Abstract:
A battery charger that is configured to charge a battery pack including a secondary battery includes: a housing; and a charging circuit unit disposed in the housing. The housing defines a first air passage in which air flows to cool the secondary battery and a second air passage in which air flows to cool the charging circuit unit. The second air passage is independent from the first air passage.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Japanese Patent Application No. 2013-146381 filed Jul. 12, 2013. The entire content of the priority application is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a battery charger. More specifically, the present invention relates to a battery charger that charges a battery pack used as a power supply for an electric power tool. 
       BACKGROUND 
       [0003]    Conventionally, a battery charger used for charging a batter pack has been desired, in order to meet increased capacity of a secondary battery in the battery pack, to increase a charging current to ensure charging capacity and shorten charging time. However, increasing the charging current causes a large current to flow into a charging circuit in the battery charger and the secondary battery in the battery pack. This causes an extreme increase in temperature of the charging circuit and the secondary battery. As a result, degradation and malfunction of the secondary battery and components constituting the charging circuit may occur. 
         [0004]    To solve the above-described problem, there is conventionally known a battery charger provided with an air intake fan that generates airflow for cooling a charging circuit therein and a secondary battery in a battery pack while the battery pack is being charged. 
       SUMMARY 
       [0005]    However, in the conventional battery charger, air for cooling both the charging circuit and the secondary battery flows in a single air passage. Hence, the charging circuit and the secondary battery cannot be cooled separately by air flowing in separate air passages. Moreover, in the conventional battery charger, the charging circuit is cooled with airflow that has previously cooled the secondary battery and has consequently increased in temperature. This degrades efficient cooling of the charging circuit. 
         [0006]    In view of the foregoing, it is an object of the present invention to provide a battery charger capable of efficiently cooling both a charging circuit in the battery charger and a secondary battery in a battery pack. 
         [0007]    In order to attain the above and other objects, the present invention provides a battery charger that is configured to charge a battery pack including a secondary battery. The battery charger includes: a housing; and a charging circuit unit disposed in the housing. The housing defines a first air passage in which air flows to cool the secondary battery and a second air passage in which air flows to cool the charging circuit unit. The second air passage is independent from the first air passage. 
         [0008]    According to another aspect, the present invention provides a battery charger configured to charge a battery pack including a battery pack casing and a secondary battery. The battery pack casing has an inlet port and an outlet port. The secondary battery is accommodated in the battery pack casing. The battery charger includes: a housing; a charging circuit unit; and a fan. The housing has an intake port and a discharge port, and includes a connecting part configured to be connected to the battery pack. The connecting part has a communication port configured to be in communication with the outlet port upon connection of the battery pack with the connecting part. The charging circuit unit is disposed in the housing. The fan is disposed in the housing and configured to draw air into the housing to generate airflow for cooling the secondary battery and the charging circuit unit. The housing defines a first air passage extending from the communication port to the discharge port, and a second air passage extending from the intake port to the discharge port. The second air passage is independent from the first air passage. The secondary battery is cooled by air flowing from the inlet port to the discharge port through the outlet port and the communication port in a state where the battery pack is connected to the connecting part. The charging circuit unit is cooled by air flowing from the intake port to the discharge port. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
           [0010]      FIG. 1  is a perspective view of a battery charger according to one embodiment of the present invention and a battery pack charged by the battery charger; 
           [0011]      FIG. 2  is a perspective view of the battery pack according to the embodiment, as viewed from a bottom side thereof; 
           [0012]      FIG. 3A  is a perspective view of an upper casing of the battery charger according to the embodiment, illustrating an interior thereof; 
           [0013]      FIG. 3B  is a perspective view of a closing member provided in the upper casing of the battery charger according to the embodiment; 
           [0014]      FIG. 4  is a plan view of the upper casing of the battery charger according to the embodiment, illustrating the interior thereof; 
           [0015]      FIG. 5A  is a plan view of a lower casing of the battery charger according to the embodiment, illustrating an interior thereof; 
           [0016]      FIG. 5B  is a right side view of the lower casing of the battery charger according to the embodiment; 
           [0017]      FIG. 6  is a cross-sectional view of the battery charger according to the embodiment, taken along a line VI-VI in  FIGS. 1 and 5A ; 
           [0018]      FIG. 7A  is a plan view of the lower casing of the battery charger according to the embodiment from which a fan, a power cable, and a charging circuit unit are omitted, illustrating the interior thereof; 
           [0019]      FIG. 7B  is a right side view of the lower casing of the battery charger according to the embodiment; 
           [0020]      FIG. 8  is a partial cross-sectional view of the battery charger according to the embodiment, taken along a line VIII-VIII in  FIG. 6 ; and 
           [0021]      FIG. 9  is a partial cross-sectional view of the battery charger according to the embodiment, taken along a line IX-IX in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    A battery charger according to one embodiment of the present invention will be described while referring to  FIGS. 1 through 9  wherein like parts and components are designated by the same reference numerals to avoid duplicating description. In the embodiment, the battery charger  1  is used for charging a battery pack  100 . First, the battery pack  100  will be described while referring to  FIGS. 1 and 2 . Next, the battery charger  1  will be described while referring to  FIGS. 1 ,  3 A through  9 . 
