Soft start universal delayer based on resistor and capacitor voltage reduction
The soft-start universal delay circuit, which uses resistors and capacitors to reduce voltage, utilizes a series and parallel structure of relays and capacitors to achieve smooth motor starting, avoids surge current and impact torque, simplifies the circuit structure, and reduces costs.
Patent Information
- Application Number
- CN202421937915.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-12
- Publication Date
- 2026-01-13
- Estimated Expiration
- 2034-08-12
AI Technical Summary
Existing motors generate high surge currents and impact torques during startup, which can damage the power supply system and mechanical devices, and also affect the normal operation of other equipment on the power grid. Furthermore, existing soft-start methods have complex circuits and are not cost-effective.
A general-purpose soft-start delay circuit using resistors and capacitors for voltage reduction utilizes a series-parallel structure of relays and capacitors. The delayed start of the motor is achieved by charging the capacitor, while a high-power resistor limits the starting current. The capacitor capacity adjusts the delay time, and the resistor achieves current limiting and voltage reduction.
It achieves smooth motor start-up, avoids surge current and impact torque, simplifies circuit structure, reduces cost, and improves cost-effectiveness.
Smart Images
Figure CN223798144U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to a technology for soft starting a motor, and more particularly to a method that uses common high-power resistors in series to achieve reduced voltage starting, forming a general-purpose delay circuit, thereby realizing soft starting. Background Technology
[0002] The most commonly used motor in engineering is the electric motor. Due to the starting characteristics of the motor, when these motors are directly connected to the power supply system for starting (hard start), they will generate surge (impact) currents as high as 5 to 7 times the rated current of the motor, causing overload of the power supply system and series-connected switching equipment. On the other hand, direct start will also generate high peak torque. This impact will not only affect the drive motor, but also damage the mechanical device, and will also affect the normal operation of other electrical equipment connected to the same power grid.
[0003] Soft start refers to gradually increasing the motor voltage from zero to the rated voltage. In this way, the starting current of the motor during the starting process changes from the previously uncontrollable overload inrush current to a controllable one, and the magnitude of the starting current can be adjusted as needed. There is no impact torque during the entire motor starting process, and the motor starts and runs smoothly.
[0004] The soft boot methods are divided into the following types:
[0005] Current-limiting start: As the name suggests, it limits the starting current of the motor. It is mainly used to reduce the starting voltage drop when starting a light load.
[0006] Ramp voltage start: The voltage increases linearly from low to high. In this starting method, the starting voltage gradually increases in the initial stage of motor startup. Once the voltage reaches the preset value, it remains constant until startup is complete.
[0007] Torque control starting: The starting torque of the motor increases linearly from small to large. Its advantages are smooth starting, good flexibility, better protection of the drive system, extension of the service life of the drive system, and reduction of the 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 relatively long.
[0008] Torque-plus-jump start: Similar to torque control start, it is also used for heavy-load start. The difference is that a sudden torque jump is used to overcome the motor's static torque at the moment of start-up, and then the torque rises smoothly.
[0009] Voltage-controlled starting: Used in light-load starting situations, it maximizes the starting torque of the motor while ensuring the starting voltage drop and minimizes the starting time, making it the optimal light-load soft-start method.
[0010] The above-mentioned soft-start methods each have their own characteristics, but the circuit design is relatively complex and the cost-effectiveness 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-purpose relays connected in series to power the motor. The coils of the two relays are connected in parallel with capacitors of different capacities. The capacitor connected in parallel with the coil of the first relay has a very small capacity, while the capacitor connected in parallel with the coil of the second relay has a very large capacity.
[0011] When the circuit is closed and powered on, the first relay is the first to engage due to the rapid charging of the capacitor, which powers the motor. Since the power supply circuit has several inexpensive high-power resistors in series, the starting current is small and will not cause a large surge current. After a period of time, the large-capacity capacitor connected in parallel with the coil of the second relay is fully charged, and the second relay engages. The engagement terminal of the second relay short-circuits all the aforementioned high-power resistors, and the motor starts and enters normal operation.
