US3484535A - Moisture proof ballast construction for plastic signs and the like - Google Patents

Description

J. F. LUCHETTA 3,484,535 MOISTURE PROOF BALLAST CONSTRUCTION FOR PLASTIC Dec. 16, 1969 SIGNS AND THE LIKE Filed June 19, 1967 United States Patent MOISTURE PROOF BALLAST CONSTRUCTION FOR PLASTIC SIGNS AND THE LIKE Julius F. Luchetta, Elmhurst, Ill., assignor to Jefferson Electric Company, a corporation of Delaware Filed June 19, 1967, Ser. No. 646,830 Int. Cl. H05k 5/04 US. Cl. 174-52 3 Claims ABSTRACT OF THE DISCLOSURE A ballast for mounting on the upper surface of a supporting member has a casing which comprises a seamless drawn sheet metal container with flared upper edges and a flanged cover with the flanges rolled under the flared upper edges. The container is preassembled with the ballast leads. A receptacle at the upper edge of each end wall of the container is filled with a thermosetting resin which forms a moisture-proof seal with the insulation of the ballast leads, the leads extending through openings in the container and wall and the opposite wall of the receptacle. Mounting brackets are secured to the end walls of the container and have bolt receiving flanges spaced above the bottom wall to accommodate a bolt locating nut so that the bottom wall can be maintained in heat conducting contact with the supporting surface.

This invention relates to an improved ballast construction which is particularly suitable for use in plastic signs. A plastic sign is a display sign having one or two translucent faces which are back lighted by fluorescent lamps powered by a fluorescent lamp ballast.

Plastic sign ballasts have a much higher failure rate than ballasts used for indoor lighting due to presence of water, and excessive heating. Due to inaccessibility of the ballast, particularly in large elevated sign installations, the labor cost of ballast replacement is many times that of replacement of indoor ballasts. The problem of long ballast life has not entirely been solved because previous attempts to overcome the water probelm aggravate the overheating problem.

Ballasts are customarily enclosed in a casing comprising an open top container called a can, and a cover. The ballast components are first placed in the can, with the terminal panel facing upwardly; then the soldered connections are made between the various leads and the lugs of the terminal panel; the ballast is then potted, which is to say, filled with an insulating material, such as an asphaltic compound or a resin; and then a dielectric insulating liner is placed over the terminal panel and submerged below the level of the potting compound. Then the potting compound is permitted to cool and solidify after which the cover is applied. In some instances, the cover is applied first, and the potting compound injected through a hole in the cover.

The ends of the cover are extended beyond the end walls of the can and provided with holes or notches to serve as mounting flanges for the fully assembled ballast. In indoor lighting, the ballast is customarily mounted on the under surface of a supporting member, but in plastic signs the ballast is more frequently mounted on the upper surface of the supporting member, with the result that the cover constitutes the base of the ballast. In both instances, however, the cover is referred to as the base and the two types of mounting can be referred to as the base-up or upright mounting, and the basedown or inverted mounting, respectively.

The top edges of the end wall are notched to accommodate the ballast leads. Thus, in the base-down mounting, the leads extend from the lower edge of the casing.

In indoor lighting with base-up mounting the ballast is generally secured to the supporting member by bolts, the bolts extending downwardly through the support and flange, and the nuts holding the base securely against the lower surface of the supporting member so that the heat developed by the ballast will be conducted into the supporting member and dissipated. The cooling effect of the supporting member is often included in the design calculations to meet temperature specifications.

In a plastic sign, however, a practice known as double nutting is employed, as shown in FIG. 7. Here the removal of the top nut in order to remove the ballast will not permit the bolt to drop down through the supporting member where it would be hard to retrieve.

Condensation within the sign, and rain which penetrates the supporting structure will wet the supporting surface. This water works its way into the ballast through the abutting joint between the end wall and the base, and it also penetrates the joint between the insulation of the lead wires and the potting compound. The double nutting practice serves to elevate the ballast above the supporting surface by a /s-inch or a A-inch with the result that moisture penetration is avoided in many instances. However, the elimination of surface contact between the base and the supporting member reduces the heat dissipating characteristics of the ballast with the result that the heat failure probability is increased although the moisture failure probability is decreased.

Furthermore, in a heavy rainstorm, the water may accumulate on the supporting surface at a greater rate than it runs off, with the result that the to inch spacing provided by double nutting is insuflicient to avoid moisture penetration. This is particularly true where the supporting member is flanged or otherwise confined.

The usual can is a structure provided with seams, as illustrated in Koke Patent No. 3,299,201. The end wall seams are also a source of moisture penetration.

