CA1173884A - Ptc heater assembly - Google Patents
Ptc heater assemblyInfo
- Publication number
- CA1173884A CA1173884A CA000358370A CA358370A CA1173884A CA 1173884 A CA1173884 A CA 1173884A CA 000358370 A CA000358370 A CA 000358370A CA 358370 A CA358370 A CA 358370A CA 1173884 A CA1173884 A CA 1173884A
- Authority
- CA
- Canada
- Prior art keywords
- heater
- ptc
- power output
- envelope
- watts
- 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
Abstract
ABRIDGEMENT
The invention relates to self-regulating strip heaters containing PTC conductive polymers. According to the invention, the strip heater is surrounded by an envelope of a material of high thermal conductivity, e.g. sandwiched between aluminum sheets. This makes it possible to use a strip heater having a higher passive power and results in an assembly having a higher active power output.
The invention relates to self-regulating strip heaters containing PTC conductive polymers. According to the invention, the strip heater is surrounded by an envelope of a material of high thermal conductivity, e.g. sandwiched between aluminum sheets. This makes it possible to use a strip heater having a higher passive power and results in an assembly having a higher active power output.
Description
3~384 This invention relates to self-regulating heaters comprising an elongate strip of a PTC conductive polymer, two (or more) parallel electrodes in electri-cal (and optionally also physical) contact with the strip, and an electrically insulating jacket. Such heaters are known and are described for example in U.S.
Patents Nos. 3,793,716, 3,823,217, 3,861,029, 4,177,376 and 4,188,276 and the Thermal Desgin Guide published by the Chemelex Divison of Raychem Corporation (H 50190 10 505 B5 1/78).
In defining such heaters, reference is often made to their "passive power output" and their "active power output". The "passive power output" of a heat is the value of the term V2/Ro, where Ro is the resistance of a unit length (usually 1 foot or 1 metre) of the heater at 21C and V is the voltage of the source of electri~
cal power connected to the heater, usually 120 or 240 volts AC. The "active power output" of a heater is the measure power output of a unit length of the heater (usually 1 foot or 1 metre) when connected to the source of electrical power, with one major surface of the heater in contact with a metal substrate which is maintained at some temperature related to the intended use of the heater, e.g. 7 to 65C, such as 10C for heaters designed to prevent pipes from freezing.
Conventional strip heaters comprise two or more elec-trodes in the form of wires in electrical contact with a PTC conductive polymer element and have passive power outputs of substantially less than 165 watts per metre (50 watts per foot) at their intended operating vol-tage; the use of such heaters having higher passive power outputs has been avoided because they give little or no useful increase in active power output and have substantial disadvantages, in particular shorter life.
~' ~.
~ 8~ MP0300 We have now discovered that if a PTC conductive polymer heater is surrounded by an envelope of metal or other material of good thermal conductivity, it is possible to make use of the heater at voltages at which its passive power output is greater than 165 watts per metre without the disadvantages previously associated with Ruch use, and that 8 very valuable increase in active power output can thereby be obtained. ~or example the addition of such an envelope surprisingly makes it possible to use, at a voltage of 240 volts, a PTC heater which has a passive power output at 120 volts of less than 165 watts/metre and at 240 volts of more than 165 watts/metre, even though such a heater, in the absence of the envelope, has an unacceptably short service life at 240 volts.
In one aspect, the invention provides a method of heating which comprises passing current through a self-regulating heater assembly comprising (a) a PTC heater which comprises (i) an elongate strip of 8 conductive polymer composition exhi~iting PTC
behavior, (ii) two elongate parallel electrodes in electrical contact with aaid strip, and (iii) an electrically insulating jacket which surrounds said ~trip and said electrodes; and :~17~ 34 (b) an envelope which surrounds said PTC heater and which is composed of a material having a thermal conductivi-ty of at least 0.1 Cal/cm C sec. preferably at least 0.3 Cal/cm C sec.;
the current being supplied by a source of electrical power having a voltage V and the heater having a passive power output at said volt-age V at least 165 watts/meter (50 watts/ft.), preferably at least 230 watts/meter (70 watts/ft.).
The heater assembly can be used to heat a solid substrate, in which case the envelope is preferably shaped to conform to the substrate; or it can be used as a space heater, in which case the assembly is preferably in the form of a coil, with space between the coils for air or other liquid to circulate.
In another aspect the invention provides a self-regulating heater assembly comprising a PTC heater and an envelope as defined above, the heater having a passive power output at 120 volts of at least 165 watts/metre.
