Battery charger

A battery charger comprising a housing including a compartment for holding battery cells, and an internal electronic charging circuit for charging battery cells in the compartment. A heat sink is located in close proximity to the compartment for physical contact by battery cells being charged to dissipate heat resulting from battery charging. The heat sink is exposed to the outside of the housing for heat dissipation, whereby fast charging is made possible.

The present invention relates to a battery charger for charging battery cells.

BACKGROUND OF THE INVENTION

The consumer type AA or AAA sized nickel metal-hydride (NiMH) or nickel cadmium (NiCd) rechargeable batteries have widely been in use. Various electrical appliances, such as digital cameras, video recorders, AV equipment, notebook computers, PDAs, cellar phones and toys, require high capacity and reliability AA or AAA sized rechargeable battery cells for operation. There is an ongoing demand for the battery charging time to be as short as possible.

However, a faster charge requires the use of a larger charging current, but a larger current may result in overheating of the batteries. As is known, overheating may damage the battery or reduce its capacity and number of life cycles. In general, a NiMH battery will only have part of its capacity available if the body rises to a temperature over about 60° C. during charging. The life cycle will also be shortened under this condition.

The subject invention seeks to mitigate or at least alleviate such problems by providing an improved battery charger.

SUMMARY OF THE INVENTION

According to the invention, there is provided a battery charger comprising a housing including a compartment for holding battery cells, and an internal electronic charging circuit for charging battery cells in the compartment. A heat sink is located in close proximity to the compartment for physical contact by battery cells being charged to dissipate heat resulting from battery charging. The heat sink is exposed to the outside of the housing for heat dissipation.

Preferably, the heat sink is located immediately behind the compartment.

More preferably, the heat sink has a part that is situated at an outer surface of the housing to dissipate heat.

Further more preferably, the heat sink part occupies an opening of the housing.

Yet further more preferably, the heat sink part lies substantially flush with a wall of the housing bearing the opening.

It is preferred that the heat sink part comprises fins.

In a preferred embodiment, the heat sink has two said parts that are situated at opposite outer surfaces of the housing.

More preferably, each heat sink part comprises fins forming part of and lying substantially flush with the corresponding outer surface.

In a preferred embodiment, the heat sink is located at an inner portion of the compartment.

More preferably, the heat sink defines the inner portion of the compartment.

Further more preferably, the heat sink includes a plurality of substantially parallel part-cylindrical channels at the inner portion of the compartment.

Yet further more preferably, the heat sink has a part situated at an outer surface of the housing for heat dissipation, and one of the channels is provided immediately behind the heat sink part.

Yet further more preferably, the channels have a diameter that is substantially the same as that of said battery cells.

Yet further more preferably, the channels have substantially the same length as said battery cells.

Advantageously, the charging circuit includes a temperature sensor in direct contact with the heat sink.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the drawings, there is shown a battery charger10embodying the invention, which has a generally flat rectangular housing100formed by upper and lower shell-like plastic parts110and120, and an electronic charging circuit (not shown) in the housing100. Each housing part110/120has over its rear end portion a rectangular opening112/122which spans transversely across the entire width of the part110/120and extends round into left and right walls thereof as respective oblong side openings114/124. The openings112and122have the same shape and size and are aligned back-to-back with each other.

The battery housing100includes a pair of battery compartments210and220provided within the housing openings112and122respectively, each for holding therein two battery cells400for charging by the charging circuit. Each compartment210/220is defined by a good thermally conducting, aluminum heat sink310/320fixed within the corresponding opening112/122. The heat sink310/320is thus located immediately behind and in close proximity to the compartment210/220, for assisting dissipation of heat generated as a result of charging of the battery cells400.

Each heat sink310/320is manufactured by way of an extrusion process, having a uniform cross-section that is symmetrical as between its left and right sides about a central axis. The heat sink310/320has two sets of left and right side cooling fins312/322facing outwards on opposite sides of the housing100. An integral base web314/324of the heat sink310/320inter-connects the two sets of fins312/322. Each set has three parallel fins312/322, i.e. upper, middle and lower fins312A-312C/322A-322C, with the lower fin312C/322C connected directly to the corresponding side of the web314/324.

The cavity as defined between the fins312/322and the base web314/324of the heat sink310/320constitutes the compartment210/220, having an inner portion defined by the web314/324. The compartment210/220is about deep enough to fully contain the battery cells400.

The base web314of the upper heat sink310is shaped to have a pair of generally semi-cylindrical channels316which extend parallel to each other and to the fins312for locating two AA sized battery cells400. The channels316have a diameter practically the same as, or marginally larger than, that of the battery cells400and about the same length for matching them, such that the physical contact area between the cells400and the channels316is maximized for efficient heat transfer from the former to the latter. For better heat conduction, the two channels316lie immediately at the back of the corresponding sets of fins312, whereby the channels316are spaced apart.

The base web324of the lower heat sink320is also shaped to have a pair of similar channels326lying immediately at the back of the corresponding sets of fins322, except a pair of narrower channels328are formed between the two channels326. The inner channels328serve to locate two AAA sized battery cells420, in place of the AA sized battery cells400by the outer channels326. Likewise for contact area and heat transfer, the inner channels328are made to have practically the same diameter as the battery cells420. On either side, the larger and smaller channels326and328merge slightly together such that their cross-sections are less than semi-circular.

The two heat sinks310and320are fixed within the corresponding housing openings112and122, facing in opposite directions, say by rivets to respective back plates116and126of and interfacing the two housing parts110and120. For either heat sink310/320, the lower fins312C/322C are relatively shorter than the others and are concealed by the corresponding housing part110/120just below the side openings114/124.

The upper and middle fins312A&B/322A&B of each heat sink310/320extend outwards and occupy the relevant side openings114/124, generally matching and lying flush therewith. As these fins312A&B/322A&B are situated right at the outer surface of the housing100and form part of the housing wall bearing the outer surface, they are exposed to the outside of the compartment210/220or housing100for open heat dissipation.

A pair of electrical contacts450is located adjacent opposite ends of each channel316/326/328for contacting and holding the battery cells400/420in position. The lower housing part120supports a pair of folding contact prongs130that acts as a power plug for connection to a mains power socket.

The charging circuit will not be described in detail for clarity (as its circuitry is generally known in the art), except that it includes a temperature sensor500for control and/or overheating protection. The sensor500is mounted in direct contact with both heat sinks310and320for detecting the temperature of the battery cells400/420via the heat sinks310/320.

Given its high thermal conductivity, the heat sinks310and320are capable of dissipating the battery heat efficiently and relaying the battery temperature accurately to the charging circuit/sensor500without delay.

With the use of a heat sink in a battery charger of the subject invention, as heat can be dissipated quickly, a relatively larger charging current can be used without overheating the batteries, whereby fast charging (in less than 30 minutes) is made possible, within size limitation of the charger.

The subject battery charger may be modified for use with any other sizes of batteries, such as the C and D sized battery cells. It may also be designed for recharging all types of batteries such as those made of NiMH, NiCd or any other materials, either in a battery pack form or single piece form.

The heat sink is made of a high thermal conductivity material, whether of metal or non-metal, for direct contact with the bodies of the batteries, and may be made in any shape, configuration and/or dimension, with or without fins.

The invention has been given by way of example only, and various other modifications and/or variations to the described embodiments may be made by persons skilled in the art without departing from the scope of the invention as specified in the accompanying claims.