Technical Field

The present invention relates to a heater for aquariums, particularly of the immersion type. Background Art

Heaters for aquariums are currently known which use as a heating element a resistor which, when electric current flows through it, is heated due to the Joule effect. Such heating element is contained in a containment body, which is generally cylindrical and is adapted to keep it separated from the water of the aquarium.

Further, it is connected to an electric power supply circuit by means of a switch that is controlled by a bimetallic lamina, which by deforming according to its temperature closes or opens the switch.

More particularly, such bimetallic lamina supports, at one end, one of the two contacts of the switch, and has, at the other end, an elastically deformable fold in order to move away or closer the contact associated with the lamina with respect to the other contact of the switch, which is associated with the containment body.

Thus, by moving the contacts apart, the deformation of the lamina needed to close the switch increases and consequently so does the temperature of the lamina at which the switch opens the circuit, in case of heating, or closes it in case of cooling. Vice versa, by moving the contacts of the switch mutually closer, the deformation of the lamina needed to close the circuit decreases and accordingly the temperature of the lamina at which the switch closes or opens the circuit decreases.

As an alternative, the lamina, instead of having a fold, is connected to an elastically deformable supporting element whose function is equivalent to that of a fold.

The deformation of the fold or of the supporting element is imposed by a threaded piston, which is coupled to a female thread support provided in the containment body. By turning within the female thread, the piston moves longitudinally, deforming the fold or the supporting element.

Generally, the containment body is inserted in the tank of the aquarium at the end where the heating element is accommodated, while the other end, directed toward the outside of the tank, has a knob that can be turned and which, by means of a guiding rod, turns the piston, thus adjusting the deformation of the fold or of the supporting element and as a direct consequence the closing or opening temperature of the circuit, i.e., the temperature set for the water of the aquarium.

The heating element usually comprises a metallic electrical conductor, which when crossed by current is warmed by Joule effect and thus heats the environment that surrounds it.

Currently, the heating element is provided by means of a nickel- chromium wire that is wound in a spiral and is supported by a rigid elongated element, generally made of cordierite. One drawback of these heating elements is that, if the heater is extracted from the water of the aquarium, such elements tend to overheat due to the consequent reduction in heat dissipation.

If the region of the heater where the heating element is accommodated is not affected by water, but is in contact only with air, the dispersion of the heat generated by the heating element is in fact reduced, causing the overheating of the heater.

To obviate this drawback, one currently known solution has a laminar heating element that is shaped like a cylindrical sector and is arranged so as to face, from the inside of the containment body, the outside of the heater. Such lamina has portions covered with an ink that has a positive thermal coefficient, so that the heating element self-protects against overheating by limiting the current that flows through it as its temperature increases.

This solution, however, suffers drawbacks, including the fact that the lamina faces the outside of the heater only at a perimetric portion thereof, concentrating thereat the emission of heat flow.

Further, the lamina generally does not adhere accurately to the containment body, thus limiting heat transmission by conduction.

Disclosure of the Invention The aim of the present invention is to provide a heater for aquariums that obviates this drawback without overheating even if it is extracted from the water of the aquarium.

Within this aim, an object of the invention is to provide a heater for aquariums whose heat flow emission is substantially uniform along its lateral perimeter.

Another object of the invention is to provide a heater for aquariums that is structurally simple and easy to use and can be manufactured with substantially low costs.

This aim and these and other objects, which will become better apparent hereinafter, are achieved by a heater for aquariums, particularly of the immersion type, comprising a substantially test-tube-shaped main body for containing an electric control circuit for a heating element, characterized in that said heating element comprises a thermistor with positive thermal coefficient, which is supported within said main body, substantially in an axial position with respect to it, by means for transmitting the heat generated by said thermistor with positive thermal coefficient toward the outside of said main body.

Brief description of the drawings

Further characteristics and advantages of the invention will become better apparent from the following detailed description of four preferred but not exclusive embodiments of the heater for aquariums according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a perspective view of a second embodiment of a heater for aquariums, according to the invention;

Figure 2 is a partially sectional side elevation view of the heater for aquariums according to the invention, shown in Figure 1 ;

Figure 3 is a sectional view, taken along the line ITT-III, of the heater for aquariums according to the invention, shown in Figures 1 and 2; Figure 4 is an enlarged-scale exploded and partially schematic perspective view of a detail of the heater for aquariums according to the invention, shown in Figures 1 , 2 and 3;

Figure 5 is a partially sectional side elevation view of a first embodiment of the heater for aquariums, according to the invention; Figure 6 is an enlarged-scale partially schematic perspective view of a detail of the heater for aquariums, according to the invention, shown in Figure 5;

Figure 7 is a sectional view, taken along the line VII-VII, of the heater for aquariums according to the invention, shown in Figure 5; Figures 8 and 9 are enlarged-scale sectional views of details of heaters for aquariums according to the invention, provided in additional alternative embodiments. Ways of carrying out the Invention

It is noted that anything found to be already known during the patenting process is understood not to be claimed and to be the subject of a disclaimer.

