WO1997001207A1

WO1997001207A1 - Rechargeable battery and charger

Info

Publication number: WO1997001207A1
Application number: PCT/GB1996/001510
Authority: WO
Inventors: Marc Borrett; Andy White
Original assignee: Innovision Research And Technology Ltd.
Priority date: 1995-06-23
Filing date: 1996-06-21
Publication date: 1997-01-09
Also published as: GB9512881D0; AU6233696A

Abstract

This invention provides a rechargeable battery which includes within its casing (11) a receiver (13) for receiving energy to recharge the battery from a charging transmitter which may be coupled to the receiver (13) without removing the battery from the apparatus that it powers. The charging transmitter is also disclosed.

Description

RECHARGEABLE BATTERY AND CHARGER

The present inventon relates to improvements in rechargeable batteries and to a charging apparatus therefor.

It is often desired to use rechargeable batteries instead of "single life" batteries, the main advantage being that they can be re-used many hundreds of times. This is not only economical but also saves visits to the shops to buy "single life" batteries. A disadvantage with both rechargeable and single life batteries is that they need to be removed from the product they are powering to be recharged or replaced respectively. Some people are not particularly adept at changing batteries, and thus this operation is not appealing.

To avoid this difficulty, certain electrical apparatus (such a mobile telephones and electric razors) have been produced with rechargeable batteries therein. When the power has been drained from the batteries, the product is connected to a charger unit specifically designed for the apparatus. Some of these charger units simply connect an electrical power source to charge the batteries through physical contacts. Other units connect an electrical power source to charge the batteries without the use of contacts by transferring energy using electromagnetic coupling. A disadvantage however is that each apparatus has to have its own charger unit.

It is an object of the present invention to provide a rechargeable battery and a charging apparatus therefor which obviate or mitigate these difficulties.

According to the present invention there is provided a rechargeable battery comprising a battery casing, at least one battery cell in the casing, and a charging receiver in the casing connected to the battery cell, said charging receiver being adapted to charge the or each battery cell upon receipt of a charging signal from a charging transmitter.

Preferably the battery casing is substantially the size of a standard AAA, AA, C or D battery.

Preferably the charging receiver includes an induction circuit and a rectifier which, on receipt of a charging signal, produces a DC output to charge the or each cell.

The induction circuit is preferably formed from a coil on a ferrite core and at least one capacitor.

The invention further provides a charging apparatus having a charging transmitter for sending a charging signal to a battery as above defined, said apparatus having a surface upon which an electrical piece of equipment housing at least one battery as above defined can be placed to charge the battery.

Preferably the charging transmitter includes a resonant circuit, an oscillator to drive the resonant circuit, and a frequency sensor to sense the frequency at the resonant circuit and to alter the frequency of the oscillator to maintain substantially optimum resonant frequency at the resonant circuit.

Preferably the charging apparatus further comprises a transmitter output sensor connected to an automatic level controller to maintain the output of the transmitter within preset limits related to the presence of a battery to be charged and the efficiency of the charging process. The charging apparatus may further include an indicator means such as a meter, to indicate whether the or each battery is correctly orientated relative to the charging apparatus.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:-

Figure 1 shows a perspective view of a toy car housing a plurality of rechargeable batteries on a charging apparatus;

Figure 2 shows a perspective view of the location of the batteries in the toy car;

Figure 3 shows a cross-section view of a battery according to the invention;

Figure 4 shows a circuit diagram of the charging receiver of Figure 3;

Figure 4a shows an embodiment of a coil on a ferrite core which may be used in the circuit of figure 4; and

Figure 5 shows an embodiment of a circuit diagram for the charging apparatus of Figure 1.

Referring to Figure 1 there is shown a battery-powered toy motor car or automobile 1 placed on a charging apparatus 2 in accordance with the invention. The car 1 uses rechargeable batteries in accordance with the present invention. The charging apparatus 2 has a housing 3 which may be formed of plastics or other material. The upper surface 4 of the housing 3 provides a platform upon which a car 1, or other apparatus, housing rechargeable batteries can be placed. A charging transmitter, which will be described later, is located in the housing under the surface 4. A mains lead 5 and a plug connect the charging apparatus to an electrical wall socket 6. Mounted on the surface 4 is a charge level indicator 7 in the form of three light emitting diodes (LEDs). Referring now to Figure 2, there is shown the underside 8 of the car 1 having a battery compartment recess 9. Housed within a recess 9, are three rechargeable batteries 10a,10b,10c in accordance with the invention.

