Apparatus for lowering the sound level of a ballast

Abstract: The invention relates to an apparatus for lowering the sound level of a ballast, said ballast comprising a base plate (1) and a sheet iron package with its winding as well as fastening brackets (2) fixed to the opposte ends of the base plate (1) and provided with holes (3) or recesses for fastening the ballast with screws or the like to a lighting fixture. In the vicinity of said holes (3) or recesses the flat, especially sheet-like fastening brackets (2) are separate from said base plate (1) and are connected to the base plate (1) through the intermediary of an elastic, flexible or low-friction spacer (4).

Description: The present invention relates to an apparatus for lowering the sound level of a ballast, said ballast comprising a base plate and a sheet iron package with its winding as well as fastening brackets fixed to the opposte ends of the base plate and provided with holes or recesses for fastening the ballast with screws or the like to a lighting fixture. A problem with type of ballasts has always been that a sufficient lowering of the sound level thereof is difficult. Thus, it is not sufficient to bring down the internal sound level of a ballast itself but also the sound level of a ballast fastened to a lighting fixture must be held below certain levels. A primary object is to bring the sound level of a ballast fastened to a lighting fixture to below 25 dB, and it would be particularly desirable to bring the sound level even to below 20 dB. One source of the sound has been found to be the fact that the oscillation of a sheet iron package in contact with the jacket sheet of a ballast (the lengthening and shortening of the entire package at a very low amplitude) transmits to the sheet metal housing of a ballast and further through the fastening points to the body of a lighting fixture. One possibility of reducing the sound level is to dimension the sheet iron package of a ballast for a low induction density, whereby the amplitude of said oscillation is reduced but the material costs of a ballast will increase. Attempts have also been made to solve the sound problem of a ballast in such a manner that, even if made of the same continuous sheet material, the fastening brackets and the base plate of a ballast are connected with each other through the intermediary of relatively thin, bent sheet sections, which absorb the the transmission of oscillation to the fastening brackets. However, this prior known solution is not mechanically strong since between the fastening brackets and the base plate of a ballast there are only thin webs of sheet whereby, as a result of even a minor loading, the base plate of a ballast may come into contact with a lighting fixture and the result will be a very high and disturbing level of sound. An object of the invention is to find such a solution for lowering the sound level of a ballast, which is mechanically firm, economically feasible, and provides a possibility of dimensioning a ballast for a high induction density. This object is achieved by the invention on the basis of the characterizing features set forth in the annexed claims. Two embodiments of the invention will now be described in more detail with reference made to the accompanying drawing, in which fig. 1 shows a ballast provided with an apparatus of the invention in a side, plan, and end view, the side view showing the partial sections along a line I-I shown in the end view, and fig. 2 shows an alternative embodiment for the invention in a similar manner, the partially sections of the side view being taken along a line II-II shown in the end view. The ballast includes a sheet metal housing 1 which tightly surrounds a sheet iron package fitted with a ballast winding. The alternating current passing through the winding creates in the sheet iron package an alternating magnetic field, wherein the induction density fluctuates between zero and a maximum value. If it is desirable to save active basst material, the peak value of induction density increases accordingly. The fluctuation of induction density occurring in the sheet iron package causes variation in the dimensions of the sheet iron package. Especially in the longitudinal direction of a ballast, the sheet iron package has a length fluctuating typically at an amplitude of 0,05 - 0,06 µ. This amplitude can be higher or lower depending on the induction density. The sheet metal housing 1 reduces the stray field of a ballast. Since the sheet iron package is in contact with the sheet metal housing 1, the oscillatory motion of the sheet iron package transmits also to the sheet metal housing. If such an oscillating sheet metal housing is fastened directly to a lighting fixture, the result will be a considerable increase in the sound level as compared to the sound produced by a ballast itself. However, the sound level of a ballast fastened to a lighting fixture can be substantially reduced with a fastening apparatus of the invention, whose embodiments will be described in more detail hereinbelow. In the case of fig. 1, the edge extensions of the base plate of a sheet metal housing 1 are folded to form U-slots 1a opening towards each other. The slots 1a are provided with spacers 4 of an elastic material for securing the edges 2b of a fastening bracket 2. The fastening bracket 2 is a sheet-like element and includes in the middle a fastening hole 3 for a fastening screw. The thickness of said sheet-like fastening bracket 2 around the fastening hole 3 is not substantially greater than what is found in conventional ballasts including no absorption. Thus, no modifications are required to the fastening mechanisms of a ballast. The sheet-like fastening bracket 2 is folded at its edge portions 2b in such a manner that, with the exception of said fastening edges 2b, the fastening bracket 2 is located slightly below the base level of a ballast, whereby the ballast when fastened to a lighting fixture is held at a distance from the body of said lighting fixture. The elastic spacer 4 may be e.g. some silicone-based material. Since the amplitude of motion to be absorbed is very small, just a very small amount of material is required for spacer 4. The embodiment shown in fig. 2 only differs from that of fig. 1 in that the edges 2a of a fastening bracket 2 are designed as U-shaped engagement grooves for securing the edges 1b of a recess made in the distal end of a base plate 1. Also in this case, the location of the bending and engagement grooves 2a of edges 1b is selected in such a manner that the bottom of a fastening bracket 2 will lie slightly below the level of base plate 1 in order to retain a ballast fastened to a lighting fixture at a distance from the body of said lighting fixture. The elastic spacers 4 fitted in grooves 2a provide a motion absorbing barrier between the fastening bracket 2 and the edges 1b of base plate 1. In this case, the fastening bracket can be made of a single sheet, which is doubled by folding or by securing two webs of sheet on top of each other with an adhesive or by welding. Since the question in the absorption of a sound level is primarily about preventing the amplitude of motion occurring longitudinally of a ballast from transmitting to fastening brackets 2 mounted on the opposite ends of a ballast, the elastic spacers 4 can also be replaced with strips or fils of some low-friction material. This can be e.g. a graphite film which, in addition to good sliding characteristics, is electrically conducting for providing the grounding of a ballast in a lighting fixture. Also the elastic spacer 4 can be electrically conducting. However, if an electrically non-conducting spacer 4 is used, the fastening bracket 2 is connected with a grounding wire 5 to the sheet metal housing 1. The fastening bracket 2 can be made of the same sheet metal as said sheet metal housing 1, but nevertheless it is a separate element from the sheet metal housing 1. The U-shaped slots 1a or 2a secure a snap-fitted connection, which is mechanically strong. In the vicinity of a fastening hole 3 the thickness of said fastening bracket 2 can be kept desirably thin, typically less than 1,5 mm. Within the scope of the annexed claims, the structural embodiment of the invention can also be other than what is described in the above examples. For example, the sheet metal housing 1 need not envelope the entire ballast, but it can be limited to cover just the base plate, a sheet iron package resting thereupon in contact with the base plate.

