Note: Descriptions are shown in the official language in which they were submitted.
CA 02810620 2015-10-20
MULTIPLE STAGE OPEN COIL ELECTRIC RESISTANCE HEATER WITH BALANCED
COIL POWER ARRANGEMENT AND HEATER COOL END TERMINATION AND
METHOD OF USE
Field of the Invention
The present invention is directed to a multistage open coil electric
resistance
heater and method for use, and in particular, to a multistage heater
configuration
whereby the coil runs of each stage are arranged to provide a balanced power
arrangement for the heater.
Background Art
The use of a single resistance wire formed into a helical coil for use in
electric
resistance heating either for heating moving air, for radiant heating, or for
convection
heating is well known in the prior art. In one type of heater, the resistance
coils are
energized to heat air passing over the coils, the heated air then being
directed in a
particular manner for heating purposes. One application using such a heater is
an
electric clothes dryer.
Examples of open coil heaters are found in United States Patent Nos.
5,329,098,
5,895,597, 5,925,273, 7,075,043, and 7,154,072, all owned by Tutco, Inc. of
Cookeville, Tennessee. One type of an open coil electric resistance heater is
a two
stage heater described in United States Patent No. 7,075,043. A side view of
this type
of heater is shown in Figure 1 and dOgnated by the reference numeral 10. The
heater
CA 02810620 2013-03-26
has two heater elements 10a and 10b, optimally for use in a clothes dryer. The
elements 10a and 10b are supplied with electricity via terminals 12 extending
from the
terminal block 28. The heater elements 10a, 10b are supported by a support
plate 14,
which in turn supports a plurality of support insulators 16, typically made of
ceramic
5 material and which are well known in the art. The support insulators 16
support and
isolate coiled portions of the elements, 10a and 10b, during operation of the
heater.
The heater 10 includes opposing sidewalls (one shown as 6 in Figure 1),
wherein
projections in the plate 14 extend through slots 20 in the sidewall 6 to allow
the
sidewalls to support the plate.
10 Each of the electric heater elements, 10a and 10b, is arranged in series
of
electrically continuous coils which are mounted on the plate 14 in a spaced-
apart
substantially parallel arrangement. Each heater assembly 10a and 10b is
arranged
substantially equally and oppositely on both sides of the plate. Crossover
portions 22a
and 22b of each heater element 10a and 10b are provided wherein each crossover
links
one coil of each of the elements mounted on one side of the plate 14 with
another coil
of the same element found on the other side of the plate.
Electricity is supplied to the heater assembly through the terminal block 28.
The
heater elements, 10a and 10b, are arranged so that the terminal connector
portions or
wire leads 32 and 34 which extend from an end 38 of each of the mounted coil
sections
to the terminal block are as short as possible. This aids in eliminating or
reducing the
need for supporting the connector portions. For the longer runs, the wire
leads, 32 and
34, are partially enclosed with an insulating member 36. The insulating member
36
2
CA 02810620 2015-02-20
may be formed from any type of insulating material suitable for this purpose,
e.g., a
ceramic type. The insulating member is generally tubular in shape and rigid.
Another type of heater manufactured by Tutco, described in US Patent No.
7,947,932 is an improvement over the heater shown in Figure 1, in that the
heater coils
are parallel to air flow to minimize noise, prevent coil shadowing, and
promote heat
transfer from the heater coils to the air stream.
In the manufacture of appliances and equipment, especially clothes dryer
manufacture,
that require open coil electric heaters mounted in an air duct to heat air
flowing through the
duct, there is a constant need to provide an inexpensive method of making an
electric heater
having multiple stages of heat such that each stage provides some heat to each
side of a
support plate. In the prior art of open coil heaters having heater coils
supported by ceramic
insulators held in metal plates, one method of providing two stages of heat is
to have one
heater coil completely assembled on one side of the plate and the second coil
on the opposite
side, see United States Patent No. 7,154,072. Upon energizing the first stage
of heat, only the
air on one side of the plate is heated making for a less than desirable heat
distribution for the
first heating stage.
