Abstract:
A power tool system includes a power tool, a power tool battery pack and a battery pack charger. The power tool battery pack is separable from and attachable to the power tool, and electrically connectable to the power tool electrical terminals when attached to the power tool. The power tool battery pack has at least one battery cell, a receiver coil, and a control circuit for controlling the amount of power that is provided to the at least one battery cell. The battery pack charger has at least one transmitter coil for generating a magnetic field which induces a voltage in the receiver coil, and a control circuit for controlling the amount of power that is provided to the transmitter coil.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application derives priority from U.S. Provisional Application No. 61/660,938, filed on Jun. 18, 2012, which is hereby fully incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a charger for power tool battery packs and particularly a wireless charger for power tool battery packs. 
     BACKGROUND 
     It is desirable to rapidly and efficiently charge power tool battery packs due to the increased demands placed by users on their power tools. As more users use different cordless power tools on the jobsite, the demand for charged batteries throughout the day has increased. 
     However, certain difficulties arise when charging multiple batteries from a single power source. Firstly, the charger must accommodate batteries having different levels of charge. Secondly, the charger must be capable of handling dynamic situations as users randomly remove or insert battery packs, without disrupting individual charging cycles. In addition, users desire to charge multiple types of batteries efficiently, such as battery packs having different voltages. Lastly, it is desirable for the battery charger to be able to address these concerns while maintaining its ability to rapidly and efficiently charge the multiple batteries. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial schematic of the wireless charger. 
         FIG. 2  shows the wireless charger, where  FIGS. 2A-2B  are front and side views, respectively. 
         FIG. 3  shows a power tool battery pack on a wireless charger. 
         FIG. 4  is a circuit schematic of some of the components of the wireless charger. 
         FIG. 5  is a circuit schematic of some of the components of the battery pack. 
     
    
    
     DESCRIPTION 
       FIGS. 1-2  show a wireless charger  100  for charging multiple power tool battery packs  200 . Persons skilled in the art shall understand that “battery pack” and “power tool battery pack” as used herein shall mean a set of rechargeable battery cells  201  disposed in a housing  202  that for use with a tool that is powered by an electrical motor, such as a drill  300 , circular saw, reciprocating saw, jigsaw, etc. Persons skilled in the art shall recognize that power tool battery pack  200  may be the power tool battery packs disclosed in U.S. Pat. Nos. 7,405,536, 7,618,741, 7,602,146 and/or 8,044,640, which are hereby incorporated in full by reference, modified so as to be chargeable by a wireless charger. 
     The wireless charger  100  has a housing  101  with a deck  101 D where a user can place multiple battery packs  200 . Battery packs  200  are preferably sandwiched between deck  101 D and wall  102 . Deck  101 D has several wireless charging circuits  120 , which are described in more detail below. Power for the wireless charging circuits  120  may be received from a power cord  115 . 
     With such construction, the user can slide in battery pack  200  via opening  101 I. If deck  101 D is disposed on an angle relative to the ground, the battery pack  200  may slide all the way to the bottom wall  104  of wireless charger  100 . The user can continue sliding in battery packs  200 . 
     Deck  101 D preferably has indicator lights  106  right underneath battery packs  200  showing the charging status of the battery pack  200  thereabove. Once the bottom battery pack  200  is fully charged, the user can remove the pack  200  via the gap  103  between the bottom wall  104  and wall  102 . 
     Persons skilled in the art will recognize that the different wireless charging circuits  120  can be controlled so that (a) only one battery pack  200  is charged at a time (once the battery pack  200  is charged, the next battery pack  200  can be charged), (b) each battery pack  200  is charged concurrently, and/or (c) the user can choose the order in which the battery packs  200  are charged (or the user can choose to charge all battery packs  200  at the same time). 
     Housing  101  may also have wheels  105  for facilitating transportation of wireless charger  100 . Persons skilled in the art will also recognize that it is preferable to provide housing  101  with protrusions  107  with holes therethrough, which can be used for securing wireless charger  100  on a surface, such as a wall. 
     Wall  102  may also have a wireless charger circuit  120  thereon so as to allow users to charge other devices, such as cellphones  310 , power tool battery packs (including those manufactured/sold by other manufacturers), etc. It may be advantageous to provide such charger circuit with anti-slip strips  120 S. Persons skilled in the art will recognize that such devices may also be charged if placed on deck  101 D. 
     Wireless charger  100  may also have a non-wireless charger circuit  270  to which a battery pack  200  may be electrically connected thereon. Persons skilled in the art will recognize that battery pack  200  will have terminals  205  to electrically connected to the terminals of charger circuit  270 . Charger circuit  270  may be powered by AC received from power cord  115 . Persons skilled in the art will recognize that battery pack  200  may be connected so as to power one or more of the wireless charging circuits  120 . Persons skilled in the art shall recognize that charger circuit  270  may be the charger circuits disclosed in U.S. Pat. Nos. 7,405,536, 7,618,741, 7,602,146 and/or 8,044,640, which are hereby incorporated in full by reference. 