According to my invention I provide a drawn seamless can, and provide mounting brackets at the lower portions of the end walls thereof so that when the ballast is mounted on the upper surface of a supporting structure, the cover will be located at the top of the ballast. According to this arrangement the ballast is entirely waterproof unless the accumulated water is deep enough to cover the ballast. At the same time, I provide mounting brackets such that the bottom of the can will be maintained in heat conducting contact in the upper surface of the supporting member even though double nutting is employed. Thus, I greatly reduce the probability of failure due to both the major causes, water penetration and overheating.

Furthermore, I provide an improved arrangement for bringing the leads through the end walls of the ballast which provides a waterproof seal. This eliminate creepage of moisture along the joint between the wire insulation and the potting compound, which creepage occurs under moist or humid conditions even though there is no standing water on the supporting surface. My lead seal construction also permits the ballast to be mounted in a vertical position without danger of having water run down the leads and into the ballast. Furthermore, my improved construction which permits upright mounting of the ballast has the advantage that the dielectric insulating liner is not disposed between the heat generating components and that surface of the casing which is in heat conducting contact with the supporting member. This dielectric insulating liner has lower heat conduction than the poting compound, and hence low temperature operation is improved when it is located above the core and coil assembly as provided in my invention.

A further object of my invention is to provide a con- 3 tainer and sealed lead combination in the form of a preassembled unit to facilitate ballast assembly.

To summarize the foregoing, my invention reduces the probability of failure due to overheating and moisture penetration, and still permits a double nut mounting. Furthermore, by sealing the leads to the container, the ballast may be handled by the leads without damage to the soldered connections.

Other objects, features, and advantages will become apparent as the description proceeds.

With reference now to the drawings in which like reference numerals designate like parts:

FIG. 1 is an exploded elevation of a ballast casing embodying my invention;

FIG. 2 is a plan view of the container portion of the FIG. 1 casing, with some leads preassembled thereto;

FIG. 3 is an end view of FIG. 2;

FIG. 4 is a vertical section along line 44 of FIG. 2, and showing a preassembled lead;

FIG. 5 is a fragmentary elevation along line 5-5 of FIG. 2;

FIG. 6 is a detail of the interlocking edges of the container and the cover; and

FIG. 7 is a fragmentary section showing the manner of mounting.

The casing comprises a container 10 and a cover 11. The container has a flared edge 12 and the cover has a flange 13. After final assembly and potting, the flange 13 is rolled over the flared edge 12 to provide a rolled seam 14, as shown in FIG. 6. For a completely waterproof ballast casing, a head of sealing compound 40 may be applied to the flared edge 12 as shown in FIG. 4, or to the inner surface of the flange 13.

The container 10 comprises a bottom 15, end walls 16, and side walls 17. Lead receiving openings 18 are formed in the end walls 16. A receptacle 19 is located at the upper edge of the inner surface of each end wall 16. The receptacle, as shown in FIGS. 2, 4 and 5, comprises a side wall 20, a bottom wall 21 which abuts the container wall 16, end walls 22, and flanges 23 which are spot welded at 24 to the container walls 16. Openings 25 are formed in the side wall which are in substantial alignment with the lead receiving openings 18. The edges of openings 18 and are rolled edges, as shown in FIG. 4.

The type of ballast shown has at least six leads and usually eight or more. A set of openings 18, 25, is provided for each lead or for each pair of leads. It will be observed that the openings 18 and 25 are of a width sufficient to receive two leads side by side so that the six openings will accommodate up to twelve leads.

The leads are separately threaded through each hole and the receptacle 19 is filled with a suitable thermosetting sealing material 27, Such as polyester, epoxy, urethane or silicone thermosetting resins. The sealing material 27 forms a bond with the surface of the insulation of the lead 26, and also with the painted metal walls of the receptacle. The leads 26 are customarily insulated with neoprene or as imilar non-fibrous insulating material, and the thermosetting sealing compound forms a bond with the neoprene or other insulation which not only prevents any seepage of water along the surface of the insulation, but also provides a mechanical connection which permits the ballast to be handled by the leads, the bond being sufficiently strong that it will not be broken by the forces encountered in handling the leads of a relatively heavy ballast.

The fact that the sealing material also makes a bond with the wall of the receptacle avoids the possibility that a crevice will open up between the sealing material 27 and the container, due to flexing of the container in handling, or due to thermal expansion, which would serve as a moisture path bypassing the bond with the lead insulation.

