GB2256531A

GB2256531A - Heatsinking of electrical fittings

Info

Publication number: GB2256531A
Application number: GB9111453A
Authority: GB
Inventors: Kevin Ray
Original assignee: GREENFIELDS EUROP Ltd
Current assignee: GREENFIELDS EUROP Ltd
Priority date: 1991-05-28
Filing date: 1991-05-28
Publication date: 1992-12-09
Also published as: GB9111453D0

Abstract

A heatsink (20) is sandwiched between a fitting plate (12) (which may include, for example, a switch or outlet socket) and a fitting box and electronic circuitry is mounted inside the heatsink in thermal contact therewith. Heatsink (20) may be in the form of a square annulus having fins (22). Circuit board (24) is disposed within aperture (26) and triac (30) has its heatsink tab (32) lying flat against surface (34) of the heatsink. Heatsink (20) is partly filled with potting resin (42). The fitting may be secured to a junction box. <IMAGE>

Description

HEATSINKING OF ELECTRICAL FITTINGS This invention relates to electrical fittings, and in particular is concerned with heats inking of electrical fittings so as to dissipate heat generated thereby.

Typical of the electrical fittings with which this invention is concerned are light dimmers, motor speed controllers, motor power controllers and power factor regulators. Modern fittings of this type may employ a solid-state switch such as a triac, and whereas triacs generate little heat compared with, say, rheostats, the dissipation of heat is still a problem when large loads are involved.

In accordance with one aspect of the present invention, there is provided a combination of an electrical fitting box, an electrical fitting plate, a heatsink sandwiched between the fitting box and the fitting plate, and an electronic circuit disposed inside the heatsink in thermal contact therewith.

In accordance with another aspect of the present invention, there is provided an electrical fitting for attachment to an electrical fitting box (such as a standard mains wall box, pattress box, or junction box), comprising a heatsink, electronic circuitry (such as a light dimmer circuit, motor speed controller circuit, or power factor regulator circuit), a face plate, and means for attaching the fitting to the fitting box, wherein:: the heatsink comprises an annular member having opposite faces, a finned peripheral surface, and an aperture extending through the member between the opposite faces, one of the faces being suitable for fitting to the fitting box; the face plate is mounted across the other face of the heatsink (and may be a blanking plate, or may include a switch, an outlet socket, a spur outlet, a variable control device, a holder for a fuse, and/or an indicator, respectively connected to the electronic circuitry); the electronic circuitry is mounted at least partly within the aperture of the heatsink (and may be potted in resin therein) and has at least one heat-generating component in thermal contact with the heatsink; and the attachment means is arranged for attaching the fitting to the fitting box such that the heatsink is sandwiched between the face plate and the fitting box.

By sandwiching the heatsink between the plate and the box, the heatsink can provide good thermal contact with the surrounding air, a pleasing design can be achieved, and the fitting can be readily used with existing installations.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of one embodiment of a fitting shown spaced apart from a fitting box; Figure 2 is a side view, partly in section, of the Figure 1 fitting mounted on a pattress box; Figure 3 shows a second embodiment of a fitting mounted on a junction box of an electrical installation.

Referring to Figures 1 and 2, the face plate of the electrical fitting 10 is provided by a standard high-current mains switch 12 with neon indicator 14, for example Crabtree type 4013/3. The rear rim 16 of the switch 12 is mounted on the front face 18 of a heatsink 20 which is in the form of a square annulus having five peripheral heatdissipating fins 22. A circuit board 24 is disposed within the aperture 26 through the annul us and has four terminal posts 28 (two of which are shown) which are connected into corresponding terminal sockets at the back of the switch 12. Electronic components are mounted on the circuit board 24 including a triac 30 which is disposed so that its heatsink tab 32 lies flat against an inside surface 34 of the heatsink 20 and is secured thereto, for example by a nut and bolt.

A connector block 36 is electrically connected by wiring 38 to the circuit board 24 and provides for connection to external wiring 40.

After assembly, the inside of the heatsink 20 is partly filled with resin 42 so that the circuit board 24 and part of the connector block 36 are potted in the resin. The switch 10 has a pair of fixing holes 44, and aligned holes are provided in the heatsink 20 or the potting resin 42 so that a pair of fixing screws 46 can pass through the holes into engagement with threaded holes 48 of a standard metal wall box 50 (Figure 1), or plastics pattress box 50 (Figure 2).

Figure 3 shows, as an example of many possible modifications to the above arrangement, an alternative embodiment of fitting 52 in which the heatsink 20 is general circular rather than square and has a blanking face plate 54. The fitting is secured to a standard junction box 56 which is connected to a supply conduit 58 and via a feed conduit 60 to a standard box-mounted socket outlet 62.

Claims

1. An electric fitting for attachment to an electrical fitting box comprising a heatsink, electronic circuitry, a face plate and attachment means for attaching the fitting to the electric: fitting box, wherein: the heatsink comprises an annular member having opposite faces, a finned peripheral surface, and an aperture extending through the member between the opposite faces, one of the faces being suitable for mounting against the fitting box; the face plate is mounted across the other face of the heatsink; the electronic circuitry is mounted at least partly within the aperture of the heatsink and has at least one heat-generating component in thermal contact with the heatsink; and the attachment means is arranged for attaching the fitting to the fitting box such that the heatsink is sandwiched between the face plate and the fitting box.

2. A fitting as claimed in claim 1, wherein the faces of the heatsink are generally square, rectangular, or circular.

3. A fitting as claimed in claim 1 or 2, wherein the face plate includes a switch, an outlet socket, a spur outlet, a variable control device, a holder for a fuse, and/or an indicator, respectively electrically connected to the electronic circuitry.

4. A fitting as claimed in claim 1 or 2, wherein the face plate is a blanking plate.

5. A fitting as claimed in any preceding claim, wherein the electronic circuitry is configured as a light dimmer, motor speed controller, motor power controller, or power factor regulator.

6. A fitting as claimed in any preceding claim, wherein the electronic circuitry is potted in resin within the aperture of the heatsink.

7. A fitting as claimed in any preceding claim, wherein the attachment means includes a pair of holes extending through the face plate, such that a screw can pass through each hole and through the thickness of the heatsink for engagement with the fitting box.

8. An electrical fitting substantially as described with reference to the drawings.

9. A combination of a fitting as claimed in any preceding claim and an electrical fitting box having a size and shape complementary to the size and shape of said one face of the heatsink.

10. A combination as claimed in claim 9, wherein the fitting box is a standard mains wall box, pattress box, or junction box.

11. A combination of an electrical fitting box, an electrical fitting plate, a heatsink sandwiched between the fitting box and the fitting plate, and an electronic circuit disposed inside the heatsink in thermal contact therewith.