This invention relates to energy conversion and in particular to the conversion of light energy, including solar energy to useful electrical energy at low intensity levels. BACKGROUND OF THE INVENTION

Many electrical devices (hereinafter termed "loads") operate over a range of currents, some loads have an operating current which is less than the initial turn-on current. Examples include incandescent lamps and electric motors. In the case of an incandescent lamp, the resistance of the filament increases as the temperature of the filament increases, thus reducing the current required for continued operation. In the case of an electric motor, the back e.m.f. generated after the motor commences operation increases the resistance in the motor windings, thus reducing the required operating current.

In environments where the current delivered to this type of load is variable, the situation can arise where sufficient current is available for normal operation but insufficient current is available to turn the load on. One example is automatic operation of an electrical motor using solar energy. Under normal circumstances, a solar panel employing photovoltaic cells is connected to the motor, when the intensity of light incident on the panel is sufficient to provide the required "turn-on current", the motor will start. At this stage, the motor is operating in its low resistance region and maximum current is being drawn from the solar panel, once the motor is turned on the current drawn from the solar panel decreases to the "operating current" for the motor.

The major disadvantage of this arrangement is that if the available current is between the operating current and the turn-on current, the load will not perform work. OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to alleviate at least to some degree the aforementioned problems associated with the prior art.

In one aspect therefore, the invention resides in an energy convertor having an output connectable to a load, the load having a turn-on current which exceeds its operating current, the current conv rtor further

comprising an input connectable to a solar panel. The current convertor is operable to deliver a current sufficient to turn the load on in response to a current being delivered to said input. In one preferred application of the present invention, the load is an electric motor.

In another aspect, the invention resides in a current convertor for use in an energy convertor for converting a low input current to a higher output current in order to turn a load on, the convertor including an input, an electrical energy storage device in which electrical energy delivered to the input is progressively stored, an output through which current can be delivered to the load and a switching circuit, the switching circuit being operable after the required energy to turn on the load has been stored in the storage device, to deliver the energy from the storage device to the output.

In another aspect, the invention resides in a vent suitable for use in conjunction with an electric motor, the motor being driven via an energy convertor for enabling forced exhausting of air from the interior of an enclosure, the vent having a vent body including an inlet, an outlet and a convergent passage extending between the inlet and the outlet, a rotary air forcing assembly adjacent said outlet and the electric motor being coupled to said air forcing assembly, the electric motor being connectable to said energy convertor in order for the electric motor to drive said rotary air forcing assembly.

The energy storage device can be any suitable device for accumulating or integrating charge at one rate and releasing the charge at another rate. For example, a rechargeable battery, capacitor, a coil or oscillator can be employed.

The switching circuit can include active circuit elements such as transistors, preferably one or more low resistance active elements can be employed in series with the load. For example, a unijunction field effect transistor can be employed to good effect in order to maximize the current delivered from the energy storage device to the load.

The vent can be suitable for exhausting air from any enclosure and can be designed to fit walls, roofs or other structures. The vent body can be of any shape, including domed, otherwise rounded or of conventional slope, but where applied to a roof, it is preferable to employ a generally

pyramidal shaped vent body which forms a canopy where the outlet is adjacent the apex of the canopy. Advantageously, a bell-mouth inlet is located below the apex inside the canopy and upstream of the outlet in order to improve exhaust efficiency via the venturi effect. The vent body can include apertures to assist ventilation.

The vent body preferably includes convergent side walls defining the passage which extends between a relatively wide inlet and a relatively narrow outlet, this is to assist in accumulating hot air adjacent the outlet via the stack effect. The walls can be opaque or they can be translucent to transparent in the case of a sky light. The walls are preferably mounted on a peripheral frame which also serves to mount the vent body in its operative position relative to the enclosure. The frame can be of any configuration but preferably forms a peripheral rim for the inlet. The frame can be made from any suitable material but is preferably made from one or more extrusions. The frame can therefore be assembled in any length or any shape in order to provide flexibility of construction.