         [0023]    In the following description, the terms “upward”, “downward”, “upper”, “lower”, “above”, “below”, “beneath”, “right”, “left”, “front”, “rear” and the like will be used assuming that the battery charger  1  is resting on a level surface and the battery pack  100  is connected to the battery charger  1  resting on a level surface. Directions related to the battery charger  1  and the battery pack  100  will be given based on direction arrows illustrated in each drawing. 
         [0024]    As illustrated in  FIGS. 1 and 2 , the battery pack  100  primarily includes a battery pack casing  101 , and a secondary battery  102  accommodated in the battery pack casing  101 . The secondary battery  102  is charged by connecting the battery pack  100  to the battery charger  1 . The secondary battery  102  is a lithium-ion battery. For example, the lithium-ion battery consists of five cells connected in series to output 18V. 
         [0025]    The battery pack casing  101  is formed into substantially a rectangular parallelepiped shape. The battery pack casing  101  has a front wall in which an inlet port  101   a  is formed, and a bottom wall in which a pair of slide grooves  101   b  and an outlet port  101   c  are formed. 
         [0026]    The inlet port  101   a  is formed with a plurality of holes for drawing air into the battery pack casing  101 . The outlet port  101   c  is formed at a rear portion of the bottom wall of the battery pack casing  101 . The outlet port  101   c  is formed with a plurality of holes for discharging air drawn into the battery pack casing  101 . The inlet port  101   a  is in communication with the outlet port  101   c  inside the battery pack casing  101 . During charging of the battery pack  100 , air is drawn into the battery pack casing  101  through the inlet port  101   a , and discharged from the battery pack casing  101  through the outlet port  101   c . Hence, an air passage (not illustrated) is defined in the battery pack casing  101  from the inlet port  101   a  to the outlet port  101   c . The secondary battery  102  is cooled while the air flows from the inlet port  101   a  to the outlet port  101   c . The air used for cooling the secondary battery  102  is discharged from the battery pack casing  101  through the outlet port  101   c.    
         [0027]    The slide grooves  101   b  are formed at respective left and right end portions of the bottom wall of the battery pack casing  101 , extending in a front-rear direction. The slide grooves  101   b  are provided for mechanically connecting the battery pack  100  to the battery charger  1 . 
         [0028]    Further, a charging connecting part  101 A is provided at an approximate center region of the bottom wall of the battery pack casing  101 . The charging connecting part  101 A is electrically connectable to the battery charger  1  via contact terminals (not illustrated) thereof. 
         [0029]    As illustrated in  FIG. 1  and  FIGS. 3A through 6 , the battery charger  1  includes a battery charger casing  10  as an example of a housing, a charging circuit unit  31 , a fan  4 , and a power cable  7 . 
         [0030]    As illustrated in  FIG. 1 , the battery charger casing  10  is formed into substantially a rectangular parallelepiped shape that is elongated in the left-right direction. The battery charger casing  10  includes an upper casing  2  (as an example of an upper housing), and a lower casing  3  (as an example of a lower housing) disposed below the upper casing  2 . The upper casing  2  and the lower casing  3  are made of resin with heat-resisting properties and electrical-insulating properties. 
         [0031]    The upper casing  2  constitutes an upper half of the battery charger casing  10 . The upper casing  2  is formed in a rectangular box-like shape with a bottom opening. 
         [0032]    The upper casing  2  has a top wall at which a battery connecting part  21  is provided. The battery connecting part  21  as an example of a connecting part is connectable to the battery pack  100 . The battery connecting part  21  is disposed at a right portion of the top wall of the upper casing  2  and occupies approximately half of a surface area of the top wall of the upper casing  2 . As illustrated in  FIG. 1 , the battery connecting part  21  has a communication port  21   a , a terminal connecting part  21 A, and a pair of engaging parts  21 B. 
