GB2277384A

GB2277384A - Electrically heated mirror

Info

Publication number: GB2277384A
Application number: GB9317654A
Authority: GB
Inventors: David James Snowdon
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-03-23
Filing date: 1993-08-25
Publication date: 1994-10-26
Anticipated expiration: 2013-08-25
Also published as: FR2703207A1; GB2277384B; GB9317654D0; FR2703207B1; GB9306011D0

Abstract

An electrical heating device 8 associated with a mirror to remove or prevent condensation is powered by a voltage reduction unit, such as a transformer, which reduces the mains electrical supply to 30 - 50 volts. Operation may be controlled by a humidity detecting switch. In a second embodiment (Fig 7) an accumulator (14) and charging circuit (15) are provided behind the mirror housing, for attachment to the transformer output. <IMAGE>

Description

Electrical Heating Device The invention relates to an electrical heating device associated with a mirror which acts in a safe manner to remove or prevent condensation forming on the reflective surface of the mirror.

A common problem which occurs when mirrors are located in moist or humid environments, is that condensation is prone to form on the glass obscuring the reflective surface of the mirror and causing inconvenience to the user, for example, in bathrooms, changing rooms in public and private leisure facilities or in commercial hotels, where the problem of condensation is particularly acute due to the relatively small areas and nonavailability of external ventilation.

It is known from the automotive field to use electrical heating devices to demist rear windows and external mirrors. Previous attempts to extrapolate this technology to mirrors located, for example, in bathrooms has proved unsuccessful in practice. In bathrooms and other domestic and commercial situations the electrical power required to supply heating elements associated with mirrors, is derived from mains electricity and not from the inherently safe extra low voltage isolated D.C. battery systems found in automotive applications. The United Kingdom has particularly stringent regulations (IEEE wiring regulations) regarding the safety of mains powered electrical devices in bathroom environments.Therefore, in order to comply with safety requirements, mains electrical power supplied to bathrooms or changing rooms must be kept out of reach, for example, light switches are either located outside these rooms or are mounted on the ceiling and operated with an insulating pull cord.

The present invention, however, relates to an electrical heating device consisting of a voltage reduction unit, such as a transformer, which is suitable to reduce the normal mains electrical supply found in homes and other recreational or industrial premises to a safe, but effective voltage from which there is negligible risk to the user of an electrical shock. In the EC, voltages below 50 volts derived from earth screened transformers to European standard EN 60742 are known as Safety Extra Low Voltages (SELV). A SELV is safe to touch and can, therefore, be used in bathrooms etc., without representing a risk of causing an electrical shock, provided that the transformer, for example, is either removed from the bathroom or is mounted out of reach.

The voltage reduction unit is constructed in such a manner that the risk of electrical shock to the user from the voltage reduction unit is reduced to a minimum. It is, furthermore, installed in such a way that maximum safety is achieved. For example, the voltage reduction unit can be accommodated within a housing means. Such housing means can be adapted to be mounted on a ceiling or wall remote from the user and can contain other components necessary for the operation of the voltage reduction unit. Therefore, not only is the output electrical supply safe, but the parts of the electrical heating device utilising the mains voltage are safely constructed.

The present inventor has found that previously known heated bathroom mirrors have not been effective either because they failed to comply with the relevant safety requirements or because they operated at an unsuitable voltage. As stated hereinbefore, a mains voltage above the upper limit of SELV presents an unacceptable safety risk. However, the present inventor has surprisingly found that the application of a 12 volt system adapted from an automotive heated device results in a less than optimum transformer and interconnecting cable design, so that, the heated mirror fails to be effective for use in domestic or commercial situations as described hereinbefore.

The present inventor has further found that the heated mirror of the present invention operates most effectively when supplied with a voltage of between 30 and 50 volts, more preferably between 30 and 35 volts. When supplied with such voltages derived directly from the mains source, the electric heating device of the present invention very effectively demists a mirror located in a humid environment and furthermore, does not present a safety hazard.

The applying of a higher voltage to the heating device, but which is still below the upper limit of the SELV, means that the transformers which can be suitably used are smaller, lighter and less expensive and the inter connecting conductor size is also reduced, compared with transformers and conductors which are required with lower voltages, typically 12 volts. -For example, increasing the supply voltage from 12 to 48 volts equates to a current reduction by a factor of 4. This allows a reduction in conductor size by a factor of approximately 3.5.