In another aspect, the invention resides in a system for circulating air between an enclosure and a confined air space above the enclosure, and for taking into account seasonal variations in ambient temperatures of the atmosphere, the system comprising a fan assembly communicating between the enclosure and the confined air space, the fan assembly comprising a fan housing and a fan module, the fan module being mounted in the housing so that the module can be physically moved so that flow of air through the fan assembly can be reversed. Preferably, there is employed a second fan assembly communicating between the confined air space and the atmosphere, the arrangement being that air can be vented into the confined air space and to the atmosphere via the second fan assembly during summer and warm air can be drawn into the enclosure from the confined air space during winter.

The first fan assembly preferably utilises solar power and preferably involves an energy convertor. Alternatively, the power delivered to the first fan assembly can be supplied by a rechargeable battery where the battery is charged using power delivered thereto from an array of solar cells.

It will therefore be appreciated that implementation of the teachings of the present invention to the rotary ventilator will enable the forced ventilation to occur over a greater range of conditions than was possible in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention can be more readily understood and be put into practical effect, reference will now be made to the accompanying drawings and wherein:-

Figure 1 is a circuit diagram illustrating a preferred current convertor and a preferred energy convertor according to the aforementioned aspects of the present invention;

Figure 2A is a schematic diagram illustrating application of the present invention to a fan type rotary air forcing assembly;

Figure 2B is a diagram similar to Figure 2A illustrating application of the present invention to a ventilator type rotary air forcing assembly;

Figure 3 is a cut-away perspective view illustrating a typical vent according to the present invention which utilises the ventilator arrangement of Figure 2B;

Figure 4 is a transverse cross-sectional view through the vent of Figure 3;

Figures 5 and 6 are respective transverse cross-sectional and perspective views illustrating a preferred frame suitable for use with the vent of Figure 3;

Figures 7A and 7B illustrate an alternative embodiment of an energy convertor applicable to the present invention.

Figure 8 is a modified circuit illustrating a current convertor which can be utilised in a preferred energy convertor according to the present invention in order to drive- the first fan assembly;

Figures 9 and 10 are respective plan and horizontal cross-sectional views illustrating a fan assembly which can be employed with the present invention; and

Figures 11A, 11B and 11C are schematic views illustrating seasonal adjustment and operation of another typical fan assembly according to the present invention.

BEST MODE AND OTHER EMBODIMENTS OF THE INVENTION

Referring to the drawings and Initial ly to Figure 1, there is illustrated an energy convertor 10 employing a current convertor 11 by which current delivered from a solar panel 12 can be stored in an energy storage device which in this case is a capacitor 13 prior to that energy being delivered to a load 14 via a switching circuit 15. An optional rechargeable battery 16 can be employed so that when light intensity on panel 12 is high, excess current can be used to charge the battery.

In the illustrated embodiment, photovoltaic cells mounted on the solar panel produce a fairly constant current which is proportional to the amount of light falling on the cells. At low light intensity, the cells become current limited.

A direct current brushless motor, which can be employed as the load 14 and which is electronically commutated, has a starting current approximately equal to full load current. This is due to the one pole-pair found in the small motors.

Due to the above characteristics of the cells and motors, direct connection would mean that the motor would not start until full output current was available from the solar panel. The circuit design allows starting at lower cell output currents by storing current in a large electrolytic capacitor 13 which in this case is a 2200 micro Farad capacitor. When the capacitor discharges, a large current pulse is delivered to the motor to make it rotate half a revolution. This half a revolution is enough for the electronic commutation to reverse the polarity of the motor winding which makes the motor continue running.

The capacitor is sized economically for the largest energy pulse generated from stored energy, from the cells maximum energy point at low light intensity to the minimum running voltage of the motor. The switching circuit 15 employs a 15 amp power transistor T2 which in this case is a 15 N05L MOTOROLA ® MOSFET which has very low on-resistance, with very large current capabilities and fast turn-on times to give the maximum possible energy pulse from the capacitor.

Resistors Rl , R2 and R4 determine the turn-on voltage of transistor Tl and hence transistor T2 and also the turn-off voltage of transistors Tl and T2. These resistors also determine the pulse time for capacitor

discharge depending on supply current from the solar panel 12. The turn-on and off voltages are made different by the fact that the motor negative is at the positive rail voltage before turn-on and at the negative rail voltage after turn-on. This changes the base current for Tl through R4 for the different conditions.

Resistor R3 simply pulls the gate of transistor T2 to ground (negative rail) while Tl is turned off.

