EP1351259A1

EP1351259A1 - Resistor

Info

Publication number: EP1351259A1
Application number: EP03002156A
Authority: EP
Inventors: Amerigo Barbieri; Sergio Caretti
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-02-13
Filing date: 2003-02-03
Publication date: 2003-10-08

Abstract

Resistor equipped with two or more cylindrical resistive elements (4,5) in contact in several portions. At least one of the cylindrical resistive elements (5) of the resistor winds around the remaining resistive elements (4).

Description

The present invention relates to a resistor. In general, resistors are devices that originates a resistance to the electrical energy flow and are used to transform electrical energy into heat in order to disperse it through the Joule effect.
Known resistors are normally of two types and in particular wirewound resistors and strip resistors. The latter have the advantage of allowing greater heat dissipation, thanks to the larger heat exchange surface which they are provided with. Therefore, with the same number of watts supplied, the strip resistor can work at lower temperatures than those at which a wirewound resistor works and consequently it has a longer useful life. Nonetheless, strip resistors have considerably higher production costs and considerably larger overall dimensions that do not allow easy positioning inside the instruments which they are destined to.
For this reason, if they were used in air-flow air conditioning devices, for example, the internal layout of the device would be affected by the geometry of the resistor.
The object of the present invention is to solve the problems of prior art by providing a resistor that guarantees good heat dissipation and which is small in size and is thus extremely easy to position inside the device it is destined to.
Another object of the present invention is to provide a resistor which is simple and inexpensive to produce.
These and other features are achieved by the present invention which relates to a resistor provided with two or more cylindrical resistive elements, characterized in that the resistive elements are contacting each other in several zones and that at least one of cylindrical resistive elements winds around the remaining cylindrical resistive elements.
In this way the heat exchanging surface of the resistive element is increased while obtaining, at the same time, a resistor with smaller overall dimensions compared with a strip resistor.
According to a preferred aspect, the present invention provides a first cylindrical resistive element arranged in a core on which one or more cylindrical resistive elements are spirally wound.
This embodiment permits to obtain optimum dispersion capacities with smaller resistors, making it possible to considerably save on production costs, since less material is required for their production.
According to another preferred aspect of the present invention, the distance between two adjacent turns is within the range of 0.3 mm to 20 mm.
A decrease in the distance between turns causes an increase in the number of turns that wind around the cylindrical resistive element positioned in order to form the core of the resistor and in this manner the working heat exchanging surface increases. The distance between two adjacent turns is preferably within the range 0.5 mm and 3 mm.
It has been noted that in this lower range in relation to the wider range, good thermal dispersion capacities are obtained thanks to perfect balance between the increase in the dissipating surface, due to the body increase of the cylindrical element spirally wound, and the shielding effect that this has on the cylindrical resistive element arranged in a core.
Further characteristics and advantages of the present invention shall become more apparent from the description that follows, provided purely as a non-limiting example with reference to the accompanying schematic drawings, in which:

figure 1 is a side view of an embodiment of a resistor according to the invention;
figure 2 is a side view of an alternative embodiment of a resistor according to the invention;
figure 3 is a side view of a further alternative embodiment of a resistor according to the invention;
figure 4 is a perspective view in a cross-section of an alternative embodiment of the resistor according to the invention;
figure 5 is a perspective view of a resistor device according to the invention.

