GB2025694A - Rolled capacitor - Google Patents

Abstract

Wound capacitor comprising a dielectric foil (1), two metal layers (2,3), and a third layer (6), the third layer being arranged as the outer turn of the capacitor roll (7 Fig. 3) and contacted by a large contact (8) of strip metal form. <IMAGE>

Description

SPECIFICATION Rolled capacitor The invention relates to a wound capacitor in which two metal layers are in such a way covered by a third metal layer that there will result an internal series connection. Such an arrangement is suitable for the elimination of radio intereferences.

From the German Offenlegungsschrift (DE-OS) 2,229,407 there is known a wound capacitor in which two coatings evaporated on to one surface of a plastics foil or paper, are covered by a third coating likewise evaporated on to a plastics foil or paper.

Such a capacitor is preferably used as a X- or Y-capacitor for the elimination of radio interferences.

As is well known, for eliminating radio interferences, there is used one capacitor of class X having a high capacity, and one or two capacitors of class Y having low capacities. In so doing, the X-capacitor is inserted between the conductors of a network, and the one or more Y-capacitors are inserted between one conductor and ground. It has also been proposed already, to combine all capacitors of an X Y-capacitor arrangement, in one capacitor roll.

Radio interference elimination circuits often require symmetrical capacitor arrangements. Therefore, a further capacitor terminal is required which can then be used, for example, as an earth-wire terminal.

Relative thereto, however, contacting the terminals causes considerable difficulties. For example, if a lead-in conductor were to be inserted in the roll, the very thin coating at the point of contact might easily by destroyed.

According to the present invention there is provided a wound capacitor comprising a dielectric foil, two metal layers side-by-side on a first surface of the dielectric foil, a third metal layer overlaying the said two metal layers forming an internal series connection, the third metal layer on the outer winding end being arranged at the outer roll circumference, and a contact arranged and extending over a large portion of the circumference and electrically connected to the third metal layer.

The invention will now be explained in greater detail with reference to Figures 1 to 4 of the accompanying drawings, in which: Figure la shows the layer structure at the begin ninginside) of a capacitor roll, Figure 1b shows the layer structure at the end (outside) of the capacitor roll, Figure 2 shows the layer structure of an alternative capacitor roll; Figure 3 shows one contact arrangement for the capacitor roll of Figure 1 or Figure 2 in end view and Figure 4 shows a variant contact form relating to Figure 3, and in side view.

In the drawings corresponding parts are indicated by the same reference numerals.

In Figure 1,the reference numeral 1 indicates a polypropylene (PP) foil serving as the first dielectric foil. It may, for example, have a thickness of 15 microns. This PP foil 1 is provided with two metal coatings 2 and 3 which are deposited in such a way on one surface of the PP foil 1 that the centre thereof includes a non-metatlized strip 4. The metal coatings 2 and 3 consist of evaporated aluminum or tin. In a suitable way, these metal coatings 2 and 3 are contacted separately; for this purpose, for example, the capacitor roll may be provided with two face contact layers.

The reference numeral 5 indicates a PP foil serving as the second dielectric foil which, preferably, has the same thickness and width as the PP foil 1, and carries a metal coating 6. This metal coating 6, inside the capacitor roll, comes to lie on the non-metallized surface of the PP foil 1. The metal coating 6 is arranged in such a way as to partly cover the metal coatings 2 and 3. The metal coating 6 consists of a tin-lead alloy and is designed to be narrower than the PP foil 5.

As can be seen in particular from Figure 1 b, the metallized PP foil 5 at the end of the roll, as a dead foil, forms the end winding.

As is shown in Figure 2, however, the capacitor roll may also be built up in such a way that the metal coating 6 is not deposited on a second dielectric foil, but on the PP foil 1 opposite the metal coatings 2 and 3. The metal coating 6, in turn, is designed narrower than the PP foil 1 and partly covers the metal coatings 2 and 3.

