WO2001082321A1

WO2001082321A1 - A contactor control circuit

Info

Publication number: WO2001082321A1
Application number: PCT/IB2001/000642
Authority: WO
Inventors: Dennis Goldman; Stephen John Poston
Original assignee: Dennis Goldman; Stephen John Poston
Priority date: 2000-04-20
Filing date: 2001-04-20
Publication date: 2001-11-01
Also published as: AU6051601A

Abstract

A contactor control circuit has a central controller connected to a mains input control failure detector circuit. When the mains input power switches off, the mains input control failure circuit instructs the central controller which in turn controls a drive circuit to produce a pulsed signal after a predetermined delay. The drive circuit produces the pulsed signal which switches a latching relay off. When mains power is again detected, the central control circuit instructs the drive means to produce a second pulsed signal which toggles the latching relay to an on position. This allows the latching relay to be used as a contactor without requiring a holding current.

Description

A CONTACTOR CONTROL CIRCUIT

BACKGROUND OF THE INVENTION

THIS invention relates to a contactor control circuit.

Contactors typically require a holding current to keep them in an on position. The continuous holding current tends to reduce the life of the contactor due to the continuous coil heating effect. Contactors having a high amperage are relatively costly, in that snubber circuits and the like need to be incorporated to reduce arcing. Certain contactors may also be responsive to voltage spikes and the like on the mains input line without the provision of appropriate protection circuitry. SUMMARY OF THE INVENTION

According to the invention there is provided a contactor control circuit comprising a controller, drive means responsive to the controller, and arranged to produce first and second typically pulsed signals of a predetermined minimum duration to toggle a latching relay between first and second corresponding states into which it is preferably mechanically biased, the drive means including charge storage means for generating the pulsed signals.

Preferably, the first state is an on state, the second state is an off state, the first pulsed signal is responsive to an applied voltage after a first predetermined delay, and the second pulsed signal is responsive to removal of the applied voltage, after a second predetermined delay, the applied voltage typically being a mains voltage or a voltage derived therefrom.

Conveniently, the control circuit includes delay circuitry for generating the first and second predetermined delays.

The delay circuitry including a first voltage zero crossing detector for detecting when an AC input which is connected to a switched AC output via the latching relay crosses zero, and a second current zero crossing detector for detecting when the switched AC output current crosses zero, for respectively, delaying on and off switching of the latching relay via the controller and the drive means until respective zero voltage crossing of the AC input and zero current crossing of the AC output occurs.

The contactor control circuit may further include a detector to detect the level of the mains voltage or a voltage derived therefrom.

The contactor control circuit may also include a low voltage control circuit connected to the controller via an opto-isolated input. Preferably, the contactor control circuit according further includes configuration input means to enable a user to instruct the controller to operate in different modes.

The contactor control circuit also preferably includes a drive means failure detection circuit to detect if the drive means is working.

According to the present invention there is further provided contactor control circuit comprising :

a controller;

a detector connected directly or indirectly to a power source and to the controller, the detector being adapted to detect whether there is or is not an applied voltage from the power source and to provide an input to the controller; and

drive means responsive to the controller, and arranged to produce first and second signals to toggle a latching relay between an on and an off position, depending on whether there is or is not an applied voltage from the power source respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a functional block circuit diagram of a first single phase contactor embodiment of the invention;

Figure 2 shows a more detailed circuit diagram of part of the block diagram of Figure 1 ; Figure 3 shows a functional block circuit diagram of a second three phase contactor embodiment of the invention; and

Figure 4 shows a series of timing diagrams illustrating the manner in which the single phase contactor of Figure 1 operates.

DESCRIPTION OF EMBODIMENTS

Referring first to Figure 1 , a single phase contactor circuit 10 of the invention has a central controller 12 in the form of an application specific IC (ASIC) which is fed with a low voltage power supply 14 driven by a mains input 16.

A mains input control failure detector circuit 18 monitors the level of the power supply 14, and provides a signal to the ASIC controller in the event of the mains input power failing (i.e. turning off).

