Cordless electrical appliances

Electrical connectors – Contact terminal – Having treated surface or distinct contact surface layer

Patent

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Details

439887, 439928, H01R 924

Patent

active

054135109

DESCRIPTION:

BRIEF SUMMARY
This invention relates to cordless electrical appliances such as hot water jugs, kettles and electric irons. Such appliances are provided with a base or stand upon which the appliance can be placed for the supply of electrical power to the appliance. It is the base rather than the appliance which is connected to the mains power supply. The base includes a female socket connector which is connected to the power supply and is arranged to be engaged by a male pin connector on the appliance when it is placed on the base. Likewise the act of removing the appliance from the female socket connector disengages the male pin connector from the female socket connector. Such an appliance and base therefor will hereinafter be termed an electrical appliance and base of the kind referred to.
With such an arrangement if electrical connection is made and broken between the pins of the male pin connector and the contacts of the female socket connector whilst the latter are live i.e. connected to the mains supply, arcing will occur which may cause unacceptable heating and erosion at the points of electrical contact. To avoid this problem the appliance may be provided with an snap-acting switch as proposed in UK Patent Application GB-A2208332 which is operated by interengagement of appliance and base and serves, when open, electrically to isolate the appliance from the male pin connector. Desirably the said switch serves to isolate the male pin connector from the appliance whilst electrical contact is made and broken between the male pin connector and the female socket connector thus avoiding the possibility of arcing.
As an alternative to providing an isolating switch as aforesaid the undesirable effects of arcing may be contained by thickly silver plating the pins of the terminal pin connector and/or by providing the pins and the female socket connector with copper backed silver contacts. These solutions, as also the provision of an isolating switch, are costly and it is an object of the present invention to provide a simple and inexpensive solution to the problem of arcing between male pin and female socket connectors of cordless electrical appliances.
This invention is based on the discovery that the undesirable effects of arcing can be overcome by providing a female socket connector having a copper backed silver contact mounted on a leaf spring and as an associated male pin connector, a pin of copper as opposed to brass. Copper backed silver contacts are in common use. Typically the thickness of the silver in such contacts is from 0.1mm to 0.3 mm with a copper backing of, for example, 0.7 mm. However the pins of male pin connectors are commonly made of brass. We have found that in use the mechanical wiping action of pin on silver contact which results as the pin is moved into and out of engagement with the leaf spring mounted contact and the making and breaking of the current results in a transfer of silver from the silver face of the leaf spring mounted contact onto the copper pin. The high thermal conductivity of the copper pin reduces the temperature at the contact/pin interface as does the heat sink effect of the copper backing of the contact. In the result wear at the contact interface is reduced. We have found that the silver transferred to the pin forms an atomically bonded surface layer, the thickness of which appears to reach an equilibrium during life testing.
Thus from a first aspect the invention provides an electrical appliance and base of the kind referred to wherein at least one electrical connection between the male pin and female socket connectors is formed by a leaf spring mounted copper backed silver contact, and a corresponding male pin being made at least in the contact forming region, of copper.
In one embodiment, both the line and neutral connections are formed as aforesaid.
Coppers which have proved suitable for male pins are industrially pure coppers according to BS2870 designated C101 and C106 (table 8) preferably with a hardness value of 70 to 95 HV. These coppers are examples of coppers substa

REFERENCES:
patent: 1966263 (1934-07-01), Roller
patent: 2058068 (1936-10-01), Duvall
patent: 2163704 (1939-06-01), Ritz-Woller
patent: 2497452 (1950-02-01), Hammell
patent: 4026627 (1977-05-01), Benasutti
patent: 4189204 (1980-02-01), Brown et al.
Dewent's Abstract No. 900 18 E/42, SU 890 464, publ. week 8242 MIRONENKO V G.
Patent Abstracts of Japan, vol. 2, No. 136, abstract of JP 53-102838, publ. 1978 Jul. 9, SHIN NIPPON SEITETSU K.K.

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