CA1244863A - Electric blanket or pad having improved positive temperature coefficient heater circuit - Google Patents
Electric blanket or pad having improved positive temperature coefficient heater circuitInfo
- Publication number
- CA1244863A CA1244863A CA000489350A CA489350A CA1244863A CA 1244863 A CA1244863 A CA 1244863A CA 000489350 A CA000489350 A CA 000489350A CA 489350 A CA489350 A CA 489350A CA 1244863 A CA1244863 A CA 1244863A
- Authority
- CA
- Canada
- Prior art keywords
- conductors
- cable
- pad
- heating
- conductor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000004020 conductor Substances 0.000 claims abstract description 71
- 238000010438 heat treatment Methods 0.000 claims abstract description 56
- 239000000463 material Substances 0.000 claims abstract description 17
- 239000004744 fabric Substances 0.000 claims description 4
- 238000005485 electric heating Methods 0.000 claims 1
- 230000000694 effects Effects 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 4
- 241000353097 Molva molva Species 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 229920001940 conductive polymer Polymers 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000002861 polymer material Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/40—Heating elements having the shape of rods or tubes
- H05B3/54—Heating elements having the shape of rods or tubes flexible
- H05B3/56—Heating cables
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
- H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
- H05B3/146—Conductive polymers, e.g. polyethylene, thermoplastics
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
- H05B3/34—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater flexible, e.g. heating nets or webs
- H05B3/342—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater flexible, e.g. heating nets or webs heaters used in textiles
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B2203/00—Aspects relating to Ohmic resistive heating covered by group H05B3/00
- H05B2203/002—Heaters using a particular layout for the resistive material or resistive elements
- H05B2203/003—Heaters using a particular layout for the resistive material or resistive elements using serpentine layout
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B2203/00—Aspects relating to Ohmic resistive heating covered by group H05B3/00
- H05B2203/017—Manufacturing methods or apparatus for heaters
Landscapes
- Engineering & Computer Science (AREA)
- Textile Engineering (AREA)
- Resistance Heating (AREA)
- Control Of Resistance Heating (AREA)
- Surface Heating Bodies (AREA)
Abstract
Abstract of the Disclosure An electrically heated device, heating pad or mattress pad having a heating cable comprising two conductors separated by a layer of positive temperature coefficient material wherein the electrical power supplied to the conductors produces its primary I2R
heating effect in the PTC material and the two ends of each of the conductors are connected together and each conductor has means to connect it to one power supply terminal.
heating effect in the PTC material and the two ends of each of the conductors are connected together and each conductor has means to connect it to one power supply terminal.
Description
~2~363 ELECTRIC BLANKET OR PAD HAVING IMPROVED POSITIVE
TEMPERATURE COEFFICIENT ~EATER CIRCUIT
Back~round of the Invention This invention relates generally to electric blankets, heating pads and mattress pads and, more specifically, to a novel heating element circuit for use in such blankets and pads.
Electric blankets, electric mattress pads and heating pads are silimar in that all three include some type of elongated flexible heating element which is disposed in a tortuous configuration within a fabric or plastic sandwich designed to enclose and obscure the heating element. The fabric or plastic sandwich is sometimes termed a shell and it includes a plurality o~
passageways through which the heating element is threaded so that the heat therefrom is deli~ered uniformly across the face of the blanket or pad. There are normally a number of spaced lengths of the heating element which are disposed across the surface of the blanket or pad with these portions of the heating element being spaced close enough so that when the element is energized the user gets the illusion of more or less uniform warmth across the entire surface of the blanket or pad.
In the prior art blankets and pads there have typically been some means to control the application of electrical energy to the pad and also means to sense any overheat conditions at local areas in the pad. The local heat sensing is nec~ssary since the control means for the blanket or pad might sense that power is required at the same time an overheat oondition exists at some point in ~ ., the blanket or pad. Such a local overheat condition may be caused by the heating element being folded upon itself or covered by the mattress or a blanket so that temperature tended to increase in that particular area.