     Wireless charger  100  may have a lamp or light  130 , which may be powered by AC received from power cord  115  or from a battery pack  200  connected to the charger circuit  270 . Preferably such lamp  130  will output at least 1000 lumens. 
     Similarly, wireless charger  100  may have a radio  140 , which may be powered by AC received from power cord  115  or from a battery pack  200  connected to the charger circuit  270 . 
     Referring to FIGS.  1  and  4 - 5 , the wireless charger circuit  120  preferably has at least one transmitter coil LT, while the battery pack  200  has at least one receiver coil LR. An alternating current in the transmitter coil LT generates a magnetic field which induces a voltage in the receiver coil LR. This voltage is used to charge battery pack  200 . 
     Persons skilled in the art will recognize that the wireless charger circuit  120  could have multiple transmitter coils LT. Alternatively it could have a moving transmitter coil LT so that, when the battery pack  200  is placed on wireless charger circuit  120 , transmitter coil LT moves towards battery pack  200 . Persons skilled in the art will recognize that battery pack  200  may have a magnet (not shown) that is used by wireless charger circuit  120  to locate the location of battery pack  200 , and move transmitter coil LT via servo motors (not shown) towards battery pack  200 . 
     Preferably the battery pack  200  has a control circuit  202 , which controls the amount of power sent to the cells  201 . Control circuit  202  interacts with microcontroller  202 C to ensure that cells  201  are not overcharged. 
     Battery pack  200  may also have a communication circuit  203  that provides control information to the wireless charger circuit  120 . Communication circuit  203  may send the control information by modulating a reflected load signal  203 S. This information would be received by a communication circuit  122  on the wireless charger circuit  120 , which demodulates the information from the reflected load signal  203 S. 
     The wireless charger circuit  120  preferably has a control circuit  124  that controls the amount of power to be converted and transmitted to the battery pack  200 . Control circuit  124  can take into account the information sent by control circuit  202  via the communication circuits  203 ,  122 , and adjust the amount of power transmitted to battery pack  200 . 
     The wireless charger circuit  120  has a power conversion circuit  126  with a transmitter coil LT and a resonance capacitor CT in series with the transmitter coil LT. Power may be converted by a half bridge inverter  125  connected to the inductor/capacitor series circuit. Persons skilled in the art shall know that it may be preferable to provide an impedance matching system by adding a multiplexer  127  and multiple additional transmitter coils LT to the wireless charger circuit  120  as shown in  FIG. 4 . 
     The battery pack  200  may have a receiver coil(s) LR (LR 1 , LR 2 ) with a resonance capacitor CR in series with receiver coil(s) LR (LR 1 , LR 2 ) for efficient power transfer. In addition, a capacitor CP in parallel with receiver coil LR (and resonance capacitor CR) can be used for detection purposes. 
     A full-bridge rectifier RR is preferably connected to the receiver coil LR and capacitors. Rectifier RR may be a diode rectifier or switched rectifier. Persons skilled in the art will recognize that it is preferable to provide rectifier RR with a capacitor CRR to smooth the DC voltage output. 
     A switch SR may be provided on the output of rectifier RR for connecting and disconnecting the battery cells  201 . Switch SR may be controlled by control circuit  202  and/or microcontroller  202 C. 
     Persons skilled in the art will recognize that battery pack  200  can modulate the reflected load signal  203 S by switching capacitor CC, which is preferably controlled by communication circuit  203 . This reflected load signal  203 S can be demodulated by sensing the current and/or voltage going through transmitter coil LT. Preferably the modulation will be in a digital format with a transmission speed of 2 Kbit/second. Bit encoding is preferably bi-phase. The byte format may be as follows: start-bit, 8 bit data (b0-b7), parity-bit, stop bit. The packet structure may be as follows: preamble (&gt;=11 bit), header (1 byte indicating packet type and message length), message (up to 27 bytes), and checksum (1 byte). 
     With such arrangement, the wireless charger circuit  120  can provide a signal and sense for the presence of a potential receiver. The battery pack  200  receives the signal from wireless charger circuit  120  and indicates its presence by communicating the received signal strength. The battery pack  200  can then communicate its identifier and power requirements. The wireless charger circuit  120  can use that information to configure itself for transferring power to the battery pack  200 . 
     Once power is being transferred to battery pack  200 , the control circuit  202  and/or microcontroller  202 C can calculate the difference between a desired power level being sent to the battery pack  200  and the actual power level being sent to the battery pack  200 . The communication circuit  203  can then send a message to the wireless charger circuit  120  effectively telling the wireless charger circuit  120  to increase or decrease the amount of power being sent to the battery pack  200 . The wireless charger circuit  120  can decode the message and configure itself accordingly. 
     Referring to  FIGS. 3 and 5 , persons skilled in the art will recognize that battery pack  200  may have multiple receiver coils LR 1  and LR 2  on different planes, e.g. against the bottom wall and/or against a side wall. This allows the user to place the battery pack  200  on the bottom wall or on the side wall to charge the battery pack  200 . 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the scope of the invention.