U.S. patent application number 10/294864 was filed with the patent office on 2003-06-26 for capacitor post with improved thermal conductivity.
Invention is credited to Sagal, E. Mikhail.
Application Number | 20030117765 10/294864 |
Document ID | / |
Family ID | 21830759 |
Filed Date | 2003-06-26 |
United States Patent
Application |
20030117765 |
Kind Code |
A1 |
Sagal, E. Mikhail |
June 26, 2003 |
CAPACITOR POST WITH IMPROVED THERMAL CONDUCTIVITY
Abstract
The present invention provides an improved electrolytic
capacitor device and a method of constructing the same. The
capacitor includes a central support post that is inserted into an
arbor hole in the center of the active element. The present
invention provides a capacitor post that has a core material of
metal or thermally conductive polymer that has an outer protective
layer formed thereon. The outer protective layer is net shape
insert molded over the core using a thermally conductive,
electrically insulative polymer material that protects the support
core from interfering with the electrical operation of the
capacitor while increasing the capacitor's ability to transfer
waste heat from the active element to the exterior of the device.
The outer layer further includes an integrally formed thermal
transfer pad that resides adjacent to the outer can of the
capacitor when the capacitor post is installed. The method of the
present invention provides for net shape injection molding the
protective layer over the inner core component to provide a
composite support post having an integral thermal interface pad for
incorporation into the finished capacitor device.
Inventors: |
Sagal, E. Mikhail; (Warwick,
RI) |
Correspondence
Address: |
BARLOW, JOSEPHS & HOLMES, LTD.
101 DYER STREET
5TH FLOOR
PROVIDENCE
RI
02903
US
|
Family ID: |
21830759 |
Appl. No.: |
10/294864 |
Filed: |
November 14, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10294864 |
Nov 14, 2002 |
|
|
|
10026256 |
Dec 21, 2001 |
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Current U.S.
Class: |
361/302 |
Current CPC
Class: |
H01G 2/08 20130101; H01G
2/14 20130101 |
Class at
Publication: |
361/302 |
International
Class: |
H01G 004/35 |
Claims
What is claimed:
1. A core element for a capacitor comprising: a solid central core
element, having an outer surface; and a polymer coating disposed on
said outer surface of said central core, said polymer coating
defining a top edge.
2. The core element of claim 1, wherein the core element is capable
of remaining in the capacitor after assembly without affecting
operation of the capacitor.
3. The core element of claim 1, wherein said central element is
metallic.
4. The core element of claim 1, wherein said polymer coating is a
thermally conductive, electrically insulative polymer
composition.
5. The core element of claim 4, wherein said thermally conductive
polymer composition further comprises a base polymer matrix with a
thermally conductive filler loaded therein.
6. The core element of claim 5, wherein said base polymer matrix is
a dielectric material.
7. The core element of claim 5, wherein said base polymer matrix is
elastomeric polymer.
8. The core element of claim 5, wherein said thermally conductive
filler is selected from the group consisting of: carbon fiber,
chopped glass, boron nitride, metallic flakes, alumina and mixtures
thereof.
9. The core element of claim 1, further comprising: a thermal
transfer interface pad radially extending outward from said top
edge of said polymer coating, said thermal transfer pad being
integrally formed with said polymer coating.
10. The core element of claim 5, wherein said coating of thermally
conductive polymer is net shape insert molded.
11. A core element for a capacitor comprising: a solid metallic
central core member, having an outer surface; a net shape insert
molded thermally conductive, electrically insulative polymer
coating disposed on said outer surface of said central member,
wherein said core element is capable of remaining in the capacitor
after assembly without affecting operation of the capacitor; and a
thermal transfer interface pad integrally formed with said polymer
coating.
12. The core element of claim 11, wherein said thermally conductive
polymer composition comprises a base polymer matrix with a
thermally conductive filler loaded therein.
13. The core element of claim 12, wherein said base polymer matrix
is a dielectric material.
14. The core element of claim 12, wherein said base polymer matrix
is elastomeric polymer.
