GB2144915A

GB2144915A - Multisection wound capacitors and terminations

Info

Publication number: GB2144915A
Application number: GB08321700A
Authority: GB
Inventors: Rodney Graham Cooper
Original assignee: CAMBRIDGE ELECTRONIC IND
Current assignee: CAMBRIDGE ELECTRONIC IND
Priority date: 1983-08-11
Filing date: 1983-08-11
Publication date: 1985-03-13
Also published as: DE8423230U1; GB8321700D0

Abstract

A metallised capacitor has inner and outer sections (10,12) wound from metallised film, the inner section projecting to a small extent axially beyond the outer section at least at one end of the winding. The axially displaced end faces (32,34) of the inner and outer sections are sprayed to provide terminal connections, whilst the cylindrical surface (36) of the projecting end(s) of the inner section remains demetallised in order to isolate the terminal connections from one another. The invention enables high volumetric efficiency to be achieved in a multiple section capacitor whilst avoiding difficult and/or detrimental manufacturing techniques. <IMAGE>

Description

SPECIFICATION Improvements in metallised capacitors Field of the invention This invention relates to a metallised capacitor particularly a multiple, eg dual, metallised capacitor, and method of manufacture thereof.

Prior art Dual capacitors having wound inner and outer sections wound from metallised film are well known. In order to achieve maximised volumetric efficiency, it is in general aimed to employ windings of not widely dissimilar widths.

US Patent No 3921041 discloses a dual wound metallised film capacitor wherein inner and outer sections of substantially equal width are enabled by insertion of at least one turn of insulated separator sheet between the two wound sections, this sheet projecting beyond the end faces of the wound sections at least at one end of the capacitor. The end faces of the sections are metal sprayed to enable electrical connections to be made.

Disadvantages of the construction described in this US Patent are that efficient metal spraying without deposition of metal on the separator sheet is not possible, effective removal of metal spray from the separator sheet is difficult without damaging the end bond, that the insulation between the sections and associated with the separator is easily damaged, that it is not easy to find a wholly suitable material to constitute the separator, that making terminal wire connections to the inner unit is difficult, and that the projecting separator can shield the end of the inner section during metal spraying.

Object of the invention It is an object of this invention to provide a metallised capacitor and method of manufacture thereof minimising or avoiding the abovedescribed disadvantages of the known construction.

The invention According to one aspect of the present invention, there is provided a metallised capacitor having a wound inner capacitor section and a wound outer capacitor section, the wound outer section being slightly narrower than the wound inner section so that the end faces of the respective sections at least at one end of the capacitor lie in axially displaced planes each metal sprayed to provide individual terminal connections, the projecting end(s) of the cylindrical surface of the wound inner unit being devoid of sprayed metal.

According to another aspect of the invention, there is provided a method of manufacturing a metallised capacitor wherein an inner section is wound on a core, a slightly narrower outer section is wound on the inner section so that the end faces of the respective sections at least at one end of the capacitor lie in axially displaced planes, and the axially displaced end faces of the wound inner and outer sections are metal sprayed to provide individual terminal connections, the projecting end(s) of the cylindrical surface of the wound inner section being masked during metal spraying and/or having metal spray removed therefrom.

The wound capacitor sections can be stepped at both ends to produce a multiple, eg dual, isolated unit. However, for reasons of volumetric efficiency it is generally preferred to produce units in which the sections are stepped at one end only: in this case the end faces of the wound capacitor sections lying in a common plane at one end of the capacitor are metal sprayed to provide a common terminal connection.

The invention is applicable to dual capacitors, having wound inner and outer sections only, and also generally to multiple capacitors including one or more further similar wound sections arranged in stepped configuration.

Insulation between adjacent capacitor sections is preferably provided by means of a number of turns of unmetallised film of the full width of the capacitor, eg unmetallised end turns of the inner section.

Each capacitor section may conveniently be wound of metallised polymer film, eg polypropylene film.

The inner section may be wound on a hollow core tube; this can be utilised to enable a common terminal lead attached to a metal sprayed common connection at one end of the capacitor to be led through to the other end, whereby the finished capacitor, which has a metal or plastics casing, can have three terminal leads protruding from one end.

In accordance with conventional practice, each section may be wound from two metallised films simultaneously drawn from supply rolls thereof, one such film having a non-metallised strip along one longitudinal edge and the other having a non-metallised strip along the opposite longitudinal edge.

Whilst the final turns of the inner section are being wound, the metallisation may be vapourised from the surface of at least one film by means of a pair of electrodes (one retractable), thereby to form the insulation which isolates the inner section from the next, eg outer, section. Alternatively a sheet of insulating material, eg plastics film, of appropriate width may be interleaved between the successive windings to form the insulation between adjacent wound capacitor sections. In accordance with this invention, the further section(s) are similarly wound from two metallised (edge non-metallised) films of slightly narrower width, so that the already wound inner section or sections project at one or both ends of the capacitor.

Description of drawings A practical construction of dual metailised capacitor and method of manufacture thereof will now be described by way of example with reference to the accompany drawings, in which;- Figure 1 shows a capacitor in accordance with the invention during course of winding the outer section; Figure 2 shows the completed capacitor windings; Figure 3 shows a finished capacitor; and Figure 4 is a circuit diagram of the finished capacitor.

