GB2160749A

GB2160749A - Electrically-powered heating panels

Info

Publication number: GB2160749A
Application number: GB08515302A
Authority: GB
Inventors: Leonard Charles Owers
Original assignee: THERMONETTE APPLIANCES Ltd
Current assignee: THERMONETTE APPLIANCES Ltd
Priority date: 1984-06-21
Filing date: 1985-06-17
Publication date: 1985-12-24
Also published as: GB8515302D0; GB8415907D0; GB2160749B

Abstract

A multi-heat electric panel blanket eg a blanket 10 is provided with coils 1,2, of a dual coil heating element. A single coil heating element 3 is connected in series with coil 1. The circuit is provided with four terminals A, B, C and D and current limiting means eg comprising a diode 8 is connected across B and C. The dual coil heating element is disposed tortuously over the area of an electric blanket and is interlocated with the single coil element 3, which is also tortuously disposed. A selection switch S is provided. The blanket 10 is operable whereby:- (A) one of the coils of the dual coil heating element is connected in series with the single coil heating element 3, with the diode 8 by-passed (terminals A, B); or (B) one of the coils of the dual coil heating element is connected in series with the single coil heating element 3, with the diode 8 included in the circuit (terminals A, C); or (C) all three heating coils are connected in series with the diode 8 in circuit (terminals A, D); so that three differing heat outputs are available. A modification, (Figure 3), makes available four different heat outputs and a resistor may replace the diode. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electrically-powered heating panels BACKGROUND TO THE INVENTION This invention relates to electrically-powered heating panels.

As used herein, the term "electrically-powered heating panel" is intended to include electricallypowered under-carpet heaters, blankets, mattresses and pads. The invention is particularly applicable however, to electrically-powered blankets, or, more simply, "electric blankets".

The present invention is concerned with that form of electrically-powered heating panel comprising a tortuously-disposed dual coil heating element (as herein defined), interlocated with a tortuously-disposed single coil heating element (as herein defined).

As used herein, a "dual coil heating element" is defined as an inner heating coil covered with afirst insulation, with an outer heating coil wound on the first insulation and insulated with a second insulation, and a "single coil heating element" is defined as a single heating coil covered with insulation.

SUMMARYOF THE INVENTION According to the present invention, an electricallypowered heating panel comprises a tortuously-disposed dual coil heating element (as herein defined) interlocated with a tortuously-disposed single coil heating element (as herein defined), and provided with current limiting means as well as selectable connecting means, the panel being operable whereby (A) one ofthe coils of the dual coil heating element is connected in series with the single coil heating element with the current limiting means by-passed; or (B) one of the coils ofthe dual coil heating element is connected in series with the single coil heating element with the current limiting means included in the circuit; or (C) all three heating coils are connected in series with the current limiting means in circuit; so thatthree different heat outputs are available.

All three heating coils may be connected in series with the current limiting means by-passed, so that fourdiffering heat outputs are available.

The current limiting means may comprise diode means connected between the single coil heating element and one of the coils ofthe dual coil heating element.

Alternatively, the current limiting means may comprise resistor means connnected between the single coil heating element and one ofthe coils ofthe dual coil heating element. The resistor means may serve as an additional heating element.

The invention also comprises any novel subject matter or combination including novel subject matter herein disclosed, whether or notwithin the scope of or relating to the same invention as any of the succeeding claims.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments ofthe invention will now be described byway of example only, with reference to the accompanying drawings, wherein: Figure 1 is a circuit diagram, Figure 2 illustrates one modification of the circuit of Figure 1, Figure 3 illustrates another modification ofthe circuit of Figure 1, and Figure 4 is another circuit diagram.

In the figures, like reference numerals refer to like features and components.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS With reference first to Figure 1, a three-heat electrical panel in the form of an electric blanket 10 is shown wherein outer and inner coils 1 and 2 are the coils of a dual coil heating element. Insulation between coils 1 and 2 is indicated by numeral 7. The single coil heating element 3 is shown connected in series with outer coil 1. The circuit is provided with four leads, namely leads A, B, Cand D. Current limiting means comprising a diode 8 is provided, connected across leads Band C. The two coils 1,2 of the dual coil elements are ofthe same resistance value. Resistance of coil 3 is about 1.5 times that of coils 1 and 2.

The dual coil heating element is disposed tortuously oversubstantiallythe whole area of an electric blanket. The blanket of this embodiment uses tunnelcontructed blanket material but alternatively, sheets of blanket material may be secured together by adhesive. The dual coil element is interlocated with the single coil element 3, which is also tortuously disposed. Figure 2 of U.K. Patent No. 1,456,684 illustrates this kind of arrangement in more detail.

