Soft start universal delayer based on resistor and capacitor voltage reduction

Abstract

The invention discloses a soft start universal delayer based on resistor and capacitor voltage reduction. A first path of a 220V alternating current power supply is connected with a working ground through an R0 and an LEDA in sequence, and a second path of the 220V alternating current power supply is connected with the working ground through a normally open contact of an Re1, a normally open contact of an Re2 and a motor in sequence; r3, R4, R5 and R6 form a current-limiting resistor circuit, resistors R1 and R2 and capacitors C1 and C2 form a capacitor step-down circuit, and a third path of the 220V alternating-current power supply enters a pin 1 of a bridge rectifier B1 through a switch S1 and the capacitor step-down circuit in sequence; a pin 2 of the bridge rectifier B1 is connected with a pin 4 of the bridge rectifier B1 through a coil of a relay Re1 and a coil of a relay Re2 in sequence; the C4 and the C5 are connected in parallel, the C3 is connected in parallel with a coil of the Re1, the C4 and the C5 which are connected in parallel are connected in parallel with a coil of the Re2, and soft start of the motor is achieved through a resistance-capacitance circuit.

Description

Technical Field

[0001] The invention relates to a motor soft starting technology, in particular to a technology that uses common high-power resistors in series to achieve voltage reduction starting, forming a universal time delay circuit, thereby achieving soft starting. Background Art

[0002] The most commonly used in engineering projects are electric motors. Due to the starting characteristics of motors, when these motors are directly connected to the power supply system for starting (hard start), surge (impact) currents as high as 5 to 7 times the rated current of the motor will be generated, causing the power supply system and the series-connected switchgear to overload. On the other hand, direct starting will also produce higher peak torque, which will not only impact the drive motor, but also damage the mechanical device and affect the normal operation of other electrical equipment connected to the same power grid.

[0003] Soft start means that the voltage of the motor is gradually increased from zero to the rated voltage. In this way, the starting current of the motor during the starting process is controllable instead of the uncontrollable overload impact current in the past. The starting current can be adjusted as needed. There is no impact torque in the whole process of motor starting, but a smooth starting operation.

[0004] The soft start start modes are divided into the following categories: Current limiting starting: As the name implies, it limits the starting current of the motor. It is mainly used to reduce the starting voltage drop during light load starting.

[0005] Ramp voltage start: The voltage rises linearly from small to large. In this starting method, the starting voltage gradually increases in the initial stage of motor starting. When the voltage reaches the preset value, it remains constant until the starting is completed.

[0006] Torque control starting: The starting torque of the motor increases linearly from small to large. Its advantages are smooth starting, good flexibility, better protection for the traction system, extended service life of the traction system, and reduced impact on the power grid when the motor starts. It is the optimal heavy-load starting method. The disadvantage is that the starting time is long.

[0007] Torque plus jump control starting: Similar to torque control starting, it is also used for heavy load starting. The difference is that the jump torque is used to overcome the static torque of the motor at the moment of starting, and then the torque rises smoothly.

[0008] Voltage controlled starting: used in light load starting situations, it can maximize the starting torque of the motor while ensuring the starting voltage drop, shorten the starting time as much as possible, and is the optimal light load soft starting method.

[0009] The above-mentioned soft start methods each have their own characteristics, but the design circuits are relatively complex and the cost performance is not very high. In some construction environments, the power of the motor is not very high, such as below 4000W. A simpler soft start power-on delay circuit can be designed. This circuit uses two general relays in series to power the motor. The coils of the two relays are connected in parallel with capacitors of different capacities. The parallel capacitance of the first relay coil is very small, and the parallel capacitance of the second relay coil is very large.

[0010] When the switch is closed and powered on, the first relay is energized first due to the rapid charging of the capacitor to supply power to the motor, and there are several cheap high-power resistors in series in the power supply circuit, so the starting current is small and will not cause a large surge current; after a period of time, the large-capacity capacitor in parallel with the second relay coil is fully charged, the second relay is energized, and the energizing terminal of the second relay short-circuits all the above-mentioned high-power resistors, the motor is started, and enters normal operation.

[0011] The components used in this delay circuit are all cheap and commonly used equipment with small size. For example, the low voltage generated by capacitor charging does not use a large transformer but a compact capacitor to step down the voltage. The motor current limiting starting is achieved using a common high-power resistor in series. It is very low cost and has a high cost-performance ratio, but you must pay attention to safety. Summary of the invention

[0012] The technical problem to be solved by the present invention is to provide a motor soft start design technology which has a simple structure, reliable use and low cost.