The PTC heater preferably comprises two ~or more) elect-rodes in the form of wires which are embedded in and in physical contact with the PTC strip. ~lowever, the invention includes other types of PTC heater, for example those in which one or more of the electrodes is separated from the PTC strip by a layer of another conductive material, e.g. a conductive polymer composition exhibit-ing ZTC behavior, and those which comprise a laminar PTC element and two or more laminar electrodes.
The passive power output of a heater is of course dependent on the resistivity of the PTC composition and the size and shape of ~7~38 -~
tlle electrodes and the PTC element. For a conventional strip heater, e.g. as described in the example below, the passive power output is preferably 165 to 655 watts/metre (50 to 200 watts/ft~, preferably 230 to 655 watts/metre (70 to 200 watts/ft). For the broad range of heaters contemplated by this invention, the preferred ranges of passive power outputs are better expressed by a term which includes the width of the PTC element over which heat is produced. Thus the passive power output of the heaters used in this invention is prefer-ably 217 Dito 862 D, especially 302 D to 862 D, watts/metre, where D is the largest cross-sectional dimension ~in centimetres) of the PTC strip which lies between the electrodes.
- 4a -7~88~
The active power output of the PTC heater is substantially increased by the presence of the envelope, and preferred heater assemblies have an active power output at 10C which is at least 1.5 times the active power output at 10C of the PTC heater without the envelope.
The envelope is preferably formed by a pair of elongate sheets with the heater sandwiched between them?
the sheets contacting each other either side of the heater. The sheets are preferably 0.025 to 1.3 mm, e.g.
0.075 to 0.2 mm, thick and composed of a material having a thermal conductivity of at least 0.3, e.g. aluminum. They may be secured together and/or to the heater by means of an adhesive, e.g. an epoxy adhesive.
It is important that the envelope and the PTC
heater should be in intimate thermal contact, and the envelope preferably contacts (either directly or through an adhesive) at least the areas of the insulating jacket adjacent those parts of the heater in which heat is generated. Preferably there are no voids between the envelope and the heater. It is preferred that the envelope should extend outwards from the PTC heater in the form of fins, so that the exposed surface area of the envelope is at least 1.5 times, e.g. at least 2 times, the surface area of the :insulating jaoket of the PTC heater, especially at least 2 times. The envelope may also serve to limit access of oxygen to the PTC composition as taught by Canadian Application Serial No. 340~963 filed November 30, 1979.
~ ~ 7~884 The heater assemblies can comprise two or more PTC
heaters. The heaters may be spaced apart from each other and connected by an envelope which surrounds each of them e.g. a plurality of parallel strip heaters sandwiched between a pair of metal sheets.
The invention is illustrated by example only in the accompanying drawings, in which Figure 1 is an isometric view, partly in cross-section, of a heater assembly; and Figure 2 is a graph showing the relationship between the electrical current and the substrate temperature in the tests described in the Example.
Referring now to Figure 1, this shows a PTC heater comprising electrodes 1 and 2 embedded in a strip 3 of a PTC conductive polymer composition which is sur-rounded by an insulating jacket 4. The heater is sandwiched between a pair of aluminum sheets 5 and 6 which are bonded to each other and to the heater by means of an adhesive (now shown).
The invention is further illustrated by the following Exarnple.
EXAMPLE
_ _ The PTC heater used was a 61 cm length of a PTC
strip heater as shown in Figure l. The electrodes were copper wires 1.3 mm in diameter, with a center-to-~7~8 ~
center spacing of 7.6 mm. The PTC element was 10 mm wide and 1.8 mm thick and was composed of a composition com-prising a dispersion of carbon black in a mixture of polyethylene and an ethylene/ethyl acrylate copolymer.
The insulating jacket was composed of a polyurethane and was about 0.25 mm thick. The heater had a passive power output of about 250-275 watts/metre. The active power output of this heater, alone or as part of a heater assembly, was measured by securing the heater or heater assembly to an aluminum plate 1.25 x 15.25 x 61 cm, connecting the heater to a 120 volt AC power supply and allowing the system to reach equilibrium while maintaining the plate at a desired temperature. In the tests, the heater alone (Sample A) or the heater sandwiched between two identical aluminum sheets 61 cm long and 0.003 cm thick, and having widths of 11.4, 6.3, 3.8 and 1.9 cm (Samples B, C, D and E) was used. Figure 2 shows the relationship between the temperature of the plate and the current passing through the heater. The Table below shows the calculated active power output (current x applied voltage) of the heater when the plate is at 50F (lODC).
TABLE
Width of Active Power SampleMetal Envelope (cm)at 10C (watts/metre) A none 70 B 11.4 140 C 6.3 145 D 3.8 150 E 1~9 140
Patents Nos. 3,793,716, 3,823,217, 3,861,029, 4,177,376 and 4,188,276 and the Thermal Desgin Guide published by the Chemelex Divison of Raychem Corporation (H 50190 10 505 B5 1/78).
