to the alternator, and evaluating the operation of the alternator based on parameters collected only after the load has been coupled to the alternator for a first predetermined period of time. The method may further include a step of detecting the speed of the alternator or motor driving it, and in one aspect, the load is applied to the alternator only after motor speed or alternator speed reaches a predetermined level. The load may be automatically decoupled from the alternator after the load has been coupled to the alternator for a second predetermined period of time.

Description:
RELATED APPLICATION  
       [0001]    The present application claims the benefit of priority from U.S. Provisional Patent Application Serial No. 60/214,254, entitled “AUTOMATIC ELECTRICAL SYSTEM TESTING APPARATUS AND METHODS,” filed Jun. 26, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to testing alternators, and more specifically, to an alternator testing method and system controlling the coupling of a load to the alternator during the test.  
         BACKGROUND OF THE INVENTION  
         [0003]    An alternator converts mechanical motions into alternating current (AC) by electromagnetic induction. The alternating current is then passed through a rectifier assembly, such as a full-wave rectifier bridge comprising diodes, to convert the AC into DC to power other electrical systems. For example, an alternator in an automotive vehicle is driven by the engine to power the vehicle&#39;s electrical system, such as for charging the battery, powering headlights, and the like. The alternator output, however, is not perfectly smooth. The waveform of an alternator output is similar to a low-magnitude ripple riding on a DC component.  
           [0004]    Alternator tests are conducted when alternators are under load, i.e., a load is coupled to the output terminals of the alternator to draw current therefrom. Alternator testers often have a set of probes or wires to couple to the output terminals of the alternator for detecting parameters of the alternator output, such as the output voltage, the ripple amplitude, the average current of the output, and so on. Usually, handheld alternator testers for testing vehicle alternators use a load capable of drawing up to 10 amperes of current. For alternators used in an automotive vehicle, the test of alternator under load may be conducted by turning on electrical accessories powered by the alternator, such as the head lights, radio, air conditioner, and the like.  
           [0005]    Several problems may occur when testing alternators. First, since the ripple component of the alternator output is a small signal, the ripple waveform is subject to noise interference and may be difficult to observe. Second, when the load is coupled to the alternator, the alternator output waveform may not respond to, or does not always respond to the change of load immediately. Accordingly, the alternator output is unstable until a certain period of time has elapsed. If the tester determines alternator operation based on parameters collected from the unstable waveform, error in test results will occur. Third, using electrical accessories on a vehicle as a load draws inconsistent currents from the alternator. The alternator output level therefore tends to fluctuate, which makes precise test difficult. In addition, the load used in alternator tests generates a lot of heat, which causes safety concerns.  
         SUMMARY OF THE INVENTION  
         [0006]    Accordingly, there exists a need for accurately determining the health of an alternator. There is another need to provide a stable load for use in alternator tests. Still another exists for evaluating the health of an alternator based on a stable alternator output. An additional need exists for providing high resolution signals for testing an alternator. There is still another need for dissipating heat generated by the load during the alternator test.  
           [0007]    These and other needs are addressed by the present invention. The invention is an alternator testing method and system that provides high resolution signals and stable loads during alternator tests. According to one aspect of the invention, evaluation of the alternator operation is based on parameters collected after the load is coupled to the alternator for a predetermined period of time, so that the parameters reflect a stable alternator output. In another aspect, the load is coupled to the alternator for a very short period of time to reduce the heat generated during the test. In still another aspect, the load is housed in a handheld housing and capable of drawing large currents, for example, 50 amperes, from the alternator in order to produce better signal resolution.  
           [0008]    The method according to the present invention comprises the steps of: coupling a load to the alternator, evaluating the operation of the alternator based on parameters collected after the load has been coupled to the alternator for a first predetermined period of time.  
           [0009]    In one aspect of the invention, the alternator may be driven by a motor, such as an engine powered by fossil fuels. According to one embodiment of the invention, the method further includes a step of detecting motor speed or alternator speed. The load is applied to the alternator only after the motor speed or alternator speed reaches a predetermined level. In another aspect of the invention, the load is decoupled from the alternator after the load has been coupled to the alternator for a predetermined period of time.  
           [0010]    The system of the present invention comprises a load, and a terminal for receiving an alternator output signal representative of an alternator characteristic, and a switch device for selectively coupling the load to the alternator. A controller is configured for determining the characteristics of the alternator output signal and for generating a first switch operation signal to control the switch device to couple the load to the alternator. The controller determines the characteristics of the alternator output signal based on parameters collected after the load has been coupled to the alternator for a predetermined period of time.  
           [0011]    According to one aspect of the invention, the system is contained in a housing having a size suitable to be held in one&#39;s hand. The system may further include a cooling device, such as a fan, for dissipating the heat generated by the load. The controller generates a second switch operation signal to control the switch device to decouple the load from the alternator after the load has been coupled to the alternator for a predetermined period of time.  