[0012] The components used in this type of delay circuit are inexpensive and commonly used, and are small in size. For example, the low voltage generated by capacitor charging does not use a large transformer but a small capacitor to step down the voltage. The current limiting start of the motor is achieved by using common high-power resistors in series. The cost is very low and the cost performance is high, but safety should be taken into account. Summary of the Invention
[0013] The technical problem to be solved by this utility model is to provide a motor soft-start design technology that is simple in structure, reliable in use, and low in cost.
[0014] To achieve the above objectives, this utility model provides a soft-start universal delay circuit based on resistor and capacitor voltage reduction, comprising 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. One end of the 220V AC power supply is connected to the other end of the 220V AC power supply via a first channel, sequentially through resistor R0 and the light-emitting diode LEDA. As long as the 220V AC power supply is supplying power normally, the light-emitting diode LEDA will light up. The other end of the 220V AC power supply is connected to the other end of the 220V AC power supply via a second channel, sequentially through the normally open contact of relay Re1, the normally open contact of relay Re2, and the motor. Resistors R3, R4, R5, and R6 constitute the current-limiting resistor circuit. The normally open contacts of relay Re2 are connected in series across them. Resistors R1 and R2, capacitors C1 and C2 constitute the capacitor step-down circuit, and bridge rectifier B1 constitutes the rectifier circuit. One end of the 220V AC power supply is connected to pin 1 of bridge rectifier B1 via switch S1 and the capacitor step-down circuit along the third channel. Pin 3 of bridge rectifier B1 is connected to the other end of the 220V AC power supply. Pin 2 of the DC output terminal of bridge rectifier B1 is connected to pin 4 of the DC input terminal of bridge rectifier B1 via the coils of relay Re1 and Re2. Simultaneously, pin 2 of the DC output terminal of bridge rectifier B1 is connected to pin 4 of the DC input terminal of bridge rectifier B1 via the power supply circuit of relay Re1 (i.e., forward electrolytic capacitor C3), the power supply circuit of relay Re2 (i.e., forward electrolytic capacitor C4 and forward electrolytic capacitor C5), where forward electrolytic capacitors C4 and C5... The forward electrolytic capacitor C3 is connected in parallel with the coil of the relay Re1, and the forward electrolytic capacitors C4 and C5 are connected in parallel with the coil of the relay Re2.
[0015] The parallel capacitance of the forward electrolytic capacitors C4 and C5 in the relay Re2 coil power supply circuit must be much larger than the capacitance of the forward electrolytic capacitor C3 in the relay Re1 coil power supply circuit in order to achieve the required motor delayed start function.
[0016] The 220V AC power supply is connected to pin 1 of bridge rectifier B1 via switch S1, resistor R1, and capacitor C1 along the third channel to form the capacitor step-down circuit. Capacitors C1, C2, and resistor R2 are connected in parallel. The capacitance of capacitors C1 and C2 in parallel needs to be adjusted appropriately according to different power frequency voltages and frequencies to obtain a suitable operating voltage for the downstream circuit. Attached Figure Description
[0017] Appendix Figure 1 Appendix Figure 2 Appendix Figure 3 This document, attached to provide a further understanding of the present invention, forms part of this application. Figure 1 This is a schematic diagram of a general-purpose soft-start delay circuit based on resistor-capacitor voltage reduction; attached. Figure 2 It is a typical capacitor-based step-down voltage regulator circuit; (Attached) Figure 3 It is a full-wave rectifier capacitor step-down voltage regulator circuit. Detailed Implementation
[0018] The embodiments of this utility model are further described below with reference to the accompanying drawings.
[0019] First, we will briefly introduce the working principle of capacitor voltage reduction to better understand the innovation of this invention.
[0020] Capacitor step-down circuit
[0021] If the low-voltage control circuit does not have strict requirements on the constants of the power supply, it can adopt... Figure 1 The capacitor-based step-down power supply shown is a typical capacitor-based step-down voltage regulator circuit.
[0022] A resistor-capacitor (RC) step-down circuit reduces voltage by using a resistor and capacitor connected in parallel. Normally, the resistor value should be determined based on the ratio between the input and output voltages. Specifically, if the input voltage Vin needs to be stepped down to the output voltage Vout, the required resistor value R can be calculated using the following formula:
[0023]
[0024] Where X C The impedance value of the capacitor can be calculated based on the selected capacitor and the operating frequency. It is important to note that the selected resistor's power rating must be greater than the circuit's output power; otherwise, the resistor may overheat and fail.