Where such folding or covering of the heating element occurs, the heat is not dissipated from the element at the same speed as in other areas of the blanket or pad and dangerous overheat conditions begin to develop.
The temperature sensing means to respond to such overheat conditions have typically taken the form oi bimetallic thermostats positioned throughout the pad or continuous sensing wires which more or less parallel the heating element to sense any overheat conditions through-out the length of the element. A third alternative involves the use of a heating element which includes positive temperature coefficient material as the heating element. This type of material is self-regulating in that increases in local temperature along the length of the heating element cause that portion of the element to receive less current and thereby reduces the power input to the overheated area. There are a number of prior art patents disclosing heating element configurations for use in such PTC blankets.
One of the problems encountered in the prior art PTC heating element circuits is the fact that a break in one of the conductors included in the heating element causes serious arcing at the location of the break and has required that certain safety modules be included in the circuits for such blankets. These safety modules include means for disabling or shutting off the blanket when an open circuit is sensed in either one of the conductors. Since the inclusion of such circuit module to shut off the blanket in the event of an open circuit is expensive, it would be desirable to devise a circuit which would eliminate the necessity for the safety module or safety circuit.
~ ~zaX~63 Summary of the Invention The present invention involves an electric blanket, heating pad or mattress pad having a positive temperature coefficient heating cable including two conductors which are separated by a layer of positive temperature coefficient material. The cable is disposed in a tortuous manner in the blanket, heating pad or mattress pad with the ends of the cable being connected so that the ends of each of the two conductors are connected together. A cord connector is provided to supply power to each of the two conductors. In the event of a break or open circuit in either of the two conductors in the heating cable, there is a very small voltage drop across the break since the ends of the brokèn conductor are connected together. Thus, the only difference in voltage at the break would be a consequence of the location of the break with respect to the ends of the conductor. A break at the middle would produce no drop across the break whereas a break at one end of the conductor would produce a drop equal to the total voltage drop through the length of the conductor which would be on the order of less than 10 volts.
Accordingly, it is an object of the present invention to provide an improved electric blanket circuit utilizing a positive temperature coefficient heating cable which has the ends of the heating cable connected together to minimize the voltage drop across any brea~
which may occur in either one of the conductors in the cable.
It is a fuxther object of the present invention to provide an improved PTC heating element circuit which avoids the need for a safet~ module to interrupt the circuit in the event of an open circuit in one of the conductors.
It is another object of the present invention to provide an improved heating circuit for an electric blanket, mattress pad or heating pad having an elongated PTC heatin~ element which is connected to be supplied with power from both ends to eliminate any arcing problem which might occur in the event of a break in one of the conductors.
Further ob]ects and advantages will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out in the claims annexed to and forming a part of the specification.
Brief Description of the Drawings Fig. 1 is a schematic diagram showing an electric blanket embodying my invention;
Fig. 2 is a greatly enlarged cross-sectional view of the heating cable of the type used in the blanket of Fig. 1, and Fig. 3 is a schematic wiring diagram of the blanket of Fig. 1 showing the positive temperature coefficient heating material as a series of distributed parallel resistances.
Description of the Preferred Embodiment Referring to the drawings, there is shown in Fig. 1 an electric blanket, heating pad or mattress pad 10. The blanket or pad 10 includes a shell 13 which conventionally consists of several layers of fabric secured together to form passageways through which a heating element 12 is threaded. The element 12 as shown in Fig. 1 is disposed in a tortuous configuration having a plurality of parallel legs interconnected together to dispose the heating element 12 across the entire surface of the shell 13 so that heat is distributed relatively uniformly to the entire surface. The heating element 12 terminates in ends 12a and 12b which extend into a connector module 14 which is shown schematically in greatly enlarged form. The connector module 14 would be no more than a few inches square and would be attached to "` lZ~ 3 the blanket 13. Also extending into the connector module 14 are conductors 16 and 18 which form parts of a power cord 20 which terminates in a plug 22.
To better understand the nature of the heating element 12 reference should be had to Fig. 2 which is a greatly enlarged cross-sectional view of the heating element 12. The element 12 includes a pair of spaced conductors 24 and 26 which are separated by a layer of PTC material 28 which also surrounds the conductors 24 and 26 to form a somewhat barbell type configuration.
