The invention relates to rechargeable alkaline manganese (RAM) batteries. More particularly, the invention relates to RAM batteries having an overcharging protection circuit built into the battery.
Disposable or single-use alkaline batteries have been used as sources of electrical power in a variety of applications. In electronic devices, single-use alkaline batteries, or primary cells, provide an inexpensive and long-lasting power supply. Nonetheless, in some high-drain and repeated use applications consumers demand a rechargeable power supply to reduce the need to change batteries and to reduce operational cost. For example, cordless phones typically use the rechargeable nickel-cadmium (NiCd) battery system as a power source in a battery pack configuration of 2 to 4 cells in-series. NiCd batteries are readily available at a reasonable cost from a large number of suppliers and the charging circuitry for these batteries is usually very simple. However, the NiCd battery uses Cadmium (Cd) as an active electrochemical ingredient, which is extremely toxic and should be avoided from an environmental point of view. In addition, NiCd batteries exhibit a “memory effect” if recharged prior to complete discharge that limits the amount of charge that can be accepted by the battery, thereby reducing the effective duration with which an electronic device can be used. Another rechargeable battery is the nickel-metal hydride (NiMH) battery. Although these batteries do not exhibit a noticeable “memory effect” as previously described, the cost of these batteries is significantly greater than NiCd. For these reasons and others, it is desirable to provide an alternative rechargeable battery that is inexpensive, does not exhibit a “memory effect”, and is environmentally benign. It is further desirable to provide such a battery in a manner that permits easy replacement of NiCd or NiMH batteries in existing electronic devices without modification of the built-in charging circuit.
Rechargeable alkaline manganese (RAM) batteries are secondary cells that overcome many of the aforementioned problems with NiCd and NiMH batteries. These batteries are described in U.S. Pat. Nos.: 5,281,497; 5,424,145; 5,626,988; 6,099,987; and, 6,361,899, which are hereby incorporated by reference. When RAM batteries are charged using the voltages provided in charging circuits designed for use with NiCd batteries, dangerous conditions such as off-gassing and cell leakage can result. Special chargers are therefore normally required for RM batteries. Although it would be desirable to replace the original equipment manufacturer (OEM) NiCd or NiMH battery packs in existing electronic devices with RM battery packs, the embedded charging circuits in those devices are incompatible with RAM batteries and would cause overcharging. There is therefore still a need for an alternative rechargeable battery that can be safely recharged using an existing charging circuit (in an existing electronic device) that is meant for use with a different type of rechargeable battery.
A rechargeable alkaline manganese (RAM) battery or battery pack comprising an overcharging protection circuit that allows the RAM battery or battery pack to be charged using a charging circuit designed for use with a different type of rechargeable battery, for example a NiCd or NiMH rechargeable battery. The battery of the present invention is particularly advantageous as a replacement battery for use in devices having an embedded charging circuit designed for use with NiCd or NiMH batteries. The overcharging protection circuit may be provided in a battery pack that allows the individual RAM cells to be removed and replaced. Alternatively, the overcharging protection circuit may be installed in the device itself. When the battery pack is provided as original equipment in an electronic device, an activation key may be provided that prevents discharge of the batteries before the device is used.
The overcharge protection circuit comprises a rectifier, a shunt regulator, and a voltage divider. The rectifier prevents back-charging of the charging circuit through discharge of the battery. The shunt regulator allows the charging circuit to charge the battery until a specified voltage has been reached, after which the battery is by-passed. The voltage divider limits the voltage supplied by the charging circuit to a suitable value for safely charging the RAM battery. The exact arrangement of components in the overcharge protection circuit is unimportant, provided that these three functions are provided. Some or all of the components of the overcharge protection circuit could be replaced by integrated circuits that perform the functions previously described without affecting the way in which the invention works. The overcharge protection circuit may be provided separately or integrated with the RAM battery or battery pack and co-operates therewith to achieve a desired result; that is, the safe charging of the RAM battery or battery pack by an existing charging circuit meant for use with a different type of rechargeable battery.
