JP2003070289A - Dc motor drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high output DC motor drive circuit for motor lift or the like, in which a relay of smaller switching capacity can be used. SOLUTION: A forward relay coil RC1 and a reverse relay coil RC2 on the DC power supply side are connected in parallel with capacitors C4 and C5, respectively. An AC power supply relay coil RC3 is connected in parallel with a capacity C3 of higher capacitance and connected in series with a start control relay RL4. When an ascend switch sw2 or a descend switch sw3 is turned on, an AC power supply relay RL3 is closed following to closure of a relay RL1 or RL2 due to the difference of capacitance. When the ascend switch 2 or the descend switch sw3 is turned off, the start control relay RL4 is opened and the AC power supply relay RL3 is opened instantaneously. The relay RL1 or RL2 is opened after the capacitor C4 or C5 is discharged, and a motor is short-circuited through a normal close contact to stop abruptly. Since a large current does not flow through the relay RL1 and RL2 at the time of start and stop, a relay of smaller switching capacity can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC motor drive circuit, and more particularly, to prevent a peak current from flowing through the relay during start-up and braking, thereby enabling use of a relay having a smaller switching capacity. The present invention relates to a DC motor driving circuit.

[0002]

2. Description of the Related Art For example, an apparatus for rotating and driving direct current in both forward and reverse directions, such as an electric unloading apparatus, is provided with a forward / reverse switching circuit composed of a forward rotation relay and a reverse rotation relay. When the forward rotation switch is turned on, the forward rotation relay is turned on to rotate the direct current motor forward, and when the reverse rotation switch is turned on, the reverse rotation relay is turned on to reverse the direct current motor. When the forward rotation switch or the reverse rotation switch is turned off, the forward rotation relay or the reverse rotation relay is turned off, and the + power supply line and the −power supply line of the DC motor are short-circuited through the normally closed contact of the forward rotation relay and the reverse rotation relay. , The DC motor is electromagnetically braked and suddenly stops.

Generally, the switching capacity of a relay is almost constant under the influence of the contact voltage in an AC load, but is inversely proportionally decreased in the DC load when the contact voltage exceeds a certain value. For example, in the case of a relay having a switching capacity of 15 A, the switching capacity decreases when the circuit voltage exceeds 13 VDC in the case of a DC inductive load, and the switching capacity drops to about 0.5 A at 100 VDC. Therefore, in a high-voltage high-output device such as an electric unloading device, an electromagnetic contactor or an electromagnetic switch with a large switching capacity must be used, resulting in high cost. Also, in order to prevent the relay from being damaged by the back electromotive force of the DC motor that flows through the normally closed contact of the relay when switched off, insert a resistor in series to suppress the current flowing through the relay contact below the switching capacity. However, heat generation and current loss due to these short circuit resistances are large.

Therefore, there is a technical problem to be solved in order to prevent a DC inrush current from flowing to the relay at the time of starting and braking, to enable the use of a relay having a smaller switching capacity and to reduce the cost. Will occur,
The present invention aims to solve the above problems.

[0005]

SUMMARY OF THE INVENTION The present invention is proposed to achieve the above-mentioned object, and an AC power supply relay and a DC power supply relay after a rectifier are turned on / off by a switch to start a DC motor. In a DC motor drive circuit that controls stop, a capacitor is connected in parallel to the DC power relay coil, a capacitor having a larger capacity than the capacitor in the DC power relay circuit is connected in parallel to the AC power relay coil, and a start control relay is connected in series. A switch for turning on / off the power supply of the DC power relay coil and the start control relay coil is provided.The AC power relay is closed after the DC power relay is closed due to the difference in the capacitance of the capacitor when the switch is turned on, and the start control relay is opened when the switch is opened. Opening opens the AC power relay, and then opens the DC power relay circuit Capacitor is intended to provide a DC motor drive circuit being characterized in that configured to open the discharge to the DC power source relay.