Another method to improve heat distribution is to route the first stage coil
so a portion
of the heater coil is on one side of the support plate with the remainder of
the coil routed on
the opposite side, see United States Patent No. 7,075,043 as one example. When
these types of
heaters are energized, heat is supplied to both sides of the duct during first
stage heating. The
second heat stage coils are similarly assembled to complement the first stage.
This is an
expensive design, as the ends of the heating
3
CA 02810620 2013-03-26
element wire must be covered with special designed ceramic tubes or ceramic
beads for
electrical isolation to prevent grounding or reduction of electrical
clearance, see the
insulating members 36 in Figure 1 as an example. Some designs use special
designed
ceramics to secure the heating element wire ends to prevent shorting,
grounding, or
the reduction in electrical clearance as the wires are routed to terminals. A
well
accepted method long used is to provide individual termination points located
immediately adjacent to the element coil ends. This is an expensive
alternative, as
power connections must be routed to multiple locations. Also, it is often
impractical as
some terminal locations may require power connections be made in excessively
hot
areas resulting in rapid deterioration under heat. Therefore, there is a need
in the
industry for a two stage, open coil electric heater that is inexpensive and
has an
arrangement wherein the first stage of the heater heats both sides of the air
duct with
the second heating stage complementing the first.
In the prior art there are usually either threaded style bolts or studs or
blade or
quick connect termination for power connection. Crimp style terminals made of
flat
metal stock for blade or quick connect termination crimped around resistance
ends is
well known and is presently sold by the TYCO Corporation. In the prior art, it
is a
common practice when bolt and threaded stud terminal style terminals are
required for
power connection, that these terminals are attached to element wire ends by
welding,
crimping, or pressure connection.
Welding is usually done by first mechanically staking the element wire ends
into
a slot in the head of a terminal bolt and then welding the two together.
Crimping
4
CA 02810620 2013-03-26
heating element wire ends to threaded bolts is accomplished by creating a tube
style
opening in one end of threaded stud terminals, inserting the heating element
wire ends
into the tube openings, and then mechanically closing the tubes so as to
create a crimp
connection. The least desirable connections are pressure connections in which
resistance wire coil ends are looped around terminal bolts or threaded studs,
then
"sandwiched" between a combination of washers and nuts, whereby subsequent
tightening of the nuts create electrical connections.
In the prior art, heating elements made as above are routed and assembled into
the intended positions with heavy termination bolts attached to the coil ends.
When a
common threaded terminal power connection is needed, as for two stage or other
multiple stage heaters, common element wire ends share a common terminal bolt
or
stud. When this type of connection is needed, the various methods of
connection
described above are followed except two or more element wire ends are
connected to
the required common terminal. For the welded connection, two or more common
element wire ends are placed in the terminal bolt slot, mechanically staked
then welded
as above. For the crimp method, two or more common element wire ends are
placed
into the tube opening and crimped as above. For the pressure connection
method, two
or more common element wire ends are looped together then "sandwiched" as
above
and the termination completed. Thus, for the three prior art termination
methods
above, at least one end each of heater wire elements of multiple stage heaters
share at
least one common terminal bolt.
5
CA 02810620 2013-03-26
A shortcoming with respect to the termination of heater coils is that when
threaded stud or bolt style termination for heaters is needed, prior art
methods require
the heating element wire ends to be first secured to heavy and cumbersome
terminal
bolts; the coil and terminal bolt assembly routed and subsequently secured to
the coil
support insulators. If the pressure connection method is used so as to allow
heating
element coils to be first assembled into a heater and then to connect to
terminal bolts
or threaded studs, this process is cumbersome and labor intensive. Also
pressure
electrical connections depend too much on the manual skill and attention of
the person
performing the task unlike a mechanical connection and thus generally are
avoided if
possible.
When threaded style terminations are required in the industry, there is needed
a
means to first make secure electrical connections between resistance wire coil
ends and
lightweight, easy to handle connectors that can later be attached to the
terminal bolts
or threaded studs whichever is used.