         [0033]    The communication port  21   a  is formed at a rear portion of the battery connecting part  21 . The communication port  21   a  is formed with a plurality of slits extending in the front-rear direction and arrayed in the left-right direction. When the battery pack  100  is connected to the battery charger  1  at the battery connecting part  21 , the communication port  21   a  opposes the outlet port  101   c  of the battery pack  100 . With this configuration, when the battery pack  100  is connected to the battery charger  1 , air introduced into the battery pack casing  101  through the inlet port  101   a  and discharged from the battery pack casing  101  through the outlet port  101   c  can be drawn into the battery charger casing  10  through the communication port  21   a.    
         [0034]    The terminal connecting part  21 A is disposed at an approximate center region of the battery connecting part  21 . When the battery pack  100  is connected to the battery charger  1  at the battery connecting part  21 , the terminal connecting part  21 A is engaged with the charging connecting part  101 A of the battery pack  100  to allow contact-terminals (not illustrated) of the terminal connecting part  21 A to come into contact with contact-terminals (not illustrated) of the battery pack  100 . Thus, electrical connection between the battery pack  100  and the battery charger  1  is established. 
         [0035]    As illustrated in  FIG. 4 , screws  21 E is screwed into the top wall of the upper casing  2  and the terminal connecting part  21 A from a lower side thereof to fix the terminal connecting part  21 A to the top wall of the upper casing  2 . The terminal connecting part  21 A includes a plurality of connection terminals  21 C. The connection terminals  21 C and the charging circuit unit  31  are electrically connected by connection lines  21 D. 
         [0036]    The engaging parts  21 B are disposed on respective left and right sides of the terminal connecting part  21 A, each extending in the front-rear direction. When the battery pack  100  is being connected to the battery charger  1  at the battery connecting part  21 , the battery pack  100  is guided into connection with the battery charger  1  by sliding the slide grooves  101   b  of the battery pack  100  along the engaging parts  21 B. The connection between the battery pack  100  and the battery charger  1  is stably maintained as a result of engagement of the pair of slide grooves  101   b  with the engaging parts  21 B. 
         [0037]    The upper casing  2  is formed with a discharge port  2   a , spanning from a left wall of the upper casing  2  to the top wall of the upper casing  2 . The discharge port  2   a  is formed with a plurality of slits extending in a vertical direction and arrayed in the front-rear direction. The discharge port  2   a  is in communication with the communication port  21   a  inside the battery charger casing  10 . The discharge port  2   a  discharges air that has been introduced into the battery charger casing  10  through the communication port  21   a  and an intake port  3   a  (described later). 
         [0038]    As illustrated in  FIGS. 3A and 4 , the upper casing  2  has a first supporting part  22 , a rib part  23 , a plurality of (two in the embodiment) fastening parts  24 , and a plurality of (four in the embodiment) first engagement parts  26  at a lower surface of its top wall. As illustrated in  FIG. 3B , the upper casing  2  also includes a closing member  25  that is attached to the rib part  23 . 
         [0039]    The first supporting part  22  is provided for supporting the fan  4  inside the battery charger casing  10 . The first supporting part  22  is formed integrally with the upper casing  2 . The first supporting part  22  protrudes downward from the lower surface of the top wall of the upper casing  2 . The first supporting part  22  includes a front support rib and a rear support rib arranged in confrontation with each other in the front-rear direction. The front support rib of the first supporting part  22  is disposed at a position opposing a frontmost slit of the plurality of slits in the discharge port  2   a  in the left-right direction. The rear support rib of the first supporting part  22  is disposed at a position opposing a rearmost slit of the plurality of slits in the discharge port  2   a  in the left-right direction. 
         [0040]    The rib part  23  includes a first rib  23 A and a second rib  23 B. The first rib  23 A and the second rib  23 B are formed integrally with the upper casing  2 . The first rib  23 A and the second rib  23 B protrude downward from the lower surface of the top wall of the upper casing  2 . The first rib  23 A and the second rib  23 B extend in the left-right direction from a position where the communication port  21   a  is disposed to a position where the first supporting part  22  is disposed, while maintaining a constant interval therebetween in the front-rear direction. Approximate left-right center portions of the first rib  23 A and the second rib  23 B have slanting portions, respectively, which slant with respect to the front-rear direction. 