15. The core element of claim 12, wherein said thermally conductive
filler is selected from the group consisting of carbon fiber,
chopped glass, boron nitride, metallic flakes, alumina and mixtures
thereof.
16. A capacitor comprising: an outer can having an open end and a
closed end and a hole in the center of said closed end; a wound
capacitor roll having a central arbor hole, said capacitor roll
received within said outer can; a core element having a solid
metallic central core member, said central core member having an
outer surface and a net shape insert molded thermally conductive,
electrically insulative polymer coating disposed on said outer
surface of said central core member, said coating having an
integrally formed thermal transfer interface pad extending radially
outward therefrom, said core element being received in said arbor
hole of said capacitor roll and said hole in said closed end of
said outer can with said thermal interface pad in communication
with said closed end of said outer can; a closure cap received in
said open end of said outer can; and a means for fastening said
closure cap, said core element to said outer can.
17. The core element of claim 16, wherein said central element is
metallic.
18. The core element of claim 16, wherein said polymer coating is a
thermally conductive, electrically insulative polymer
composition.
19. The core element of claim 18, wherein said thermally conductive
polymer composition further comprises a base polymer matrix with a
thermally conductive filler loaded therein.
20. The core element of claim 19, wherein said base polymer matrix
is a dielectric material.
21. The core element of claim 19, wherein said base polymer matrix
is elastomeric polymer.
22. The core element of claim 19, wherein said thermally conductive
filler is selected from the group consisting of: carbon fiber,
chopped glass, boron nitride, metallic flakes, alumina and mixtures
thereof.
23. The core element of claim 19, wherein said coating of thermally
conductive polymer is net shape insert molded.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of and claims priority from
earlier filed U.S. patent application Ser. No. 10/026,256, filed
Dec. 21, 2001.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a capacitor post for use
within a large high voltage capacitor, and more particularly to a
capacitor core post for use within a capacitor that has
electrically insulative properties while also having thermally
conductive properties to improve the heat dissipating properties
between the internal active elements of the capacitor foil roll and
the package (or can) in which the capacitor is encased. The
improved capacitor construction of the present invention provides
improved heat dissipation for a capacitor and an economical
construction adaptable to automated large-scale manufacturing.
[0003] Electrolytic capacitors, and specifically aluminum
electrolytic capacitors, generate internal heat during operation
because of fluctuating current ("ripple current") and internal
resistance (Effective Series Resistance--"ESR"). The heat is
generated internally in the active element of the roll and must
diffuse outward to the packaging (or can) before it can be carried
away by convection, conduction and/or radiation to the ambient
environment. Radial and axial heat flows serve to conduct the heat
from the core of the capacitor to the sides and bottom of a
cylindrical package in which the capacitor may be encased.
Construction details of the capacitor can facilitate or introduce
resistance to these heat flows. Thus, it is desirable to use
construction designs for capacitors which minimize the addition of
internal resistance and which facilitate the conduction of heat
from the core to the outside environment.
[0004] Traditionally, the capacitance of a capacitor, among other
parameters, determines the required dimensions and size of the
roll. In the past, the smallest arbor hole (or center opening)
possible was used to maximize the amount of foil in the capacitor
roll while minimizing the size of the package or can required to
enclose the roll, thus producing a dense roll that allowed little
heat to dissipate through the arbor hole. In addition, a common
construction technique employed with this design involved the use
of a "potting" material between the capacitor and the can to aid in
anchoring the roll. The practice involves embedding the roll in
asphalt, wax, etc. While potting anchors the roll, it does not
promote efficient heat flow from the roll to the can, because the
potting materials are generally insulators. Accordingly, the heat
must pass through the large thermal resistance of the insulating
potting compound before being diffused to the package.
[0005] Another known construction technique involves the use of
indentations in the can or packaging of the capacitor to assist in
anchoring the roll and to promote heat transfer through the
increased contact surface area between the can side wall and the
roll at multiple points (called "rilled construction"). However, a
paper layer is normally wound around the outer surface of the
active element (the portion of the roll where the two electrodes
are present) and is thus interposed between the active layers of
the roll and the can. This interposed paper layer contributes to
the internal thermal resistance. This practice is particularly
detrimental when the active element is small and several layers of
paper must be used.