The PTC material 28 is in turn enclosed in an insulating coating 30. The PTC material 28 may be any suitable conductive polymer which exhibits positive temperature coefficient resistance characteristics at suitable temperatures as is well-known in the art. Possible compositions for the PTC material 28 are disclosed in the Kelly U. S. Patent No. 4,277,673. The conductors 24 and 26 must be of sufficiently high conductivity so that the primary heating effect created in the heating cable 12 is in the PTC material 28 and not in the conductors 24 and 26. Details of the flexible conductors suitable for use in such application are disclosed in Crowley U. S. Patent No. 4,309,596.
In a typical electric blanket application, the length of the heating element 12 would be on the order of 150 feet and the voltage drop over the length of one of the conductors 24 or 26 would be on the order of 10 volts when connected to a conventional 110 volt AC power supply. It has been conventional in the past to connect one of the conductors 24 at one end to one side of the power line and the other end of the other conductor to the other side of the power line. The purpose of connecting opposite ends to the opposite sides of the power line is to obtain a uniform potential between the two conductors 24 and 26 throughout the length of the heating element 12. Thus, the heat dissipated at any place along the leng~h of the heating element 12 would be the same. Although less desirable, it is also possible to connect the conductors at one end of the cable 12 to each of the power supply terminals to thereby energize the element 12 One of the problems which was found to exist with electric blankets using this type of heating element involved the results of having a break in one of the conductors. In such a situation, there would be a substantial voltage drop across the broken ends of the wire, the drop being on the order of 100 volts. This type of voltage drop would cause an arc which had some tendency to dissociate the polymer material into a flammable gas. It was therefore necessary to devise some type of circuit module which would disable the circuit or open the circuit whenever there was a break in one of the conductors which might cause the arcing situation discussed above. An example of one such safety circuit module is disclosed in the U. S. Patent to Carlson No.
4,436,986. However, such circuit modules tend to be costly and are difficult to justify 'o the consumer who knows nothing of the need for such a safety module. In our present invention, we have devised a method of connecting the conductors so that the circuit module is rendered unnecessary.
Referring to Fig. 1, the end of the heating element 12a includes conductor ends 24a and 26a and the end 12b includes conductor ends 24b and 26b. Within the module 14, the ends of conductor 24 which comprise 24a and 24b are connected together at 32. The ends of conductor 2& which are designated as 26a and 26b are connected at 34. These common connections 32 and 34 are connected to the power cord conductors 16 and 18 respectively. There is provided a fuse 36 in series with the cord conductor 16 and the heating element 12.
Fig. 3 provides a schematic diagram ~f the circuit described above in connection with Fig. 1. In Fig. 3, the heating element 12 is shown as including the conductors 24 and 26 with a plurality of parallel resistances 28a connected therebetween. The resistances 28a are merely employed to illustrate how the PTC layer 28 would function in the circuit. The I2R heating produced in the heating element 12 is primarily a result of the current flowing through the PTC material 28 which may be considered an infinite n~mber of parallel resistances connected between the conductors 24 and 26.
The diagram of Fig. 3 shows clearly the loop connection of each of the conductors 24 and 26 wherein the ends of each conductor are connected together. In this arrangem~nt, power cord conductor 16 supplies power to both ends of conductor 24 of the heating element 12 and power cord conductor 18 supplies power to both ends of the conductor 26. As a consequence, if either of the conductors 24 or 26 breaks and opens the circuit at some particular point over its length, there will be a minimal voltage drop at the break because both segments of the broken conductor will still be connected to the power supply. If the break is in the middle of the conductox, there would be no voltage drop while if it were at one end there would exist whatever drop occurred over the length of the longer conductor which would only be about 10 volts.
In contrast with only one end of each conductor connected to the power supply, a break in one of the conductors will result in a voltage drop across the break of about 100 volts since the unpowered end of the conductor away from the break tends to assume the voltage of the other side of the line giving almost full line voltage across the break.