Referring now to Figures 2-4, a prior art heater subassembly 20 is disclosed.
Figures 2 and 3 depict a support plate 21 as part of the subassembly 20. The
support
plate 21 has a number of openings 23, which are sized to retain insulators 25.
The
insulators 25 are configured to connect to and support the coils 27 and 29.
The heater assembly 20 is a two stage heater, although more stages could be
employed if so desired. The two stage heating is accomplished by the pair of
resistance
wire coils 27 and 29, with coil 27 representing the first stage and coil 29
representing
the second stage.
6
CA 02810620 2013-03-26
. .
Coil 27 has opposing terminal ends 31 and 33, with coil 29 having opposing
terminal ends 35 and 37. Terminal ends 31 and 35 have a first type of terminal
39
attached thereto. Terminal ends 33 and 37 have a second type of terminal 41
attached
thereto. Terminal 41 is a conventional blade end crimp style terminal whereby
the end
of the resistance wire is crimped to one end of the terminal. The other end is
a flat
configuration for connection as is well known in the art. Since these blade
end crimp
type terminals are well known, a further description is not necessary.
Referring now to Figures 5 and 7a-7c, the terminal 39 has a crimp end 43 and
flat end 45. The crimp end 43 includes a pair of flanges 47, with a slot 49
between the
flanges. The slot 49 receives the end of the coil wire and the flanges 47 are
crimped to
form a tight connection between the coil wire end and crimp end 45. The flat
end 45
has an opening 51 that is sized to receive a stud or bolt or other elongated
terminal
member for connection. As described above, the terminal 39 can hold a bolt
during
assembly of the heater, with the bolt making the power connection once the
heater is
finally assembled. In the alternative, the terminal 39 can be used once the
heater is
completely assembled to attach to a particular stud or bolt using the
necessary
combination of washers and nuts for a secure connection. Thus, the manufacture
of
the heater assembly has maximum capability when assembling the heater to
accommodate different modes of assembly.
Referring now to Figures 2-4 and 6, the arrangement of the coils 27 and 29
produces a termination zone 53 of the coils at one end of the support plate
21.
Referring to Figure 6, one end of a completed heater 60 is shown. The heater
60
7
CA 02810620 2013-03-26
, .
includes the support plate 21, insulators 25, and coils 27 and 29, and their
respective
terminals 39 and 41. The heater 60 includes a circular duct 61 (other shaped
ducts
could be used) that is linked to the support plate using openings in the duct
and the
protrusions on the support plate as is well known in the art. The support
plate 21
divides the duct into two halves, but other plates could be used to create
more sectors
of the heater.
The heater 60 supports a power terminal 63, which includes a ceramic bushing
65, with elongated members, e.g., threaded studs 67, extending from each end.
One
stud 67 attaches to both terminals 39 of the coils 27 and 29 using nut 69 and
washer
71 (other combinations of washers and nuts or other fasteners may be
employed). The
other stud 67 is attached to power. The blade terminals 41 are attached to two
other
terminals 73 and 74 as conventionally done for these types of heaters. The
terminals
73 and 74 have connectors 76 opposite the connection to terminals 41 to
complete the
circuitry of the heater.
By the configuration of the coils and formation of the termination zone 53,
the
terminations of the coil ends are located at one end of the heater. By
positioning this
end into upstream of the flow of air (where ambient air is introduced into the
heater),
the termination zone is on the cool side of the heater so that the effects of
heated air
on the terminations is minimized. Also, the terminals are all in the same
location, which
makes it easier to routing wiring and installing the heater.
The unique configuration of the coils is best seen in Figures 2-4 and 6.
Figure 2
represents the coils mounted to the side 75 of the support plate 21 (shown as
the right
8
CA 02810620 2013-03-26
side of the heater of Figure 6) with Figure 3 showing the coils mounted to the
side 77
of the support plate 21 (shown as the left side of the heater of Figure 6).
For ease of
understanding, the sides 75 and 77 each have a reference mark 79.