The safe and effective low voltage derived from the voltage reduction unit is fed via the electrical conductors of reduced size, to a heating element which is in close proximity to the electrically insulated rear of a mirror. The voltage output from the voltage reduction unit and the resistance of the heating element are so matched as to generate sufficient heat to remove or prevent condensation on the reflective surface of the mirror.

The lower current of the electrical heating device of the present invention has the further advantage, that the heating elements also have reduced cross-sectional areas. Hence, it is possible to produce with relative ease, heating elements of small depth which cover the entire rear surface of the mirror with a constant density. This ensures that the heating power transfer will be uniform resulting in the even removal of condensation from a mirror without the development of local hot spots.

Therefore, the present invention relates to an electrical heating device for use in association with a mirror which comprises a voltage reduction means for reducing the voltage of the input electricity derived from the mains supply and a conducting means for conducting electricity of reduced voltage derived from the voltage reduction means to a heating means, wherein the voltage reduction means is dimensionally suitable for reducing the voltage of the input electricity to a voltage of between 30 and 50 volts.

The present invention further relates to an electrical heating device for use in association with a mirror which comprises an accumulator for storing electricity, for example, the reduced voltage supply derived from the voltage reduction unit and conducting means for conducting the electricity derived from the accumulator to a heating means. This enables the electrical heating device to be used in association with a mirror for limited periods without direct connection to the mains supply.

The mirror may either be situated in a fixed location, or alternatively may be portable. The electrical accumulator and conducting means, such as, associated charging circuitry, may be attached to the mirror unit as a permanent fixture. For example, the accumulator can be located at the rear of the mirror, preferably in a rear housing. The charging circuitry may be arranged so that the heating element will only activate when disconnected from the mains voltage, therefore, ensuring complete safety.

In this case, due to the absence of interconnecting cables and the need to keep the weight of and cost of the product to a minimum, the most effective result is achieved when the heating element is supplied with as low a voltage as possible in line with available batteries. Taking into account the storage capacity of rechargeable cells, then the optimum supply voltage will preferably be between 2.4 and 6.0 volts.

The voltage reduction unit of an embodiment of the invention is constructed and designed as described herein, to ensure that after its installation and during use it is inherently safe. A particular advantage, therefore, of the voltage reduction unit of the present invention is that it can only be installed in such a manner that no risk of electrical shock occurs, but at the same time it is able to supply a suitable voltage to the electrical heating device to result in effective removal of condensation.

Hence, by utilising safe, but effective low voltages as described herein, condensation can be safely and successfully prevented or removed from mirrored surfaces in inherently damp and humid locations, such as bathrooms, by the action of electrical heating.

Reference is now made to the accompanying drawings, which are in no way intended to limit the invention, in which: Figure 1 shows a plan view of an electrical heating device according to an embodiment of the invention.

Figure 2 shows a plan view of the rear of a mirror, with a cut out section.

Figure 3 shows a side view of a mirror and electrical heating device according to an embodiment of the invention.

Figure 4 shows a perspective view of an embodiment of the invention including the housing.

Figure 5 shows a rear view of the housing.

Figure 6 shows a perspective view of a mounted embodiment of the invention.

Figure 7 shows a side view of a mirror and an electrical heating device according to a second embodiment of the invention.

The electrical heating device 1 shown in Figure 1 comprises housing means 2 having a voltage reduction unit 3 and a cord operated switch 4, together with such electrical connecting and terminating devices 5 as are necessary to interconnect the electrical components. The housing means 2 is so constructed that when correctly installed, using the built in locations 6, to a ceiling or wall, then the cord operated switch 4 can be used to switch on the normal mains voltage. The cord operated switch 4, therefore, being accessible to the user at a point remote from the housing means 2. At the same time, dangerous components of the mains voltage are kept within the ceiling or wall mounted housing means and out of reach of the user.Power output leads 7 which conduct the safe and effective output voltage of between 30 and 50 volts, are built into the housing means 2 and are also not accessible to the installer.

The voltage reduction unit would typically be a transformer constructed with two separated insulated windings arranged such that the maximum output voltage would be between 30 and 50 volts, preferably between 30 and 35 volts, to earth or between conductors. The transformer may also incorporate an earthed screen between the windings for extra safety.

As a further alternative, the manual cord operated switch 4, can be replaced by a remote switch located on a wall and accessible to a user. In addition, the switch 4 can be replaced by a humidity detecting switch which is connected to provide automatic operation when the humidity level in the environment reaches a pre-set level.