[0006] Other methods of construction employ a variable arbor hole
to control the roll diameter for a snug fit into the can and leave
a predetermined void volume in the center of the roll for gas
buildup. The use of a large variable arbor has proven to be
impractical and abandoned as a commercial technique due to
difficulties in process control and collapse of the resulting
un-supported arbor hole (which leads to elevated ESR of the
capacitor). In addition, the close control of the roll diameter
required a varying number of extra turns of paper on the exterior
of the roll (contributing to heat buildup) unless a very highly
variable mandrel was used. Moreover, an adequate press fit between
the roll and the can is almost impossible to manufacture when a
variable mandrel was used. Without an extremely good press fit,
small air gaps result between the can and the surface of the roll
and act as insulators, thus contributing to internal
resistance.
[0007] Another technique describes the use of a small air gap
between the exterior of the roll and the can with indenting
(rilling) of the can to force mechanical and thermal contact at a
number of points around the periphery of the roll. In addition, an
indentation in the can bottom was included to help support the
arbor hole against collapse. A low profile roll was also used in an
attempt to shorten the axial thermal path to the can bottom and to
limit the collapse of the arbor hole. Again, this construction
suffers from several commercial disadvantages and was never widely
practiced due, in part, to manufacturing implementation problems
and arbor hole collapse.
[0008] Presently, a number of manufacturers offer variations of the
techniques set forth above. The variations focus on extracting heat
from the roll via extended cathode foils that reach and contact the
can bottom. These designs provide for rolls that mostly fill the
can and are wound on standard diameter mandrels; therefore, there
are air gaps around the roll periphery. The cathodes are extended
down beyond the anode foil to contact the can bottom. The roll is
anchored by compression between the cover and the can bottom.
Currently available capacitors based on the extended cathode and
the rilled can construction techniques typically do not incorporate
large arbor holes. Instead, extra paper is wound around the outside
of the active element to permit the can to be indented (rilled) for
anchoring the roll. The disadvantage of these practices is that the
heat dissipation is mainly forced into the axial direction down the
cathode foils to the can bottom. Thus, these designs suffer by
stifling radial heat flow.
[0009] In an effort to employ the above techniques, yet minimize
the occurrence of collapsing the central arbor hole, prior art
capacitors have employed metallic posts inserted within the center
of the capacitor. The post thereby provides a solid core to prevent
collapse of the arbor hole while providing a thermal path through
which heat can be dissipated. The capacitor posts of the prior art
are typically made of a metallic material and typically include a
plate at the lowermost end. However, these prior art capacitor
posts and mounting plates must be electrically insulative for
proper operation of the capacitor. The metallic prior art capacitor
post/plate structure is commonly powder coated to make it
electrically insulative. However, such powder coating is expensive
and time consuming to carry out.
[0010] Therefore, there is a need for an electrolytic capacitor
support core and a method of constructing the same in which
internal thermal resistances are reduced and heat dissipation from
the core or center of a capacitor to the packaging is increased.
There is also a need for a capacitor core that is injection
moldable from thermally conductive, electrically insulative polymer
materials to provide a more effective path for transfer of heat
from the active element of the capacitor.
SUMMARY OF THE INVENTION
[0011] The present invention provides for a novel assembly and
method of constructing an electrolytic capacitor in which the
dissipation of heat from the active elements of the capacitor is
increased. The capacitor post assembly of the present invention has
many advantages over prior art posts in that it maintains the
metallic core for support of the arbor hole in the roll and for
heat transfer from the core of the capacitor in addition to having
an integrally formed electrical insulation component. The post is
preferably insert injection molded from thermally conductive
polymer materials, which enables the part to be inexpensively made
in large quantities. However, other molding techniques known in the
art may also be used.