On side 77, it can be seen that there are two runs of the second stage coil 29
and one run of the first stage coil 27. On the opposite side 75, there is one
full run and
two half runs of the first stage coil 27, and two half runs of the coil 29.
This
configuration means that when the first stage heater is used, air passing on
both sides
75 and 77 of the support plate is heated. Similarly, during a two stage
heating, air
passing on both sides is heated from both coils 27 and 29. If the runs on each
side
were considered to be in thirds, side 77 has two thirds of the coil 29 and one
third of
the coil 27, with side 75 having two thirds of the coil 27 and one third of
the coil 29.
Figure 4 shows the runs of coils in one drawing, which more clearly depicts
the
crossovers between the plate 21 and crossovers between coils 27 and 29 on each
side
of the plate 21. For side 77, coil 29 has both ends 80 of the coil portion
(see Figure 5
to more clearly see the end of the coil portion of the coil) terminate on side
77, with the
two runs linked by crossing over at crossover portion 82 to the two half runs
on side 75,
which are linked by crossover portion 85.
Coil 27 has one coil end 78 terminate on side 77, with one crossover at
crossover
portion 84 to side 75 to another long run. The long run on side 75 links to
one of the
short runs on the same side by crossover portion 88, which in turn links to
another
short run on the same side by another crossover portion 90 so that the coil
end
terminates on side 75 at end 31 and terminal 39. While the free and uncoiled
ends of
9
CA 02810620 2013-03-26
, .
the coils 27 and 29 could cross over the support plate 21 to attach to the
desired
terminal as shown in Figure 6 for coil end 35, the ends of the coils
themselves, i.e., 78
and 80, are separated by the support plate 21.
Figures 2 and 3 also show the runs of the coils 27 and 29 in a sinusoidal
pattern
or configuration. Each of the resistance wire coils 27 and 29 has a
longitudinal axis
generally parallel to an air flow path of the heater. At least a portion of
the insulators
25 that support the coils 27 and 29 are offset from the path. These offset
insulators 25
when combined with the insulators 25 on the path cause at least a portion of
the
resistance wire coil to have a sinusoidal shape as disclosed in application
11/987,542
noted above. It is this sinusoidal shape that provides advantages in terms of
noise
reduction, reduction of the shadowing problem, minimizing vibration resonancy,
and
better filling the volume of the heater for maximized heat transfer. While
this sinusoidal
shaped coil conflguration is a preferred one, other coil configurations could
be
employed such as a straight configuration that has no sinusoidal pattern.
While the figures show a particular arrangement of terminals for each side of
the
plate 21, the terminals 39 and 41 could be switched if the terminations on the
heater
duct dictated such a switch.
It should be also understood that the configuration of the coils and creation
of
the termination zone 53 can be used with any types of terminals for the ends
31, 33,
35, and 37 of the coils. Also, while a two stage heater is shown, additional
coils could
be employed without departing from the equal partitioning of the coils for
each stage
on each side of the plate and maintaining termination at the cool or upstream
end of
CA 02810620 2013-03-26
the heater. The support plate 21 is typically metal in these types of heaters,
but it can
be any material capable of providing the desired strength and stability during
the heater
operation, a non-metallic material, composite and the like. The other heat
components
can also be made of any materials that are capable of functioning in the
environment of
open coil resistance heaters.
In use, the heater can be used to heat air passing over the coils in the known
fashion. Also, the inventive terminal configuration allows the terminals 39 to
be
attached to one end of the coil prior to heater assembly or during an early
stage of the
assembly. The lightweight nature of the terminal avoids the problem
encountered
when heavy bolts have been used in the past. The use of the terminal 39
enables a
secure termination at the power terminal to be easily made using nuts and
washers.
While the prior art heaters provide adequate means to heat air or a fluid for
a
heating application, the heaters still are in need of improvement and the
present
invention responds to this need.
