Electronic control device with automatic protection against the condition of exhausted battery for bistable type solenoid valve, particularly for watering systems

Abstract: An electronic control device for bistable type solenoid valve is described, particularly for watering systems, that comprises a power supply battery (B) and a logic control unit (M) to transfer electric power from the battery (B) to the solenoid valve (X L ). The device provides a protection against the condition of exhausted battery that is based on the presence of a condenser (C) set in parallel to the battery (B) and a switch (S) having first switching means (P1) interposed between the battery (B) and the condenser (C) and second switching means (P2, P3) interposed between the condenser (C) and the solenoid valve (X L ). The switch (S) is operated by said logic control unit (M) in order to determine, in a first operating condition, the charging of the condenser (C) and, in a second and third operating condition, the application of control voltages with opposite sign from the condenser (C) to the solenoid valve (X L ) for the closing and, respectively, the opening of the same solenoid valve. The logic control unit (M) is programmed in such a way that each request for the opening of the solenoid valve brings about the setting of the switch (S) in said first operating condition for the charging of the condenser (C) in first place, then the preliminary activation of the switch (S) in said second operating condition for the closing of the solenoid valve after a first preset time has elapsed since the previous closing control of the same solenoid valve, then again the return of the switch (S) in said first operating condition for the new charging of the condenser (C) and finally the starting of the switch (S) in said third operating condition for the opening of the solenoid valve after a subsequent second preset time shorter than the first one.

Description: The present invention concerns an electronic control device with automatic protection against the condition of exhausted battery for bistable type solenoid valve, particularly for watering systems. Watering systems for lawns, gardens, kitchen gardens and cultivated spaces are generally based on the use of solenoid valves that determine the delivery of water in the various sectors to be watered. The control of the solenoid valves is entrusted to programmable electronic control devices with various complexity that can be connected with the power of mains or operate with battery, in which case, for power saving reasons, valves with bistable type electric actuators are essential. In the second case what obviously happens is that the battery goes down and it is then necessary to detect the condition of exhausted battery and to operate on the controlled solenoid valves in order to lock them in a closing position. In this way, considering that bistable type solenoid valves require driving controls of short duration, it is possible to prevent that at a certain point of the discharging of the battery the latter still has sufficient energy to control the opening of the solenoid valve but not its subsequent closing, with the consequence that the watering would continue without interruption until the moment in which someone notices the problem. For such reason the control devices of the type with battery are usually provided with electronic circuits capable to detect the lowering of the battery voltage to a minimum value below which no further activation of the solenoid valves being controlled is permitted. In this way, besides, what happens is that the detection circuit determines the locking of the system when in reality the battery still has sufficient energy for several additional activations. In addition, the detection circuit has a cost of its own, that obviously affects the total cost of the control device. Object of the present invention is now to realise an electronic control device supplied with battery for bistable type solenoid valve, particularly but not exclusively for watering systems, that does not require a detection circuit for the condition of exhausted battery. According to the invention such object has been attained with an electronic control device for bistable type solenoid valve, comprising a power supply battery and a logic control unit to transfer electric power from the battery to the solenoid valve, characterized in that it comprises a condenser set in parallel to the battery and a switch having first switching means interposed between the battery and the condenser and second switching means interposed between the condenser and the solenoid valve, said switch being operated by said logic control unit in order to determine, in a first operating condition, the charging of the condenser and, in a second and third operating condition, the application of control voltages with opposite sign from the condenser to the solenoid valve for the closing and, respectively, the opening of the same solenoid valve, said logic control unit being programmed in such a way that each request for the opening of the solenoid valve brings about the setting of the switch in said first operating condition for the charging of the condenser in first place, then the preliminary activation of the switch in said second