Having summarized the invention, preferred embodiments thereof will be described with reference to the accompanying figures, in which:
a shows a 2-cell series embodiment of the present invention;
b shows another 2-cell series embodiment of the present invention;
a shows a 3-cell series embodiment of the present invention;
b shows another 3-cell series embodiment of the present invention;
a shows a 4-cell series embodiment of the present invention; and,
b shows another 4-cell series embodiment of the present invention.
Referring to
Specifications for components in
The principle of the overcharge protection circuit (OPC) in
Each cell is in parallel with a sub-circuit, OPCx, of the overcharging protection circuit. For example, cell-1 is in parallel with OPC-1 that comprises a shunt regulator U1, along with a voltage divider comprising resistors R1 and R2.
As long as cell-1 voltage is low all charge current flows through the cell. As soon as the cell voltage reaches a specified charge voltage (for example, 1.65V), charge current is by-passed by the shunt regulator U1 and does not charge the cell-1, thus keeping the cell voltage at 1.65V to avoid overcharging of the RAM cell.
The voltage divider comprising resistors R1 & R2 determines the final charge voltage supplied to the RAM cell. The rectifier diode D3 prevents RAM cell discharge by back-feeding the constant current (CC) power source.
The same principle applies to the cell-2.
Although the overcharge protection circuit is normally used with a CC power source (for example, a solar panel, a current regulated power supply, etc), it may be adapted for connection to a constant voltage (CV) power source in special situations.
The nominal voltage (at load current 100 mA) of the CC power supply should be higher than the total voltage of the cells in series. In this embodiment, the CC power supply is specified around 100 mA (max. <110 μA) for the AMS431LCN, etc. However, the shunt regulator still has a low rate of electronic leakage. For instance, the shunt regulator AMS431 LCN in
In one embodiment of the rechargeable battery or battery pack of the present invention, an activation key may be used for a fresh battery pack installed in a charging circuit to prevent cell leakage prior to initial use in the device. The activation key functions as a switch that disconnects the charge circuit from the battery when the batteries are not in use or are in storage at no load. The activation key may comprise an electrically non-conductive “pull tab” that is placed between two contacts to interrupt the connection between the battery and the charging circuit. The pull tab is removed prior to using the device to permitting recharging of the battery via the overcharge protection circuit. An alternative activation key means could be a conventional two pin jumper contact; in this case, the connection with the charge circuit is interrupted when the jumper is removed and installation of the jumper “key” connects the two jumper contacts, permitting the charging circuit to operate. Other suitable activation switch means can be used as long as they fulfill the requirement of preventing electronic leakage while the battery packs are in storage at no load (for example, while on the shelf in a retail store).
The overcharge protection circuit may be provided either as part of a battery pack or separately installed within the device. Irregardless of the foregoing, the individual cells may be removable from the overcharging protection circuit to permit replacement thereof.
Referring to
Specifications for components in
In tests it was shown that when a series RAM battery pack is charged by a low rate CC power supply, the voltage of the cells in the pack stays equal over a number of cycles. Based on this principle, the OPC can be simplified for a pack application. An embodiment of an OPC for charging a RAM battery pack having two AA cells in series is shown in
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Specifications for components in
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In any of the embodiments of an overcharge protection circuit described herein, means to prevent electronic leakage before use may be provided, for example, an activation key, jumper, or switch.
Other embodiments of the present invention will be evident to persons skilled in the art. Equivalents of components described herein may be substituted to achieve the same function without having an effect on the way in which the invention works. The preferred embodiments described herein are provided by way of example and are not meant to be construed in a limiting sense.
This application claims the benefit of U.S. 60/604,430, filed Aug. 26, 2004, which is hereby incorporated herein by reference.
Number | Date | Country | |
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60604430 | Aug 2004 | US |