         [0041]    The fastening parts  24  protrude downward from the lower surface of the top wall of the upper casing  2 . One of the fastening parts  24  is provided at a position intermediate in the front-rear direction between a left end portion of the first rib  23 A and a left end portion of the second rib  23 B. The other of the fastening parts  24  is provided at a position intermediate in the front-rear direction between an approximate left-right center portion of the first rib  23 A and an approximate left-right center portion of the second rib  23 B. The fastening parts  24  are provided for fastening the closing member  25  to the rib part  23 . 
         [0042]    The first engagement parts  26  are formed integrally with the upper casing  2 . The first engagement parts  26  protrude downward from the lower surface of the top wall of the upper casing  2  at positions in the vicinity of respective corners thereof. The first engagement parts  26  are provided for attaching the upper casing  2  to the lower casing  3 . 
         [0043]    As illustrated in  FIG. 3B , the closing member  25  has a shape such that a space defined by the first rib  23 A and the second rib  23 B is covered in a state where the closing member  25  is attached to the rib part  23 . The closing member  25  includes a guide part  25 A and a flat part  25 B. Further, the closing member  25  has a plurality of (two in the embodiment) fastening holes  25   a , a first stepped part  25   b , a second stepped part  25   c , and a third stepped part  25   d.    
         [0044]    The guide part  25 A is provided integrally with the flat part  25 B and positioned on a right side of the flat part  25 B. The guide part  25 A opposes the communication port  21   a  in a vertical direction in a state where the closing member  25  is attached to the rib part  23 . When water droplets have entered into the battery charger casing  10  through the communication port  21   a , the guide part  25 A guides the water droplets out of the battery charger casing  10 . 
         [0045]    The flat part  25 B has a width in the front-rear direction that is substantially the same as the interval between the first rib  23 A and the second rib  23 B in the front-rear direction. 
         [0046]    The fastening holes  25   a  are formed in the flat part  25 B at positions corresponding to the fastening parts  24 . 
         [0047]    The first stepped part  25   b  is provided at a rear edge of the flat part  25 B. 
         [0048]    The second stepped part  25   c  is provided at a front edge of the flat part  25 B. The third stepped part  25   d  is provided at a front edge of the guide part  25 A. The third stepped part  25   d  continuously extends from the second stepped part  25   c . The first stepped part  25   b  is formed into a shape in accordance with the shape of the first rib  23 A. The second stepped part  25   c  and the third stepped part  25   d  in combination are formed into a shape in accordance with the shape of the second rib  23 . 
         [0049]    When the closing member  25  is attached to the rib part  23 , the first rib  23 A is engaged with the first stepped part  25   b , and the second rib  23 B is engaged with the second stepped part  25   c  and the third stepped part  25   d.    
         [0050]    As illustrated in  FIGS. 4 and 6 , the closing member  25  is attached to the rib part  23  by inserting screws  25 C into the fastening holes  25   a  and screwing the screws  25 C into the fastening parts  24 . As a result of attachment of the closing member  25  to the rib part  23 , a duct  6  is defined by the rib part  23 , the closing member  25 , and the lower surface of the top wall of the upper casing  2 . 
         [0051]    The duct  6  provides an air passage from the communication port  21   a  to the fan  4 . A first air passage  5  is defined by the air passage (not illustrated) in the battery pack  100  from the inlet port  101   a  to the outlet port  101   c , the duct  6 , and the discharge port  2   a . The first air passage  5  provides communication between the inlet port  101   a , the outlet port  101   c , the communication port  21   a , and the discharge port  2   a . Thus, in the first air passage  5 , air is drawn into the battery pack casing  101  through the inlet port  101   a , and flows through the outlet port  101   c  and the communication port  21   a  to be introduced into the battery charger casing  10 , and is then discharged from the battery charger casing  10  through the discharge port  2   a.    
         [0052]    As illustrated in  FIG. 9 , the closing member  25  is attached to the rib part  23  in a state where the first stepped part  25   b  is engaged with the first rib  23 A, and the second stepped part  25   c  and the third stepped part  25   d  are engaged with the second rib  23 B. More specifically, top edges of the first stepped part  25   b , the second stepped part  25   c , and the third stepped part  25   d  have an L-shaped cross-section as viewed in the left-right direction, respectively. Thus, a contact area between the bottom edge of the first rib  23 A and the L-shaped top edge of the first stepped part  25   b  when the first rib  23 A and the first stepped part  25   b  are engaged with each other becomes greater, compared to a case where the top edge of the first stepped part  25   b  has an I-shaped (i.e. flat shaped) cross-section. Likewise, the L-shaped top edge of the second stepped part  25   c  makes a contact area between the bottom edge of the second rib  23 B and the top edge of the second stepped part  25   c  greater, and the L-shaped top edge of the third stepped part  25   d  makes a contact area between the bottom edge of the second rib  23 B and the top edge of the third stepped part  25   d  greater. Hence, the duct  6  has a highly airtight structure. 