In use, when it is desired to recharge the batteries in the car 1, the car 1 is placed on the charging apparatus 2. The charging transmitter in the apparatus transmits a signal to the batteries to recharge them (the method by which this may be done is described more fully below) . In order to ensure maximum coupling between the charging transmitter and the batteries, the car may be moved relative to the surface 4 until all three LEDs are illuminated. The car 1 can thus have its batteries recharged without removing them from the battery compartment recess 9.

Instead of a car, any other apparatus, such as a torch, tape recorder, radio, mobile or cordless telephone or the like, having batteries therein in accordance with the invention may be placed on the surface 4 to recharge the batteries without removing the batteries from the apparatus.

Referring to Figure 3 there is shown a rechargeable battery according to the present invention. The battery comprises a battery casing 11. The casing 11 is substantially the same size as a standard AAA, AA, C or D battery, so that the battery is compatible with battery-powered electrical apparatus. The casing

11 has an electrically conductive end Ila and an electrically conductive projection lib. Inside the casing is a battery cell

12 having its positive terminal connected to projection lib and its negative terminal connected to end Ila. A charging receiver

13 is connected to the positive and negative terminals of battery cell 12, the charging receiver being adapted to charge the battery cell upon receipt of a charging signal from a charging transmitter. Referring to Figure 4, the charging receiver 13 includes an induction circuit formed from a pick up coil 14 wound on a core 15 (core 15 may be a ferrite core of generally "dumb-bell" shape with the coil 14 mounted along the thinner diameter section, as shown in Figure 4a) and a pair of capacitors 16a,16b. The charging receiver also includes a rectifier formed from two diodes 17a,17b and a thermal trip 18 in series with the cell 12. On receipt of a charging signal induced into the core 15 from a charging transmitter in the charging apparatus, the charging receiver produces a DC output to charge the or each cell 12. The thermal trip 18 operates to interrupt the charging of the cell when the temperature of the cell reaches a peak indicating the end of the charging process.lt should be understood that while the cell 12 is considered to be a single cell for the purposes of this description it could in practice be a plurality of cells connected in series.

Referring to Figure 5, there is shown a schematic circuit of the charging transmitter for sending a charging signal to the charging receiver 13. In Figure 5 a charging transmitter 18 is formed from a series L-C resonant circuit 20 having a capacitor 20a in series with a coil 20b on a ferrite core 20c. A voltage controlled oscillator 21 drives the circuit 20 and produces a square wave output at the series resonant frequency of the resonant circuit 20, i.e. at about 7.5KHz. An automatic level controller 22 formed by a resistor 22a and a FET 22b passes the desired level of signal, via a buffer amplifier 23, to a low pass filter 24. The output of the low pass filter 24 is sinusoidal and is connected, via a signal level controller 25, to high power amplifier 26. The signal level controller 25 is a variable resistor which is preset to the maximum safe output level of current in the resonant circuit 20.

To ensure efficient charging of the battery the resonant frequency of the circuit 20 should be in the range 5-125 KHz and preferably in the range 7.5-25 KHz.

A frequency sensor for sensing the frequency at the circuit 20 is formed from a phase comparator 27, connected via a squaring amplifier 28a to a tapping on the coil 20b and via a squaring amplifier 28b to the output of the amplifier 26, i.e. the input to the circuit 20. At resonance in the circuit 20, the signals compared by the amplifiers 28a and 28b will be 90 degrees apart so that the comparator 27 will produce an output voltage, smoothed by a smoothing circuit 29 comprising a resistor 29a and a capacitor 29b, which controls the oscillator 21 to maintain substantially optimum resonant frequency. Any change in the resonance frequency is fed back to produce a change in the oscillator control voltage at the output of the smoothing circuit to bring the circuit 20 back into optimum resonance.

An output sensor 30 is provided by an induction circuit comprising a coil 30a, a capacitor 30b and a rectifier 30c connected in series. The coil 30a is linked inductively to the coil 20c in the circuit 20 so that the output of the sensor 30 across the capacitor 30b has characteristics similar to those of the charging receiver 13 in the battery as described above. The output of the sensor 30 is connected, via variable resistor 31, to the FET 22b in the automatic level controller 22 which maintains the output of the transmitter within certain preset limits related to the presence of a battery to be charged and the efficiency of the charging process. A meter 32 gives a reading of the level of the output of the transmitter 18 as sensed by the sensor 30. The meter may be a moving pointer type of meter or three LEDs which light up according to the strength of the output of the transmitter (e.g. one LED means a weak output, two LEDs mean an average output, and three LEDs mean a strong output) .