An opto-isolated input 20 is fed by means of a low voltage control circuit 22, and provides an alternative input to the controller to increase the versatility thereof. A configuration input 24 determines the mode of operation of the controller. The controller may be provided with an addressable input in the form of a serial data stream via the opto-isolated input 20.

An indicator 26 provides the status information of the contactor including its on or off position and any fault conditions which may arise.

An opto-isolated output 28 enables the status information to be transmitted to a remote monitoring system which is typically capable of monitoring the status of a number of contacts within an entire installation. The micro-controller 12 delivers an output signal to a contactor drive circuit 30 which in turn drives a latching relay or contactor 32 to switch between a live input 34 and a switched live output 36. It will be appreciated that the latching relay 32 is being used in place of a more conventional contactor.

In this specific embodiment, the latching relay 32 is a Gruner type 720 dual coil relay, with a 20ms 12V pulse being required from the drive circuit 30 to drive the two relay coils.

A storage capacitor 38 which is fed from the power supply 14 is used as a primary energy storage device for driving the contactor coils via the drive circuit 30.

A drive failure detection circuit 40 provides an input to the micro-controller 12 to detect if the latching relay 32 has been driven to the on or off contact position.

A zero crossing detector 42 senses when the AC voltage at the live input 34 crosses zero, and signals the ASIC controller when this occurs. The zero crossing detector 42 produces a high signal at every positive mains AC cycle. A zero current detector 43 senses a zero current condition on the switched live output via a resistive current shunt 43A. The current zero crossing detector 43 has particular application in the case of an inductive load where the current and voltage are out of phase.

Referring now to Figure 2, a more detailed circuit diagram of part of the contactor circuit of Figure 1 is shown. The ASIC controller 12 is formed with first and second drive outputs 46 and 48 for driving the respective on and off coils of the latching relay 32 via the drive circuit 30, which includes base resistors 54 and 56 connected to the bases of respective drive transistors 58 and 60. Protection diodes 62 are shunted across the on and off coils 50 and 52.

The drive failure detection circuit 40 is constituted by potential divider in the form of resistors 64 and 66 which provide a feedback signal to the ASIC controller 12. It is envisaged that the application specific IC can be extended to include those circuit components enclosed in broken outline at 69 in Figure 1.

The three phase contactor 70 of Figure 3 is similar to the single phase contactor of Figure 1. A three phase input 74 and a switched three phase output 48 is provided, with the latching relay 76 being arranged simultaneously to switch between all three phases. The zero crossing detector 42 of Figure 1 is replaced with three phase failure detector circuits 78.1 , 78.2 and 78.3, which are arranged to detect failure in any one of three phases. The existence of a low or zero signal on any of the detection circuits for a predetermined time is sensed at the controller, which responds by turning the latching relay 76 to the off position.

Referring now to Figure 4, not-to-scale timing diagrams of the mains input 80 and the contactor drive output 82 are shown. After a time period t1 , typically 2s, after the mains input has gone high at 84, the contactor drive circuit 30 generates a pulse 86 having a duration or width t2 (20ms) which is sufficient to drive the coil 50 of the latching relay 32. The time delay t1 is determined by the zero crossing detector 42 and the mechanical response time of the contacts to close. Ideally, the mechanical switching delay (typically 10ms) is taken into account at the ASIC controller in time t1 so that the contact closes just as the AC live input crosses zero. The pulse width t2 is determined by the specifications of the particular latching relay. As was previously mentioned, in the case of the Gruner latching relay, the pulse width is 20ms and the pulse amplitude is 12V. After the latching relay has been driven into the closed position, the contactor drive signal goes low. Eventually, in the event of the mains input control fail detect going low at 88, the contactor drive circuit 30 generates a pulse 90 a predetermined time period t3 (typically Is) thereafter, with the time period t3 being determined by the ASIC controller 12 which uses the signal from the mains input control fail detect circuit 18 in conjunction with the signal from the current zero crossing detector 43 and the mechanical response time (typically 6ms) of the latching relay contacts to open. The pulse 90 similarly has a duration t2, and is generated by the discharging storage capacitor 38. The pulse 90 is sufficient to energize the second coil of the latching relay 32 to disconnect the relay contacts and cause them to toggle into the off position.