Figure 1 shows a possible embodiment of a resistor 1 according to the present invention wherein two cylindrical elements 2, 3, and in particular two wires with a circular section, in resistive material, are stranded around each other so that they are essentially in touch for their entire length. In this case, both cylindrical elements 2, 3, have a helical course and constant distance between turns. In the alternative embodiment shown in figure 2, one cylindrical element 4 made of a resistive material is arranged to form a core, around which is spirally wound a further cylindrical element 5 made of a resistive material. The cylindrical element 5 is spirally wound around the cylindrical element 4 which is arranged in a core so that the distance between the turns, or the pitch 17, is constant. The cylindrical elements 4, 5 have a circular section and different diameters. In particular, the cylindrical element 4 arranged in a core has a considerably larger diameter than the wound cylindrical element 5. Alternatively, the two cylindrical elements 4, 5 could have the same diameter and/or different shaped section, for example the cylindrical element 4 arranged in a core could have a rectangular section and the wound cylindrical element 5 could have an elliptical section. Although cylindrical elements with any section may be used, a circular section is particularly suitable for the wound cylindrical element 5. Advantageously, the diameter of the cylindrical elements is generally included between 0.09 and 5.0 mm.
The number of cylindrical elements made of a resistive material and wound on the cylindrical element 4 arranged in a core could, as shown in figure 3, be greater than one in order to further increase the heat exchanging surface. In this case, there are two or more cylindrical elements 5 parallel to each other and wound around the core, or alternatively two or more stranded cylindrical elements wound around each other in order to form a single resistive element wound itself around the core cylindrical element 4.
The distance between the turns, or pitch 17, if there is only one cylindrical element spirally wound around the core, or the distance 17 between two adjacent turns, if several parallel cylindrical elements are wound around the core, is varied according to the heat dissipation value to be obtained, measured in cm²/ohm. The distance between two adjacent turns is generally within the range of 0.3 mm and 20 mm. Preferably, the distance 17 between two adjacent turns is within the range of 0.5 mm to 3 mm. As already mentioned, in this narrow range, compared with the wider range, good heat dissipation capacities are obtained thanks to the perfect balance between the increase in dissipating surface, due to the larger mass of cylindrical element spirally wound around, and the shielding effect that this has on the cylindrical element in a core arrangement. The invention shall now be further explained by means of the following examples.

EXAMPLE I

A 2500 Watt 220V alternate current resistance is required for an air conditioner nozzle having dimensions of 170 x 570 mm, crossed by an air flow provided at a mean velocity of 4 m/s.
In order to prevent problems concerning tightness of the air conditioner materials, the resistor must work at "obscure heat", correspondent to a wire temperature of about 200°C.
These requirements must be optimally obtained according to prior art with a resistor made of a traditional single-wire resistance spirally wound on a ceramic support with the following characteristics:

Ni/Cr alloy 35/20;
actual diameter = 1.1 mm;
ohm/m =1.095;
length =16.52 m;
unit weight = 7.88 g/m;
total weight = 130.22 g;
cm²/ohm =31.54.

The same resistor can be assembled according to the present invention using a cylindrical resistive element acting as a core on which a second wire is wound. In detail, the first cylindrical element, that is the element 4 in figure 2, has the following characteristics:

Ni/Cr alloy 35/20;
actual diameter = 0.75 mm;
length = 8.26 m;
ohm/m 2.36;
unit weight = 3.66 g/m;
cm²/ohm 9.99.

Wound around this wire, at a pitch of 1 mm, is a second cylindrical resistive element, corresponding to the cylindrical element 5 in figure 2, having the following characteristics:

Ni/Cr alloy 35/20;
actual diameter = 0.4 mm;
length = 29.8 m;
ohm/m 8.69;
unit wheight = 1.04 g/m;
cm²/ohm 1.445..

The resulting element 1 has the following characteristics:

length = 8.26;
ohm/m 2.18;
unit wheight = 7.43 g/m;
total wheight = 61.57 g;
cm²/ohm 31.67.

It can be noticed that, the same result being achieved (superficial temperature of the wire equal to 200°C), evident advantages are obtained with the resistor according to the present invention:

the length and therefore overall dimensions are lower (8.26 m compared to the previous value of 16.52 m) making it much easier to place the resistor inside the air conditioner nozzle;
it is possible to obtain a saving in production costs thanks to the decrease in material used; in fact, the resistor weight is 61.57 g compared to 130.22 g of the resistor according to prior art.

Moreover, by sizing the length of the resistive elements in an appropriate manner, the present invention allows considerably greater heat dissipation values, compared to those according with the prior art. It will be possible for the operating resistor, to work with lower superficial temperatures of the wire compared to the resistor according to prior art, this leading to the advantage of a longer useful life of the apparatus on which the resistor is fitted.

EXAMPLE II

The following example II shows that, given two resistors 1 according to the invention and in particular according to the embodiment shown in figure 2, with a resistive element 4 arranged in a core and a wound resistive element 5, and in which the first resistor has a winding having a pitch between turns chosen in the range 0.5 - 3 mm and the second resistor having a winding with a pitch chosen in the range between 3 and 20 mm, the dissipation capacity of the sample chosen in the restricted range is greater than the dissipation capacity of the sample of resistor made with a distance between turns included in the range from 3 to 20 mm. Moreover, it will be noticed how the increased dissipation capacity occurring in the restricted range is not equal to the expected one, being evident from an experimental verification that this enhancement in the dissipation capacity is surprisingly greater than the one suggested by the expectations .
In both resistors the resistive element arranged in a core, that is the cylindrical element 4 in figure 2, has the following characteristics:

Ni/Cr alloy 35/20;
actual diameter = 0.95 mm.