[0025] The basic principle of capacitor voltage reduction is: because a capacitor has capacitive reactance in alternating current, it can be approximately equivalent to a voltage-reducing resistor, and its impedance is given by the formula X. C =1 / 2πfC1 is determined, and the AC frequency f is 50Hz.
[0026] Furthermore, based on Ohm's law I=U / X, an empirical formula can be obtained.
[0027] I=69080*C1
[0028] The unit of C1 is fa (F), and the unit of I is ampere (A).
[0029] The load current capability of the capacitor step-down shown is only related to the capacitance, which is actually determined by the rectification characteristics of the capacitor. The step-down capacitor can be selected based on this formula.
[0030] Figure 2 The working process is as follows: During the negative half-cycle of the mains input, C1 is charged through D1, which enables the positive half-cycle of the mains input to charge the load and filter capacitor C2 in the forward direction through C1 and rectifier diode D2. A simple diode parallel voltage regulator is used here.
[0031] It can be seen that the rectification after capacitor voltage reduction is half-wave rectification. Figure 3 The capacitor-based step-down circuit shown uses a bridge rectifier circuit with diodes D1 to D4, therefore it is a full-wave rectifier. It can be seen that the rectification efficiency of this circuit is higher than... Figure 2 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 size of the circuit.
[0032] If let Figure 2 , Figure 3 When operating with an open load, the capacitor's stabilizing current will obviously flow entirely through the Zener diode. Therefore, the biggest weakness of this circuit is that the Zener diode often burns out. When selecting a Zener diode (DW), its power dissipation P should be greater than I. C *V Z (where I) C The rectified current of the capacitor is V. Z (This refers to the stable voltage of the Zener diode).
[0033] Working principle of a soft-start universal delay circuit based on resistor-capacitor voltage reduction
[0034] exist Figure 1 The capacitor step-down circuit in the circuit and Figure 3 The full-wave rectifier capacitor buck regulator circuit shown is slightly different. Figure 1 The capacitor step-down circuit does not require voltage regulation and does not need to consider the reverse breakdown of the Zener diode, so the capacitor step-down circuit is more stable in this case.
[0035] Capacitors R1, R2, C1, and C2 form a capacitor-based step-down circuit, enabling the full-wave rectifier bridge B1 to output a 48V DC voltage. The capacitances of C1 and C2 need to be adjusted appropriately depending on the power frequency and voltage level (see the table at the end of this document). The coils of relays Re1 and Re2 are connected in series between the DC output and input terminals of bridge rectifier B1, with a current of 27mA flowing through the coils. B1 uses a rectifier bridge with a reverse voltage of 380V and a current of 1.5A.
[0036] Although relay coils themselves do not have positive and negative polarities, attention must be paid to their 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 ground) respectively to ensure the normal operation of the relay.
[0037] Specifically, one end of the relay coil needs to be connected to the positive terminal 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, which will stimulate 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.
[0038] Electrolytic capacitor C3 is connected in parallel to the coil of relay Re1, and electrolytic capacitors C4 and C5 are connected in parallel to the coil of relay Re2, with C4 and C5 in parallel. Note the polarity of the electrolytic capacitors. Once the two contacts of relay Re1 are closed, 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.
[0039] Since the capacitance of the capacitor (C4+C5) in parallel with the coil of Re2 is much larger than that of 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 supplies power to the motor through the step-down resistors R3~R6. Since the step-down resistors also act as current limiters, the starting current of the motor is limited to below 8A (power supply voltage 240V AC), and the motor soft start begins.
[0040] After a period of time, the parallel electrolytic capacitors C4 and C5 are fully charged to about 48V. Relay Re2 is turned on, and the step-down resistors R3~R6 are short-circuited and no longer play a step-down role. The power supply voltage is fully applied to the motor, so the soft start of the motor ends and the motor enters normal operation.
[0041] LEDA is a power indicator light, and a series resistor R0 is connected across the two ends of the mains power supply.
[0042] Production and Precautions
[0043] Changing the capacitance of electrolytic capacitors C4 and C5 can adjust the delay length, but if the capacitance is too large, the leakage current will also increase accordingly, and the required delay will not be achieved.