The object of the circuit is to boost the current from the cells at low light intensity by pulsing a capacitor. The current pulses must be of sufficient size to rotate the motor enough for electronic commutation to work.

The circuit elements in the illustrated embodiment as used are listed below:

Ml - 4.5 watt - fan motor - 12 volts and identified as a EBM-W2G113B001-01.

SI - 5 watt - solar cell - 12 volts - type ARCO GENESIS G100.

R3 - 1 K - resistor - .25 watt.

R2 to R4 - 18 K - resistor - .25 watt.

Rl - 1.2 K - resistor - .25 watt.

Cl - 2200 micro Farad - capacitor - 25 volts.

Dl - 5 amp - diode.

T2 - 15 amp - transistor MOSFET - 15 N05L MOTOROLA ®.

Tl - Transistor PNP - BC327.

As can be seen, the effect of the current convertor 11 is to provide the energy convertor 10 with a current which at least reaches or exceeds the turn-on current for the load 14 when low light intensities are incident on the solar panel 12.

Typical applications of the energy convertor of Figure 1 are illustrated in Figures 2A and 2B where like numerals have been used to illustrate like features. As can be seen, in each case, the load is a DC motor 17 which drives a fan 18 and a ventilator 19 respectively.

In the case of Figure 2A, the fan operates at low light levels, whereas without the inclusion of the current convertor 11, the fan would not normally operate under those conditions. Thus, the fan has a greater range of operation over the period of a day. The fan can operate into the night until the battery 16 is discharged.

Similarly, the same thing applies in relation to Figure 2B except that the DC motor 17 is employed to drive a ventilator 19 which includes ventilator blades 20 which enables wind assistance for the operation of the ventilator. In other words, the ventilator will normally operate under wind power but where the wind levels are sufficiently reduced, the solar panel 12 and current convertor 11 will supply the drive to the motor 14 in order to drive the ventilator. As for the embodiment of Figure 2A, the inclusion of the energy convertor 10 employing current convertor 11 will enable the ventilator 19 to operate in conditions where there is no wind and therefore for a longer period than was otherwise known in the prior art.

Referring to Figure 3, there is illustrated a further application of the invention as applied to a ventilator according to Figure 2B. In this case, a vent 21 according to the invention is illustrated and where appropriate, like numerals have been used to illustrate like features. In the illustrated embodiment, the vent 21 has a body in the form of a pyramidal shaped canopy having side walls 22 converging between a broad inlet 23 and a narrower outlet 24 represented by the ventilator 19. The walls 22 of the vent body are constructed from fluted polycarbonate sheets.

A base frame 25 forms a peripheral rim defining the inlet 23 and in this embodiment is an extruded section.

Referring to Figures 4, 5 and 6, it can be seen that the extruded section includes a channel 26 in which the edges of the wall sheets are mounted along with various flanges to be described below.

A plurality of ventilation apertures 29 are located in a flange 30 which depends from the channel 26. The apertures 24 are located at spaced intervals about the entire periphery of the frame. A fabric non-return flap 31 is employed to cover the apertures 29 in order to prevent backflow of air, rain water or debris into the interior of the canopy through the apertures 29.

Figure 4 shows the vent in cross-section and as can be seen, the whole structure forms a canopy in which hot air can be trapped by virtue of the stack effect and exhausted to the atmosphere. The walls 22 converge to a bell-mouth opening to the ventilator, illustrated at 28. With this arrangement, ventilation is enhanced by virtue of the venturi effect.

Referring specifically to Figures 5 and 6, details of the channel 26 and its relationship with the walls 22 is more clearly seen. Like numerals again illustrate like features. As can be seen, the edge 32 of the wall 22 is located within the channel 26. The wall 22 is in abutment with parallel spaced beads 33 and 34 and is located adjacent its edge 32 by locating lugs 38 and 39. The wall portion adjacent edge 32 is spaced from the channel walls to allow for expansion. On assembly, a sealant 35 is located in the space between the beads 33 and 34 and exteriorly of bead 34 as shown in order to seal the periphery of the vent.

In addition, the peripheral frame 25 is made from a two part extrusion with a generally C-shaped extrusion 36 providing the channel 26, and the extrusion 37 (part of which is shown in Figures 5 and 6) is so mounted that the fabric non-return flap 31 can, on assembly, be located and clamped between the extrusions in sandwich fashion. The extrusion 37 can be locked in place as illustrated in Figure 5.