Summary of the Invention
It is an object of the invention to provide an improved electrical resistance
heater, including one has improved power distribution characteristics. The
invention, in
one aspect, is an improvement over an open coil electrical resistance heater
subassembly that includes a support plate dividing the heater into at least
two portions,
at least two resistance wire coils, a plurality of insulators mounted to the
support plate
along a defined path, whereby each insulator is configured to provide support
to a
11
CA 02810620 2013-03-26
portion of the resistance wire coil, the at least two resistance wire coils
being
partitioned generally equally on each side of the support plate, the at least
two
resistance wire coils each having first and second coil ends with a lead
extending from
each of the first and second coil ends, wherein each of the first and second
coil ends
are located at one end of the support plate. The improvement of the invention
comprises the at least two resistance wire coils being arranged with respect
to the
support plate so that the coil power for each coil is distributed generally
evenly between
the top and bottom of the support plate and across the width of the support
plate.
Each of the at least two resistance wire coils can have a first terminal on
one coil
end and a second terminal on the other coil end, the first terminal further
comprising a
first end crimped to the one coil end and a second flat end with an opening
sized to
receive an elongated member of a terminal.
The at least two resistance wire coils can have their coil ends arranged on
one
side of the support plate with the other of the at least two resistance wire
coils having
one coil end on one side of the support plate and the other coil end on the
other side of
the support plate.
One of the at least two resistance wire coils can have its coil ends arranged
on
one side of the support plate with the other of the at least two resistance
wire coils
having one coil end on one side of the support plate and the other coil end on
the other
side of the support plate.
Another aspect of the invention is a heater having the inventive subassembly
as
a part thereof. The heater can include a heater duct having a power terminal
mounted
12
CA 02810620 2013-03-26
on one end thereof. At least one of the terminal ends is an elongated member
extending from the power terminal, wherein each of the at least two resistance
wire
coils has a first terminal on one coil end and a second terminal on the other
coil end,
the first terminal further comprising a first end crimped to the one coil end
and a
second flat end with an opening sized receiving the elongated member of the
power
terminal for connection to power.
The open coil electrical resistance heater can comprise a duct of defined
cross
section, a support plate supported by the duct to divide the duct into two
portions, at
least two resistance wire coils adapted to connect to a power source for
energizing of
the heater, a plurality of insulators, each insulator mounted to the support
plate to
support portions of the resistance wire coils, wherein the at least two
resistance wire
coils are partitioned generally equally on either side of the support plate,
each of the
resistance wire coils having first and second coil ends with a lead extending
from each
of the first and second coil ends, wherein each of the first and second coil
ends are
arranged at one end of the heater, and further wherein the at least two
resistance wire
coils are arranged with respect to the support plate so that the coil power
for each coil
is distributed generally evenly between the top and bottom and across the
width of the
heater support plate.
The invention also includes an improvement in a method of method of heating
air using an open coil electrical resistance heater. The improvement
comprising using
the multiple stage open coil electrical resistance heater described above for
the heating.
13
CA 02810620 2013-03-26
The subassembly or the heater can have at least two electrical resistance
coils which
comprise two runs, each of the two runs extending along a top surface of the
support
plate and generally the length of the support plate; and four runs, each of
the four runs
extending generally along a bottom surface of the support plate and generally
about
half the length of the support plate; or wherein the two runs are along the
bottom
surface and the four runs of each of the at least two electrical resistance
wire coils are
along the top surface. The crossovers for the two runs can be at the ends of
the
support plate where the coil portions of at least two electrical resistance
wire coils
terminate and/or crossovers for the four runs can be at a middle portion of
the support
plate.
Brief Description of the Drawings
Figure 1 shows a side view of a prior art multi-stage open coil electric
heater.
Figure 2 shows one side of an arrangement of the coils and terminations of a
prior art electric heater.
Figure 3 shows the bottom view of the other side of the arrangement of the
coils
and terminations of the electric heater of Figure 2.
Figure 4 is schematic representation of the runs of the coils of the prior art
electric heater depicted in Figures 2 and 3.
Figure 5 shows the coils and their terminations removed from the electric
heater.
Figure 6 is an end view of a prior art electric heater, showing the heater
duct,
the heater support plate, the coils, and terminations of the coils.
14
CA 02810620 2013-03-26
Figures 7a-7C show a typical terminal for a heater coil.