         [0053]    The lower casing  3  constitutes a lower half of the battery charger casing  10 . The lower casing  3  is formed in a rectangular box-like shape with a top opening. 
         [0054]    As illustrated in  FIG. 5B , the lower casing  3  is formed with an intake port  3   a , spanning from a right wall of the lower casing  3  to a bottom wall of the lower casing  3 . The intake port  3   a  is formed with a plurality of slits extending in the vertical direction and arrayed in the front-rear direction. The intake port  3   a  draws air into the battery charger casing  10 . The intake port  3   a  is in communication with the discharge port  2   a  inside the battery charger casing  10 . Thus, a second air passage  8  is defined in the battery charger casing  10  from the intake port  3   a  to the discharge port  2   a.    
         [0055]    As illustrated in  FIG. 5A , the lower casing  3  has a plurality of (four in the embodiment) second engagement parts  32 , and a second supporting part  33 . 
         [0056]    The second engagement parts  32  are formed integrally with the lower casing  3 . The second engagement parts  32  protrude upward from an upper surface of a bottom wall of the lower casing  3  at positions in the vicinity of respective corners thereof. That is, the second engagement parts  32  are provided at positions corresponding to the first engagement parts  26 . Lower ends of the first engagement parts  26  are engaged with upper ends of the corresponding second engagement parts  32 , and the respective pairs of the first engagement parts  26  and the second engagement parts  32  are fastened by screws (not illustrated), inserting the screws thereinto from a lower side of the bottom wall of the lower casing  3 . Hence, the upper casing  2  is assembled to the lower casing  3  to provide the battery charger casing  10 . 
         [0057]    The second supporting part  33  is provided for supporting the fan  4  inside the battery charger casing  10  in cooperation with the first supporting part  22  of the upper casing  2 . The second supporting part  33  is formed integrally with the lower casing  3 . The second supporting part  33  protrudes upward from the upper surface of the bottom wall of the lower casing  3 . The second supporting part  33  is includes a front support rib and a rear support rib arranged in confrontation with each other in the front-rear direction. The second supporting part  33  is provided at a position corresponding to the first supporting part  22 . 
         [0058]    The charging circuit unit  31  is provided in the battery charger casing  10 . More specifically, the charging circuit unit  31  is accommodated in an internal space defined by the lower casing  3 . 
         [0059]    The charging circuit unit  31  primarily includes a line filter  31 A, an FET  31 B, a transformer  31 C, a diode  31 D, and a board  31 E. The connection lines  21 D are connected to the charging circuit unit  31  to electrically connect the charging circuit unit  31  to the battery pack  100  via the connection terminals  21 C. By adjusting and controlling a charging current and a charging voltage based on prescribed conditions, the charging circuit unit  31  carries out charging of the battery pack  100  in a safe and rapid fashion. 
         [0060]    The board  31 E is a substantially rectangular shape in a plan view. The board  31 E is disposed between the intake port  3   a  and the second supporting part  33 . The line filter  31 A, the FET  31 B, the transformer  31 C, and the diode  31 D are disposed on an upper surface of the board  31 E in this order from left to right. The line filter  31 A, the FET  31 B, the transformer  31 C, and the diode  31 D are elements emitting heat during charging of the battery pack  100 . Heat dissipating fins are attached to the FET  31 B and the diode  31 D. 
         [0061]    As illustrated in  FIG. 6 , in a state where the upper casing  2  is assembled to the lower casing  3 , the closing member  25  is positioned above the charging circuit unit  31 . Hence, the first air passage  5  and the second air passage  8  are independent from each other. 
         [0062]    As illustrated in  FIGS. 7 and 8 , the lower casing  3  is formed with a first drainage port  3   b , a plurality of (two in the embodiment) second drainage ports  3   c , and a third drainage port  3   d.    
         [0063]    The first drainage port  3   b  is formed at a left end portion of the lower casing  3 . Water droplets that have entered the battery charger casing  10  through the discharge port  2   a  are drained out of the battery charger casing  10  through the first drainage port  3   b.    
