Multiple element cylindrical metallized film capacitors and method of making the same

A multiple element, cylindrical metallized film capacitor and method of making the same are provided which facilitate the winding and making of electrical connections to a small value element of the multiple element capacitor. First and second dielectric films are metallized on one side thereof and are wound in cylindrical form with the non-metallized side of one film being in contact with the metallized side of the other. Selective portions of one or both of the metallized sides are removed in order to provide a multiple element device. In one embodiment, a metal strip having a metal tab extending therefrom is wound in an area where one of the metallized sides has been removed and an insulated strip is wound to surround the metal strip which forms one plate of a small capacitor. In another embodiment only a portion of the width of a metallized side of a film is removed providing more turns for the small capacitor to which an electrical connection can be made. In another embodiment, the winding is made on a metal core which forms a plate of the small capacitor. In still another embodiment the small capacitor is wound on an insulated core, the end of which is sprayed along with the turns of the small capacitor in order to facilitate making an electrical connection thereto. Advantageously, according to the present invention an extremely small size capacitor on the order of 0.05 microfarad in combination with a 3.95 microfarad capacitor may be readily and rapidly wound and connections made thereto in a manner which is more efficient, faster, and more economical than previous methods.

BACKGROUND OF THE INVENTION 
This invention relates to multiple element, cylindrical, metallized film 
wound capacitors, and more particularly to such capacitors and the method 
of making the same which utilize at least one very small integrally wound 
element to which electrical connections must be made. 
In U.S. Pat. No. 3,921,041 entitled "Dual Capacitor" by the inventor of the 
present invention, there is disclosed a method for winding a dual 
capacitor utilizing two metallized films. After winding has progressed 
through a predetermined number of turns for one of the capacitors, the 
metallized layer of one of the films is removed over a selected area and 
an insulating sheet or strip having a length sufficient to encircle the 
capacitor at least once is inserted between the layers to extend beyond 
one end of the capacitor and to separate the portions of the metallized 
film which have been removed. The winding is then completed and each end 
of the wound section is metal plated. Leads are secured to the plated ends 
from which the insulating sheet or strip extends, one lead being placed 
within, and the other without, the insulating barrier. This has been 
proved to be a very effective method of winding a multiple element 
capacitor. There is a problem, however, when the inner capacitor section 
is extremely small, for example, 0.15 to 0.25 inch diameter for making 
capacitors of the size of approximately 0.05 microfarad. Because of the 
small number of turns, it is difficult to make lead connections by metal 
flame spraying the end of the section of the small capacitor and soldering 
an electrical lead thereto inside a barrier. Furthermore, great care must 
be provided in selectively removing the metallized layer in order to 
provide the proper plate size in order to obtain a 0.05 microfarad 
capacitor. 
SUMMARY 
Accordingly, it is an object of the present invention to provide a new and 
improved method of making a multiple element, cylindrical metallized film 
capacitor which is simple, economical and efficient. 
A further object of this invention is to provide a new and improved 
multiple element, cylindrical, metallized film capacitor wherein it is 
simple to make external connections, even for low value capacitor sections 
thereof. 
Still another object of this invention is to provide a new and improved 
multiple element, cylindrical, metallized film capacitor and a method of 
making the same which lends itself to efficient winding techniques which 
do not slow the winding process in order to accommodate making electrical 
connections to extremely small elements of multiple element capacitors. 
In carrying out this invention in one illustrative embodiment thereof, the 
method of making a multiple element, cylindrical, metallized film 
capacitor from first and second dielectric films which are selectively 
metallized on one side thereof is provided. The films are wound in 
cylindrical form with the non-metallized side of one film being in contact 
with the metallized side of the other film. A section of the metal layer 
of one of the films is removed before or as the capacitor is being wound 
and a metal strip is inserted between the first and second films having a 
predetermined size for forming one plate of a small capacitor of the 
multiple element capacitor. An insulating strip is then inserted for 
isolating the plate so formed from the other plates of the multiple 
element capacitor and the winding is completed. 