In the first resistor the wound cylindrical element 5, has the following characteristics:

Ni/Cr 35/20 alloy;
actual diameter = 0.45 mm;
winding pitch p₁=1.27mm.
obtained dissipation capacity = 90.76 cm²/ohm.

In the second resistor the wound cylindrical resistive element 5 has the following characteristics:

Ni/Cr 35/20 alloy;
actual diameter = 0.45 mm;
winding pitch p₂=3.5 mm;
obtained dissipation capacity = 67.20 cm²/ohm.

Therefore, the dissipation capacity of the sample, characterized by a pitch between turns included in the range from 0.5 to 3 mm, is greater than the dissipation capacity of the sample characterized by a pitch in the range between 3 and 20 mm. Proceeding in an experimental verification of obtained results, measuring the resistance at the ends of each conductor, the following values are found:

104 cm²/ohm in the case of the sample characterized by a pitch between turns included in the range from 0.5 mm to 3 mm; and
69 cm²/ohm in the case of the sample characterized by a pitch between turns included in the range from 3 mm to 20 mm;

It can be noticed that obtained dissipation values are not those expected, but greater, and in particular in the case of the sample characterized by the narrow pitch between turns, that is the range 0.5 - 3 mm, increase in the dissipation is surprisingly 15% greater than the expected one. Thus the present invention exceeds real expectations from the range selection.
Figure 4 shows a resistor with the cylindrical element 6 arranged in a core having a rectangular section, and with a wound cylindrical element 7 having a cylindrical section. This embodiment in practice is equivalent to a strip, but even if it has the same overall dimensions of a strip resistor its performance is considerably higher. Moreover, although the cylindrical element 6 arranged in a core with a rectangular section costs slightly more than a cylindrical element with a circular section, the reduction in length and weight, with the same performance, justifies and compensates this increase in cost.
Figure 5 shows the application of resistors according to the invention in heating devices particularly suitable for this application. Said strip type heating devices are assembled with a pair of supporting plates 9 of insulating material, such as micanite, arranged parallel to each other and provided with a series of holes 12 of equal diameter.
In detail, each hole 12 in the upper plate corresponds to a hole in the lower plate and both hold in position and support a resistor 1 according to the invention, bent in a substantially spiral ellipsoidal shape. In order to hold the spiral 8 more firmly in place, spiral which is made with a resistor 1 according to the invention, it may have saddle-shaped portions (not shown). The saddle-shaped portions are merely portions of the spiral 8 appropriately bent around the plates, the course of which resembles, at these plates, the outline of a saddle or a sinusoidal curve.
Naturally, in these "strip-type" devices any type of resistor according to the invention can be used, such as a resistor having a core element, that acts as a core for the winding, characterized by a rectangular section, such as the one shown in figure 4.
The cylindrical elements in resistive material utilized in the present invention are made of a known and normally used (for this purpose) material, such as constantan, Ni/Cr alloys and other metal alloys.

Claims

Resistor provided with two or more cylindrical resistive elements characterized in that said resistive elements are in contact at several portions and that at least one of the cylindrical resistive elements winds around the remaining resistive elements.
Resistor according to claim 1, characterized in that a first cylindrical resistive element is arranged in a core and is spirally wound by the remaining cylindrical resistive element(s).
Resistor according to 2, characterized in that a first cylindrical resistive element is arranged in a core and the remaining resistive element spirally wound around the first is made of two or more cylindrical resistive elements stranded around each other.
Resistor according to claim 1 or 2, characterized in that the distance between two adjacent turns is within the range 0.3 mm to 20 mm.
Resistor according to claim 4, characterized in that the distance between two adjacent turns is within the range 0.5 and 3 mm.
Resistor according to any of the previous claims, characterized in that said resistive elements have a circular section and a diameter between 0.09 mm and 5.0 mm.
Resistor according to any of the previous claims, characterized in that said first cylindrical resistive element arranged in a core has a rectangular section.
Resistor according to any of the previous claims, characterized in that said cylindrical resistive elements are made of the same material.
Heating device characterized in that it comprises at least one resistor according to any of the previous claims from 1 to 7.