The dual coil heating element comprises the inner coil 2 wound on a central core of rayon and covered with an insulating sheath (which is insulation 7) of thermoplastics material. Asuitablethermoplastics material is a polyethylene compound, such as ALKATHENE (Registered Trade Mark), which is obtainable from l.C.I. Limited of the U.K. The material enables electrical conduction to take place between coils 1 and 2 at an elevated temperature. The outer coil 1 is wound on the insulating sheath 7 and itself covered with an outer sheath of insulating material such as polyvinyl chloride (P.V.C.).

A heat selection switch Sis provided, having High, Medium and Low selector positions. The switch makes lines (L) and neutral (N) connections of an A.C.

powersupplyto leads, A, B, Cand D.

With the heat selection switch S in the "High" setting, the circuit from line to neutral is via lead A, coil 1, coil 3, and lead B. Coil 2 is by-passed by virtue of leads Cand D being connected to neutral at the switch S. Diode 8 is also by-passed. Heating is at a maximum as resistance, (coil 1 in series with coil 3), is at a minimum and currentflows on all half-cycles of the supply.

With the heat selection switch Sin the "Medium" setting, the circuit from line to neutral is via lead A, coil 1, coil 3, diode 8, (half-cycles), and lead C. The coil 2 is by-passed by having neutral potential at both ends, both leads Cand Dbeing connected to neutral atthe switch S.

With the heat selection switch S in the "Low" setting, the ci rcuit from line to neutral is via lead A, coil 1, coil 3, diode 8 (half-cycles), coil 2 and lead D. Heating is at a minimum because current only flows on alternate half-cycles ofthe supply and the maximum resistance, (all the coils and the diode 8 are connected in series), is in circuit.

Thus three differing heat outputs are available from the blanket 10.

In the event of overheating in the electric blanket 10, such as by energising it when folded or bundled, the polyethylene-compound material ofthe inner insulating sheath 7 of the dual coil heating element enables electrical conduction to take place between outer and inner coils 1 and 2 at the elevated temperature, whereby a short-circuit occurs between these coils. A low resistance circuitfrom line to neutral will be set up which causesfuse Fto blow. The actual value ofthe low resistance circuit will depend upon the position along the dual coil heating element atwhich shortcircuiting between the coils 1 and 2 occurs and upon the setting ofthe heat selection switch S. To illustrate this, three short-circuit positions X, Yand Zhave been marked along the coils 1,2.

If overheating is now considered, with the heat selection switch Son "High" or"Medium", itwill be seen that electrical conduction between coils 1 and 2 atX,will give a "dead" short and fuse Fwill blow.

Short-circuiting at Ygives a rather complex series "parallel network of resistances which will necessarily have an effective resistance much lowerthan will arise inany"normal"operation,(itwill be lower than the resistance of coil 1), and hence fuse Fcan be easily rated to fuse correctly. Short-circuiting atZgives an in-circuit resistance equal to the resistance of coil 1 alone, and hence fuse Fcan again be easily rated to blow.

Wherever short-circuiting occurs, atX, Vor Z, with the switch Sin the "Low" position, itwill be appreciated that the in-circuit resistance will never exceed the resistance of coil 1.Thusfuse Fan again be easily rated to blow.

Figure 2 illustrated a modification wherein an electric blanket 1 Oa is provided with current limiting means in the form of a resistor 15 connected across leads Band C, instead ofthe diode 8. The resistor 15 serves as an additional heating element, and has a resistance value about 1.5 times that of coil 1.

Figure 3 illustrates afour-heatelectric blanket 10b, which likethe blanket 10 of Figure 1, is provided with current limiting means in the form of diode 8.

However, if desired, a resistor, (like resistor 15 of Figure 2), can be used to replace the diode.

A heat selection switch S1 is provided, having positions Pi, P2, P3and P4. Position P4 is a "high" heat setting; position Piisa"low" heating setting; positions P2 and P3 are intermediate heat selector positions. The switch S1 makes line (L) and neutral (N) connections of an A.C. power supply to leads A, B, C, D and Eas indicated.

With the heat selection switch S1 in the "P4" position, the circuit from line to neutral is via lead A, coil 1, coil 3, and lead B. Coil 2 is by-passed by virtue of leads Band D being connected to neutral at the switch.

Diode 8 is by-passed as leads Cand Dare also connected to neutral. Heating is at a maximum as resistance, (coil 1 in series with coil 3), is at a minimum and currentflows on all half-cycles ofthe supply.

With the heat selection switch in the "P3"position, thecircuitfrom line to neutral isvia lead A, coil 1,coil3, lead B, lead D, coil 2 and lead E. Diode 8 remains by-passed.

With the heat selection switch S1 in the "P2" position, the circuitfrom lineto neutral is via lead A, coil 1, coil 3, diode 8, (half-cycles), and lead C, coil 2 being by-passed.