[0013] To achieve the above-mentioned purpose, the present invention provides a soft-start universal delay circuit based on resistance and capacitor voltage reduction, which includes a 220V AC power supply, a power indicator circuit, a capacitor voltage reduction circuit, a rectifier circuit, a relay Re1, a relay Re1 coil power supply circuit, a relay Re2, a relay Re2 coil power supply circuit, a current limiting resistor circuit, and a motor circuit. The voltage reduction resistor R0 and the light-emitting diode LEDA constitute the power indicator circuit. The first path of the 220V AC power supply is connected to the working place through the resistor R0 and the light-emitting diode LEDA in sequence. As long as the 220V AC power supply is normally powered, the light-emitting diode LEDA is lit. The second path of the 220V AC power supply is connected to the working place through the normally open contact of the relay Re1, the normally open contact of the relay Re2, and the motor in sequence; the resistor R3, the resistor R4, the resistor R5, and the resistor R6 constitute the current limiting resistor circuit. The resistor R3, the resistor R4, the resistor R5, and the resistor R6 are connected in series across Connected to the two ends of the normally open contact of relay Re2; resistor R1, resistor R2, capacitor C1, and capacitor C2 constitute the capacitor step-down circuit, and the third path of the 220V AC power supply enters the rectifier circuit, i.e., pin 1 of the AC input terminal of bridge stack B1, through switch S1 and the capacitor step-down circuit in turn; pin 2 of the DC output terminal of bridge stack B1 is connected to pin 4 of the DC input terminal of bridge stack B1 through the coil of the relay Re1 and the coil of the relay Re2 in turn; at the same time, pin 2 of the DC output terminal of bridge stack B1 is connected to pin 4 of the DC input terminal of bridge stack B1 through the coil power supply circuit of the relay Re1, i.e., the forward electrolytic capacitor C3, and the coil power supply circuit of the relay Re2, i.e., the forward electrolytic capacitor C4 and the forward electrolytic capacitor C5 in turn, wherein the forward electrolytic capacitor C4 and the forward electrolytic capacitor C5 are connected in parallel, the forward electrolytic capacitor C3 is connected in parallel with the coil of the relay Re1, and the parallel forward electrolytic capacitors C4 and forward electrolytic capacitors C5 are connected in parallel with the coil of the relay Re2.

[0014] The parallel capacitance of the forward electrolytic capacitor C4 and the forward electrolytic capacitor C5 of the relay Re2 coil power supply circuit must be much larger than the capacitance of the forward electrolytic capacitor C3 of the relay Re1 coil power supply circuit to achieve the required motor delayed start function.

[0015] The capacitor step-down circuit, the 220V AC power supply is connected to the AC input terminal 1 of the rectifier circuit, i.e., the bridge stack B1, through the switch S1, the resistor R1, and the capacitor C1 in sequence. The capacitor C1, the capacitor C2, and the resistor R2 are connected in parallel. The capacitance of the parallel capacitors C1 and C2 needs to be appropriately adjusted with the different power frequency voltages and the different power frequency to obtain a suitable back-end circuit working voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Attached Figure 1 , Attachment Figure 2 , Attachment Figure 3It is used to provide a further understanding of the present invention and constitutes a part of this application. Figure 1 This is the principle diagram of the soft start universal delay device based on RC voltage reduction; Figure 2 It is a typical capacitor step-down voltage stabilization circuit; Figure 3 It is a full-wave rectifier capacitor step-down voltage stabilization circuit. DETAILED DESCRIPTION

[0017] The following further describes the embodiments of the present invention in conjunction with the accompanying drawings. First, the working principle of capacitor voltage reduction is briefly introduced to better understand the innovation of the present invention.

[0018] Capacitor step-down circuit If the low voltage control circuit does not have strict requirements on the constants of the power supply, it can be used Figure 1 The capacitor step-down power supply shown is a typical capacitor step-down voltage stabilization circuit.

[0019] The RC step-down circuit achieves voltage reduction by using a resistor and a capacitor in parallel. Under normal circumstances, the selected resistance value should be determined according to the ratio between the input voltage and the output voltage. Specifically, if the input voltage Vin needs to be stepped down to the output voltage Vout, the required resistance value R can be calculated by the following formula:

[0020] Where X C is the impedance value of the capacitor, which can be calculated based on the selected capacitor and operating frequency. It should be noted that the selected resistor power must be greater than the circuit output power, otherwise the resistor will fail due to overheating.

[0021] The basic principle of capacitor voltage reduction is: because the capacitor has capacitive reactance in AC, it can be approximately equivalent to a voltage-reducing resistor, and its impedance is given by the formula X C =1 / 2πfC1, the AC frequency f of the mains is 50Hz.

[0022] According to Ohm's law I=U / X, we can get the empirical formula I=69080*C1 The unit of C1 is farad (F) and the unit of I is ampere (A).