[0012] The method of the present invention provides a method for
manufacturing a capacitor core that includes fabricating an
inactive core element to one or more predetermined dimensions and
net shape insert molding a layer of thermally conductive,
electrically insulative polymer over the core element. In addition,
a thermally conductive transfer pad is integrally molded with the
polymer layer to improve thermal transfer from the capacitor when
assembled and installed in an electronic assembly. The composite
core element may be an arbor upon which the capacitor element is
wound, capable of remaining in the capacitor after assembly without
affecting operation of the capacitor. In addition, the core element
may be inserted into an opening within the outer can housing of the
capacitor and fastened therein.
[0013] The invention also provides an improved core element for an
electrolytic capacitor consisting of an inactive core element; and
a net shape injection molded coating thereon having thermally
conductive and electrically insulative properties and an integrally
molded thermal transfer interface pad. The molding material of the
present invention is a dielectric thermoplastic, such as an
elastomeric polymer base, with a thermally conductive filler loaded
therein. The filler may be carbon fiber, copper flakes, boron
nitride, or the like. Since the polymer base is a dielectric, the
molded portion of the post will be electrically insulative while
still being thermally conductive.
[0014] The outer layer of the capacitor post of the present
invention is preferably injected molded from a net shape moldable
thermally conductive polymer composition. As the protective layer
of the present invention, which is in contact with the other
elements of the capacitor, is fabricated from elastomeric polymer
materials it is lighter than the all metallic posts of the prior
art and does not require machining to reach its final dimension.
The present invention also has the advantage of being net shape
moldable, meaning, the part that is created in the injection
molding process does not require any further processing steps after
it is removed from the mold and before it is incorporated into the
finished device. Both the lighter weight and the net-shape
moldability are distinct advantages over the prior art where
metallic parts had to be machined in several steps to achieve the
desired part geometry.
[0015] Therefore, it is an object of the present invention to
provide a capacitor post structure that can be employed without
powder coating. It is also an object for such a structure to be
thermally conductive to assist in the cooling of the capacitor
during operation both through providing a thermal transfer pathway
to the central core and an integral thermal transfer interface pad
between the capacitor can and the mounting substrate onto which the
capacitor is mounted. It is also an object of the present invention
to provide an electrolytic capacitor, which increases the
efficiency of the flow of heat from the active elements of a
capacitor in both the radial and axial directions. It is also an
object of the invention to provide a support for the arbor hole,
which is highly thermally conductive while also being electrically
insulative. Further, it is an object of the invention to provide a
capacitor support post construction, which can be easily and
inexpensively manufactured.
[0016] These and other objects and advantages will become apparent
to those skilled in the art upon a reading of the present
disclosure. The invention will be better understood by reference to
the following description taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The following drawings illustrate the best mode presently
contemplated for carrying out the present invention:
[0018] FIG. 1 is an exploded perspective view of the capacitor
manufactured in accordance with the present invention; and
[0019] FIG. 2 is a cross sectional view thereof.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Referring now to the drawings, the preferred embodiment of
the capacitor post of present invention is shown in FIGS. 1 and 2.
The overall capacitor assembly of the instant invention is
illustrated and generally indicated at 10 in FIGS. 1 and 2. As will
hereinafter be more fully described, the instant invention utilizes
a metallic post insert molded with a coating of thermally
conductive, electrically insulative polymer to provide a novel and
improved capacitor construction that allows heat to be transferred
efficiently from its core. In addition, the molded coating includes
an integral thermal interface pad that extends over one end of the
capacitor assembly to facilitate the transfer of heat from the
capacitor when it is mounted in an operable assembly.
[0021] In FIG. 1, an exploded perspective view of the preferred
embodiment is shown to include an electrolytic capacitor device 10.
The capacitor 10 includes an inactive capacitor post element 12
having a central metallic core 14 and an outer thermally
conductive, electrically insulative polymer coating 16. Integrally
molded with the polymer coating 16 is a thermal interface pad 15.