The sealed leads and the container constitute a preassembled unit, which simplifies the assembly and soldering operations. Preferably, the leads are positioned in the container and receptacle so that the length of that portion of each lead extending into the container is predetermined to permit subsequent internal connection to be made to the ballast components with no excess or slack. Then the components, such as the core-coil assembly 29, shown in dotted line, and a condenser 29a are placed into the drawn can with its preassembled leads. The internal connections are then made to the components, and the can is filled with a suitable potting compound, which may be either the usual asphaltic potting compound, or a thermosetting material which, when cured, will not soften or flow when heated. In the case of an asphaltic compound, a fiber insulating liner 28 is placed over the components 29 during the potting operation, and submerged about A of an inch below the top surface. In the case of a thermosetting potting material, the liner 28 is not necessary.

After potting, the cover 11 is placed on the edges 12 and the flanges 13 rolled over as in FIG. 6. In the case of a thermosetting potting material where there is no liner 28, the potting material can be injected through a suitable opening (not shown) in the cover 11, as shown in the aforesaid Koke Patent No. 3,299,201.

The mounting means for the ballast comprises a bracket 30 at each end, as shown in FIGS. 1 and 2. Each bracket has a wall contacting body portion 31, a flange portion 32 which extends outwardly at right angles to the body portion, and a downturned end 33. The flange portion 32 is disposed in a plane parallel to the plane of the bottom wall 15 of the can, but spaced above same by substantially inch, for example. Bolt holes 34 are provided in the flange portion 32.

When the ballast is mounted on a support member 35 by a bolt 36, a bolt retaining nut 37 is first threaded on to the bolt before the ballast is located. The retaining nut 37 prevents the bolt 36 from dropping through the support member 35. Then the ballast is placed on the support member with the bolts 36 extending through the bolt holes 34 and the nuts 38 are applied and tightened up. By virtue of this arrangement, the flange portion 32 and the downturned end 34 provide a nut receiving recess 39 for accommodation of the bolt retaining nut 37 which permits the bottom wall 15 to be urged firmly against the upper surface of the support member 35 in heat conducting relationship.

Although the downturned end 33 provides a lower edge which is disposed substantially in the plane of the lower surface of the bottom wall to provide a support abutting edge, an exaggerated clearance between the edge and the support is shown in FIG. 7. Preferably this clearance is of the order of from .01 to .03 inch to accommodate surface irregularities and in normal operation the clearance is taken up by the nut 38. Thus, as the nut 38 is tightened up, the bottom wall 15 is resiliently urged against the support surface 35, but the resilience is that provided by a slight dishing of the flange portion 32 or span, rather than a cantilever type of flexing which would overstress the bend between the body portion 31 and the flange portion 32, if the downturned end were omitted.

Although only a preferred embodiment of my invention has been shown and described herein, it will be understood that various modifications and changes may be made in the construction shown without departing from the spirit of my invention as pointed out in the appended claims.

I claim:

1. A ballast comprising a casing, ballast components disposed in said casing, potting compound surrounding said ballast components and embedding same in said casing, said casing comprising a drawn sheet metal container having a bottom wall,

two end walls, and two side walls, and an open top,

a bracket secured to each end wall comprising a wall contacting body portion, a flange portion extending longitudinally from said body portion and disposed in a plane substantially parallel to the plane of said botom wall and spaced above same, and a downturned end portion terminating substantially in the plane of said bottom wall to provide a support surface abutting edge,

said flange portion having a bolt receiving opening, and

cooperating with said downturned end portion to provide a nut receiving recess,

lead receiving openings in the upper part of at least the upper edges of said walls being flared, a flanged cover overlying said container with the flanges thereof extending inwardly and interlocking with said flared edges,

whereby said ballast may be secured to the upper surface of a horizontal supporting member with said bottom wall in heat conducting relationship thereto, said casing providing a waterproof enclosure for said ballast with respect to standing water of a depth at least as great as the height of said lead receiving openings.

2. A ballast as claimed in claim 1 which includes sealing material disposed between said flared edges and said cover.

3. A ballast as claimed in claim 1 in which said receptacle providing means compirses an elongate sheet metal member having a central portion providing a side wall, end portions each providing an end wall perpendicular to said side wall and an outwardly extending flange disposed in a plane parallel to said side wall, said flanges being secured to one of said container end walls, said central portion having a bent portion extending toward said container end wall and providing a bottom wall for said receptacle.

References Cited UNITED STATES PATENTS 921,018 5/1909 Soule l7418 X 1,774,935 9/1930 Mangin l74-63 3,329,762 7/1967 Miller 174-65 LEWIS H. MYERS, Primary Examiner D. A. TONE, Assistant Examiner U.S. Cl. X.R. 17465

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