The present invention also provides the above-mentioned DC motor drive circuit in which two DC power supply relays are combined to form a DC motor forward / reverse switching circuit.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a DC motor drive circuit, in which a DC power source is supplied to a DC motor M through a rectifier circuit B1, a smoothing circuit including a capacitor C2, diodes D1 and D2, and a forward / reverse switching circuit including a forward rotation relay RL1 and a reverse rotation relay RL2. Supply. Main switch SW1, fuse F1 and rectifier circuit B1
An AC power supply relay RL3 is inserted between and, and a capacitor C1 is connected in parallel with the relay RL3.

SW2 is a raising switch, SW3 is a lowering switch, and is formed by an interlock mechanism so that the raising switch SW2 and the lowering switch SW3 are not turned on at the same time. When the up switch SW2 or the down switch SW3 is closed, the start control relay coil RC4 is energized to close the start control relay RL4, and power is supplied from the rectifier circuit B2 to the AC power relay coil RC3 connected in series with the start control relay RL4. To be done. Start control relay RL4 and AC power relay coil R
A capacitor C3 is connected in parallel with C3, and after the start control relay RL4 is closed and the charging time of the capacitor C3 has passed, the AC power supply relay coil RC3 operates and the AC power supply relay RL3 closes.

B3 is a rectifier circuit that supplies power to the forward rotation relay coil RC1, B4 is a rectification circuit that supplies power to the reverse rotation relay coil RC2, and the forward rotation relay coil RC1 and the reverse rotation relay coil RC2 are respectively connected in parallel. Capacitors C4 and C5 are connected. Resistor R3 and capacitor for capacitor C3
Resistors R1 and R2 are connected in series to C4 and C5, respectively, to suppress the inrush peak current during charging of capacitors C3, C4, and C5.

The gist of the present invention is to provide capacitors C3, C4, C5 for delaying the relay operation, and set the charge capacity of the capacitor C3 to C
By setting it larger than 4, C5, the AC power supply relay RL3 is operated after the forward rotation relay RL1 and reverse rotation relay RL2, and the opening / closing capacity of the forward rotation relay RL1 or reverse rotation relay RL2 is turned on and off when the power is turned on and off. This is to prevent the inrush current that exceeds it from flowing.

Next, the operation of the DC motor drive circuit will be described. Forward switch S with main switch SW1 closed
When W2 is closed, the start control relay coil RC4 is energized to instantly close the start control relay RL4, and the rectifier circuit B2 starts charging the capacitor C3. At the same time, rectifier circuit B3
Is turned on, charging of the capacitor C4 is started, and the capacitance is
Since C3> C4, the charging of the capacitor C4 is completed first, the normally-open contact of the forward rotation relay RL1 is closed before the AC power supply relay RL3, and then the AC power supply relay RL3 is closed.

Even when the reverse switch SW3 is closed, the start control relay RL4 is closed and the rectifier circuit B2 starts charging the capacitor C3. At the same time, the rectifier circuit B4 charges the capacitor C5 and the charging of the capacitor C5 is completed first. Then, the AC power relay RL3 closes after the normally open contact of the reverse rotation relay RL2 closes. In this way, since the direct-current relay RL1 or reverse relay RL2 on the DC side is closed before the AC power is turned on, no arc occurs at the contacts of the forward relay RL1 or reverse relay RL2, and the forward relay RL1 or reverse relay RL1 The switching capacity of relay RL2 does not matter.

When the forward rotation switch SW2 or the reverse rotation switch SW3 is turned off, the power supply to the start control relay coil RC4 is turned off and the contact of the start control relay RL4 is instantly opened, which causes the power supply to the AC power supply relay coil RC3. Is turned off, the contact of the AC power supply relay RL3 is opened, and the power supply to the DC motor M is cut off. After shutting off the AC power supply, the DC motor M continues to rotate due to inertia and generates counter electromotive force until it stops, but the forward rotation relay RL1 or reverse rotation relay RL2 is connected until the capacitor C4 or C5 is discharged after the AC power supply is cut off. After the discharge is completed, the normally open contact opens and the normally closed contact closes. As a result, the + power supply line and the −power supply line of the DC motor M are short-circuited through the normally closed contacts of the forward rotation relay RL1 and the reverse rotation relay RL2, and the DC motor M is electromagnetically braked.