As is evident from Fig. 1, the ends of each conductor 24 or 26 are close together making it a simple matter to complete the loop connection. The resulting circuit provides a simple and effective means of over-coming the very serious arcing problem which existed with respect to the prior art PTC blankets.
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TEMPERATURE COEFFICIENT ~EATER CIRCUIT
Back~round of the Invention This invention relates generally to electric blankets, heating pads and mattress pads and, more specifically, to a novel heating element circuit for use in such blankets and pads.
Electric blankets, electric mattress pads and heating pads are silimar in that all three include some type of elongated flexible heating element which is disposed in a tortuous configuration within a fabric or plastic sandwich designed to enclose and obscure the heating element. The fabric or plastic sandwich is sometimes termed a shell and it includes a plurality o~
passageways through which the heating element is threaded so that the heat therefrom is deli~ered uniformly across the face of the blanket or pad. There are normally a number of spaced lengths of the heating element which are disposed across the surface of the blanket or pad with these portions of the heating element being spaced close enough so that when the element is energized the user gets the illusion of more or less uniform warmth across the entire surface of the blanket or pad.
In the prior art blankets and pads there have typically been some means to control the application of electrical energy to the pad and also means to sense any overheat conditions at local areas in the pad. The local heat sensing is nec~ssary since the control means for the blanket or pad might sense that power is required at the same time an overheat oondition exists at some point in ~ ., the blanket or pad. Such a local overheat condition may be caused by the heating element being folded upon itself or covered by the mattress or a blanket so that temperature tended to increase in that particular area.
Where such folding or covering of the heating element occurs, the heat is not dissipated from the element at the same speed as in other areas of the blanket or pad and dangerous overheat conditions begin to develop.
The temperature sensing means to respond to such overheat conditions have typically taken the form oi bimetallic thermostats positioned throughout the pad or continuous sensing wires which more or less parallel the heating element to sense any overheat conditions through-out the length of the element. A third alternative involves the use of a heating element which includes positive temperature coefficient material as the heating element. This type of material is self-regulating in that increases in local temperature along the length of the heating element cause that portion of the element to receive less current and thereby reduces the power input to the overheated area. There are a number of prior art patents disclosing heating element configurations for use in such PTC blankets.
One of the problems encountered in the prior art PTC heating element circuits is the fact that a break in one of the conductors included in the heating element causes serious arcing at the location of the break and has required that certain safety modules be included in the circuits for such blankets. These safety modules include means for disabling or shutting off the blanket when an open circuit is sensed in either one of the conductors. Since the inclusion of such circuit module to shut off the blanket in the event of an open circuit is expensive, it would be desirable to devise a circuit which would eliminate the necessity for the safety module or safety circuit.
~ ~zaX~63 Summary of the Invention The present invention involves an electric blanket, heating pad or mattress pad having a positive temperature coefficient heating cable including two conductors which are separated by a layer of positive temperature coefficient material. The cable is disposed in a tortuous manner in the blanket, heating pad or mattress pad with the ends of the cable being connected so that the ends of each of the two conductors are connected together. A cord connector is provided to supply power to each of the two conductors. In the event of a break or open circuit in either of the two conductors in the heating cable, there is a very small voltage drop across the break since the ends of the brokèn conductor are connected together. Thus, the only difference in voltage at the break would be a consequence of the location of the break with respect to the ends of the conductor. A break at the middle would produce no drop across the break whereas a break at one end of the conductor would produce a drop equal to the total voltage drop through the length of the conductor which would be on the order of less than 10 volts.
Accordingly, it is an object of the present invention to provide an improved electric blanket circuit utilizing a positive temperature coefficient heating cable which has the ends of the heating cable connected together to minimize the voltage drop across any brea~
which may occur in either one of the conductors in the cable.
It is a fuxther object of the present invention to provide an improved PTC heating element circuit which avoids the need for a safet~ module to interrupt the circuit in the event of an open circuit in one of the conductors.
It is another object of the present invention to provide an improved heating circuit for an electric blanket, mattress pad or heating pad having an elongated PTC heatin~ element which is connected to be supplied with power from both ends to eliminate any arcing problem which might occur in the event of a break in one of the conductors.