         [0064]    The second drainage ports  3   c  are formed at a rear end portion of the lower casing  3  at its right end. The second drainage ports  3   c  are provided at positions not overlapping with the charging circuit unit  31  in a plan view. Water droplets that have entered the battery charger casing  10  through the communication port  21   a  are drained out of the battery charger casing  10  through the second drainage ports  3   c  via the guide part  25 A of the closing member  25 . 
         [0065]    The third drainage port  3   d  is formed at a front end portion of the lower casing  3  at its left-right center. 
         [0066]    As illustrated in  FIGS. 7 and 8 , the lower casing  3  has a plurality of waterproofing walls  34 . The waterproofing walls  34  are provided for preventing water droplets entered the battery charger casing  10  from coming into contact with the charging circuit unit  31 . The waterproofing walls  34  are formed so as to protrude upward from the upper surface of the bottom wall of the lower casing  3 . The waterproofing walls  34  include a first waterproofing wall  34 A, a second waterproofing wall  34 B, and a third waterproofing wall  34 C. 
         [0067]    The first waterproofing wall  34 A is disposed between the second supporting part  33  and the charging circuit unit  31 . The first waterproofing wall  34 A extends in the front-rear direction from a front wall of the lower casing  3  to a rear wall of the lower casing  3 . The first waterproofing wall  34 A defines a first drainage area  35 A in cooperation with the bottom, front, rear, and left walls of the lower casing  3 . The first drainage port  3   b  is located in the first drainage area  35 A. With this configuration, the first drainage area  35 A and the charging circuit unit  31  are isolated from each other. 
         [0068]    The second waterproofing wall  34 B is formed so as to surround the second drainage ports  3   c  in a plan view. The second waterproofing wall  34 B defines a second drainage area  35 B in cooperation with the rear wall of the lower casing  3 . The second drainage ports  3   c  are located in the second drainage area  35 B. Hence, the second waterproofing wall  34 B isolates the charging circuit unit  31  from the second drainage area  35 B. 
         [0069]    The third waterproofing wall  34 C is formed so as to surround the intake port  3   a  in a plan view. The third waterproofing wall  34 C defines a third drainage area  35 C in cooperation with a right wall of the lower casing  3 . The intake port  3   a  is located in the third drainage area  35 C. Hence, the third waterproofing wall  34 C isolates the charging circuit unit  31  from the third drainage area  35 C. 
         [0070]    The charging circuit unit  31  is isolated from the respective drainage areas  35 A,  35 B, and  35 C by the waterproofing walls  34 . With this configuration, contact of water droplets with the charging circuit unit  31  can be effectively prevented. Further, malfunctions of the battery charger  1  due to short circuits in the charging circuit unit  31  caused by water droplets entering the battery charger casing  10  can be restrained. 
         [0071]    As illustrated in  FIG. 8 , the guide part  25 A of the closing member  25  constituting a part of the duct  6  has an inclining portion  250  and an extending portion  251 . The inclining portion  250  has a front edge at which the third stepped part  25   d  is provided, and a rear edge in confrontation with the front edge in the front-rear direction. The inclining portion  250  inclines slightly downward, while extending from the front edge toward the rear edge. The extending portion  251  extends downward from the rear edge of the inclining portion  250  toward the second drainage ports  3   c . The front edge of the inclining portion  250  is in flush with the front edge of the flat part  25 B, but the rear edge of the inclining portion  250  is further downward than the rear edge of the flat part  25 B. 
         [0072]    Water droplets that have entered the battery charger casing  10  through the communication port  21   a  move over the inclining portion  250  toward the extending portion  251 , and are drained out of the battery charger casing  10  through the second drainage ports  3   c . Hence, malfunctions of the battery charger  1  due to short circuits in the charging circuit unit  31  caused by water droplets entering the battery charger casing  10  through the communication port  21   a  can be inhibited. In addition, the degree of waterproofing of the charging circuit unit  31  can be decreased, thereby reducing costs for waterproofing the charging circuit unit  31 . 
         [0073]    Moreover, water droplets that have entered the battery charger casing  10  through the communication port  21   a  can be effectively guided to the second drainage ports  3   c  by the inclining portion  250  that is positioned lower than the flat part  25 B. Thus, the water droplets are not guided to the flat part  25 B constituting a part of the duct  6 . As a result, the fan  4  is kept away from the water droplets. Accordingly, not only malfunctions of the charging circuit unit  31  due to short circuits in the charging circuit unit  31  caused by water droplets entering the battery charger casing  10 , but also malfunctions of the fan  4  caused by water droplets entering the battery charger casing  10 , can be inhibited. 