In a circuit in which the AC power supply relay and the DC side relay are turned off at the same time, or in a circuit in which the power supply to the DC motor is cut off by the DC side relay, the maximum counter electromotive force flows at the moment when the normally closed contact is closed. It is necessary to use a relay with a large switching capacity and a short-circuit resistor so that the peak current during a short circuit does not exceed the switching capacity of the DC relay. On the other hand, in this circuit, the OFF timing of the forward rotation relay RL1 and the reverse rotation relay RL2 is set so that the DC side relay RL1 or RL2 opens after the DC motor speed decreases and the back electromotive force decreases. Delayed, the back electromotive force of the DC motor M drops below the switching capacity of the forward rotation relay RL1 and the reverse rotation relay RL2, and then the normally closed contacts of the forward rotation relay RL1 or reverse rotation relay RL2 are closed so that the capacitors C4, C5 are closed. By setting the capacities, the forward rotation relay RL1 and the reverse rotation relay RL2 can have small opening and closing capacities, and short-circuit resistance becomes unnecessary.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the technical scope of the present invention, and it is a matter of course that the present invention extends to those modifications. is there.

[0016]

As described above, in the DC motor drive circuit of the present invention, the DC side relay is closed before the AC side power supply relay is closed, and after the AC side power supply relay is opened, the DC side relay is opened with a delay. With this configuration, when the power is turned on, the switching capacity of the DC relay can be ignored, and the DC motor will be electromagnetically braked after the back electromotive force of the DC motor has dropped after the power was cut off. Smaller capacity relays can be used. Further, the DC motor braking circuit can be configured without using the short-circuit resistor for limiting the relay current, and various effects such as cost reduction, circuit miniaturization, and heat generation can be achieved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

[Explanation of symbols]

SW2 lift switch SW3 down switch RL1 Forward relay RC1 Forward relay coil RL2 Reverse rotation relay RC2 reversing relay coil RL3 AC power relay RC3 AC power supply relay coil RL4 start control relay RC4 start control relay coil B1 rectifier circuit B2 rectifier circuit B3 rectifier circuit B4 rectifier circuit C3 capacitor C4 capacitor C5 capacitor R1 resistance R2 resistance R3 resistance

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5H001 AA03 AC01 AC04 AC06 AD02                       AE01                 5H530 AA12 BB27 CC06 CC25 CD35                       CE13 DD04 DD19 EE07 EF03                 5H571 AA08 BB06 BB07 CC05 EE02                       FF02 HA04 HA16 HA20 LL23                       LL24 MM03

Claims (2)

[Claims] 1. A direct current motor drive circuit for controlling starting and stopping of a direct current motor by turning on and off an alternating current power supply relay and a direct current power supply relay after a rectifier with a switch, wherein a capacitor is connected in parallel to a direct current power supply relay coil, A capacitor having a larger capacity than the capacitor of the DC power relay circuit is connected in parallel to the AC power relay coil, and a start control relay is connected in series, and a switch for turning on / off the power of the DC power relay coil and the start control relay coil is provided,
When the switch is turned on, the AC power relay is closed after the DC power relay is closed due to the difference in the capacity of the capacitor, and the AC power relay is opened by opening the start control relay when the switch is opened, and then the capacitor in the DC power relay circuit is discharged. The DC motor drive circuit is characterized in that the DC power supply relay is opened. 2. The direct current motor drive circuit according to claim 1, wherein two direct current power source relays are combined to form a forward / reverse rotation switching circuit for the direct current motor.