Claims: An apparatus for lowering the sound level of a ballast, said ballast comprising a base plate (1) and a sheet iron package with its winding as well as fastening brackets (2) fixed to the opposite ends of the base plate (1) and provided with holes (3) or recesses for fastening the ballast with screws or the like to a lighting fixture, characterized in that the fastening brackets (2), which are flat in the vicinity of said holes (3) or recesses, especially sheet-like fastening brackets (2) are separate from said base plate (1) and are connected to the base plate (1) through the intermediary of an elastic, flexible or low-friction spacer (4). An apparatus as set forth in claim 1, characterized in that the edges (2a and 2b) of said fastening bracket (2) and the corresponding edges (1a, 1b) of said base plate (1) are shaped for a relative engagement with loose snap-fitting and between said edges (1a, 2b or 2a, 1b) is placed the spacer (4) of some elastic or low-friction material, which eliminates the clearance from said snap-fitting but, by virtue of its elasticity or slipping properties, allows a relative movement between the fastening bracket (2) and the base plate (1) with a small amplitude and in the direction of the plane of the base plate of a ballast. An apparatus as set forth in claim 1 or 2, characterized in that said spacer (4) is made of an electrically conducting material. An apparatus as set forth in claim 1 or 2, characterized in that the fastening bracket (2) is connected with a grounding wire (5) to the sheet metal housing (1).

Inventors: KUOSMANEN TEIJO, KUOSMANEN, TEIJO
Applicants: HELVAR OY, OY HELVAR
Application year: 1993
Main classification: H05B41
IPC codes: H05B41