In defining such heaters, reference is often made to their "passive power output" and their "active power output". The "passive power output" of a heat is the value of the term V2/Ro, where Ro is the resistance of a unit length (usually 1 foot or 1 metre) of the heater at 21C and V is the voltage of the source of electri~
cal power connected to the heater, usually 120 or 240 volts AC. The "active power output" of a heater is the measure power output of a unit length of the heater (usually 1 foot or 1 metre) when connected to the source of electrical power, with one major surface of the heater in contact with a metal substrate which is maintained at some temperature related to the intended use of the heater, e.g. 7 to 65C, such as 10C for heaters designed to prevent pipes from freezing.
Conventional strip heaters comprise two or more elec-trodes in the form of wires in electrical contact with a PTC conductive polymer element and have passive power outputs of substantially less than 165 watts per metre (50 watts per foot) at their intended operating vol-tage; the use of such heaters having higher passive power outputs has been avoided because they give little or no useful increase in active power output and have substantial disadvantages, in particular shorter life.
~' ~.
~ 8~ MP0300 We have now discovered that if a PTC conductive polymer heater is surrounded by an envelope of metal or other material of good thermal conductivity, it is possible to make use of the heater at voltages at which its passive power output is greater than 165 watts per metre without the disadvantages previously associated with Ruch use, and that 8 very valuable increase in active power output can thereby be obtained. ~or example the addition of such an envelope surprisingly makes it possible to use, at a voltage of 240 volts, a PTC heater which has a passive power output at 120 volts of less than 165 watts/metre and at 240 volts of more than 165 watts/metre, even though such a heater, in the absence of the envelope, has an unacceptably short service life at 240 volts.
In one aspect, the invention provides a method of heating which comprises passing current through a self-regulating heater assembly comprising (a) a PTC heater which comprises (i) an elongate strip of 8 conductive polymer composition exhi~iting PTC
behavior, (ii) two elongate parallel electrodes in electrical contact with aaid strip, and (iii) an electrically insulating jacket which surrounds said ~trip and said electrodes; and :~17~ 34 (b) an envelope which surrounds said PTC heater and which is composed of a material having a thermal conductivi-ty of at least 0.1 Cal/cm C sec. preferably at least 0.3 Cal/cm C sec.;
the current being supplied by a source of electrical power having a voltage V and the heater having a passive power output at said volt-age V at least 165 watts/meter (50 watts/ft.), preferably at least 230 watts/meter (70 watts/ft.).
The heater assembly can be used to heat a solid substrate, in which case the envelope is preferably shaped to conform to the substrate; or it can be used as a space heater, in which case the assembly is preferably in the form of a coil, with space between the coils for air or other liquid to circulate.
In another aspect the invention provides a self-regulating heater assembly comprising a PTC heater and an envelope as defined above, the heater having a passive power output at 120 volts of at least 165 watts/metre.
The PTC heater preferably comprises two ~or more) elect-rodes in the form of wires which are embedded in and in physical contact with the PTC strip. ~lowever, the invention includes other types of PTC heater, for example those in which one or more of the electrodes is separated from the PTC strip by a layer of another conductive material, e.g. a conductive polymer composition exhibit-ing ZTC behavior, and those which comprise a laminar PTC element and two or more laminar electrodes.
The passive power output of a heater is of course dependent on the resistivity of the PTC composition and the size and shape of ~7~38 -~
tlle electrodes and the PTC element. For a conventional strip heater, e.g. as described in the example below, the passive power output is preferably 165 to 655 watts/metre (50 to 200 watts/ft~, preferably 230 to 655 watts/metre (70 to 200 watts/ft). For the broad range of heaters contemplated by this invention, the preferred ranges of passive power outputs are better expressed by a term which includes the width of the PTC element over which heat is produced. Thus the passive power output of the heaters used in this invention is prefer-ably 217 Dito 862 D, especially 302 D to 862 D, watts/metre, where D is the largest cross-sectional dimension ~in centimetres) of the PTC strip which lies between the electrodes.
- 4a -7~88~
The active power output of the PTC heater is substantially increased by the presence of the envelope, and preferred heater assemblies have an active power output at 10C which is at least 1.5 times the active power output at 10C of the PTC heater without the envelope.
The envelope is preferably formed by a pair of elongate sheets with the heater sandwiched between them?
the sheets contacting each other either side of the heater. The sheets are preferably 0.025 to 1.3 mm, e.g.
0.075 to 0.2 mm, thick and composed of a material having a thermal conductivity of at least 0.3, e.g. aluminum. They may be secured together and/or to the heater by means of an adhesive, e.g. an epoxy adhesive.