The capacitor device has an outer housing or can 18 that has a hole
19 in its center to receive the capacitor post 12. The active
element of the capacitor 10 is a roll 20 that consists of a
laminate of conductive foil 22 and insulative material 24 tightly
rolled and inserted into the can 18. A cap 26 is placed into the
bottom end of the can 18 after the roll 20 is inserted into the can
18. A retaining clip 28 is further inserted into the cap 26 and
fastened with a screw 30 that engages the end of the capacitor post
element 12 in a threaded opening 32 located in the lower end of the
central metallic core 14. Connection points 34 are provided in the
cap 26 that are in electrical communication with the roll 20 that
allow the capacitor 10 to be operatively connected and function in
an electronic device. Further details of the electrical
interconnection of the components are not shown herein as such
details are well-known in the art.
[0022] In the process of constructing the capacitor 10, an arbor
(not shown) is used to roll the laminate material 22, 24 into a
tightly compressed package for use as the active roll 20 in the
capacitor 10. Before the roll 20 is installed in the can 18 the
arbor is removed leaving an arbor hole 36 in the center of the
active roll 20. This arbor hole 36 is unsupported and susceptible
to allowing one or several layers of laminate material 22, 24 to
collapse into the void thus interfering with the proper and
efficient operation of the capacitor 10. In addition, the active
roll 20 is wrapped very tightly to maintain as small and tight an
overall package as possible. This tight wrapping creates a dense
mass of electrically active material that generates a great deal of
heat during the operation of the capacitor 10. Because of the
compact geometry of the active roll 20 it is difficult to dissipate
the heat that is generated. The active roll 20 is supported about
its periphery by the can 18 itself. In addition, the portion of the
can 18 about the arbor hole 36 needs to be supported as well to
prevent it from collapsing internally.
[0023] The inactive capacitor post 12 serves both the function of
supporting the arbor hole 36 and dissipating heat from the interior
of the active roll 20. The integral interface pad 15 further
assists in dissipating heat away from the capacitor 10 by
conducting heat both from the polymer coating 16 and from the
bottom of the can 18 namely via surface 18a. The capacitor post 12
has two distinct layers. The first is a core element 14 that is
typically a metallic material such as aluminum, but may be any
metallic material. In addition, the core element 14 could be
fabricated from a highly thermally conductive polymer composition
of one of the types described below. The second layer is a polymer
coating layer 16 on the outer surface of the core element 14 which
has an integrally formed thermal transfer pad 15. The polymer
coating 16 is a thermally conductive polymer with highly dielectric
properties. The polymer coating 16 is preferably net shape insert
molded onto the core element 14 but could be formed using other
forming techniques. The polymer coating about the core element 14
is preferably 0.030 inches thick but may be thicker or thinner
depending on the desired thermal conductivity of the part and the
conductive properties of the polymer. Also, the integral interface
pad 15, in the configuration of a flange is preferably 0.030 inches
thick and 3 inches in diameter to accommodate the top surface 18a
of the can 18, but the pad 15 may be thicker or thinner or larger
or smaller in diameter depending on the application, namely the
size and configuration of the can 18. For example, in high thermal
conductivity applications the polymer coating 16 would be as thin
as allowed by the dielectric strength of the polymer material. The
dielectric properties of the polymer coating 16 are critical to the
proper functioning of the capacitor 10 in that the core 12 must be
electrically inactive to remain in place in the center of the
active roll 20 without causing an unintended discharge of the
capacitor 10 through a pathway other than the electrical contacts
34.
[0024] In accordance with the present invention, the capacitor post
12 is used as a thermal conduit within the capacitor 10. In
addition, the thermal transfer pad 15 that is integrally formed
with the outer layer 16 is disposed between the top surface 18a of
the can 18 of the capacitor 10 and the thermally conductive
mounting structure 38 to which the capacitor 10 is mounted in
operable relation, thereby providing a highly compressible thermal
interface between the can 18 and mounting structure 38 allowing
additional heat to be dissipated from the active roll 20 to the
thermally conductive mounting structure 38 with the thermal
interface pad 15 residing therebetween.