Dscnpflbn of embodiment In Fig. 1, a dual metallised capacitor is shown in course of manufacture, the inner section 10 having been wound and the outer section 1 2 being in course of winding from two metaiiised films 14, 1 6 having respective non-metallised edge strips 1 8, 20 along opposite longitudinal edges. The films 14, 1 6 are wound in slightly staggered manner, with the metallised edges projecting.

The inner section 10 has already been wound on a hollow core tube 30 from two similar but slightly wider films (eg 62.5mm wide as compared to 55mm for the outer section), and a plastics film is interleaved to provide insulation between the inner and outer wound capacitor sections. The inner section 10 has been fixed by heat sealing or with sealing tape.

The outer section 1 2 is wound with the films 14, 1 6 in line at one longitudinal edge 22 with the end face of the already wound inner section 10, so that the latter projects from within the outer section only at the other end of the capacitor, as indicated at 24.

Fig. 2 shows the completed winding, the outer winding having been fixed by heat sealing or with sealing tape. The end of the winding where the end faces of the inner and outer sections lie in a common plane is metal sprayed, as indicated at 26, to provide a common connection for a terminal lead 28.

At the other end of the completed winding, the annular, axially displaced end faces of the inner and outer sections 10, 1 2 are individually metal sprayed at 32, 34 respectively.

During this step, the projecting end of the cylindrical surface 36 of the inner section is masked to avoid deposition of metal thereon and/or any metal deposited on said projecting cylindrical surface 36 is removed. This metalfree end surface portion of the inner section provides the necessary separation between the capacitor sections, individual terminal leads 38, 40 being connected to the metal sprayed ends 32, 34 of the respective inner and outer sections by welding or soldering Fig. 3 shows a finished dual capacitor incorporating a unit as described with reference to Figs. 1 and 2 and having a resin filled casing 42 of metal or plastics according to requirements, with the three terminal leads 28, 38, 40 extending from one end thereof. This can be achieved by passing the common terminal lead 28 through the core tube 30 before the capacitor is encased.

Fig. 4 is an equivalent circuit diagram of the dual capacitor, which comprises a capacitance 42 and a capacitance 44 with one common terminal 46 and individual terminals 48, 50. The capacitances 42, 44 can be equal; in a typical case each may have a value of 2llF.

With the dual capacitor of the invention as above described, the various problems associated with the construction known from US Patent No 3921041 are obviated and, although the film width of the outer section is approximately 10% less than that of the inner section, this is not sufficiently materially to affect performance and service life in a disadvantageous manner.

It will be appreciated that the above-described arrangement may be modified in various ways within the scope of the invention as hereinbefore defined.

Claims

1. A metallised capacitor having a wound inner capacitor section and a wound outer capacitor section, the wound outer section being slightly narrower than the wound inner section so that the end faces of the respective sections at least at one end of the capacitor lie in axially displaced planes each metal sprayed to provide individual terminal connections, the projecting end(s) of the cylindrical surface of the wound inner unit being devoid of sprayed metal.

2. A metallised capacitor according to Claim 1, wherein the wound inner and outer capacitor sections have respective end faces lying in axially displaced planes at both ends of the capacitor.

3. A metallised capacitor according to Claim 1 or Claim 2, wherein the inner and outer sections constitute two radially adjacent section of three or more wound sections of which the end faces of radially adjacent sections are axially displaced, at least at one end of the capacitor.

4. A metallised capacitor according to Claim 1 or Claim 2 or Claim 3, wherein insulation between the or each pair of radially adjacent sections is provided by a number of turns of unmetallised or demetallised film, extending the full width of the winding.

5. A metallised capacitor according to any one of Claims 1 to 4, wherein each section is wound of metallised polymer film.

6. A metallised capacitor according to any one of Claims 1 to 5, wherein the inner section is wound on a hollow core tube.

7. A metallised capacitor according to Claim 6, wherein at least one terminal lead attached to a terminal connector at one end of the capacitor is lead through the hollow core tube to the other end of the capacitor.

8. A method of manufacturing a metallised capacitor wherein an inner section is wound on a core, a slightly narrower outer section is wound on the inner section so that the end faces of the respective sections at least at one end of the capacitor lie in axially displaced planes, and the axially displaced end faces of the wound inner and outer sections are metal sprayed to provide individual terminal connections, the projecting end(s) of the cylindrical surface of the wound inner section being masked during metal spraying and/or having metal spray removed therefrom.

9. A method according to Claim 8, wherein the inner and outer sections are each wound from two metallised films simultaneously drawn from supply rolls thereof, one film having a non-metallised strip along one longitudinal edge and the other film having a non-metallised strip along the opposite longitudinal edge.

1 0. A method according to Claim 9, wherein, while the final turns of the inner section are being wound, the metallisation is vapourised or otherwise removed from the surface of at least one film.

11. A metallised capacitor substantially as hereinbefore described with reference to, and as shown in, Fig. 2 of the accompanying drawings.

1 2. A method of manufacturing a metallised capacitor substantially as hereinbefore described with reference to the accompanying drawings.