In one embodiment, a metal tab extends from the metal strip in order to 
conveniently make a connection to the small capacitor so wound. In another 
embodiment, the dielectric films are wound on a metal core which forms one 
plate of a small capacitor of the multiple element capacitor. The winding 
may also be made on an insulated core, the end of which is sprayed along 
with the winding constituting one plate of the small capacitor in order to 
provide more room for making an electrical connection to the small plate. 
In a further embodiment, only a portion of the width of one of the 
metallized sides is removed, providing more end turns to which an 
electrical connection can be made. 
Advantageously, an extremely small value, thin film capacitor can be 
readily and rapidly wound along with other capacitor values and electrical 
connections made thereto in a manner which is more efficient, faster, and 
more economical than previous winding or other techniques.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the following description the term "multiple element" is used to mean 
more than one capacitor or plates of capacitors, which are wound in the 
same winding progress and are contained in a single unit. The single unit 
may be referred to as a capacitor which in reality comprises more than one 
element or capacitor. 
Referring now to FIG. 1, a multiple element, cylindrical capacitor 10 is 
shown being wound on a rotating spindle 12 of a conventional winding 
machine, for example of the type illustrated in the aforesaid U.S. Pat. 
No. 3,921,041. 
A first metallized film 14 is fed from a first supply roll 16 and a second 
metallized dielectric film 18 is passed from a second supply roll (not 
shown) over a cylindrical conductive electrode 20. The first film 14 has a 
thin metallic layer 22 which extends to the right edge of the film but 
terminates short of the left edge leaving a dielectric non-conductive 
strip 24 therealong. Similarly, the film 18 carries a thin metallic layer 
26 thereon on the front surface as viewed below the electrode 20 in FIG. 1 
which extends from the left edge of the film 18 and terminates short of 
the right edge to form a dielectric strip 28 along the right edge thereof. 
The extension of the metal to the end permits the spraying and the 
connection of electrical leads to the layers which form the plates of the 
capacitor. Accordingly, electrical leads would normally be connected to 
the right edge of the first metallized film 14 while being made to the 
left edge of the second metallized film 18. 
A second electrode 30 is mounted on a movable arm 32 in such a manner that 
it may be selectively advanced against or withdrawn from the metallized 
layer 26 on the film 18. An electrical power source (not shown) will 
normally be connected between the electrodes 20 and 30 such that when the 
electrode 30 is moved against the metallized layer 26 the resulting arcing 
vaporizes the metallic layer 26 and removes it, leaving the film 18 with a 
non-metallized region 34 where the metal 26 has been removed. The 
structure to this point and the winding process are conventional and, of 
course, the metal is removed in order to form or separate the plates of 
the capacitor to provide a multiple element device. In like manner, 
portions of the metallic layer 22 could be removed to provide a multiple 
element portion of the capacitor on the film 14. Accordingly, either of 
films 14 and 18 may carry a single plate of a multiple element capacitor 
while the other film forms two or more plates thereon, or each film may 
carry multiple plates of a multiple element capacitor. 
One of the problems encountered in winding multiple element, thin film 
capacitors of the type described involves making a satisfactory electrical 
connection to the plate formed on a very small diameter section which is 
separated from a much larger diameter section. The larger section can 
easily be coated and an electrical connection applied to the end thereof. 
With respect to the smaller wound section, it is very difficult to make an 
exterior connection to a very small number of turns. In the aforesaid U.S. 
Pat. No. 3,921,041 an insulating strip or insert is provided which extends 
out the end of the winding and acts as a barrier. Coatings are applied to 
the end of the capacitor with the barrier preventing shorting between the 
separated elements and then electrical connections are made inside and 
outside the barrier. If the separated element is extremely small, it may 
be quite difficult to make a suitable connection on the inside of the 
barrier. 