[0044] It's also important to note that when the 100W / 10Ω step-down resistors R3~R6 limit the inrush current to around 5A, the power consumption already reaches approximately 2000W (total power consumption). Therefore, if you want to increase the delay, you must replace them with step-down resistors of a higher wattage. This is because a longer delay will cause the step-down resistors R3~R6 to heat up more and more, potentially damaging them and causing additional losses. In other words, the shorter the delay start-up time, the smaller the wattage of the resistors R3~R6 can be, and vice versa. The resistance value can remain unchanged at 10Ω.
[0045] If possible, heat sinks can be installed on resistors R3 to R6 to provide a longer delay time, while also making it safer and extending the lifespan of the delay unit.
[0046] As for the cost of the 100W / 10Ω step-down resistor, it is not high. According to online stores, a 100W gold aluminum wire-wound high-power resistor costs only about 5 RMB. Therefore, the solution of using four step-down resistors to reduce the starting current is cost-effective.
[0047] In addition, the selection of parameters for resistor R1 and capacitors C1 and C2 in the capacitor step-down circuit is also very important. Their parameters vary slightly depending on the power frequency voltage and frequency, and some components may even be unnecessary. As shown in Table 1.
[0048] Table 1. Parameter selection for resistor R1, capacitor C1, and capacitor C2
[0049]
[0050] The innovations of this design are threefold: first, it uses a capacitor to reduce voltage to generate low voltage; second, it uses the voltage at the capacitor charging terminal to power the relay coil, and different capacitor capacities can adjust the delay time; and third, it uses a step-down resistor in the motor circuit to achieve current-limited motor starting.
[0051] Warning: This circuit carries a potentially lethal voltage. Do not touch or adjust the circuit while it is powered on.
[0052] The above embodiments are only used to illustrate and not limit the technical solutions of this utility model. Although the utility model has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the utility model without departing from the spirit and scope of the utility model. Any modifications or partial substitutions should be covered within the scope of the claims of this utility model.
Claims
1. A soft-start universal delay circuit based on resistor and capacitor voltage reduction, characterized in that: The soft-start universal delay circuit 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. One end of the 220V AC power supply is connected to the other end of the 220V AC power supply via a first channel, passing through resistor R0 and the light-emitting diode LEDA. As long as the 220V AC power supply is supplying power normally, the light-emitting diode LEDA will light up. The other end of the 220V AC power supply is connected to the other end of the 220V AC power supply via a second channel, passing through the normally open contact of relay Re1 and relay Re2. The normally open contact of the relay Re2 is connected to the other end of the 220V AC power supply. Resistors R3, R4, R5, and R6 constitute the current-limiting resistor circuit, and are connected in series across the two ends of the normally open contact of the relay Re2. Resistors R1 and R2, capacitors C1 and C2 constitute the capacitor step-down circuit, and bridge rectifier B1 constitutes the rectifier circuit. One end of the 220V AC power supply is connected to pin 1 of bridge rectifier B1 via switch S1 and the capacitor step-down circuit along the third channel. Pin 3 of bridge rectifier B1 is connected to the other end of the 220V AC power supply. Pin 2 of the DC output terminal of bridge rectifier B1 is connected to the relay Re1 via... The coil of the relay Re1 and the coil of the relay Re2 are connected to pin 4 of the DC input terminal of the bridge rectifier B1. At the same time, pin 2 of the DC output terminal of the bridge rectifier B1 is connected to pin 4 of the DC input terminal of the bridge rectifier B1 in sequence through the power supply circuit of the relay Re1 coil (i.e., the forward electrolytic capacitor C3), the power supply circuit of the relay Re2 coil (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 C5 are connected in parallel with the coil of the relay Re2.
2. The universal soft-start delay circuit based on resistor and capacitor voltage reduction according to claim 1, characterized in that, The 220V AC power supply is connected to pin 1 of bridge rectifier B1 via switch S1, resistor R1, and capacitor C1 in sequence along the third channel to form the capacitor step-down circuit. Capacitor C1, capacitor C2, and resistor R2 are connected in parallel. The capacitance of capacitors C1 and C2 in parallel needs to be adjusted appropriately according to different power frequency voltages and frequencies to obtain a suitable operating voltage for the back-end circuit.