Further ob]ects and advantages will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out in the claims annexed to and forming a part of the specification.
Brief Description of the Drawings Fig. 1 is a schematic diagram showing an electric blanket embodying my invention;
Fig. 2 is a greatly enlarged cross-sectional view of the heating cable of the type used in the blanket of Fig. 1, and Fig. 3 is a schematic wiring diagram of the blanket of Fig. 1 showing the positive temperature coefficient heating material as a series of distributed parallel resistances.
Description of the Preferred Embodiment Referring to the drawings, there is shown in Fig. 1 an electric blanket, heating pad or mattress pad 10. The blanket or pad 10 includes a shell 13 which conventionally consists of several layers of fabric secured together to form passageways through which a heating element 12 is threaded. The element 12 as shown in Fig. 1 is disposed in a tortuous configuration having a plurality of parallel legs interconnected together to dispose the heating element 12 across the entire surface of the shell 13 so that heat is distributed relatively uniformly to the entire surface. The heating element 12 terminates in ends 12a and 12b which extend into a connector module 14 which is shown schematically in greatly enlarged form. The connector module 14 would be no more than a few inches square and would be attached to "` lZ~ 3 the blanket 13. Also extending into the connector module 14 are conductors 16 and 18 which form parts of a power cord 20 which terminates in a plug 22.
To better understand the nature of the heating element 12 reference should be had to Fig. 2 which is a greatly enlarged cross-sectional view of the heating element 12. The element 12 includes a pair of spaced conductors 24 and 26 which are separated by a layer of PTC material 28 which also surrounds the conductors 24 and 26 to form a somewhat barbell type configuration.
The PTC material 28 is in turn enclosed in an insulating coating 30. The PTC material 28 may be any suitable conductive polymer which exhibits positive temperature coefficient resistance characteristics at suitable temperatures as is well-known in the art. Possible compositions for the PTC material 28 are disclosed in the Kelly U. S. Patent No. 4,277,673. The conductors 24 and 26 must be of sufficiently high conductivity so that the primary heating effect created in the heating cable 12 is in the PTC material 28 and not in the conductors 24 and 26. Details of the flexible conductors suitable for use in such application are disclosed in Crowley U. S. Patent No. 4,309,596.
In a typical electric blanket application, the length of the heating element 12 would be on the order of 150 feet and the voltage drop over the length of one of the conductors 24 or 26 would be on the order of 10 volts when connected to a conventional 110 volt AC power supply. It has been conventional in the past to connect one of the conductors 24 at one end to one side of the power line and the other end of the other conductor to the other side of the power line. The purpose of connecting opposite ends to the opposite sides of the power line is to obtain a uniform potential between the two conductors 24 and 26 throughout the length of the heating element 12. Thus, the heat dissipated at any place along the leng~h of the heating element 12 would be the same. Although less desirable, it is also possible to connect the conductors at one end of the cable 12 to each of the power supply terminals to thereby energize the element 12 One of the problems which was found to exist with electric blankets using this type of heating element involved the results of having a break in one of the conductors. In such a situation, there would be a substantial voltage drop across the broken ends of the wire, the drop being on the order of 100 volts. This type of voltage drop would cause an arc which had some tendency to dissociate the polymer material into a flammable gas. It was therefore necessary to devise some type of circuit module which would disable the circuit or open the circuit whenever there was a break in one of the conductors which might cause the arcing situation discussed above. An example of one such safety circuit module is disclosed in the U. S. Patent to Carlson No.
4,436,986. However, such circuit modules tend to be costly and are difficult to justify 'o the consumer who knows nothing of the need for such a safety module. In our present invention, we have devised a method of connecting the conductors so that the circuit module is rendered unnecessary.
Referring to Fig. 1, the end of the heating element 12a includes conductor ends 24a and 26a and the end 12b includes conductor ends 24b and 26b. Within the module 14, the ends of conductor 24 which comprise 24a and 24b are connected together at 32. The ends of conductor 2& which are designated as 26a and 26b are connected at 34. These common connections 32 and 34 are connected to the power cord conductors 16 and 18 respectively. There is provided a fuse 36 in series with the cord conductor 16 and the heating element 12.