In order to alleviate this problem the present invention, as before, first 
removes the metallic layer from the metallized film 18 to provide an 
intermediate dielectric region 34 in the capacitor 10. A capacitor plate 
is inserted and wound in the form of a metal sheet or foil insert 40 
having a metal tab 42 extending from the left edge or end of the capacitor 
10 being wound. The tab 42 may be integral with the foil insert 40 or may 
be suitably secured thereto by crimping, welding, soldering, etc. The tab 
42 is the portion to which an external electrical connection is made to 
the capacitor plate formed by the metal insert 40. An insulating strip or 
insert 36 is fed in the winding process after the metal strip 40 in order 
to isolate the metal insert 40 from the other capacitor elements which are 
to be wound. The insulating strip is long enough to completely surround 
metal insert 40 at least once and is wide enough to extend beyond one end 
of the capacitor 10 to form an insulating barrier which isolates the 
plates on different sides of the barrier so that they are not shorted when 
metallized. If tabs 42 are not used, the electrical connections can be 
conveniently made to the protruding edge 41 of the plate 40 inside the 
barrier 36. 
The metal insert 40 is inserted over the intermediate region 34 from which 
the metallized layer 26 of the film 18 has been removed. Accordingly, the 
metal sheet or foil insert 40 alone forms and acts as a plate for a small 
capacitor element. The capacitance of that element will depend on the size 
of the metal insert 40. If the metal layer 22 of the first metallized film 
14 is not removed, then there would be continuity between the capacitor 
plate formed by the metal sheet 40 and the next capacitor element being 
wound on the spindle 12. 
Advantageously, in accordance with this method, the capacitance of a small 
capacitor can be conveniently controlled by closely trimming the metal 
insert 40 and not requiring such precise control on the metal removal 
step, for example, which would be the case if the small capacitor was 
formed by using a separated portion of the layer 26. 
Not only can tolerances be maintained by controlling the size of the metal 
sheet or insert 40, but, no matter how small the plate formed by the 
insert 40, the tab 42 facilitates making an electrical connection thereto. 
Also, if desired, the tab can be welded directly to the can housing the 
capacitor. Of course, the tab 42 may extend out of either end of the 
capacitor. As previously stated, if the tab 42 is not employed, electrical 
connection may be made to the edge 41 of metal insert 40 inside the 
insulating barrier. 
Although, as illustrated in FIG. 1, the electrodes 20 and 30 are employed 
for the removal of metal layer 26, a supply roll of metallized film 16 may 
be provided which is preprogrammed and has the desired areas already 
removed. Also, the metal layer 22 of the film 14 may be selectively 
removed before or during the winding process for winding different 
multiple capacitor combinations. 
Another way of winding the multiple element capacitor of the type shown in 
FIG. 1 is illustrated in FIG. 2. In this embodiment, the insulating sheet 
36 and the metal sheet 40 form a single piece 44. Accordingly, in the 
winding process only one piece is required to be inserted which simplifies 
the winding operation. Alternately, a continuous supply roll of 
alternating interconnected insulating and metal sheets may be fed in the 
winding process, and the supply roll may be cut to feed a single insert 44 
as shown in FIG. 2. If the tabs 42 are not used, the metal insert 46 would 
extend beyond the left edge of film 18 so that an electrical connection 
may be made thereto. 
Another alternative would reside in providing both a continuous insulating 
layer 36 and a continuous metal layer 40 having tabs 42 positioned 
therealong which are both fed simultaneously in the winding process and 
are selectively cut so that an insulating sheet surrounds each metal 
insert after winding. Another alternative would be to preload the metallic 
inserts on a continuous insulating roll and to selectively cut the 
insulating roll as required during winding to form one plate of a small 
capacitor. 
FIG. 3 illustrates an embodiment similar to FIG. 1 except that two 
separated metal inserts 40 are fed consecutively followed by the 
insulating sheet 36 between the films 14 and 18. A demetallized region 35 
is also provided on the metallized dielectric film 14 which overlaps, in 
winding, the plastic barrier formed by the insulating strip 35. The 
purpose of this embodiment is to provide two 0.1 microfarad capacitors 
which may be externally connected in series to form a 0.05 microfarad 
capacitor which is separated from a larger value capacitor formed by the 
remainder of the metallized dielectric films 14 and 18. By utilizing two 
larger plates formed by the foils 40 of larger size, the voltage is 
divided,, thereby reducing corona discharge between the plates. In this 
particular embodiment the tabs 42 are required in order to make electrical 
connections to each of the plates formed by the foil inserts 40. 