Figure 8A is a prior art schematic illustration showing the coil and power
distribution between two sides of a heater support plate for one coil of a two
coil
heater.
Figure 88 is a prior art schematic illustration showing the coil and power
distribution between two sides of a heater support plate for the other coil in
the heater
of Figure 8A.
Figure 9A is schematic illustration showing the coil and power distribution
between two sides of a heater support plate for one coil of a heater according
to the
invention.
Figure 98 is schematic illustration showing the coil and power distribution
between two sides of a heater support plate for the other coil of a two coil
heater
according to the invention.
Figure 10 is a perspective view of one side of a heater support plate showing
the
coils C and D of Figures 9A and 98.
Figure 11 is a perspective view of the other side of the heater support plate
of
Figure 10 showing the coils C and D.
Figure 12 is an end perspective view of the heater support plate of Figures 10
and 11.
Figure 13 is an enlarged view of the coil arrangement shown in Figure 11.
Description of the Preferred Embodiments of the Invention
CA 02810620 2015-02-20
The invention relates to a duct mounted, open coil, multiple stage open coil
electric
heater using a metal support plate to retain insulators that in turn retain
convolutions of a
heating element coil. For two stage heaters, unlike the prior art heaters,
such as disclosed in
United States Patent No. 8,278,605, a new and unique coil routing provides the
ability for the
first stage of heat to provide heat to both sides of a metal support plate and
additionally heat
the air stream on each side of the duct, in a symmetrical fashion as related
to top and bottom
as well as right side to left side of the heater. This unique routing requires
neither special
ceramic insulators for insulating the heating element wire end nor carefully
separated
termination points.
The second stage of heat has an additional and new and unique routing that
again
provides a symmetrical configuration for both top to bottom and right side to
left side
symmetrical heating potential. All coil ends are located at one side of the
heater plate making
power lead routing as simple as possible.
Additionally and by utilizing a unique four (4) row configuration from right
to left,
symmetry can be maintained in both the top to bottom and right to left
directions as well as
providing for additional linear coil length, thus allowing much more usable
space to be made
available for the longer length coil runs. This added linear coil space allows
the design to
reduce the coil wire watt loading by providing enough area to utilize larger
coil wire gauges
which require additional length in order to fit in the available routing area.
Additionally, the coil
outside diameter has been reduced, allowing the designer the option of the
four (4) row
configuration by placing each row closer
3.6
CA 02810620 2013-03-26
. .
together in the right to left direction. Further and with the inventive
design, the power
termination leads can be located at the lowest temperature side of the heater,
thereby
minimizing deterioration by temperature.
The present invention is an improvement over the coil design shown in Figures
2-8B. While the prior art coil design mentioned above has a generally equal
coil
configuration between the top and the bottom of the heater, the power of the
coils is
not evenly distributed over the heater. The heater of the invention provides a
uniform
heat distribution, i.e., power, produced from top to bottom and from right
side to left
side). The inventive heater design also utilizes the length of the heater
assembly to
locate at least a portion of the heat in the front of the assembly and the
remaining
portion of heat in the back of the heater assembly.
More traditional heaters typically consist of one element or one stage, which
produces all of the heat. However, if the heater is intended to produce two
stages of
heat and one element is to produce more or less than 50% of the heat and the
other
element to produce the remaining, one could located the higher or lower
percent power
element in the location where the airflow is less pre-heated (like the inlet
side). This
method can seek to reduce radiant heat and losses, thereby making the heater
more
efficient.
There are designs on the market which attempt to easily create an even heat
distribution for a particular heater application. However, these heaters
locate the
heater sections as follows, one element in the front or inlet side of the
heater and one
located on the exit side of the heater. This design those does not produce a
uniform
17
CA 02810620 2013-03-26
heat along the length of the heater. That is, if one element of the two
elements is
used, only one end of the heater is employed for heating.
The heater of the invention specifically avoids this problem with its even
heat
distribution between top and bottom as well as across the width and along the
length of
the heater.
