PTC heating device without electronic power control
Foil-based PTC heaters are self-regulating, i.e. do not need any electronic control unit (ECU) to limit the maximum heating current. In order to establish different heating power levels the present invention proposes to choose different PTC ratio/onset characteristics. In addition, the print design of the PTC ink can be adjusted accordingly.
1. A heater element for generating heat when connected to an electrical power source, said heater element comprising:
an electrically insulating substrate having a first surface and a second surface,
a first buss layer made of a conductive material applied to said first surface of said substrate, said first buss layer comprising a first buss and a second buss extending generally along opposite sides of a first heating area of said heater element and a number of alternating first electrodes electrically connected to opposite said first and second busses and extending between said first and second busses;
a first layer of a first resistive material, said first resistive material comprising a first positive temperature coefficient material and said first layer being applied in said first heating area of said heater element such as to provide electrical communication between at least selected ones of said alternating first electrodes;
a second buss layer made of a conductive material applied to said second surface of said substrate, said second buss layer comprising a third buss and a fourth buss extending generally along opposite sides of a second heating area of said heater element and a number of alternating second electrodes electrically connected to opposite said third and fourth busses and extending between said third and fourth busses;
a second layer of a second resistive material, said second layer being applied in said second heating area of said heater element such as to provide electrical communication between at least selected ones of said alternating second electrodes; and
a switching element configured for selectively connecting an electrical power source individually to said first buss layer or said second buss layer or concomitantly to said first buss layer and said second buss layer.
2. The heater element according to claim 1 , wherein a configuration of said second buss layer and said second layer of resistive material is such that a maximum heating power dissipated during operation by said second layer of resistive material is different from a maximum heating power dissipated during operation by said first layer of resistive material.
3. The heater element according to claim 1 , wherein said second resistive material comprises a second positive temperature coefficient material and wherein a temperature coefficient of said second resistive material is different from a temperature coefficient of said first resistive material.
4. The heater element according to claim 1 , wherein said second resistive material comprises a resistive material having a resistance with none of minimal temperature dependency.
5. The heater element according to claim 1 , wherein said first resistive material comprises a first specific resistance and wherein said second resistive material comprises a second specific resistance and wherein said first specific resistance is different from said second specific resistance.
6. The heater element according to claim 1 , wherein said first layer of resistive material has a first layer thickness and wherein said second layer of resistive material has a second layer thickness, and wherein said first layer thickness is different from said second thickness.
7. The heater element according to claim 1 , wherein said first layer of resistive material comprises a plurality of first patches of first resistive material and wherein said second layer of resistive material comprises a plurality of second patches of second resistive material, and wherein an area and of said first patches of first resistive material is different from an area of said second patches of second resistive material.
8. The heater element according to claim 1 , wherein a distance between selected ones of said alternating first electrodes is different from a distance between selected ones of said alternating second electrodes.
9. The heater element according to claim 1 , further comprising a third layer of a third resistive material, said third layer being applied in said first heating area of said heater element such as to provide electrical communication between selected ones of said alternating first electrodes, and wherein a resistive property of said third resistive material is different from a resistive property of said first resistive material.
10. The heater element according to claim 1 , wherein said switching element is configured for connecting said first buss layer and said second buss layer in parallel or in series to said electrical power source.
11. The heater element according to claim 1 , wherein said electrically insulating substrate comprises a polymer foil.
12. The heater element according to claim 1 , wherein said electrically insulating substrate comprises a textile material.
13. The heater element according to claim 1 , wherein said first layer of resistive material comprises a plurality of first patches of first resistive material and wherein said second layer of resistive material comprises a plurality of second patches of second resistive material, and wherein a width of said first patches of first resistive material is different from a width of said second patches of second resistive material.
14. The heater element according to claim 1 , further comprising a fourth layer of a fourth resistive material, said fourth layer being applied in said second heating area of said heater element such as to provide electrical communication between selected ones of said alternating second electrodes, and wherein a resistive property of said fourth resistive material is different from a resistive property of said second resistive material.