With the heat selection switch in the "Pl"position, the circuitfrom line to neutral is via lead A, coil 1, coil 3, diode 8 (half-cycles), leads Cand D, coil 2 and lead E.

Heating is at a minimum because current only flows on alternate half-cycles of the supply and the maximum resistance, (all coils and diode 8 are in series), is in circuit.

Thus four differing heat outputs are available from the blanket 10b.

The arrangements of Figures 1,2 or3 result in an electric blanket which is particularly useful as an overblanket.

Figure 4 illustrates a modification wherein, a three-heat electric blanket 1 Oc is provided with current limiting means in theform of a resistor 1 5c, (serving as an additional heating element), included in lead D.

In Figure 4, the "Low" switch setting puts all three coils (1,2 and 3) and resistor 1 sic in series, the "Medium" setting puts coils 1,2 and 3 in series, (resistor 15cbeing short-circuited), and the "High" setting puts coils 1 and 2 in series (coil 3 and resistor 15being short-circuited).

In any ofthe above-described arrangements, fuse F could be replaced by a thermal fuse, employing a heating resistance connected in series.

In the above examples, typical values are as follows: Figure 1 Resistance of Coil 1 - 360 ohms) Resistance of Coil 2 - 360 ohms) With diode 8 in circuit Resistance of Coil 3 - 500 ohms) "High" output - 67 watts "Medium" output - 34 watts "Low" output - 24 watts Figure 2 "High" output - 67 watts "Medium" output - 42 watts "Low" output - 33 watts Resistor 15 - 500 ohms Figure3 Resistances of coils 1,2 and 3-as for Figure 1.

Switch Position Output with diode 8 Output with 500 ohms resistor P1 24 watts 33 watts P2 34 watts 42 watts P3 47 watts 47 watts P4 67 watts 67 watts Figure 4 "High" output - 67 watts "Medium" output - 47 watts "Low" output - 33 watts Resistor 15c - 500 ohms

Claims

1. An electrically-powered heating panel comprising a tortuously-disposed dual coil heating element, (as herein defined), interlocated with a tortuously-disposed single coil heating element, (as herein defined), and provided with current limiting meansaswell as selectable connecting means, the panel being operable whereby:- (A) one ofthe coils ofthe dual coil heating element is connected in series with the single coil heating element with the current limiting means by-passed; or (B) one of the coils ofthe dual coil heating element is connected in series with the single coil heating element with the current limiting means included in the circuit; or (C) all three heating coils are connected in series with the current limiting means in circuit; so that three differing heat outputs are available.

2. A heating panel as claimed in Claim 1,operable whereby all three heating coils are connected in series with the current limiting means by-passed, so that for differing heat outputs are available.

3. A heating panel as claimed in Claim 1 or 2, wherein the current limiting means comprises diode means connected between the single coil heating element and one of the coils ofthe dual coil heating element.

4. A heating panel as claimed in Claim 1 or2, wherein the current limiting means comprises resistor means connected between the single coil heating element and one of the coils ofthe dual coil heating element, said resistor means serving as an additional heating element.

5. A heating panel as claimed in any one of Claims 1 to 4, wherein the current limiting means is by-passed, when so required, by a short-circuit applied on appropriate operation ofthe selectable connecting means.

6. A heating panel substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

7. Aheating panel substantially as hereinbefore described, with reference to Figure 1 of the accompanying drawings, modified substantially as hereinbefore described with additional reference to Figure 2 of said drawings.

8. A heating panel substantially as hereinbefore described, with reference to Figure 3 ofthe accompanying drawings.

9. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.

10. An electrically-powered heating panel comprising a tortuously-disposed dual coil heating element, (as herein defined), interlocated with a tortuously-disposed single coil heating element, (as herein defined), and provided with resistor means as well as selectable connecting means, the panel being operable whereby: (a) one ofthe coils ofthe dual coil heating element is connected in series with the coil of the single coil heating element with the resistor means by-passed; or (b) one of the coils of the dual coil heating element is connected in series with the single coil heating elementwith the resistor means included in the circuit; or (c) all three heating coils are connected in series with the resistor means in circuit; so thatthree differing heat outputs are available.

11. A heating panel as claimed in Claim 10, wherein the resistor means is connected in series with one ofthe coils of the dual coil heating element.

12. A heating panel as claimed in Claim 10, wherein the resistor means is connected in series with the inner coil of the dual coil heating element.

13. A heating panel as claimed in any one of Claims 10 to 12, wherein the resistor means serves as an additional heating element.

14. A heating panel as claimed in any one of Claims 10 to 13, wherein current limiting means is by-passed, when so required, by a short-circuit applied on appropriate operation ofthe selectable connecting means.

15. A heating panel substantially as hereinbefore described, with reference to Figure 4 ofthe accompanying drawings.