[0025] Preferably, the capacitor post 12 is manufactured using a
metallic core element 14 and an outer layer 16 a thermally
conductive net-shape insert molded polymer composition. The polymer
layer 16 and integral thermal interface pad 15 are net-shape molded
which means that after the part is molded, such as by insert
molding, further machining of the part is not necessary because it
has been molded into its final shape and configuration as actually
used. The polymer composition that is preferred includes a polymer
base matrix such as an elastomeric polymer. The polymer is
preferably loaded with thermally conductive filler, such as carbon
fiber, copper flakes, boron nitride powder, and the like. Since the
dielectric properties are critical, other fillers such as chopped
glass may be added to enhance the dielectric properties of the
overall polymer composition. In addition, the ratios in which the
other fillers are used may be adjusted as is well known in the art
to enhance the dielectric properties of the overall composition
while maintaining high thermal conductivity.
[0026] It can be seen in FIG. 2, that in its operative position,
the capacitor post 12 is in thermal communication with the center
of the active roll 20 and provides a thermally conductive pathway
from the center of the capacitor 10 to the exterior of the
capacitor 10. In addition, the integral thermal interface pad 15 is
in contact with the outer can 18 of the capacitor 10 to provide
further thermally conductive pathways for heat to be effectively
dissipated from the capacitor 10 assembly. In this way, the
capacitor post 12 can be further attached to a heat sink (not
shown) or an other heat dissipation element such as the mounting
structure 38 in FIG. 2 to further improve the quantity of heat
removed from the capacitor 10 while it is in operation while the
thermal interface pad 15 will be compressed between the surface of
the can 18 and the attached heat sink allowing additional heat
dissipation capacity. It can also be seen that the capacitor post
12 is in close proximity to the operative components of the
capacitor 10 emphasizing the need for the polymer outer layer 16 to
provide the dielectric properties necessary not to interfere with
the electrical operation of the capacitor 10.
[0027] It is also possible that the capacitor post 12 be
manufactured from a unitary molded member of a thermally
conductive, electrically insulative polymer or the like. For
example, a polymer base matrix loaded with thermally conductive
filler material, such as PITCH-based carbon fiber, may be employed
as the material for the present invention. Such unitary
construction is unlike that found in the prior art and provides
significant advantages including low cost, ease of manufacture and
flexibility of heat geometry due to the ability to mold the
assembly as opposed to machining it. The post 12 and coating 16
thereon preferably extends through the entire length of the arbor
hole 36. However, in certain applications, it may be desirable to
have a shortened post 12 that further receives an additional post
or other structure (not shown).
[0028] The method of the present invention provides for a new
method of manufacturing an electrolytic capacitor 10 having an
inactive capacitor post 12. A highly thermally conductive core
element 14 is provided that may be metallic material or highly
thermally conductive, electrically conductive polymer. A layer of
thermally conductive, electrically insulative polymer 16 having
high dielectric properties is net shape injection molded around the
outer surface of the core element 14 and includes an integral
thermal transfer interface pad 15. The capacitor post 12 is
inserted into the center of the outer can 18 of a capacitor 10 with
the interface pad 15 adjacent to the bottom of the can 18. The
active element 20 of the capacitor 10 is inserted into the can 18
with the capacitor post 12 residing in the arbor hole 36 at the
center of the roll 20.
[0029] It can therefore be seen that the instant invention provides
a novel construction and method of manufacturing a capacitor 10
having an improved inactive capacitor post 12 that is highly
thermally conductive while providing high dielectric properties to
allow the capacitor post 12 to remain in the center of the
capacitor 10 while in operation. The capacitor post 12 providing a
thermal dissipation pathway for the heat generated in the active
element 20 of the capacitor 10 during operation while further
providing an interface pad 15 for transferring heat from the
capacitor 10 can 18 to an adjacent thermally conductive body. For
these reasons, the instant invention is believed to represent a
significant advancement in the art which has substantial commercial
merit.
[0030] While there is shown and described herein certain specific
structure embodying the invention, it will be manifest to those
skilled in the art that various modifications and rearrangements of
the parts may be made without departing from the spirit and scope
of the underlying inventive concept and that the same is not
limited to the particular forms herein shown and described except
insofar as indicated by the scope of the appended claims.
* * * * *