With reference to the figures, the reference numeral 10 generally designates a heater for aquariums, particularly of the immersion type, which comprises a main body 1 1 that is substantially shaped like a test tube and accommodates an electric control circuit 12 for a heating element 13. A particularity of the heater for aquariums 10 according to the invention is that the heating element 13 comprises a thermistor with positive thermal coefficient 14 which is supported in the main body 11, substantially in a position that lies axially thereto, by means for transmitting the heat generated by the thermistor with positive thermal coefficient 14, toward the outside of the main body 11.

Advantageously, the thermistor with positive thermal coefficient 14 comprises a ceramic plate 15, made of a material with positive thermal coefficient, which is interposed between two power supply electrodes 16a and 16b, which are connected to the electric control circuit 12.

Such heat transmission means advantageously comprise a wrapping element 17, which wraps around the thermistor with positive thermal coefficient 14, and the power supply electrodes 16a and 16b.

The wrapping element 17 is conveniently in intimate contact with the main body 11 in order to transmit thereto by conduction the heat generated by the thermistor with positive thermal coefficient 14.

Preferably, the wrapping element 17 is made of metallic material, conveniently an aluminum alloy.

In particular, in a first embodiment, the wrapping element 17 comprises a tube 18 that has a substantially quadrangular cross-section and in which the thermistor with positive thermal coefficient 14 is inserted.

In such first embodiment, the main body 11 conveniently has at least one portion 19 made of plastics, which is conveniently overmolded on the wrapping element 17 in order to obtain its intimate contact. To ensure high heat dissipation from the wrapping element 17 to the outside of the main body 1 1, in said first embodiment the portion 19, overmolded on the wrapping element 17, has heat dissipation fins 20.

In a second embodiment of the heater for aquariums 100, the wrapping element 117 conveniently comprises a substantially tubular shell 121 inserted within the main body 1 1 1. Further, the wrapping element 117 advantageously comprises means 122 for supporting the thermistor with positive thermal coefficient 114, which are adapted to support the thermistor in a position that is substantially axial with respect to the shell 121. The supporting means 122 preferably are made of heat conducting material and are adapted to transmit heat from the thermistor with positive thermal coefficient 114 to the shell 121.

In this second embodiment, the main body 1 1 1 conveniently is made of glass and is substantially cylindrical, the wrapping element 117 being inserted therein, with the shell 121 in close contact with its inner wall.

Further, in such second embodiment the supporting means 122 comprise two elements 123 which have D-shaped tubular cross-sections and are inserted in the shell 121 in an opposite manner, comprising between them the thermistor with positive thermal coefficient 1 14. In an alternative embodiment, the supporting means 222 comprise wings 224 that are arranged radially and are connected inside the shell 221 and support the thermistor with positive thermal coefficient 214, substantially in an axial position with respect to the shell 221.

With particular reference to Figure 9, in a further alternative embodiment the wrapping element 317 comprises two complementary profiles 325, which are inserted in the main body and are mutually adjacent so as to encircle, between them, the thermistor with positive thermal coefficient 314 and the power supply electrodes 316a and 316b.

The operation of the heater for aquariums 10 according to the invention is as follows.

If the part of the heater for aquariums 10 in which the heating element 13 is accommodated is extracted from the water, and the heater 10 is on, its temperature increases due to the reduction in heat dissipation with respect, to the heat dissipation ensured by contact with water. The thermistor with positive thermal coefficient 14, upon the increase of its temperature, has an increasing electrical resistivity and therefore as it heats up its electrical conductivity decreases and therefore the electrical current that flows through it decreases.

Accordingly, the amount of heat that said current generates by Joule effect by flowing across the thermistor with positive thermal coefficient 14 is also reduced.

As the temperature of the heating element 13 increases, the amount of heat that it produces therefore decreases.

The heater for aquariums 10 therefore has a capacity to generate heat that decreases with its temperature, thus obtaining an effect of self- protection against overheating.

In practice it has been found that the invention achieves the intended aim and objects, providing a heater for aquariums that not does not overheat even if it is extracted from the water of the aquarium while it is on. Further, a heater for aquariums according to the invention is provided with a heating element and with means for transmitting heat outside the main body with a structure that substantially has an axial symmetry and allows a substantially homogeneous heat emission along the perimeter of the heater. The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may further be replaced with other technically equivalent elements.

In practice, the materials employed, so long as they are compatible with the specific use, as well as the contingent shapes and dimensions, may be any according to requirements and to the state of the art.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.