In FIG. 4 metallized dielectric films 14 and 18 are wound on a metallic 
core 50 with the initial portion of the metallized dielectric film 18 
demetallized along the region 34 at which point an insulating barrier 36 
is inserted therein. In this embodiment the metal core 50 forms the plate 
of a small capacitor to which an electrical connection can be made with 
ease. In FIG. 5 it will be seen that the core 50 is surrounded by an 
insulated coating or layer 52 with the metal exposed along the left edge 
54 thereof. The metallized dielectric film 14 surrounds the metal core 50 
while the demetallized film 18 surrounds the metallized dielectric film 
14. Immediately following is the insulating barrier formed by the 
insulating layer 36. As will be seen in FIG. 6, the core 50 forms one 
plate of a small capacitor with the other being formed by the metallized 
film 14. The larger capacitor is then formed by the metallized layers 22 
and 26 of the metallized dielectric films 14 and 18, respectively. The 
core 50 is surrounded by insulation except on one edge 54 in order to 
prevent at the right edge, for example, shorting the core with the 
metallized layer 22 when it is end sprayed in order to make the electrical 
connection thereto. Although the core is shown performed with an 
insulation coating 52 thereon, it may be simply wrapped with demetallized 
zones of the film or with a separate plastic insert which extends beyond 
the ends thereof in order to separate the ends of the core from the edges 
of the capacitor to which other electrical connections are made. 
FIG. 7 illustrates another technique for producing a low value capacitance 
combined with a larger value while still using the same width of 
dielectric materials which would normally be used for the larger value 
capacitor. As seen in FIG. 7 a combination metal and plastic bar 56 is 
provided mounted on a swinging arm 58 for selectively engaging the 
metallized layer 26 of the metallized dielectric film 18. A switch 60 is 
provided for switching between the metal electrode 30 and the 
plastic-metal electrode 56. When the combination metal and plastic bar 56 
is brought into engagement with the metallized layer 26 on the metallized 
dielectric film 18, the plastic portion 55 of the bar 56 leaves a 
metallized layer 64 which extends only partially across the width of the 
metallized film 18. The metal portion of the bar 56 on coming into contact 
with the metallized layer 26 vaporizes that layer leaving a partially 
demetallized region 62 along the right side of the film 18. It will be 
noted that the metallized portion 64 extends to the left edge which is 
coated for attaching an electrical connection thereto. In order to wind a 
capacitor of a certain value, a larger number of turns will be required 
using partial demetallization than would be the case if turns of complete 
metal layers are used. This, in effect, creates a plate of a small 
capacitor having a larger number of turns on the left edge to which an 
electrical connection can be made. After the partial demetallization is 
created by the bar 56, it is removed and the bar 30 is actuated to produce 
the normal demetallized zone 34 which region receives the insulating sheet 
36 (not shown in FIG. 7) in order to provide a barrier around the small 
capacitor plate formed by the metallized layer 64 on the film 18. With a 
larger number of turns being wrapped inside the barrier, it is much easier 
to make an electrical connection thereto. At the same time, a larger value 
capacitor can then be wound on top of the smaller one using the 
conventional widths of dielectric films 14 and 18. 
The present invention has thus provided a convenient, efficient, and high 
production method for making multiple section capacitors using thin films. 
Even though certain elements of the capacitor are relatively small, for 
example, 0.05 microfarad, connections can be readily made thereto using 
several convenient approaches as described hereinbefore. 
Since other changes and modifications varied to fit particular operating 
requirements and environments will be apparent to those skilled in the 
art, the invention is not considered limited to the examples chosen for 
purposes of illustration, and covers all changes and modifications which 
do not constitute a departure from the true spirit and scope of this 
invention.