operating condition for the closing of the solenoid valve after a first preset time has elapsed since the previous closing operation of the same solenoid valve, then again the return of the switch in said first operating condition for the new charging of the condenser and finally the operation of the switch in said third operating condition for the opening of the solenoid valve after a subsequent second preset time shorter than the first one. In this way, as it will be better seen hereinafter, it is possible to have a guarantee that at a certain point of the discharging of the battery, or even in case of removal of the same battery, a residual energy however remains in the condenser that is capable to allow the closing of the solenoid valve without any further possibility to open it again. The characteristics of the present invention will be made evident by the following detailed description of an embodiment thereof that is illustrated as a non limiting example in the enclosed drawings, in which: Fig. 1 shows the equivalent electric circuit of the part of control device that provides for the protection against the condition of exhausted battery. With reference to the drawing, a battery considered to be made of a voltage generator Vb and of a equivalent internal resistance Ri is indicated by B as a whole. In sequence to the latter a series resistance Rs is set and in parallel to the series circuit consisting of Vb, Ri and Rs a condenser C is set at the ends of which a voltage Vc is thus present. A switch S with two poles P1, P2 and P3 and three operating positions ("ON" upward in Figure 1, "CHARGE" in the center, "OFF" downward) controlled by a microprocessor logic control unit M provides to charge the condenser C at the voltage Vc when the pole P1 of the switch is in the "CHARGE" position and to subsequently apply the voltage Vc thus obtained, now with a sign and then with the other one according to whether the poles P2 and P3 of the switch are in the position "ON" or "OFF," to a load representative of the solenoid valve (or solenoid valves) being controlled, or better of the bistable solenoid that controls its opening and closing for the starting and, respectively, the stopping of the watering. The operating principle of the circuit herein described, and therefore of the protection of exhausted battery that it represents, is the following. Let's consider that at the moment of the release of the switch S after a start (position "ON") or a stop (position "OFF") of the solenoid valve, therefore after a discharge of the condenser C on the charge X L (for example for a time ts= 50msec), the condenser C is at a voltage Vin, almost identical in the two cases. Subsequently, that is with the switch S in the rest position of Fig. 1, the charge voltage of the condenser varies according to the following ratio: Vc(t) = Vin+(Vb-Vin)*(1-e -[t/(Ri+Rs)*C] Therefore, after 2 seconds the voltage Vc at the ends is: Vc(2sec) = Vin+(Vb-Vin)*(1-e -[2/(Ri+Rs)*C] whereas after 8 seconds the voltage Vc becomes: Vc(8sec) = Vin+(Vb-Vin)*(1-e -[8/(Ri+Rs)*C] The difference between the two voltages Vc(8sec) and Vc(2sec) is the following: ΔVc=[Vc(8sec)-Vc(2sec)]=Vin+(Vb-Vin)*(1-e -[8/(Ri+Rs)*C] )-Vin-(Vb-Vin)*(1-e -[2/(Ri+Rs)*C] ) that is ΔVc=(Vb-Vin)*(1-e -[8/(Ri+Rs)*C] -1+e -[2/(Ri+Rs)*C] )=(Vb-Vin)*(e -[2/(Ri+Rs)*C] -e -[8/(Ri+Rs)*C] ) that is yet ΔVc=(Vb-Vin)*[e -[2/(Ri+Rs)*C] -e -[8/(Ri+Rs)*C] ] If we consider for example the following values with charged battery and exhausted battery with Rs = 68 Ohm, C = 4700 µF and X L = R L = 5 Ohm (having approximated the charge X L with a simple resistance, since the effect of the inductor of the same charge is negligible): Charged battery: Vb = 9,5V Ri= 10 Ohm Vin=Vb*e -[ts/R L *C] =9,5*e -[0,05/(5*0,0047)] =1,13V Exhausted battery: Vb = 7,0V Ri= 100 Ohm Vin=Vb*e -[ts/R L *C] =7,0*e -[0,05/(5*0,0047)] =0,84V by substituting we obtain: ΔVc (charged battery)=(9,5-1,13)*[e -[2/(10+68)*0,0047] -e -[8/(10+68)*0,0047] ]=0,036V ΔVc (exhausted battery)=(7,0-0,84)*[e -[2/(100+68)*0,0047] -e -[8/(100+68)*0,0047] ]=0,490V As it can be observed, the difference between the voltage Vc after 2 seconds and that after 8 seconds increases when decreasing the battery charges, and that by virtue of the increase of the equivalent internal resistance Ri of the battery when the same goes down. By taking advantage of this principle, the protection against the condition of exhausted battery takes place, according to the invention, in the following way. Each time that it is necessary to open the valve, the microprocessor M controls a closing operation at first (switch S in "OFF" position), while previously insuring that a possible previous closing operation has taken place since more than 8 seconds. Otherwise, it waits that 8 seconds elapse since the last aforesaid operation (switch S in "CHARGE" position). In this way there is a guarantee that the condenser C has reached the charge voltage Vc (8sec) before controlling the closing of the solenoid valve. After having sent the command for the closing of the valve, the microprocessor waits 2 seconds so as to guarantee the voltage value Vc (2sec) on the condenser C (switch S in "CHARGE" position) and at that point it sends the control for the opening of the valve (switch S in "ON" position). Substantially, the microprocessor operates in such a way that the charge voltage (Vc (8sec)) of the condenser C at the moment of the closing of the valve is always higher than the one ( (Vc (2sec)) present at the moment of the opening of the same valve. As already said, the difference between the two voltages (ΔVc= Vc (8sec)- Vc (2sec)) is as higher as the battery is the more discharged. There is therefore the guarantee that at a certain point of the exhausting of the battery the condenser C however contains a residual energy capable to allow the closing of the valve without being possible to open it again. At the same time the valve continues to be opened and closed until the battery allows it and not until the detection circuit decides for it, as in the control devices according to the known technique. In addition the present invention prevents that, in case of request for the opening of the valve with battery during the stage of replacement or, in any case, removal for any reason, the last power present in the condenser C is used to open the valve without any energy left, once the battery is disconnected, for the closing back of the same. Besides it is necessary to keep in mind that after the last possible closing enough power must be present in the battery so as to guarantee the operation of the control microprocessor. Otherwise what could in fact happen is that, while the valve is open, the microprocessor does not receive enough power from the battery to allow it to control the closing of the valve. This condition is guaranteed by choosing a proper type of microprocessor that is capable to work at voltages that are sufficiently lower than the minimum ones required for the activation of a bistable solenoid for solenoid valve. In addition it should also be considered that, having substantially removed any limit to the minimum value of battery voltage required for the activation of the solenoid valve and having thus increased the number of the possible activations of the solenoid valve, it is possible, without losing in performance as compared with a traditional central control unit, to unbalance the power supply circuit of the solenoid valve by adding a series resistance only during the stage of the valve opening, so that less power gets to the solenoid of the solenoid valve in the opening stage than in the closing stage. In case the pole P2 of the switch S is of electronic transistor type, that would be possible by using transistors with values of Vcesat (collector-emitter in conditions of saturation voltage) for the opening control circuit that are higher than the ones of the transistors of the closing control circuit.

Claims: Electronic control device for bistable type solenoid valve, particularly for watering systems, comprising a power supply battery (B) and a logic control unit (M) to transfer electric power from the battery (B) to the solenoid valve (X L ), characterized in that it comprises a condenser (C) set in parallel to the battery (B) and a switch (S) having first switching means (P1) interposed between the battery (B) and the condenser (C) and second switching means (P2, P3) interposed between the condenser (C) and the solenoid valve (X L ), said switch (S) being operated by said logic control unit (M) in order to determine, in a first operating condition, the charging of the condenser (C) and, in a second and third operating condition, the application of control voltages with opposite sign from the condenser (C) to the solenoid valve (XL) for the closing and, respectively, the opening of the same solenoid valve, said logic control unit (M) being programmed in such a way that each request for the opening of the solenoid valve brings about the setting of the switch (S) in said first operating condition for the charging of the condenser (C) in first place, then the preliminary starting of the switch (S) in said second operating condition for the closing of the solenoid valve after a first preset time has elapsed since the previous closing operation of the same solenoid valve, then again the return of the switch (S) in said first operating condition for the new charging of the condenser (C) and finally the starting of the switch (S) in said third operating condition for the opening of the solenoid valve after a subsequent second preset time shorter than the first one. Device according to claim 1, characterized in that said first preset time is equal to 8 seconds. Device according to claim 2, characterized in that said second preset time is equal to 2 seconds. Device according to claim 1, characterized in that said logic control unit (M) comprises a microprocessor that is capable to operate with a voltage lower than the minimum one required for the activation of the solenoid valve. Device according to claim 1, characterized in that it comprises means for reducing the control voltage that is applied to the solenoid valve for the opening of the same with respect to the one made available by the condenser (C). Device according to claim 5, characterized in that said means consist of a series resistance associated with the second pole (P2) of the switch (S).

Inventors: BRUNDISINI ANDREA, BRUNDISINI, ANDREA
Applicants: CLABER SPA, CLABER S.P.A.
Application year: 1999
Main classification: A01G25
IPC codes: A01G25