GB2268006A

GB2268006A - A battery charger for nickel-cadmium cells

Info

Publication number: GB2268006A
Application number: GB9212919A
Authority: GB
Inventors: Peter F Barker
Original assignee: NITECH Ltd
Current assignee: NITECH Ltd
Priority date: 1992-06-18
Filing date: 1992-06-18
Publication date: 1993-12-22
Also published as: GB9212919D0

Abstract

The charger has an access lid 11 hinged at 12 and provided with a seal 13 so that on closure of the lid 11 a cell- receiving housing is sealed to contain any gas vented from the cells on overcharging. A differential pressure sensor, sensing the pressure differential between the housing and the ambient atmosphere, is responsive to such venting to terminate charging. Alternatively, or additionally, charging may be terminated by a pyroelectric transducer which detects thermal radiation from a cell being charged. Charging may be inhibited by a switch 17 unless the lid 11 is closed. In order to avoid operation with an impaired seal 13, charging may be enabled only when a small threshold over-pressure (generated by other means) exists in the cell- receiving housing. <IMAGE>

Description

A Battery Charger Device This invention relates to battery chargers.

Battery chargers for electric batteries particularly nickel cadmium batteries, become ever more common as technology develops. Unfortunately, despite the improvements in techniques of charging, and in the control circuits, there is still the remote possibility of a failure in the charger leading to a potentially very dangerous stressing of the cell under charge.

There can be overheating leading to gas discharges and/or explosion. The invention aims to guard against such problems.

Accordingly, the invention proposes a battery charger for nickel-cadmium cells comprising an input supply to an electronic charging circuit and a battery holder to receive batteries to be charged, wherein said battery holder comprises a closed housing with a sealed access lid for containing any adverse reaction by a battery to charging, a sensor associated with said housing for sensing such a reaction, and cut-off means in said input supply to disconnect it from the charging circuit in response to signals from said sensor Such a charger allows any loose battery to be inserted and charged, whereas in the past, each individual cell has had to include a temperature sensor of its own.

Moreover, the sensing is quite independent of the electronic charging circuit itself.

An exemplary embodiment of the invention will now be described with reference to the accompanying drawings, in which Fig.1 is a side view of a charger according to the invention with the lid in place, and Fig.2 is a plan view with the lid removed.

Fig.l shows a polycarbonate or ABS plastics casing 10, with a lid 11 hinged at 12. The lid is sealed hermetically by a neoprene seal 13 along all its joint lines, and encloses the compartment 14 which receives two nickel cadmium cells 15 for recharging. The other part 16 of the casing 10 contains the charger electronics and control system.

Within compartment 14, or at least communicating with it, is a sensor (not shown).

A characteristic of all nickel cadmium cells in an overcharge situation is the fast build up of gases within the cell due to the inability of the electro chemical system to continue to recombine oxygen and hydrogen. Nickel cadmium cells are fitted with release vents which will release the build-up of gas, usually accompanied by liquid sodium hydroxide in the event of an over-pressure situation.

The charging compartment 14 is provided with a differential pressure sensor. A differential sensor would be used because this would overcome the need to take account of variations in ambient air pressure conditions, due to changes in barometric pressure, altitude and other contemporary environmental conditions. This differential pressure transducer immediately senses the venting of any, or all, of the cells in the battery being rapid-charged and would be connected to a device, independent of the fast charger circuitry, which would totally remove all power from the circuit. This latter device is either electro mechanical or totally electronic but will ensure failsafe operation.

A further possibility would be to incorporate in addition to or instead of, the pressure sensor some form of pyroelectronic transducer which would detect thermal radiation from the battery being charged and similarly to the pressure transducer, would be designed so that above a certain preset threshold the charging system would he completely deactivated.

The concept of the above system is to independently sense a distress condition in the nickel cadmium battery being fast charged in a manner that is completely independent to the fast charger itself. The advantages of the charge proposed are that it will work equally well for any kind of cells being charged and therefore does not require battery packs to be either specially manufactured to incorporate sensors or alternatively to be fitted with special sensors priorto being fast charged by the apparatus.

The charger may incorporate an interlock switch 17 so that the charging circuit can only be operated when the lid 11 is closed. In order to avoid operation if the seal 13 was impaired, a further inhibit system could be used to ensure operation only when a small threshold over-pressure generated by other means exists in the compartment.

Claims

1. ss battery charger for nickel-cadmium cells comprising an input supply to an electronic charging circuit and a battery holder to receive batteries to be charged, wherein said battery holder comprises a closed housing with a sealed access lid for containing any adverse reaction by a battery to charging, a sensor associated with said housing for sensing such a reaction, and means in said input supply which inhibit the charging circuit in response to signals from said sensor.

2. a battery charger as claimed in claim 1 wherein the housing has a hinged access lid with a neoprene seal around it.

3. A battery charger as claimed in claim 1 or 2 wherein the sensor is a pressure sensor.

4. A battery charger as claimed in claim 3 wherein the sensor is a differential pressure sensor, sensing the pressure differential between the inside of the housing and the ambient atmosphere.

5. A battery charger as claimed in any preceding claim which includes a thermal sensor.

6. A battery charger as claimed in claim 5 wherein said thermal sensor is a pyroeletric sensor.

7. A battery charger as claimed in any preceding claim wherein the lid interacts with an interlock switch which inhibits the charging circuit if the lid is not closed.

8. A battery charger as claimed in claim 3 which includes a gas constant pressure generator and the charging circuit is inhibited unless a pressure equal to said constant pressure is present in the housing.