[0023] The load current capability of the capacitor step-down shown is only related to the capacitance of the capacitor. In fact, this is also determined by the rectification characteristics of the capacitor. The step-down capacitor can be selected based on this formula.

[0024] Figure 2The working process is: C1 is charged through D1 in the negative half cycle of the AC input, which enables the positive half cycle of the input AC to be forward charged to the load and filter capacitor C2 through C1 and the rectifier diode D2. The simple diode parallel voltage stabilization used here.

[0025] It can be seen that the rectification after capacitor voltage reduction is half-wave rectification. Figure 3 The capacitor step-down circuit shown uses a bridge rectifier circuit of D1~D4, so it belongs to full-wave rectification. It can be seen that the rectification efficiency of this circuit is higher than Figure 2 , so when using step-down capacitors of the same capacity, their short-circuit output current is tested. Figure 3 The circuit is Figure 2 Twice the circuit.

[0026] If you let Figure 2 , Figure 3 When the load is open, the stabilizing current of the capacitor will obviously flow through the voltage regulator. Therefore, the biggest weakness of this circuit is that the voltage regulator is often burned out. When selecting the voltage regulator DW, its dissipated power P should be greater than I C *V Z (I C is the capacitor rectifier current, V Z is the stable voltage of the Zener diode).

[0027] Working principle of soft start universal delay device based on RC voltage reduction exist Figure 1 Capacitor step-down circuit in the circuit Figure 3 The full-wave rectifier capacitor step-down voltage regulator circuit shown is slightly different. Figure 1 The capacitor step-down circuit does not require voltage stabilization and does not need to consider the reverse breakdown of the voltage regulator diode, so the capacitor step-down circuit is more stable at this time.

[0028] Capacitors R1, R2, C1, and C2 form a capacitor step-down circuit, which enables the full-wave rectifier bridge stack B1 to output a 48V DC voltage. The capacitance of C1 and C2 needs to be adjusted appropriately with the power frequency voltage and power frequency (see the table at the end of this article). The working coils of relays Re1 and Re2 are connected in series between the DC output and DC input terminals of the bridge stack B1, and the current passing through the coils is 27mA. B1 uses a rectifier bridge stack with a reverse voltage of 380V and a current of 1.5A.

[0029] Although the relay coil itself has no positive or negative distinction, you need to pay attention to its connection method in actual use. Generally speaking, the two ends of the relay coil need to be connected to the power supply and control signal pins (or working ground) respectively to ensure the normal operation of the relay.

[0030] Specifically, one end of the relay coil needs to be connected to the positive pole of the power supply, and the other end needs to be connected to the control signal pin or ground. When the relay is working normally, the control signal will be input into the relay through the pin, stimulating the electromagnetic induction of the coil, thereby completing the closing or opening of the switch. When the control signal is disconnected, the relay returns to its original state and the switch returns to the open state.

[0031] The coil of relay Re1 is connected in parallel with electrolytic capacitor C3, and the coil of relay Re2 is connected in parallel with electrolytic capacitors C4 and C5, and C4 and C5 are connected in parallel. Pay attention to the polarity of the electrolytic capacitors. Once the two contacts of relay Re1 are combined, the power frequency voltage will be sent to the contacts of relay Re2. Four 100W / 10Ω step-down resistors R3~R6 are connected in series across the two contacts of Re2. The rated current of the relay is about 16A.

[0032] Since the capacity of the capacitor (C4+C5) in parallel with the coil of Re2 is much larger than the capacitor C3 in parallel with the coil of Re1, when the power switch S1 is turned on, the electrolytic capacitor C3 in parallel with the relay Re1 is fully charged first, and Re1 is turned on first. At this time, the live wire of the power supply supplies power to the motor through the step-down resistors R3~R6. Since the step-down resistors also play a current limiting role, the starting current of the motor is limited to less than 8A (power supply voltage 240V AC), and the motor soft start begins.

[0033] After a period of time, the parallel electrolytic capacitors C4 and C5 are fully charged to about 12V, the relay Re2 is turned on, the voltage-reducing resistors R3~R6 are short-circuited and no longer play a voltage-reducing role, and the power supply voltage is fully added to the motor, so the motor soft start ends and the motor enters normal operation.

[0034] LEDA is the power indicator light, and the series resistor R0 is connected across the industrial frequency power supply.

[0035] Production and precautions Changing the capacity of electrolytic capacitors C4 and C5 can adjust the length of the delay, but if the capacity is too large, the leakage current will increase accordingly, and the required delay will not be achieved.