In the event of a pulse 92 appearing on the mains input 16, this has no effect on the operation of the circuit for the reason that the duration t of the pulse 92 is less than t1 , the minimum response time of the contactor drive circuit. This means that all noise signals, voltage spikes and the like that can occur on the mains input and that have a duration less than t1 are effectively filtered, and do not have the effect of inadvertently switching the latching relay 32.

A predetermined time period after either of the coils 50 or 52 have been pulsed, the controller determines if they have responded by sensing a signal at the drive failure detect input 68. Based on the level of the signal, the controller is then able to determine if there has been a failure in driving either of the latching relay coils, determines if a fault condition has occurred indicating a damaged latching relay coils or contacts.

The previously mentioned opto-isolated input 20 may be used to drive the two latching relay coils in different ways if a mains input control voltage is present. First, a single byte protocol can be utilized based on a fixed baud rate with the following data bit structure which can be produced from a UART: aaaaidiv

Where:

aaaa = 4 address bits i = idle bit d = data bit i = idle bit v = authentication bit

For improved validity of the data, a parity byte can be added to the end of the eight bits, similar to that of a standard UART. The single byte protocol has applications where a UART is available, providing some reliability in various pulses on the input bit stream.

Second, a serial communications protocol could be employed. This is a multi- byte protocol based on a state machine which detects the serial data bytes and ensures that they are valid according to the byte protocol for the scheme. This has applications where reliable control of a number of different addressable contactors is required.

Simple control of the contactor could take place by means of a remote level control signal 22 via the opto-isolated input 20. A low signal could turn the latching relay 32 into the off state, and a high signal could turn the latching relay to the on state in the manner previously described. Alternatively, the presence of a continuously pulsed input can be detected to switch the contactor to the on state, with the absence of the pulse being determined by the controller 12, and switching the contactor to the off state as a result.

Claims

1. A contactor control circuit comprising a controller, drive means responsive to the controller, and arranged to produce first and second pulsed signals of a predetermined minimum duration to toggle a latching relay between first and second corresponding states, the drive means including charge storage means for generating the pulsed signals.

2. A contactor control circuit according to claim 1 wherein the first state is an on state, the second state is an off state, the first pulsed signal is responsive to an applied voltage after a first predetermined delay, and the second pulsed signal is responsive to removal of the applied voltage, after a second predetermined delay.

3. A contactor control circuit according to claim 2 wherein the applied voltage is a mains voltage or a voltage drive therefrom.

4. A contactor control circuit according to any preceding claim wherein the control circuit includes delay circuitry for generating the first and second predetermined delays.

5. A contactor control circuit according to claim 4 wherein the delay circuitry includes a first voltage zero crossing detector for detecting when an AC input which is connected to a switched AC output via the latching relay crosses zero, and a second current zero crossing detector for detecting when the switched AC output current crosses zero, for respectively, delaying on and off switching of the latching relay via the controller and the drive means until respective zero voltage crossing of the AC input and zero current crossing of the AC output occurs.

6. A contactor control circuit according to any one of claims 3 to 5 further including a detector to detect the level of the mains voltage or a voltage derived therefrom.

7. A contactor control circuit according to claim 1 further including a low voltage control circuit connected to the controller via an opto-isolated input.

8. A contactor control circuit according to any preceding claim further including configuration input means to enable a user to instruct the controller to operate in different modes.

9. A contactor control circuit according to any preceding claim further including a drive means failure detection circuit to detect if the drive means is working.

10. A contactor control circuit comprising :

a controller;

drive means responsive to the controller, and arranged to produce first and second signals to toggle a latching relay between an on and an off position, depending on whether there is or is not an applied voltage from the power source respectively. -ll¬

ll. A contactor control circuit substantially as herein described with reference to the illustrated embodiments.