           [0012]    Still other advantages and novel features of the present invention will be apparent from the following detailed description, simply by way of illustration of the invention and not limitation. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements and in which:  
         [0014]    [0014]FIG. 1 shows a block diagram of an alternator testing system implemented according to the present invention.  
         [0015]    [0015]FIG. 2 shows an exemplary circuit of components used in an alternator testing system implemented according to the present invention.  
         [0016]    [0016]FIG. 3 shows a flow chart illustrating the testing procedure carried out by an alternator testing system implemented according to the present invention.  
         [0017]    [0017]FIG. 4 shows an example of the cooling arrangement implemented according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention.  
         [0019]    [0019]FIG. 1 shows a block diagram of an alternator testing system  100  implemented according to the present invention. For purpose of illustration, the operation of the testing system is described with an alternator in an automotive vehicle. In an automotive vehicle, the alternator (not shown) is driven by the engine of the automotive vehicle to generate electricity. The output of the alternator is coupled to a battery  123  via a set of battery terminals  125  and charges the battery therefrom.  
         [0020]    Testing system  100  may be a handheld device and may have terminals for receiving an alternator output signal  113  representative of the alternator output. The alternator output signal may be the electric current generated by the alternator charging battery  123 . Alternatively, alternator output signal  113  may be a signal from a data processing system representative of the alternator output. The data processing system, for example, may be an on-board vehicle computer or other testing equipment. In another aspect, alternator output signal  113  may be a signal generated by a wireless transmission assembly that transmits signals representative of alternator characteristics wirelessly.  
         [0021]    Testing system  100  has a microcontroller  101 , an analog-to-digital converter  105  and a display  103 . Microcontroller  101  processes data and generates control signals. Analog-to-digital converter  105  converts analog signals to digital signals. Display  304  provides a communication interface with a user and may be an LCD screen, an LED indicator or the like. Microcontroller  101  may control a switch device  121 , such as an FET switch, that selectively couples a load  117  to the alternator. As illustrated in FIG. 1, switch device  121  and load  117  are serially connected and then coupled to the alternator in parallel via battery terminals  125 . If switch device  121  is on, load  117  is coupled to the alternator; if switch device  121  is off, load  117  is decoupled from the alternator. Other circuit design techniques known to persons skilled in the art can be used for controlling the coupling of the load to the alternator.  
         [0022]    Load  117  may be any component that is capable of drawing large currents from the alternator, while maintaining small voltage across it, for example, a Nichrome wire wound into a coil. As an example, load  117  may be a Nichrome coil that draws 50 amperes of current from the alternator. A Nichrome coil load is advantageous due to its ability to handle a substantial amount of current, while maintaining compact sizing. A cooling device  115 , such as a cooling fan, controlled by microcontroller  101 , may be provided to help dissipate heat generated by load  117 .  
         [0023]    While the alternator test may be conducted at any alternator speed or engine speed, the engine may be driven to a stable engine speed, such as 1500 rpm or above, to ensure the alternator generates a stable alternator output signal. As an alternative, the test may be conducted at idle engine speed. A user may indicate to the system that the engine speed has reached a certain level by observing readings from a tachometer. Alternatively, experienced users may be able to determine the engine speed based on the audible noise generated by the engine. According to an embodiment, the system may receive a signal representing an engine speed or an alternator speed from other data processing systems, such as a vehicle computer or other testing equipment or the like. The signal representing the engine speed or the alternator speed may be fed to, and processed by, microcontroller  101 .  
         [0024]    Upon the engine speed or the alternator speed reaching a predetermined level, such as 1500 rpm for the engine speed, microcontroller  101  generates a first switch control signal to turn on switch  324  so that load  117  is coupled to the alternator via battery terminals  125 . The alternator is now operating under load.  
         [0025]    Alternator output signal  151  may first pass through a bandpass filter  113  in order to eliminate harmonics as well as noise picked up at battery terminals  125 . Bandpass filter  113  may have a pass band between 100 Hz and 4 kHz. Alternator output signal  151  may then pass through an amplifier  111  to amplify signal level.  
         [0026]    Alternator output signal  151  is then fed to a detection circuit  109 . Detection circuit  109  generates a parameter signal  153  representative of parameters of the alternator output signal  151 , such as ripple amplitude, voltage level and the like. This current may use conventional filtering and load detection to produce the desired alternator parameters Copending non-provisional patent application Ser. No. ______, filed concurrently herewith and titled “Alternator Testing Method and System Using Ripple Detection,” by the same inventors and commonly assigned, describes a particular ripple detection circuit and methodology that could be implemented. The disclosure incorporated herein by reference. The parameters are used by microcontroller  101  to determine the characteristics of the alternator. Techniques using parameters of alternator output signals to determine alternator operation are described in U.S. Pat. Nos. 3,629,704, 4,459,548, and 4,315,204, incorporated herein by reference. Parameter signal  153  is next sent to analog-to-digital converter  105  and then into microcontroller  101 .  