[0036] Also note that the 100W / 10Ω drop resistors R3~R6 consume about 2000W (total power consumption) when limiting the inrush current to about 5A. Therefore, if you want to increase the delay, you must replace them with drop resistors with higher wattage, because longer delays will cause the drop resistors R3~R6 to heat up more and more, which may cause damage to the drop resistors, resulting in additional losses. In other words, the shorter the delay start time, the smaller the wattage of the resistors R3~R6 can be, and vice versa, the larger the wattage needs to be, and the resistance value can remain unchanged at 10Ω.

[0037] If conditions permit, a heat sink can be installed for the R3~R6 resistors, which can provide a longer delay and is also safer and has a longer service life.

[0038] As for the cost of 100W / 10Ω step-down resistor, it is not high. According to the online shopping mall, the price of a 100W gold aluminum shell winding high-power resistor is only about RMB 5, so the solution of using four step-down resistors to reduce the starting current is more cost-effective.

[0039] In addition, the parameter selection of the resistor R1, and the capacitors C1 and C2 in the capacitor step-down circuit is also very important. With the different power voltage and power frequency, their parameters will change slightly, and some components may not even be needed. As shown in Table 1.

[0040] Table 1 Parameter selection of resistor R1, capacitor C1, C2

[0041] This design has three innovative points. The first is to use capacitor voltage reduction to generate low voltage. The second is to use the capacitor charging terminal voltage to power the relay coil, so the difference in capacitor capacity can adjust the delay time. The third is that the motor circuit uses a voltage-dropping resistor to start the motor with current limiting.

[0042] Warning: This circuit contains voltages that are lethal. Do not touch or adjust the circuit while it is powered on.

[0043] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A soft start universal delay device based on resistor and capacitor voltage reduction, characterized in that: The soft start universal delay device includes a 220V AC power supply, a power indicator circuit, a capacitor step-down circuit, a rectifier circuit, a relay Re1, a relay Re1 coil power supply circuit, a relay Re2, a relay Re2 coil power supply circuit, a current limiting resistor circuit, and a motor circuit. The step-down resistor R0 and the light-emitting diode LEDA constitute the power indicator circuit. The first path of the 220V AC power supply is connected to the working place through the resistor R0 and the light-emitting diode LEDA in sequence. As long as the 220V AC power supply is normally powered, the light-emitting diode LEDA will light up. The second path of the 220V AC power supply is connected to the working place through the normally open contact of the relay Re1, the normally open contact of the relay Re2, and the motor in sequence; the resistor R3, the resistor R4, the resistor R5, and the resistor R6 constitute the current limiting resistor circuit. The resistors R3, the resistor R4, the resistor R5, and the resistor R6 are connected in series in sequence across the normally open contact of the relay Re2. Two ends; resistor R1, resistor R2, capacitor C1, capacitor C2 constitute the capacitor step-down circuit, the third path of the 220V AC power supply sequentially passes through switch S1 and the capacitor step-down circuit to enter the rectifier circuit, i.e., pin 1 of the AC input terminal of the bridge stack B1; pin 2 of the DC output terminal of the bridge stack B1 is sequentially connected to pin 4 of the DC input terminal of the bridge stack B1 through the coil of the relay Re1 and the coil of the relay Re2; at the same time, pin 2 of the DC output terminal of the bridge stack B1 is sequentially connected to pin 4 of the DC input terminal of the bridge stack B1 through the relay Re1 coil power supply circuit, i.e., the forward electrolytic capacitor C3, the relay Re2 coil power supply circuit, i.e., the forward electrolytic capacitor C4 and the forward electrolytic capacitor C5, wherein the forward electrolytic capacitor C4 and the forward electrolytic capacitor C5 are connected in parallel, the forward electrolytic capacitor C3 is connected in parallel with the coil of the relay Re1, and the parallel forward electrolytic capacitors C4 and forward electrolytic capacitors C5 are connected in parallel with the coil of the relay Re2.

2. A soft start universal delay device based on resistance and capacitance voltage reduction according to claim 1, characterized in that: The parallel capacitance of the forward electrolytic capacitor C4 and the forward electrolytic capacitor C5 of the relay Re2 coil power supply circuit must be much larger than the capacitance of the forward electrolytic capacitor C3 of the relay Re1 coil power supply circuit to achieve the required motor delayed start function.

3. A soft start universal delay device based on resistance and capacitance voltage reduction according to claim 1, characterized in that: The capacitor step-down circuit, the 220V AC power supply is connected to the AC input terminal 1 of the rectifier circuit, i.e., the bridge stack B1, through the switch S1, the resistor R1, and the capacitor C1 in sequence. The capacitor C1, the capacitor C2, and the resistor R2 are connected in parallel. The capacitance of the parallel capacitors C1 and C2 needs to be appropriately adjusted with the different power frequency voltages and the different power frequency to obtain a suitable back-end circuit working voltage.

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