Referring to Figures 8A and 8B, the coil configuration of each coil of the two
coil
heater shown in Figures 2 and 3 is illustrated. Referring to Figure 8A, it can
be seen
that coil A has two thirds of its length above the heater plate 50 on side 51
and a third
of its coil length below the heater plate on side 53. This means that the
power is
unevenly divided, with 2/3 power on the top and 1/3 power on the bottom. Also,
it can
be seen that across the width of the heater the coils are positioned with one
run on the
left side and one run down the middle of the heater. This means that the power
distribution across the width of the heater is not uniform. More power is on
the left
side of the heater.
Referring to Figure 8B, the other coil B in the heater of Figure 2 is shown
with its
runs above and below the heater plate. Here, one third of the run of coil is
on the top
of the heater on side 51 and two thirds of the coil run are on the bottom of
the heater
or under the heater support plate on side 53. Thus, the power division is 1/3
power on
top and 2/3 power on the bottom. Also, since three runs of coil are beneath
the heater
plate 50 and only one run of coil is on the top, the heat distribution of the
coils is also
uneven across the width of the heater. More heat will be generated on the
right side of
the heater.
18
CA 02810620 2013-03-26
The invention provides an improved coil configuration over that shown in
Figures
8A and 8B. Referring to Figures 9A and 9B, the inventive coil configuration is
shown in
terms of the runs of the coil. It should be understood that the insulators,
heater
housing, terminals etc., are not shown in these drawings since they are
already
disclosed in the prior art design of Figure 2, which is applicable to the
invention in
terms of the ends of the actual coil portions of the coils being on the same
side of the
heater so that the electrical insulators used in the prior art heaters are
avoided,
termination of the coil ends can be more simply done. In fact, all features
other than
the coil configuration being improved upon that are shown in Figures 2-7c and
described above can be applied to the invention.
The inventive coil configuration also employs two coils C and D. The
configuration of the coil C is shown in Figure 9A, and the configuration of
Coil D is
shown in Figure 9B. Coil C shows that one half of the total coil length is on
the side 51
of the heater support plate 50 with the other half of the total coil length
being on the
other side 53 of the heater support plate 50. With this configuration, it can
be seen
that the power for the coil is split evenly, 1/2 on the top of the heater and
1/2 on the
bottom. When looking across the heater, it is also seen that 1/2 the coil
length is on the
left side of the heater with the other half of the coil length on the right
side of the
heater, see the end view of the coils in Figure 9A. As such, the power is also
divided
evenly across the width of the heater.
The same configuration is shown for Figure 9B. Coil D has 1/2 of its coil
length
above the support plate 50 on side 51 and the remaining half below the support
plate
19
CA 02810620 2013-03-26
,
50 on side 53. In addition, 1/2 of the coil length is on the left side of the
heater with the
remaining half being on the right side, see the end view of the coils in
Figure 9B.
The inventive coil configuration has other advantages in terms of heater
design.
One typical problem with heater element design is radiant heat. Since radiant
heat
does not heat air directly, it can be considered a loss thereby reducing the
efficiency of
the air heating device. This can be considered from the standpoint of the
element
glowing, which heats the surrounding components but not the air.
In addition to this, the area normally available to locate heating elements is
restricted, leaving the designer with the difficulty of trying to reduce
radiant loss by
using lower watt density elements. Reducing the watt density requires more
wire
length and thus linear stringing length. To account for these facts, designers
have
typically increased the element winding arbor (increase the diameter of the
coil) in
order to account for more wire length, thus reducing the watt loading. While
these
methods do allow for more length, they are limited in other design aspects
since the
increase in the coil diameter means that the coil is less rigid at high
temperatures and
thus less mechanically stable. This loss of rigidity and mechanical stability
increases the
chances for the coil to move during heater operation and cause a short to
ground.
