Battery pack-detecting charger

A charger having a controller with an input and an output, a first terminal for connecting a battery pack to the controller, a connecting line disposed between the first terminal and the input of the controller, a current source connected to the controller for providing power to the battery pack. The current source provides power to the battery pack via the connecting line. The controller sends a pulse signal unto the connecting line via the output, so that the controller can determine whether the battery pack is connected to the charger by the presence of the pulse signal in the input of the controller.

FIELD OF THE INVENTION

This invention relates generally to battery chargers and more particularly to battery chargers with protection circuitry.

BACKGROUND OF THE INVENTION

The battery packs for portable power tools, outdoor tools and certain kitchen and domestic appliances may include rechargeable batteries, such as lithium, nickel cadmium, nickel metal hydride and lead-acid batteries, so that they can be recharged rather than be replaced. Thereby a substantial cost saving is achieved.

It is preferable to provide a charger that recognizes when a battery pack has been connected in order to begin charging.

SUMMARY OF THE INVENTION

In accordance with the present invention, an improved battery pack charger is employed. The charger includes a controller having an input and an output, a first terminal for connecting a battery pack to the controller, a connecting line disposed between the first terminal and the input of the controller, a current source connected to the controller for providing power to the battery pack, the current source providing the power to the battery pack via the connecting line, wherein the controller sends a pulse signal unto the connecting line via the output, whereby the controller determines whether the battery pack is connected to the charger by the presence of the pulse signal in the input of the controller.

Additional features and benefits of the present invention are described, and will be apparent from, the accompanying drawings and the detailed description below.

DETAILED DESCRIPTION

The invention is now described with reference to the accompanying figures, wherein like numerals designate like parts.

Referring toFIGS. 1-2, a battery pack10is connected to a charger20. Battery pack10may comprise a plurality of battery cells11connected in series and/or parallel, which dictate the voltage and storage capacity for battery pack10. Battery pack10may include three battery contacts: first battery contact12, second battery contact13, and third battery contact14. Battery contact12is the B+ (positive) terminal for battery pack10. Battery contact14is the B− or negative/common terminal. Battery contact13is the S or sensing terminal. Battery contacts12and14receive the charging current sent from the charger20(preferably from current source22, as discussed below) for charging the battery pack10.

As shown inFIG. 1, the battery cells11are connected between the battery contacts12and14. In addition, preferably connected between battery contacts13and14is a temperature sensing device15, such as a negative temperature co-efficient (NTC) resistor, or thermistor, RT. The temperature sensing device is preferably in closer proximity to the cells11for monitoring of the battery temperature. Persons skilled in the art will recognize that other components, such as capacitors, etc., or circuits can be used to provide a signal representative of the battery temperature.

The charger20preferably comprises a controller21, which in turn includes positive terminal (B+)17and negative (B−) terminal18, which are coupled to battery pack10via battery contacts12and14, respectively. The positive terminal may also act as an input, preferably an analog/digital input A/D, in order for the controller21to detect the battery pack voltage. In addition, the controller21may include another input TC, preferably an analog/digital input, which is coupled to the temperature sensing device15via the third battery contact13(S). This allows the controller21to monitor the battery temperature.

Controller21may include a microprocessor23for controlling the charging and monitoring operations. Controller21may control a charging power source for providing power to the battery pack10, such as current source22that provides current to battery pack10. This current may be a fast charging current and/or an equalization current. Current source22may be integrated within controller21.

Controller21preferably has a pulse output PO, which sends a pulse signal unto the same line that sends power to the battery pack10. The pulse signal may have an amplitude of 5 volts. Preferably the pulse signal generated by the controller21goes through a diode D23and/or a resistor R54.

With such arrangement, controller21can determine whether a battery pack10has been connected to the charger20.FIG. 2is a flowchart illustrating the process for determining whether a battery pack10has been connected to the charger20.

First, the current source22must be off (ST1). The controller21then sends a pulse signal via pulse output PO (ST2).

The controller21then checks whether the input A/D has received a pulse (ST3). If a pulse was received, a battery pack10is not connected to the charger20.

On the other hand, if a pulse was not received, the controller21would interpret this to mean that a battery pack10is connected to the charger20. Persons skilled in the art will recognize that the voltage at input A/D will be substantially constant since resistor R54and diode D23will not allow a significant current to generate an AC signal across the battery. Since the pulse was not received, controller21would then start charging battery pack10by turning on current source22(ST4).

Controller21then senses the battery voltage V0via input A/D (ST5). Controller21compares battery voltage V0to a certain threshold X (ST6). If battery voltage V0is below threshold X, charging continues and controller21continues to sense and compare the battery voltage V0.

If battery voltage V0exceeds (or is equal to) threshold X, controller21then assumes that the battery pack10has been removed from charger20and stops charging by turning the current source off. Persons skilled in the art will recognize that it is preferable to provide a relatively high threshold so as to not prematurely terminate charging, resulting in an undercharged battery pack. Accordingly, it is preferable to provide a threshold of at least 30 volts.

FIG. 3is an exemplary schematic diagram of the charger ofFIG. 1. Preferably, the values of the different components of are as follows:

Persons skilled in the art will recognize that the pulse output PO and input are pins15and7of IC2, respectively. Persons skilled in the art will also recognize that diode D23and resistor R54are the same components inFIGS. 1 and 3.

Persons skilled in the art should recognize that the charger shown inFIG. 3is connectable to a vehicle battery, rather than to an AC source. Nevertheless, persons skilled in the art will know how to modify the power supply within the charger to accept power from an AC source.

Finally, persons skilled in the art may recognize other additions or alternatives to the means disclosed herein. However, all these additions and/or alterations are considered to be equivalents of the present invention.