Via the two face contact layers of the capacitor roll, there will then result a capacitor in an internal series connection; in this arrangement the metal coating 6 serves as a dummy coating.

In Figures 3 and 4, the reference numeral 7 indicates the capacitor roll having a layer structure of the type as shown in Figures 1 or 2. This roll is respectively wound in such a way that the metal coating 6 will come to lie on the outside at the roll's circumference, surrounding the capacitor roll like a bandage. According to Figure 3, a sheet metal strip 8 extending at least over one half of the capacitor roll circumference, is applied as a contact around the capacitor roll 7 or the metal coating 6 at the roll's circumference respectively. This sheet metal strip 8 is supposed to extend over a large portion of the capacitor roll circumference, in order to safeguard a good contact and may consist, for example, of thin copper sheetmetal. This strip is attached to the tin-lead bandage and electrically connected therewith.This connection may be established, for example, by way of spot welding. In so doing, the welding heat is dissipated by the tin-lead bandage without endangering the capacitor roll itself. The sheet metal strip 8 is preferably designed to have the same width as the metal coating 6; however, it may also be designed narrower.

Instead of a sheet metal strip 8 it is also possible, as shown in Figure 4, to provide a wire 9 for serving as the contact, with this wire being wound around the capacitor roll 7 or the metal coating 6 at the capacitor roll circumference respectively. This wire 9 may be either a solid wire or a stranded wire consisting of an electrically conducting material. It is mounted to the tin-lead bandage and electrically connected therewith. It may consist, for example, of a solderable material and may be soldered to the loose end of the tin-lead bandage; this bandage will then melt around the wire 9. The wire 9, however, may also be connected to the metal coating 6, for example, by the action of compacting pressure.

Usually the capacitor roll 7 is surrounded by a covering bandage consisting e.g. of polycarbonate for protecting it from environmental influences or from being damaged (not shown in detail in the drawing). Such a covering bandage does in no way prevent the described connecting possibilities between the contacts and the tin-lead bandage; the respective connecting points become fused.

Claims (14)

1. Wound capacitor comprising a dielectric foil, two metal layers side-by-side on a first surface of the dielectric foil, a third metal layer overlaying the said two metal layers forming an internal series connection, the third metal layer on the outer winding end being arranged at the outer roll circumference, and a contact arranged and extending over a large portion of the circumference and electrically connected to the third metal layer.

2. Wound capacitor as claimed in claim 1, wherein said third metal layer consists of a tin-lead alloy coating.

3. Wound capacitor as claimed in claim 1 or 2, wherein said contact comprises a sheet metal strip surrounding at least one half of the roll circumference.

4. Wound capacitor as claimed in claim 3, wherein said sheet metal strip is attached to said third metal layer by spot welding.

5. Wound capacitor as claimed in claim 3 or 4, wherein the width of said sheet metal strip corresponds to the width of said third metal layer.

6. Wound capacitor as claimed in claim 1 or 2, wherein said contact comprises a wire of electrically conducting material wound along the circumference within the area of said third metal layer.

7. Wound capacitor as claimed in claim 6, wherein said wire consists of solderable material and is soldered to said third metal layer.

8. Wound capacitor as claimed in claim 6, wherein said wire is in pressure contact with said third metal layer.

9. Wound capacitor as claimed in claim I or 2, wherein said metal layer is applied to the second surface of the dielectric foil.

10. Wound capacitor as claimed in claim 9, wherein said dielectric foil is wider than said metal layer.

11. Wound capacitor as claimed in claim 1 or 2, wherein said metal layer is deposited on one surface of a second dielectric foil which, as a dead foil, forms the end winding of the capacitor roll.

12. Wound capacitor as claimed in claim 11, wherein said second dielectric foil is wider than said metal layer.

13. Wound capacitor as claimed in claim 11 or 12, wherein said second dielectric foil and said first dielectric foil are of equal widths.

14. Wound capacitor substantially as hereinbefore described with reference to and as illustrated in Figure 1 or 2 and Figure 3 or 4, of the accompanying drawings.