The inventive coil configuration overcomes this problem. That is, the coil
assembly reduces the element outside diameter, which is opposite to the
conventional
approach used in the prior art, i.e., increase the coil diameter. This results
in a
diameter that allows the designer to increase the linear length available for
element
length (4 coils across the width and along the length of the support plate as
opposed to
CA 02810620 2013-03-26
the 3 coil configuration of Figures 2 and 3) and use a larger diameter wire
(lower
gauge). That is, with the prior art heater design, a 240 Volt 2500 watt heater
would
require 19 gauge wire of a certain length. With the inventive coil
configuration, i.e., the
element length increase, it further allows the designer to utilize more wire
and heavier
gauge wire, e.g., be able to use 18 gauge wire instead of the 19 gauge. This
provides
the ability to reduce the watt loading further than was possible in previous
assemblies
while making a more mechanically stable coil configuration due to the heavier
gauge
wire.
Another advantage for this new invention would be the fact that designs using
the current (or prior art method) to even the heat distribution top to bottom
and right
side to left side, are forced to crossover the support plate on either the
right or left side
of the support plate. This type of crossover method can increase the
probability of
shorting to ground. This problem can often be a result of the fact these prior
art
techniques are more complex to produce and require that the element be formed
very
specifically. This, combined with the larger outside diameter elements being
used,
causes mechanical instability at high temperatures so as to allow the element
to move
more easily, increasing the likelihood of shorting to ground.
The inventive coil configuration utilizes smaller outside diameter elements
with
more mechanical stability at high temperatures, lower watt loading and more
even heat
distribution (including at least some distribution of heat "front to back"),
thus reducing
the likelihood of movement and reducing the likelihood of an element crossover
causing
a short to ground.
21
CA 02810620 2013-03-26
The coil configuration is also advantageous when a two stage coil heater is
needed whereby the coils do not provide the same level of heating. For
example, one
coil could be rated at 30% power and the other coil could be rated at 70%
power. This
heater could be operated at 300io, 70%, or 100%, thus providing three
different levels
of heat generation. With the inventive uniform heat distribution between the
top and
bottom and left to right side, a more uniform heat distribution can be
provided even
when the coils are not identical.
Figures 10-13 show perspective views of one embodiment of the inventive coil
configuration. Figure 10 shows a top view of the heater subassembly 60 with
the long
runs of each of coils C and D shown on one side of the support plate 61. Coil
C on the
outside and coil D arranged on the inside and inside of the two C coils. The
leads 63 of
coil C are shown as well. This view corresponds to the view of the top side 51
in
Figures 9A and 9B.
Figure 11 shows the underside of the heater subassembly 60, wherein the coils
C
and D are formed with their respective runs extending over only roughly half
the length
of the heater plate. The leads 64 of coil D are also shown in Figure 11.
As with the prior art configuration shown in Figure 2, the coil ends of each
of
coils C and D are all at the end of the heater so that termination is very
simple. This is
evidenced by the fact that leads 63 and 64 are on the same end of the support
plate
61.
22
CA 02810620 2015-02-20
Figure 12 shows a better view of the crossover configuration at the end of the
support
plate 61. Coil C crosses over the support plate 61 at 65. While not shown,
Coil D crosses over
the support plate 61. at end opposite shown in Figure 12.
The crossover between adjacent coil portions for coil C on the same side of
the support
plate is shown at 67 in Figure 12. The crossover over of adjacent coil
portions for coil D is
shown as 69 in Figure 12.
Referring to Figure 13, the crossover for the half length coils C and D on the
same side
of the support plate are shown in an enlarged fashion. The crossover for
adjacent coil portions
for coil C is shown at 71. and the crossover for the adjacent coil portions
for coil D is shown at
73.
Even though the coils are shown in the drawings with the long runs on the top
half of
the heater plate, the long runs could be located on the underside of the
heater plate with the
half length runs on the top of the support plate.
As such, an invention has been disclosed in terms of preferred embodiments
thereof
which fulfills each and every one of the objects of the present invention as
set forth above and
provides a new and improved heater and method of use.
Of course, the scope of the claims should not be limited by the preferred
embodiments
set forth in the examples, but should be given the broadest interpretation
consistent with the
description as a whole. It is intended that the present invention only be
limited by the terms of
the appended claims.
23