The desired low, effective voltage output is fed from the output leads 7 which terminate on the rear of the mirror unit 11 and are fed, according to one embodiment of the invention, to the heating element 8 as shown in Figures 2 and 3. The heating element may be of a coiled or serpentine configuration located on the rear surface of a mirror unit, however, the shape of the heating element can be varied. The non-reflective rear surface of the mirror is insulated from the electrical heating element 8 by a layer of insulating material 10. The outer face of the heating element 8 is covered by a further layer of insulating material 9, the whole forming a multi layer sandwich structure which is electrically safe as shown in Figure 3.

Figures 4, 5 and 6 show in detail a preferred construction of the housing means 2.

In Figure 4, the housing means 2 is constructed in two halves, 2a, 2b. The two halves of the unit can be separated by removing screws 20 which are accessible on the front half 2a of the housing means 2. When the two halves of the housing means are separated, mounting bosses 21, as shown in Figure 5, which are mounted in the rear half 2b are visible in each corner of the rear half 2b. The rear of the housing means can, therefore, be used as a template to mark the positions of the mounting boss onto the mounting surface 22, for example, a bathroom ceiling (Figure 6).

As shown in Figure 5, the mains supply is connected via the electrical connecting and terminating devices 5, for example, by connecting the electrical heating device to the lighting circuit, which would normally be protected by a 5 or 6 amp fuse or circuit breaker. The electrical heating device should be internally fused and consume a maximum of 250mA.

Figure 6 shows the housing means securely mounted to a desired surface 22, for example, the ceiling of a bathroom, by means of screws 23 in the rear 2b of the housing means 2. For safety and aesthetic reason, the front 2a of the housing means 2 acts as a cover and is secured onto the rear 2b by means of the screws 20.

In a further possible embodiment of the invention shown in Figure 7, the low voltage derived as above, is terminated on the rear of the mirror unit 11 via an insulated connector 12. This insulated connector 12 is part of a permanently attached housing 13 containing an electrical accumulator 14 and its associated charging circuitry 15. The mirror 11 can be of a similar construction to that shown in Figures 2 and 3, with the exception that the supply to the heating elements 8 is derived from the accumulator 14. The circuitry 15 is so arranged that the heating element 8 will only activate when disconnected from the mains voltage ensuring complete safety.

Claims

1. An electrical heating device for use in association with a mirror which comprises a voltage reduction means for reducing the voltage of the input electricity derived from the mains supply and a conducting means for conducting electricity of reduced voltage derived from the voltage reduction means to a heating means, wherein the voltage reduction means is dimensionally suitable for reducing the voltage of the input electricity to a voltage of between 30 and 50 volts.

2. An electrical heating device according to Claim 1, wherein the voltage reduction means is dimensionally suitable for reducing the voltage of the input electricity to a voltage of between 30 and 35 volts.

3. An electrical heating device according to Claim 1 or 2, wherein the voltage reduction means is a transformer.

4. An electrical heating device according to any of claims 1 to 3, wherein the voltage reduction means is located in a housing, wherein said housing is remote from said heating means.

5. A mirror for use in humid environments which comprises a reflective surface wherein at least a part of the rear of said reflective surface is insulated, in association with an electrical heating device according to any of claims 1 to 4.

6. A mirror according to Claim 5, wherein the heating means is located on the insulated rear of the reflective surface of the mirror.

7. An electrical heating device for use in association with a mirror, which comprises an accumulator for storing electricity and conducting means for conducting electricity from the accumulator to a heating means.

8. An electrical heating device according to Claim 7, wherein the accumulator is capable of storing electricity supplied to said accumulator with a voltage of between 2.4 and 6 volts.

9. An electrical heating device according to claim 7 or 8, wherein at least the accumulator and conducting means are located within a housing means.

10. An electrical heating device according to any of Claims 7 to 9, comprising a cut off means so that electricity will only be supplied from the accumulator to the heating means when the accumulator is disconnected from the mains electricity supply.

11. A mirror for use in humid environments which comprises a reflective surface, wherein at least a part of the rear of said reflective surface is insulated and an electrical heating device according to any of Claims 7 to 10.

12. A mirror according to Claim 11, comprising an electrical heating device is according to Claim 9, wherein the housing means is located at the rear of the mirror and the heating means is located on the insulated rear of the reflective surface of the mirror.

13. An electrical heating device substantially as hereinbefore described with reference to any of Figures 1 to 6.

14. An electrical heating device substantially as hereinbefore described with reference to Figure 7.