         [0027]    According to one embodiment of the invention, although parameters of alternator output signal  151  may be available upon load  117  coupling to the alternator via battery terminals  125 , microcontroller  101  will evaluate the alternator health based on parameters picked up only after load  117  has been coupled to the alternator for a predetermined period of time, such as 0.75 second. The predetermined period of time, chosen to occur when the alternator output signal is stable, may be set empirically based on parameters like alternator model, alternator rating, types of load.  
         [0028]    In another aspect of the invention, after load  117  has been coupled to the alternator for a predetermined period of time, for example, one second, microcontroller  101  will issue a second switch control signal to turn off switch device  121 , which in turn decouples load  117  from the alternator. Since load  117  is coupled to the alternator for a short period of time, heat generated by the current passing load  117  is minimal. The predetermined period of time is chosen at a point of time before the load becomes too hot due to the current passing through it. The predetermined period of time may be empirically set based on parameters like the threshold temperature, alternator model, alternator rating, types of load.  
         [0029]    A cooling device  115 , such as a fan, controlled by microcontroller  101 , may be implemented to help dissipate the heat generated by load  117 . Testing system  100  may have a temperature sensor  119  disposed near load  117  for generating a temperature signal to microcontroller  101  indicating the temperature near or at load  117 . Based on the detected temperature, microcontroller  101  controls the operation of cooling device  115 : if the temperature is higher than a predetermined temperature, such as 70° C., microcontroller  101  issues a signal to turn on cooling device  115 ; if the temperature is lower than the predetermined temperature, microcontroller  101  issues a signal to turn off cooling device  115 .  
         [0030]    [0030]FIG. 2 shows an example of a control circuit  207  for coupling load  117  to the alternator and a regulation circuit  205  for controlling operation of a fan for purpose of cooling. Control circuit  207  includes a logic IC  206  that receives a control signal from microcontroller  101  and in response generates a switch control signal  208  to control the ON/OFF of a FET switch  121 , which in turn controls the coupling of load  117  to the alternator.  
         [0031]    Regulation circuit  205  controls the operation of a fan. A transistor  204  regulates the voltage to the fan. The fan couples to the power source through a FET switch  202 , which is controlled by a control signal generated by microcontroller  101 . The FET switch  202 , in response to the content of the control signal, turns on or off the power to the fan. When the temperature at load  117  is too high, microcontroller generates a control signal to control FET switch  202  to couple the fan to the power source and turns on the fan. If, the temperature of load  117  drops below a predetermined temperature, microcontroller  101  generates another control signal to control the FET switch  202  to turn off the power of the fan.  
         [0032]    [0032]FIG. 3 shows a flow chart illustrating the testing procedure carried out by an alternator testing system implemented according to the present invention. At steps  301  and  303 , microcontroller  101  determines whether the engine speed or alternator speed has reached a predetermined speed. If not, microcontroller continues the determination. If yes, microcontroller  101  generates a switch control signal to turn on the switch and couple the load to the alternator. Microcontroller  101  also turns on a timer (Step  305 ). At step  307 , microcontroller  101  reads the timer and determines if the load has been coupled to the alternator for more than 0.75 second. If not, microcontroller  101  continues the determination; otherwise, microcontroller  101  starts to determine the health of the alternator based on parameters of the alternator output signal collected after 0.75 second (step  309 ). Then microcontroller  101  determines if the load has been coupled to the alternator for more than 1 second (step  311 ). If not, microcontroller  101  continues the determination; otherwise, microcontroller  101  issues a switch control signal to turn off the switch and decouple the load from the alternator (Step  313 ). Microcontroller  101  then generates a determination result to the display and resets the timer (steps  315  and  317 ).  
         [0033]    [0033]FIG. 4 shows an example of the cooling arrangement implemented according to the present invention, with part of a housing  400 . Housing  400  has a size suitable to be held in one&#39;s hand and receives a circuit board  450  having microcontroller  101 , detection circuit  109 , bandpass filter  113 , amplifier  111  and other components. A temperature sensor  119  is disposed at a location near a Nichrome coil  117 , as the load sensing element. Switch  121 , that may be an FET-type switch, is in serial connection with coil  117 . An air inlet  411  is disposed on one side of the housing and a fan  401  is disposed on the other side of the housing, so that a linear channel  413  between air inlet  411  and fan  401  forms an air flow path when fan  401  is in operation. The channel is defined by a wall  410  that isolates the airflow path from the remainders of the housing. The heat generated by coil  117  will be dissipated to the surrounding air and drawn out from the housing  400  through an outlet established by fan  401  itself, as depicted.  
         [0034]    The embodiments described above may be used with any desired system or engine. Those systems or engines may comprise items utilizing fossil fuels, such as gasoline, natural gas, propane and the like, wind and hybrids or combinations thereof. Those systems or engines may be incorporated into other systems, such as an automobile, a truck, a boat or ship, a motorcycle, a generator, an airplane and the like. The embodiments may include or be utilized with any appropriate voltage level, such as about 12 Volts, about 42 Volts and the like.  
         [0035]    While this invention has been described in connection with an exemplary embodiment, it is to be understood that the invention is not limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.