         [0074]    The fan  4  is adapted to generate airflow that cools the charging circuit part  31  and the secondary battery  102 . As illustrated in  FIGS. 4 to 6 , the fan  4  is supported in the battery charger casing  10 . More specifically, the fan  4  is sandwiched between the first fan-supporting part  22  and the second supporting part  33  in the vertical direction. The fan  4  is disposed between the charging circuit unit  31  and the discharge port  2   a  in the left-right direction. Further, the fan  4  is disposed opposite to the intake port  3   a  with respect to the charging circuit unit  31  in the left-right direction. 
         [0075]    As illustrated in  FIG. 6 , a left edge of the closing member  25  is positioned so as to oppose a substantial vertical center of the fan  4 . Hence, the fan  4  spans both the first air passage  5  and the second air passage  8 . With this configuration, the fan  4  can draw air into the battery charger casing  10  through the communication port  21   a  and the intake port  3   a , and discharge the air from the battery charger casing  10  through the discharge port  2   a.    
         [0076]    The power cable  7  is connectable to a commercial power supply (not illustrated) and adapted to supply power to the charging circuit part  31  and the fan  4 . The power cable  7  has one end connected to the fan  4  and the charging circuit unit  31 , and another end connectable to a commercial power supply (not illustrated). 
         [0077]    Next, an operation of the battery charger  1  for charging the battery pack  100  will be described. When the power cable  7  is connected to the commercial power supply (not illustrated), and the battery pack  100  is connected to the battery charger  1  at the battery connecting part  21 , charging of the battery pack  100  starts. Upon start of the charging of the battery pack  100 , the fan  4  starts to rotate. 
         [0078]    The rotating fan  4  draws air through the inlet port  101   a  and discharges the air through the discharge port  2   a . The secondary battery  102  of the battery pack  100  is cooled using the first air passage  5 , while the air flows from the inlet port  101   a  to the discharge port  2   a . The rotating fan  4  also draws air through the intake port  3   a  and discharges the air through the discharge port  2   a . The charging circuit unit  31  of the battery charger  1  is cooled using the second air passage  8 , while the air flows from the intake port  3   a  to the discharge port  2   a.    
         [0079]    More specifically, as illustrated in  FIGS. 4 and 6 , the first air passage  5  is a path that starts at the inlet port  101   a  of the battery pack  100 , runs through the outlet port  101   c  of the battery pack  100  and the communication port  21   a  of the battery charger  1 , and ends at the discharge port  2   a  of the battery charger  1 . When the fan  4  starts rotating, a negative pressure is generated in the first air passage  5 , and air flows into the battery pack casing  101  through the inlet port  101   a . The air that has flowed into the battery pack casing  101  cools the secondary battery  102 , and is then discharged from the battery pack casing  101  through the outlet port  101   c . The air that has been discharged from the battery pack casing  101  through the outlet port  101   c  flows into the battery charger casing  10  through the communication port  21   a . The air that has flowed into the battery charger casing  10  flows through the duct  6  toward the fan  4 . Then, the air is discharged from the battery charger casing  10  through the discharge port  2   a.    
         [0080]    Note that, the first air passage  5  extends from the inlet port  101   a  to the discharge port  2   a  through the outlet port  101   c  and the communication port  21   a  in a state where the battery pack  100  is connected to the battery charger  1 . However, in a state where the battery pack  100  is not connected to the battery charger  1 , the first air passage  5  extends from the communication port  21   a  to the discharge port  2   a.    
         [0081]    As illustrated in  FIGS. 5 and 6 , the second air passage  8  is a path that starts at the intake port  3   a  and ends at the discharge port  2   a . When the fan  4  starts rotating, air flows into the battery charger casing  10  through the intake port  3   a . The air that has flowed into the battery charger casing  10  cools the charging circuit unit  31 , while flowing toward the fan  4 . Then, the air is discharged from the battery charger casing  10  through the discharge port  2   a.    
         [0082]    In other words, when the fan  4  starts rotating, the fan  4  generates a first airflow flowing from the inlet port  101   a  to the discharge port  2   a  through the outlet port  101   c  and the communication port  21   a , thereby cooling the secondary battery  102  in the battery pack  100 , and also generates a second airflow flowing from the intake port  3   a  to the discharge port  2   a , thereby cooling the charging circuit unit  31  in the battery charger casing  10 . 
         [0083]    The battery charger  1  cools both the secondary battery  102  in the battery pack  100  and the charging circuit unit  31  in the battery charger  1 , while charging the battery pack  100 . When the charging circuit unit  31  detects that the secondary battery  102  is fully charged, the battery charger  1  stops charging and the fan  4  stops rotating. 