Fig. 3 provides a schematic diagram ~f the circuit described above in connection with Fig. 1. In Fig. 3, the heating element 12 is shown as including the conductors 24 and 26 with a plurality of parallel resistances 28a connected therebetween. The resistances 28a are merely employed to illustrate how the PTC layer 28 would function in the circuit. The I2R heating produced in the heating element 12 is primarily a result of the current flowing through the PTC material 28 which may be considered an infinite n~mber of parallel resistances connected between the conductors 24 and 26.
The diagram of Fig. 3 shows clearly the loop connection of each of the conductors 24 and 26 wherein the ends of each conductor are connected together. In this arrangem~nt, power cord conductor 16 supplies power to both ends of conductor 24 of the heating element 12 and power cord conductor 18 supplies power to both ends of the conductor 26. As a consequence, if either of the conductors 24 or 26 breaks and opens the circuit at some particular point over its length, there will be a minimal voltage drop at the break because both segments of the broken conductor will still be connected to the power supply. If the break is in the middle of the conductox, there would be no voltage drop while if it were at one end there would exist whatever drop occurred over the length of the longer conductor which would only be about 10 volts.
In contrast with only one end of each conductor connected to the power supply, a break in one of the conductors will result in a voltage drop across the break of about 100 volts since the unpowered end of the conductor away from the break tends to assume the voltage of the other side of the line giving almost full line voltage across the break.
As is evident from Fig. 1, the ends of each conductor 24 or 26 are close together making it a simple matter to complete the loop connection. The resulting circuit provides a simple and effective means of over-coming the very serious arcing problem which existed with respect to the prior art PTC blankets.
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Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrically heated device comprising an elongated heating cable including two spaced conductors separated by a layer of positive temperature coefficient material, said cable heating primarily from the heating produced by current passing through said positive temperature coefficient material when said conductors are energized by an electric current, two layers of flexible material defining an envelope within which said cable is disposed, said envelope being formed to be disposed in a planar configuration, said heating cable being mounted in said envelope to be disposed in a tortuous shape when said envelope is in said planar configuration, said cable having a plurality of parallel spaced transversely extending portions to supply heat uniformly to said envelope, said cable having tow ends which are jointed together at a common point where power is supplied to said cable, the ends of each of said conductors of said cable being connected together to form a continuous loop of each conductor, and a power supply cord having two conductors one of which connects to each of said loop connected conductors and to a separate power supply terminal.
2. The electrically heated device of claim 1 wherein the resistances of said conductors and of said positive temperature coefficient material layer are related so that a break in either of said conductors when said power supply is a conventional domestic electric power supply is less than thirty volts and thereby producing minimal arcing at said break.
3. The electrically heated device of claim 2 wherein said cable dissipates on the order of one to four watts per foot when energized by a conventional domestic power supply.
4. The combination of claim 1 wherein said device comprises an electric blanket having said cable disposed in a tortuous configuration in a fabric blanket shell, said cable being in excess of 100 feet in length and each said conductor having a total resistance of less than 200 ohms.
5. The combination of claim 1 wherein said device comprises an electric heating pad, said cable being on the order of 20 feet in length and having a wattage of on the order of 3 watts per foot.
6. The electrically heated device of claim 1 wherein said envelope comprises a generally rectangular configuration with said ends of said cable being disposed in the middle of one edge of said rectangle, said cable being arranged in a plurality of interconnected parallel legs which extend generally perpendicular to said one edge, said cable having portions extended along said edge from said middle to the outer most of said parallel legs.
7. The combination comprising an electrically heated flexible pad having an elongated heating element distributed in a tortuous configuration across said pad to obtain substantially uniform temperature at any point on said pad, said heating element including a pair of spaced conductors and a layer of positive temperature coefficient resistance material extending between said conductors and enveloping said conductors, means connecting the two ends of each conductor together to form a loop conductor, power supply means connecting each of said loops to one side of an alternating current power supply, the resistance of each of said conductors being less than one-sixth of the resistance of the PTC layer disposed between said conductors so that in the event of a break in one of said conductors, the voltage drop at the break will be less than might be required to cause arcing of said break in said conductor.