Referring to Figures 7A and 7B, a further embodiment of the present invention will be described in relation to a wind drive rotary ventilator. A conventional rotary ventilator's effectiveness decreases as the wind speed slows down and ceases in the absence of wind.

As described earlier, the present invention overcomes this deficiency by employing a solar powered 12 volt direct current motor to power the rotary ventilator in predetermined conditions for low speed or nil winds.

A photovoltaic solar panel 12 is employed to charge an energy storage device which in this case is a battery 16, which on operation of a switching circuit employing power transistor 40 drives the motor 41 and thereby the ventilator 42. In times of high wind, there is no requirement for the motor to operate and as a consequence, the power transistor 40 is off when the motor is operating at a predetermined speed. As a consequence, the wind action on the ventilator 42 drives the ventilator.

A proximity switch or optical switch 43 is employed to detect the speed of the rotary ventilator or the motor 41. A retriggerable timer 44 is triggered during each rotation of the rotary ventilator or the motor. Thus, the timer does not time out under normal operation, it only times out once the rotary ventilator or motor speed has slowed to a predetermined level. Once the retriggerable timer times out, the power transistor 40 is switched on and power is delivered from the battery 16 to the motor in order to drive the fan.

By selecting the circuit elements in appropriate fashion, operation of the rotary ventilator can be achieved at low wind speeds.

Referring to Figure 8, there is illustrated an energy convertor 100 employing a current convertor 111 by which current delivered from a solar panel 112 can be stored in an energy storage device, which in this case, is a capacitor 113 prior to that energy being delivered to a load 114 via a switching circuit 115. An optional rechargeable battery 116 can be employed so that when light intensity on panel 112 is high, excess current can be used to charge the battery. Where it is desirable to use the battery power at say night, a switch 117 is employed to switch on a supply circuit 118 which creates the desired operating voltage across zener diode 119. The switch 117 can be a suitable timer switch so that it operates only at night, or alternatively, the switch can employ a manual switch so that the load 114 can be driven when there is clearly insufficient light or current to be delivered from the solar panel 112.

Referring to Figures 9 and 10, there is illustrated a fan assembly 120 including a fan housing 121 and a fan module 122. In the illustrated embodiment, the fan housing is permanently secured in a ceiling partition 123. The fan module 122 includes a fan 124 which is electrically driven and in the illustrated embodiment of Figure 8 corresponds to the load 114. The fan housing 121 includes a removable ceiling diffuser 125 isolated from frame members 126 by vibration isolators 127 and as can be seen, the fan module 122 is retained in place on fan module mounting plates 128 by gravity. The fan module can be accessed by removing the ceiling diffuser and a person can then reach into the housing and simply turn the fan module over in order to reverse air flow.

Referring to Figures 11A, 11B and 11C, operation of a similar fan assembly to that of Figures 9 and 10 will now be described. However, in this embodiment, the fan housing and module is removable from the ceiling for the purpose of altering the direction of air flow through the housing. Where appropriate, like numerals having been used to illustrate like features. As can be seen in Figure 11, the fan module 122 is driven via battery 116 which is in turn, charged using an appropriate energy convertor 100 (not shown in Figure 11). In the illustration of Figure 11, there is represented the summer operation of the fan assembly and in this case, air is drawn from an enclosure 129 into a confined air space usually a ceiling

space 130 of a building. The ceiling space is in turn, ventilated using a suitable wind driven ventilator located in the roof of the building (not shown). In the embodiment of Figures 11B and 11C, a typical fan assembly 120 of Figure 11A is shown partially removed from the ceiling 123 and in Figure 11B, the fan module 122 has been removed, reversed and then the assembly has been replaced ready for winter operation. A filter 131 has also been inserted into the fan housing 121 so that air can be filtered as it is drawn from the ceiling space 130 into the enclosure 129. Thus, warm air can be supplied to the enclosure in winter.

Whilst the above has been given by way of illustrative example of the present invention, many variations and modifications thereto will be apparent to those skilled in the art without departing from the broad ambit and scope of the invention as herein set forth. INDUSTRIAL APPLICATION

The present invention may be applied to the starting of electric motors which, for example, may be used to rotate ventilators.