If no battery is present in the proximity of the charging transmitter the resonant circuit 20 requires very little power and the output sensor 30 controls the FET 22b to provide only that power. When a battery is present the sensor 30 senses the increased power requirement of the circuit 20 and controls the FET 22b to increase the power suplied.

Energy is transferred from the transmitter 18 to the battery 10 by the electromagnetic coupling between the coil 20b of the transmitter 20 and the coil 14 of the charging receiver. It will be appreciated that depending on the proximity and orientation of the core 15 of a battery charging receiver to the transmitter 18, so the amount of energy transmitted between the transmitter 18 and core 15 will vary, and hence the output of the transmitter 18: this also effects the resonant frequency of the circuit 20 and hence the need to maintain the optimum resonant frequency as described above, which in turn provides optimum transfer of energy between the transmitter and receiver. The meter 32 will thus give an indication as to whether the or each battery is correctly orientated relative to the charging apparatus.

Whilst the invention has been described showing each battery with one cell, a battery could have more than one cell charged by one charging receiver. Also, other circuits to those described above could be used. Each cell may be a Nickel Cadmium cell, or other type. It is envisaged that a consumer may purchase a charging apparatus, and a number of batteries of the invention as required. The apparatus or a battery could be sold alone or in combination. The invention thus covers a battery, a charging apparatus, or combinations thereof.

The surface of the charging apparatus may be shaped to accommodate different shaped objects. For example it could be slightly curved to prevent objects which roll such as torches from rolling off the surface.

In a modification of the invention the thermal trip 18 is replaced by a "GAS GAUGE" chip which monitors not only the temperature of the battery but also the rate of change of voltage across the battery to terminate the charging process when it is complete.

Further modifications will be apparent to those skilled in the art without departing from the scope of the present invention.

Suitable values for the various circuit components shown in the drawings are:-

Coil 14 100 turns

Capacitors 16a, 16b 1_/zF 250V

Diodes 17a, 17b IN4003

Capacitor 20c 1/JF 400V

Oscillator 21 7.5 KHz sine wave

Resistor 22a 10K

FET 22b ZUN 1306

Amplifier 23 LM 324

Resistor 25 5K

Amplifier 26 H7 128

Amplifiers 28a, 28b LM 324

Resistor 29a 100K

Capacitor 29b 215pF

Resistor 31 500K

Claims

1. A rechargeable battery comprising a battery casing, at least one battery cell in the casing, and a charging receiver in the casing connected to the battery cell, said charging receiver being adapted to charge the battery cell upon receipt of a charging signal from a charging transmitter.

2. A rechargeable battery as claimed in claim 1, in which there is provided means for terminating process when it is completed.

3. A rechargeable battery as claimed in claim 2, in which the battery casing is substantially the size of a standard AAA, AA, C or D battery.

4. A rechargeable battery as claimed in claim 1, in which the charging receiver includes an induction circuit and a rectifier which, on receipt of a charging signal, produces a DC output to charge the or each cell.

5. A rechargeable battery as claimed in claim 1, in which the induction circuit is formed from a coil on a ferrite core and at least one capacitor.

6. Apparatus for charging a battery and having a charging transmitter for sending a charging signal to a battery as above defined, said apparatus having a surface upon which electrical apparatus housing at least one battery as above defined can be placed to charge the battery.

7. Apparatus as claimed in claim 6, in which the charging transmitter includes a resonant circuit, an oscillator to drive the resonant circuit, and a frequency sensor to sense the frequency at the resonant circuit and to alter the frequency of the oscillator to maintain substantially optimum resonant frequency at the resonant circuit.

8. Apparatus as claimed in claim 7, in which the resonant circuit is a series L-C circuit.

9. Apparatus as claimed in claim 7, in which the resonant frequency of the resonant circuit is in the range 5-125 KHz

10. Apparatus as claimed in claim 9, further including a transmitter output sensor connected to an automatic level controller to maintain the output of the transmitter within preset limits related to the presence of a battery to be charged and the efficiency of the charging process.

11. Apparatus as claimed in claim 10, further including indicator means such as a meter, to indicate whether the or each battery is correctly orientated relative to the charging apparatus.