It is important that the envelope and the PTC
heater should be in intimate thermal contact, and the envelope preferably contacts (either directly or through an adhesive) at least the areas of the insulating jacket adjacent those parts of the heater in which heat is generated. Preferably there are no voids between the envelope and the heater. It is preferred that the envelope should extend outwards from the PTC heater in the form of fins, so that the exposed surface area of the envelope is at least 1.5 times, e.g. at least 2 times, the surface area of the :insulating jaoket of the PTC heater, especially at least 2 times. The envelope may also serve to limit access of oxygen to the PTC composition as taught by Canadian Application Serial No. 340~963 filed November 30, 1979.
~ ~ 7~884 The heater assemblies can comprise two or more PTC
heaters. The heaters may be spaced apart from each other and connected by an envelope which surrounds each of them e.g. a plurality of parallel strip heaters sandwiched between a pair of metal sheets.
The invention is illustrated by example only in the accompanying drawings, in which Figure 1 is an isometric view, partly in cross-section, of a heater assembly; and Figure 2 is a graph showing the relationship between the electrical current and the substrate temperature in the tests described in the Example.
Referring now to Figure 1, this shows a PTC heater comprising electrodes 1 and 2 embedded in a strip 3 of a PTC conductive polymer composition which is sur-rounded by an insulating jacket 4. The heater is sandwiched between a pair of aluminum sheets 5 and 6 which are bonded to each other and to the heater by means of an adhesive (now shown).
The invention is further illustrated by the following Exarnple.
EXAMPLE
_ _ The PTC heater used was a 61 cm length of a PTC
strip heater as shown in Figure l. The electrodes were copper wires 1.3 mm in diameter, with a center-to-~7~8 ~
center spacing of 7.6 mm. The PTC element was 10 mm wide and 1.8 mm thick and was composed of a composition com-prising a dispersion of carbon black in a mixture of polyethylene and an ethylene/ethyl acrylate copolymer.
The insulating jacket was composed of a polyurethane and was about 0.25 mm thick. The heater had a passive power output of about 250-275 watts/metre. The active power output of this heater, alone or as part of a heater assembly, was measured by securing the heater or heater assembly to an aluminum plate 1.25 x 15.25 x 61 cm, connecting the heater to a 120 volt AC power supply and allowing the system to reach equilibrium while maintaining the plate at a desired temperature. In the tests, the heater alone (Sample A) or the heater sandwiched between two identical aluminum sheets 61 cm long and 0.003 cm thick, and having widths of 11.4, 6.3, 3.8 and 1.9 cm (Samples B, C, D and E) was used. Figure 2 shows the relationship between the temperature of the plate and the current passing through the heater. The Table below shows the calculated active power output (current x applied voltage) of the heater when the plate is at 50F (lODC).
TABLE
Width of Active Power SampleMetal Envelope (cm)at 10C (watts/metre) A none 70 B 11.4 140 C 6.3 145 D 3.8 150 E 1~9 140
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of heating which comprises passing current from an electrical power source through a self-regulating heater assembly comprising a PTC heater which comprises (i) an elongate strip of a conductive polymer composition exhibiting PTC behavior, (ii) two elongate parallel electrodes in electrical con-said heater (a) being surrounded by an envelope which is composed of a material having a passive power output, at the voltage of said electrical power source, of at least 165 watts/metre.
2. A method according to Claim 1 wherein said PTC heater has a passive power output of 217 D to 862 D watts/metre, where D is the largest cross-sectional dimension in centimetres, of the PTC strip between the electrodes.
3. A method according to Claim 1 wherein said PTC heater is sandwiched between a pair of elongate sheets which contact each other either side of the heater and which are composed of a material having a thermal conductivity of at least 0.3 Cal/cm. °C sec.
4. A method according to Claim 3 wherein the exposed surface area of said sheets is at least 1.5 times the surface area of the insulating jacket of the PTC
heater.
heater.
5. A method according to Claim 1, 3 or 4 wherein the heater has an active power output at 10°C which is at least 1.5 times the active power output at 10°C of the PTC
heater without the envelope.
heater without the envelope.
6. A method according to Claim 1, 3 or 4 wherein the supply voltage is 120 or 240 volts AC.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000358370A CA1173884A (en) | 1980-08-15 | 1980-08-15 | Ptc heater assembly |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000358370A CA1173884A (en) | 1980-08-15 | 1980-08-15 | Ptc heater assembly |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1173884A true CA1173884A (en) | 1984-09-04 |
Family
ID=4117658
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000358370A Expired CA1173884A (en) | 1980-08-15 | 1980-08-15 | Ptc heater assembly |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1173884A (en) |
-
1980
- 1980-08-15 CA CA000358370A patent/CA1173884A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |