Voltage-leveling monolithic self-regulating heater cable

Patent metadata

Field	Value
Publication number	US-10470251-B2
Application number	US-201715583848-A
Country	US
Kind code	B2
Filing date	May 1, 2017
Priority date	Apr 29, 2016
Publication date	Nov 5, 2019
Grant date	Nov 5, 2019

Abstract

A self-regulating electric heater cable includes a monolithic heater core of PTC material encapsulating a pair of bus wires, and a conductive layer disposed on an outer surface of the heater core such that the conductive layer levels the voltage generated at the outer surface of the heater core when an electric current is passed through the bus wires. The conductive layer draws the current evenly through lobes of PTC material encapsulating the bus wires. The conductive layer may be a coating, such as a conductive ink or paint, or may be an extruded or wrapped material applied to the heater core. Standard heater cable layers are applied over the conductive layer, including an electrically insulating layer that contacts a portion of the conductive layer and also may be separated, at points, from the conductive layer by one or more air gaps.

First claim

What is claimed is:

1. An electric heater cable having a length and comprising:
a first bus wire and a second bus wire parallel to the first bus wire, the first and second bus wires each extending the length of the heater cable;
a heater core extending the length of the heater cable and comprising a positive temperature coefficient (PTC) semiconductive polymer, the heater core encapsulating and spacing apart the first and second bus wires and dissipating, to a surrounding environment as heat, a current applied to one or both of the first bus wire and the second bus wire; and
a conductive layer disposed in surface contact with an outer surface of the heater core and leveling an electric potential across the outer surface of the heater core, the conductive layer extending entirely along the length of the heater cable and entirely covering the outer surface of the heater core.

2. The electric heater cable of claim 1 , wherein the conductive layer has a uniform thickness.

3. The electric heater cable of claim 1 , wherein the conductive layer is one of a conductive ink and a conductive paint both having a sufficiently high electrical conductivity to draw the current to the outer surface of the heater core.

4. The electric heater cable of claim 1 , further comprising:
an insulating layer disposed over the conductive layer and over the heater core and providing a dielectric separation to the heater core;
a ground layer disposed over the insulating layer and providing an earth ground for the heater cable; and
an outer jacket disposed over the group layer and forming an exterior surface of the heater cable, the exterior surface exposed to the surrounding environment.

5. The electric heater cable of claim 4 , wherein a second conductive layer is disposed on an inner surface of the insulating layer.

6. The electric heater cable of claim 1 , wherein the heater core has a barbell cross-sectional shape, the heater core forming a first lobe around the first bus wire, a second lobe around the second bus wire, and a web between the first and second bus wires, and wherein the conductive layer is disposed in surface contact with the outer surface of the heater core such that the conductive layer draws the current evenly through the first and second lobes.

7. A self-regulating heater cable comprising:
a pair of bus wires;
a monolithic heater core comprising at least one positive temperature coefficient (PTC) material, the heater core contacting and encapsulating the pair of bus wires, the at least one PTC material forming an outer surface of the heater core; and
a conductive layer disposed on at least a first portion of the outer surface of the heater core such that a voltage measured at the first portion of the outer surface, the voltage caused by an electric current carried by the pair of bus wires, is leveled.

8. The heater cable of claim 7 , wherein the heater cable has a length and the conductive layer extends entirely along the length of the heater cable.

9. The heater cable of claim 7 , wherein the conductive layer entirely covers the outer surface of the heater core.

10. The heater cable of claim 7 , wherein the conductive layer is further disposed on a second portion of the outer surface, the second portion spaced lengthwise from the first portion such that a third portion of the outer surface, the third portion disposed between the first portion and the second portion, is not in contact with the conductive layer.

11. The heater cable of claim 7 , wherein the conductive layer is one of a conductive ink and a conductive paint applied to the outer surface of the heater core.

12. The heater cable of claim 7 , wherein the conductive layer is a flexible conductive material and is wrapped around the heater core.

13. The heater cable of claim 7 , wherein the conductive layer is an extruded layer.

14. The heater cable of claim 7 , further comprising an electrically insulating layer disposed over the conductive layer and over the heater core and providing a dielectric separation to the heater core, wherein one or more air gaps are disposed between the insulating layer and the conductive layer.

15. The heater cable of claim 7 , wherein the heater core has a cross-sectional shape including a first lobe formed around a first bus wire of the pair of bus wires and a second lobe formed around a second bus wire of the pair of bus wires, and wherein the conductive layer is disposed in surface contact with the outer surface of the heater core such that the conductive layer draws the current evenly through the first and second lobes.

16. A method of making an electric heater cable, the method comprising:
extruding one or more positive temperature coefficient (PTC) materials over a pair of bus wires to form a heater core that encapsulates the pair of bus wires and has an outer surface; and
applying a conductive layer onto the outer surface of the heater core, the conductive layer positioned to draw an electric current carried by the pair of bus wires evenly through heater core such that a voltage measured at the outer surface in contact with the conductive layer is leveled.

17. The method of claim 16 , wherein applying the conductive layer comprises coating the outer surface with one or both of a conductive ink and a conductive paint.

18. The method of claim 16 , wherein applying the conductive layer comprises co-extruding a conductive material together with the one or more PTC materials.

19. The method of claim 16 , wherein applying the conductive layer comprises extruding a conductive material onto the heater core.

20. The method of claim 16 , further comprising combining one or more polymer compounds with one or more conductive fillers to produce a first PTC material of the one or more PTC materials.

Assignees

• Pentair Thermal Man Llc
• Nvent Services Gmbh

Inventors

• Kazemi Mohammad
• Martin Peter
• Kiss Linda D B
• Park Edward H
• Robison Jennifer

Classifications

• H05B3/565 Primary

  flat cables · CPC title

• H05B3/146 Primary

  Conductive polymers, e.g. polyethylene, thermoplastics · CPC title

• H05B2203/02

  Heaters using heating elements having a positive temperature coefficient · CPC title

• H05B3/56

  Heating cables · CPC title