         [0084]    Since the communication port  21   a  of the battery charger  1  is in communication with the outlet port  101   c  of the battery pack  100  when the battery pack  100  is connected to the battery charger  1 , the rotation of the fan  4  can cause air to be drawn into the battery pack casing  101  through the inlet port  101   a  of the battery pack  100 . Hence, the secondary battery  102  in the battery pack  100  can be cooled by the air flowing in the air passage (not illustrated) defined in the battery pack casing  101 . 
         [0085]    Further, the rotation of the fan  4  can cause air to flow in the second air passage  8  running from the intake port  3   a  to the discharge port  2   a . Hence, the charging circuit unit  31  can be cooled by the air flowing in the second air passage  8 . With this configuration, it is not necessary for heat generating elements constituting the charging circuit unit  31 , such as the FET  31 B, the transformer  31 C, and the diode  31 D, to enhance heat resistivity, and costs therefor can thus be reduced. 
         [0086]    Moreover, by utilizing the duct  6 , the first air passage  5  and the second air passage  8  are partitioned from each other, and thus, independent from each other. The first air passage  5  serves as a dedicated cooling path for cooling the secondary battery  102 , and the second air passage  8  serves as a dedicated cooling path for cooling the charging circuit unit  31 . Hence, situations can be avoided in which airflow which has cooled one of the secondary battery  102  and the charging circuit unit  31  is required to be used to cool the other. Accordingly, both the secondary battery  102  and the charging circuit unit  31  can be sufficiently cooled using the dedicate cooling paths, thereby preventing degradation of the secondary battery  102  in the battery pack  100  and malfunctions of components constituting the charging circuit unit  31  caused by elevated temperatures of the secondary battery  102  and the charging circuit unit  31 . 
         [0087]    Further, since the first air passage  5  includes the duct  6  running from the communication port  21   a  to the fan  4 , the first air passage  5  and the second air passage  8  can be made independent from each other, using a low-cost, simple method. 
         [0088]    Further, since the rib part  23  is provided inside the battery charger casing  10 , and the duct  6  is defined by the battery charger casing  10 , the rib part  23 , and the closing member  25  attached to the rib part  23 , the duct  6  can be easily provided by using the rib part  23  and the closing member  25 . The rib part  23  also serves as a reinforcing member for reinforcing the battery charger casing  10 . 
         [0089]    Further, since the fan  4  is disposed both in the first air passage  5  and in the second air passage  8 , airflow in the first air passage  5  and airflow in the second air passage  8  can both be generated by the single fan  4 . Hence, it is not necessary to provide separate fans for the respective air passages  5  and  8  in the battery charger  1 . As a result, size increases in the battery charger  1  can be avoided, and costs for providing additional fans can be reduced. 
         [0090]    Further, the fan  4  rotates so as to draw air through the inlet port  101   a  and the intake port  3   a  and to discharge the air through the discharge port  2   a . The fan  4  is positioned on a side where the discharge port  2   a  is formed and on a downstream side of the charging circuit unit  31  in a direction in which the air flows. With this configuration, the fan  4  cools the secondary battery  102  with air drawn through the inlet port  101   a , and also cools the charging circuit unit  31  with air drawn through the intake port  3   a . The air that has cooled the secondary battery  102  and the charging circuit unit  31  is discharged through the discharge port  2   a.    
         [0091]    Thus, compared to a case where the secondary battery  102  and the charging circuit unit  31  are cooled by air directly from the fan  4 , the fan  4  provides efficient airflows from the inlet port  101   a  to the discharge port  2   a  and from the intake port  3   a  to the discharge port  2   a  for cooling the secondary battery  102  and the charging circuit unit  31 , respectively, with the result that the efficiency of cooling the secondary battery  102  and the charging circuit unit  31  is increased. 
         [0092]    Further, a spigot joint structure between the stepped parts  25   b ,  25   c ,  25   d  and the ribs  23 A,  23   b  enables the duct  6  in the first air passage  5  to maintain high air tightness. Hence, air intake by the fan  4  is carried out efficiently. 
         [0093]    Further, since the fan  4  is positioned opposite to the intake port  3   a  with respect to the charging circuit unit  31  in the left-right direction, the charging circuit unit  31  in its entirety can be cooled reliably and efficiently by the airflow running through the second air passage  8 . 
         [0094]    While the present invention has been described in detail with reference to the embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the present invention.