8. The combination of claim 7 wherein said heating element is throughout its length spaced from other portions thereof except at the ends where said conductors are interconnected together.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US67890984A | 1984-12-06 | 1984-12-06 | |
| US678,909 | 1984-12-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1244863A true CA1244863A (en) | 1988-11-15 |
Family
ID=24724805
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000489350A Expired CA1244863A (en) | 1984-12-06 | 1985-08-23 | Electric blanket or pad having improved positive temperature coefficient heater circuit |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS61138485A (en) |
| AU (1) | AU574853B2 (en) |
| CA (1) | CA1244863A (en) |
| DE (1) | DE3541151C2 (en) |
| FR (1) | FR2574612A1 (en) |
| GB (1) | GB2168580B (en) |
| NZ (1) | NZ213296A (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5218185A (en) * | 1989-08-15 | 1993-06-08 | Trustees Of The Thomas A. D. Gross 1988 Revocable Trust | Elimination of potentially harmful electrical and magnetic fields from electric blankets and other electrical appliances |
| US4998006A (en) * | 1990-02-23 | 1991-03-05 | Brandeis University | Electric heating elements free of electromagnetic fields |
| US5081339A (en) * | 1990-06-01 | 1992-01-14 | Sunbeam Corporation | Water bed heater |
| US5451747A (en) * | 1992-03-03 | 1995-09-19 | Sunbeam Corporation | Flexible self-regulating heating pad combination and associated method |
| US5801914A (en) * | 1996-05-23 | 1998-09-01 | Sunbeam Products, Inc. | Electrical safety circuit with a breakable conductive element |
| ATE369771T1 (en) * | 1999-09-22 | 2007-09-15 | Matsushita Electric Ind Co Ltd | SURFACE HEATING ELEMENT |
| GB0216932D0 (en) * | 2002-07-20 | 2002-08-28 | Heat Trace Ltd | Electrical heating cable |
| US9370045B2 (en) | 2014-02-11 | 2016-06-14 | Dsm&T Company, Inc. | Heat mat with thermostatic control |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB706606A (en) * | 1951-06-21 | 1954-03-31 | Saint Gobain | Improvements in or relating to electric resistance heaters |
| US3628093A (en) * | 1970-04-13 | 1971-12-14 | Northern Electric Co | Thermostat overheat protection system for an electric appliance such as a blanket |
| CA1156300A (en) * | 1980-04-01 | 1983-11-01 | Gordon S. Carlson | Electric blanket safety circuit |
| US4309596A (en) * | 1980-06-24 | 1982-01-05 | Sunbeam Corporation | Flexible self-limiting heating cable |
-
1985
- 1985-08-23 CA CA000489350A patent/CA1244863A/en not_active Expired
- 1985-08-29 NZ NZ21329685A patent/NZ213296A/en unknown
- 1985-10-07 FR FR8514824A patent/FR2574612A1/en not_active Withdrawn
- 1985-10-28 AU AU49119/85A patent/AU574853B2/en not_active Ceased
- 1985-11-21 DE DE19853541151 patent/DE3541151C2/en not_active Expired - Fee Related
- 1985-12-05 JP JP27428285A patent/JPS61138485A/en active Pending
- 1985-12-06 GB GB08530116A patent/GB2168580B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE3541151C2 (en) | 1995-01-19 |
| NZ213296A (en) | 1989-04-26 |
| AU4911985A (en) | 1986-06-12 |
| AU574853B2 (en) | 1988-07-14 |
| GB2168580B (en) | 1988-05-11 |
| JPS61138485A (en) | 1986-06-25 |
| GB8530116D0 (en) | 1986-01-15 |
| FR2574612A1 (en) | 1986-06-13 |
| GB2168580A (en) | 1986-06-18 |
| DE3541151A1 (en) | 1986-10-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |
