Solid state soft starters (SSRVs) are designed to reduce the damaging effects of surge currents that cause mechanical stress in equipment and system components. At ABB Inc. The main emphasis is on expanding the functions of “soft” starters, which can also be used as motor protective shutdown devices. The operation of such starters is based on monitoring the motor current, voltage and temperature. A new approach to solving the problem is to smoothly increase the torque, rather than the voltage on the motor. The soft starter calculates the real stator power, its losses, etc. as a result, the actual power transferred to the rotor. It is important that the motor torque no longer depends directly on the voltage supplied to the motor or on its mechanical characteristics. The increase in torque occurs in accordance with the timed acceleration schedule. Low-voltage “soft” starters from Eaton (S752. Circuits for TS106-10 SB01 and S811) use voltage with pulse-width modulation (PWM) with an amplitude of 24 V to control the contactor winding. At the same time, in steady state, the device consumes only 5 W. Danfoss Ci-tronic motor management devices cover a range of up to 20 kW (depending on input voltage). The smallest soft starter module MCI-3 is only 22.5 mm wide. The MCI-15 module is designed to operate with a motor with a power of up to 7.5 kW at a voltage of 480 V. An important characteristic of SSRV starters is the smooth stop of the motor. ABB's PST Series soft starters include a plain text HMI to easily set soft stops for centrifugal pumps, crushers, agitators and the like. The devices continuously monitor engine torque to determine...

For the diagram "Device for protecting the electric motor from overheating"

Protection of electric motors from overcurrent is carried out by thermal relays built into magnetic starters. In practice, there are cases of failure due to overheating at the rated current value, at elevated ambient temperatures or difficult heat exchange conditions, and the thermal relays do not operate. ...

For the diagram "Soft starting device for power tools"

Failures of hand-held power tools that sometimes occur - grinders, electric drills and jigsaws - are often associated with their high starting current and significant dynamic loads on gearbox parts that occur when the engine starts abruptly. Soft start device collector The electric motor described in has a complex circuit, it contains several precision resistors and requires painstaking setup. By using the KR1182PM1 phase regulator microcircuit, it was possible to produce a much simpler device for a similar purpose that does not require setup. You can connect to it without any modification any hand-held power tool powered by a single-phase 220 V, 50 Hz network. Start and stopping the engine are carried out by the power tool switch, and in its off state the device does not consume current and can remain connected to the network indefinitely. Scheme The proposed device is shown in the figure. The XP1 plug is plugged into the power socket, and the power tool's power plug is inserted into the XS1 socket. T160 current regulator circuit You can install and connect in parallel several sockets for tools that operate one after the other. When the power tool motor circuit is closed by its own switch, voltage is supplied to the phase regulator DA1. Capacitor C2 begins to charge, and the voltage across it gradually increases. As a result, the delay in turning on the internal thyristors of the regulator, and with them the VSI triac, in each subsequent half-cycle of the mains voltage decreases, which leads to a smooth increase in the current flowing through the motor and, as a result, an increase in its speed. With the capacitance of capacitor C2 indicated in the diagram, acceleration to maximum speed takes 2...2.5 s, which practically does not create a delay in operation, but completely eliminates thermal...

For the "Thrinistor regulator" circuit

The proposed thyristor power regulator (Fig. 1), specifically designed for controlling a commutator electric motor (electric drill, fan, etc.). has some features. Firstly, an electric motor with a power thyristor is included in one of the diagonals of the rectifier bridge, and mains voltage is applied to the other. In addition, the same thyristor is controlled not by short pulses, as in traditional devices, but by wider ones, due to which short-term load outages, characteristic of a running electric motor, do not affect the stability of the regulator. A generator of short (fractions of milliseconds) positive pulses is assembled on a unijunction transistor , used to control the auxiliary thyristor VS1. The generator is powered by trapezoidal voltage, obtained by limiting the positive half-waves of the sinusoidal voltage with a frequency of 100 Hz by the Zener diode VD1. A simple thermostat on a triac With the appearance of each half-wave of this voltage, capacitor C1 begins to charge through a circuit of resistors R1 R3. The charging speed of the capacitor can be adjusted within certain limits by a variable resistor R1. As soon as the voltage on the capacitor reaches the threshold of the transistor (it depends on the voltage at the bases of the transistor and can be adjusted by resistors R4 and R5), a positive pulse appears on resistor R5, which then goes to the control electrode of the thyristor VS1. This trinistor opens, and a longer (compared to the control) pulse that appears on resistor R6 turns on the power trinistor VS2. Through it, the supply voltage is supplied to the electric motor M1. The opening moment of the control and power thyristors, and therefore the power on the load (in other words, the rotational speed of the electric motor shaft) is controlled by a variable resistor R1. Since an inductive load is included in the anode circuit of the thyristor VS2,...

For the diagram "THREE-PHASE MOTOR IN A SINGLE-PHASE NETWORK"

Household electronicsTHREE-PHASE MOTOR IN A SINGLE-PHASE NETWORK. BASHKATOV, 338046, Ukraine, Donetsk region, Gorlovka-46, Kirova St., 14 A -42 Sometimes at home there is a need to connect a three-phase electric motor alternating current into a single-phase network. The same need arose for me when connecting an industrial sewing machine. In a garment factory, such machines operate in a workshop that has a three-phase network, and no problems arise. The first thing I had to do was change the winding connection diagram electric motor from star to delta, observing the polarity of the winding connection (beginning - end) (Fig. 1). This switching allows you to turn on the electric motor in a single-phase 220 V network. The power of the sewing machine according to the plate is 0.4 kW. Purchasing working, and even more so starting, metal-paper capacitors of the MBGO, MBGP, MBGCh type with a capacity of 50 and 100 microfarads, respectively, for an operating voltage of 450...600 V turned out to be an impossible task due to their high cost on the flea market. Automatic shutdown of radio equipment Using instead of metal-paper polar (electrolytic) capacitors and powerful rectifier diodes D242, D246. did not give a positive result. The electric motor stubbornly did not start, apparently due to the finite resistance of the diodes in the forward direction. That’s why the idea of ​​launching something that seemed absurd at first glance came to mind. electric motor using a short-term connection of a conventional electrolytic capacitor to an alternating current network (Fig. 2). After startup (overclocking) electric motor the electrolytic capacitor is turned off and the electric motor operates in two-phase mode, losing up to 50% of its power. But if you provide for a supply of power ahead of time, or it is known that such a supply exists (as in my case), then you can come to terms with this drawback. By the way, and during work electric motor with a working phase-shifting capacitor, the electric motor also loses up to 50%...

For the circuit "Short-circuited turns meter"

Measuring equipmentShort-circuited turns meter Short-circuited turns in the coils of a line transformer, in deflection coils, etc. are very difficult to detect. For these purposes, you can use a short-circuited turns meter, the principle is scheme which is shown in the figure. Transistor T1, together with coil L1 and capacitors C1, C2, forms a generator with capacitive feedback. Transistor T2 contains a voltmeter that measures the amplitude of the generated signal. Resistor R7 restrains the current value of transistor T2. When connecting a working coil to the input of the meter, the readings of the measuring device should practically not change. If the coil has short-circuited turns, the quality factor of the oscillating circuit decreases and the instrument readings will decrease. Triac TS112 and circuits on it The procedure for setting up the meter is as follows. Before turning it on, the variable resistor R2 slider is set to the bottom position according to the diagram. Then turn on the power. The current value should be about 0.1 mA. By moving the variable resistor slider up. achieve self-excitation of the generator. In this case, the collector current of the transistor will increase abruptly to approximately 0.4 mA. When the input jacks are short-circuited, the oscillations should be interrupted (this will be indicated by a decrease in the milliammeter readings). The sensitivity of the device is checked by creating short-circuited turns on a working coil. Transistors of the KT312 type can be used in the meter. KT315."Radio Electronics" (USA). 1-74. ...

For the "Smooth brightness switch" circuit

A smooth brightness switch (SBD) is a self-powered device designed for integration into various crafts, for example, as an original light-color indicator of the power on. In the author's version, the PPYA is built into a stand for a toy Christmas tree. The power supply of the PPY is turned on when a “bag with gifts”, in which there is a permanent magnet, is installed on a stand (behind the trunk of a toy Christmas tree). The magnet closes the contacts of the reed switch, and the PPY remains on until the bag is moved to another location on the stand (on the side or in front of the tree trunk). PPYA (Fig. 1) consists of: - resistive voltage divider R1-R2; - sawtooth voltage generator on elements DA1.1, DA1.2, R4...R6, C1; - analog inverter based on DA1.3 elements. R7, R8; - current amplifiers on field-effect transistors VT1 and VT2; - LEDs with ballast resistors HL1. R9 and HL2, R10. When the reed switch SF1 is closed, the battery voltage GB1 is supplied to the voltage divider R1-R2, at the midpoint of which half the supply voltage is set, providing the operating points of the operational amplifiers DA1.1, DA1.2, DA1.3. Soldering iron underheating circuit Capacitor C1, periodically recharging, ensures a smooth increase and decrease in voltage at the output (pin 1) of DA1.1, which ensures control of the operation of VT2. From output DA1.1, the signal is also supplied to the analog inverter (inverting amplifier with unity gain) DA1.3 and from this output (pin 8), a 180° phase-shifted signal controls the operation of transistor VT1. Transistors VT1 and VT2 open when the voltage across them increases the gates are more than +1.4...+1.6 V and the LEDs light up. included in stock chains. Thus, the LEDs alternately (out of phase) switch with a frequency determined by the chain R4-R5-C1. Using potentiometer R5, the generation frequency is set from 0.2 to 2 Hz. The PPY circuit uses super-bright yellow and green LEDs. Operating current of LEDs HL1 and HL2...

For the diagram "PUMP CONTROL UNIT"

Consumer Electronics PUMP CONTROL UNITTo periodically fill the reservoir or, conversely, remove liquid from it, you can use a device that fundamentally scheme which is shown in Fig. 1, and the design is in Fig. 2. The use of reed sensors in it has some advantages - there is no electrical contact between the liquid and the electronic unit, which allows it to be used for pumping out condensation water, a mixture of water and oils, etc. In addition, the use of these sensors increases the reliability of the unit and the durability of its operation. Fig.1 In automatic mode, the device operates as follows. When the liquid level in the tank increases, the ring permanent magnet 8 (Fig. 2), which is attached to the rod 6 connected to the float 9, approaches the upper level reed switch 3 (SF2 in the diagram) from below and causes it to close. SCR VS1 opens, relay K1 is activated, turning on the pump motor with contacts K1.1 and K1.2 and self-blocking with contacts K1.3 (if the relay is not clearly self-blocking, its winding must be bypassed with an oxide capacitor with a capacity of 10... T160 current regulator circuit 50 μF). Puc2The pump pumps out the liquid, its level in the tank decreases, approaching the set lower level. The magnet approaches Gorkom 2 (SF3 according to the diagram) of the lower level and causes it to short-circuit. SCR VS2 opens, relay K2 is activated and its contacts K2.1 break the circuit of the control electrode of the SCR. The thyristor closes, turning off the pump motor. If, after closing the contacts of reed switch 3 and turning on the pump, for some reason the liquid level continues to rise, the alarm reed switch 4 closes and the electric bell NA1 sounds. When the liquid level changes, the rod together with the float 9 performs reciprocating movements in the guide rings 7. 5 studs serve for...

For the scheme "Smooth switching on of the kinescope filament"

TelevisionSmooth switching on of the kinescope filament The circuit shown in the figure is used for kinescopes with Un = 6.3 V and filament current In = 0.3 A, i.e. for most black and white picture tubes. IC DA1 is attached to a radiator with an area of ​​~20 cm2 (you can use the free area of ​​the board made of foil fiberglass). The adjusted resistor R1 sets the required filament voltage (7 V), preferably with the SZ turned off. The voltage rise time is determined by the capacitance of the capacitor SZ. In reality, the voltage increases for more than 30 seconds (the more, the slower due to leakage through R1). S. DMITRIEV, 429541, Chuvashia, Morgushsky district, Kalaykasy. The second device provides heating of the kinescope filament in black-and-white monitors "Electronics" MC6105 and the like. For an hour of warming up, the monitor's line scan operation is blocked. After smooth heating, the full voltage of 12V is supplied to the kinescope filament through the closing contacts K1.1. The device is assembled on a small printed circuit board and installed perpendicular to the monitor board in any free space. Relay K1 - type RES-64 RS4.569.724 or other reed switch for an operating voltage of no more than 7 V and a current of no more than 5 mA. When replacing the relay, you need to change the resistance of resistor R5 accordingly. The device does not require adjustment. A. DAINEKO, 247416, Gomel region, Svetlogorsk district, village of Polesie, lane. Vostochny, 11.(RL-8/96)...

For the "Phase inverted cascade" circuit

For the amateur radio designer, phase-inverted cascade. A single-transistor phase-inverted cascade provides the same output voltages, but the output resistances are not equal. This drawback is eliminated in the cascade, fundamentally scheme which is shown in the figure. A current generator is made on transistor T1. As a result, a high-resistance internal resistance of the generator is connected in parallel with resistor R6. A resistance is connected in parallel with resistor R5 collector transition of transistor T2, many times greater than the resistance of resistor R1. Thus, the output resistances will be determined by the resistances of resistors R5 and R6. When using the elements indicated on the circuit diagram and transistors with a static gain of 60 (transistors T1) and 30 (transistors T2), the cascade provided a gain of approximately 4.8. The device can use transistors MP40 (T1) and KT315 (T2). "Radio fernsehen eleckfronik" (GDR), 1974, N 13...

Starting an induction motor smoothly is always a difficult task because starting an induction motor requires a lot of current and torque, which can burn out the motor winding. Engineers are constantly proposing and implementing interesting technical solutions to overcome this problem, for example, using a switching circuit, autotransformer, etc.

Currently, similar methods are used in various industrial installations for the uninterrupted operation of electric motors.

The principle of operation of an induction electric motor is known from physics, the whole essence of which is to use the difference between the rotation frequencies of the magnetic fields of the stator and rotor. The magnetic field of the rotor, trying to catch up with the magnetic field of the stator, contributes to the excitation of a large starting current. The motor runs at full speed, and the torque value also increases along with the current. As a result, the winding of the unit may be damaged due to overheating.

Thus, it becomes necessary to install a soft starter. Soft starters for three-phase asynchronous motors allow you to protect units from the initial high current and torque that arise due to the sliding effect when operating an induction motor.

Advantages of using a circuit with a soft starter (SPD):

1. reduction of starting current;
2. reduction in energy costs;
3. increasing efficiency;
4. relatively low cost;
5. achieving maximum speed without damaging the unit.

How to start the engine smoothly?

There are five main soft starting methods.

• High torque can be created by adding an external resistance to the rotor circuit as shown in the figure.

• By including an automatic transformer in the circuit, the starting current and torque can be maintained by reducing the initial voltage. See the picture below.

• Direct starting is the simplest and cheapest method because the induction motor is connected directly to the power source.
• Connections using a special winding configuration - the method is applicable for motors intended for operation under normal conditions.

• Using SCP is the most advanced method of all the methods listed. Here, semiconductor devices such as thyristors or SCRs, which control the speed of an induction motor, successfully replace mechanical components.

Commutator motor speed controller

Most circuits for household appliances and electrical tools are based on a 220 V commutator motor. This demand is explained by its versatility. The units can be powered from direct or alternating voltage. The advantage of the circuit is due to the provision of effective starting torque.

To achieve a smoother start and have the ability to adjust the rotation speed, speed controllers are used.

You can start an electric motor with your own hands, for example, in this way.

Electric motors are widely used in all areas of human activity. However, when starting the electric motor, a sevenfold current consumption occurs, causing not only an overload of the power supply network, but also heating of the stator windings, as well as failure of mechanical parts. To eliminate this undesirable effect, radio amateurs advise using soft starters for the electric motor.

Smooth engine start

The stator of an electric motor is an inductance coil, therefore, there are active and reactive components of resistance (R). The value of the reactive component depends on the frequency characteristics of the power supply and during startup ranges from 0 to the calculated value (during the operation of the tool). In addition, the current called starting current changes.

The starting current is 7 times the rated value. During this process, the windings of the stator coil heat up and, if the wire that makes up the winding is old, then an interturn short circuit is possible (as the value of R decreases, the current reaches its maximum value). Overheating leads to a reduction in the service life of the tool. To prevent this problem, there are several options for using soft starters.

By switching the windings, the motor soft start device (USP) consists of the following main components: 2 types of relays (on-time and load control), three contactors (Figure 1).

Figure 1 - General diagram of the soft start device for asynchronous motors (soft start).

Figure 1 shows an asynchronous motor. Its windings are connected using a star connection type. Starting is carried out with closed contactors K1 and K3. After a certain time interval (set using a time relay), contactor K3 opens its contact (shutdown occurs) and contact K2 switches on. The diagram in Figure 1 is also applicable for motor soft starters of various types.

The main disadvantage is the formation of short-circuit currents when 2 circuit breakers are turned on simultaneously. This problem is corrected by introducing a switch into the circuit instead of contactors. However, the stator windings continue to heat up.

When electronically controlling the starting frequency of an electric motor, the principle of frequency variation of the supply voltage is used. The main element of these converters is frequency converter including:

1. The rectifier is assembled on powerful semiconductor diodes (a thyristor version is possible). It converts the mains voltage into pulsating direct current.
2. The intermediate circuit smoothes out interference and ripple.
3. An inverter is necessary to convert the signal received at the output of the intermediate circuit into a signal with variable amplitude and frequency characteristics.
4. The electronic control circuit generates signals for all components of the converter.

Principle of operation, types and choice

When increasing the rotor torque and IP by 7 times, to extend the service life, it is necessary to use a soft starter, which meets the following requirements:

1. Uniform and smooth increase in all indicators.
2. Control of electric braking and engine starting at certain time intervals.
3. Protection against power surges, loss of any phase (for a 3-phase electric motor) and various types of interference.
4. Increased wear resistance.

The principle of operation of a triac soft starter: limiting the voltage value by changing the opening angle of triac semiconductors (triacs) when connected to the stator coils of an electric motor (Figure 2).

Figure 2 - Scheme of soft start of an electric motor using triacs.

Thanks to the use of triacs, it becomes possible to reduce inrush currents by 2 or more times, and the presence of a contactor allows you to avoid overheating of triacs (in Figure 2: Bypass). The main disadvantages of triac soft starters:

1. The use of simple circuits is possible only with light loads or idle start. Otherwise, the scheme becomes more complicated.
2. Overheating of windings and semiconductor devices occurs during prolonged startup.
3. The engine sometimes does not start (leading to significant overheating of the windings).
4. When the electric brake is applied, the windings may overheat.

Soft starters with regulators in which there is no feedback (1 or 3 phases) are widely used. In models of this type, it is necessary to set the electric motor start time and voltage immediately before starting. The disadvantage of the devices is the inability to regulate the torque of moving mechanical parts according to the load. To eliminate this problem, you need to use a device to reduce Ip, protect against different phase differences (occurs during phase imbalance) and mechanical overloads.

More expensive soft starter models include the ability to monitor the operating parameters of the electric motor in continuous mode.

Devices containing electric motors are equipped with soft starters based on triacs. They differ in the circuit and method of regulating the mains voltage. The simplest circuits are circuits with single-phase regulation. They are performed on one triac and allow you to soften the load on the mechanical part, and are used for electric motors with a power of less than 12 kV. Enterprises use 3-phase voltage regulation for electric motors with a power of up to 260 kW. When choosing the type of soft starter you must be guided by the following parameters:

1. Device power.
2. Operating mode.
3. Equality of Ip of the motor and soft starter.
4. The number of starts in a certain time.

To protect pumps, soft starters are suitable that protect against impacts from the hydraulic component of the pipe (Advanced Control). Soft starters for tools are selected based on loads and high speeds. In expensive models, this type of protection in the form of a soft starter is present, but for budget models you need to make it yourself. Used in chemical laboratories to smoothly start a fan that cools liquids.

Reasons for using the grinder

Due to the design features, when starting an angle grinder, high dynamic loads occur on the tool parts. During the initial rotation of the disk, The gearbox axis is subject to inertia forces:

1. An inertial jerk can tear the grinder out of your hands. There is a threat to life and health, since this tool is very dangerous and requires strict adherence to safety precautions.
2. When starting, an overcurrent occurs (Istart = 7*Inom). Premature wear of the brushes and overheating of the windings occur.
3. The gearbox is wearing out.
4. Destruction of the cutting disc.

An untuned instrument becomes very dangerous, because there is a possibility of causing harm to health and life. Therefore, it is necessary to secure it. For this purpose, they assemble the soft starters for power tools with their own hands.

DIY creation

For budget models of angle grinders and other tools, you need to assemble your own soft starter. This is not difficult to do, because thanks to the Internet, you can find a huge number of schemes. The simplest and, at the same time, effective is a universal soft starter circuit based on a triac and a microcircuit.

When you turn on an angle grinder or other tool, damage to the windings and gearbox of the tool occurs due to a sudden start. Radio amateurs found a way out of this situation and proposed a simple soft start for a do-it-yourself power tool (diagram 1), assembled in a separate block (there is very little space in the case).

Scheme 1 - Scheme for soft start of a power tool.

The soft starter is implemented with your own hands on the basis of KR118PM1 (phase control) and a power unit using triacs. The main highlight of the device is its versatility, because it can be connected to any power tool. It is not only easy to install, but also does not require preliminary configuration. Basically, connecting the system to the instrument is not complicated and is installed in the break of the power cable.

Features of the soft starter module

When the grinder is turned on, voltage is applied to KR118PM1 and a smooth increase in voltage occurs at the control capacitor (C2) as the charge increases. The thyristors located in the microcircuit open gradually with a certain delay. The triac opens with a pause equal to the delay of the thyristors. For each subsequent voltage period, the delay gradually decreases and the tool starts smoothly.

The time to gain revolutions depends on capacity C2 (at 47 microns, the start-up time is 2 seconds). This delay is optimal, although it can be changed by increasing the capacitance C2. After turning off the angle grinder, capacitor C2 is discharged thanks to resistor R1 (discharge time is approximately 3 seconds at 68k).

This circuit for adjusting the speed of the electric motor can be upgraded by replacing R1 with a variable resistor. When the resistance value of the variable resistor changes, the power of the electric motor changes. Resistor R2 performs the function of controlling the amount of current that flows through the input of triac VS1 (it is advisable to provide cooling by a fan), which is the control one. Capacitors C1 and C3 serve to protect and control the microcircuit.

The triac is selected with the following characteristics: the maximum direct voltage is up to 400–500 V and the minimum current passing through the transitions must be at least 25 A. When manufacturing a soft starter according to this scheme, the power reserve can range from 2 kW to 5 kW.

Thus, to increase the service life of tools and motors, it is necessary to start them smoothly. This is due to the design feature of electric motors of asynchronous and commutator types. When starting up, there is a rapid current consumption, which causes wear and tear on the electrical and mechanical parts. Using a soft starter allows you to protect your power tool by following safety regulations. When upgrading a tool, it is possible to purchase ready-made models, as well as assemble a simple and reliable universal device, which is not only different, but even superior to some factory soft starters.

Many electric tools, especially from previous years, are not equipped with a soft start device. Such tools are launched with a powerful jerk, which results in increased wear on bearings, gears and all other moving parts. Cracks appear in varnish insulating coatings, which are directly related to premature failure of the tool.

To eliminate this negative phenomenon, there is a not very complicated circuit based on an integrated power regulator, which was developed back in the Soviet Union, but it is still not difficult to buy on the Internet. Price from 40 rubles and above. It is called KR1182PM1. Works well in a variety of control devices. But we will assemble a soft start system.

Soft starter circuit diagram

Now let's look at the diagram itself.

As you can see, there are not very many components and they are not expensive.

Will need

• Microcircuit – KR1182PM1.
• R1 – 470 Ohm. R2 – 68 kilo-ohms.
• C1 and C2 – 1 microfarad - 10 volts.
• C3 – 47 microfarads – 10 volts.

A breadboard for mounting circuit components “so as not to bother with making a printed circuit board.”
The power of the device depends on the brand of triac that you install.
For example, the average value of the open state current for different triacs:

• BT139-600 - 16 amperes,
• BT138-800 - 12 amperes,
• BTA41-600 - 41 amperes.

Assembling the device

You can install any others that you have and that suit your power, but you need to take into account that the more powerful the triac, the less it will heat up, which means the longer it will work. Depending on the load, you need to use a cooling radiator for the triac.
I installed the BTA41-600, you don’t have to install a radiator for it at all, it is powerful enough and will not heat up during repeated short-term operation, at a load of up to two kilowatts. I simply don’t have a more powerful tool. If you plan to connect a more powerful load, then think about cooling.
Let's assemble the parts for installing the device.

We also need a “closed” socket and a power cable with a plug.

It is good to adjust the breadboard to size using large scissors. It cuts easily, simply and neatly.

We place the components on the breadboard. It’s better to solder a special socket for the microcircuit; it costs a penny, but makes the work much easier. There is no risk that you will overheat the legs of the microcircuit, you do not need to be afraid of static electricity, and if the microcircuit burns out, it can be replaced in a couple of seconds. It is enough to take out the burnt one and insert the whole one.

We solder the parts immediately.

We place new parts on the board, checking the diagram.

We solder it carefully.

For a triac, the sockets need to be slightly drilled.

And so on in order.

We insert and solder the jumper and other parts.

We solder.

We check compliance with the circuit and insert the microcircuit into the socket, not forgetting the key.

We insert the finished circuit into the socket.

We connect the power to the outlet and circuit.

Please watch the video testing this device. The change in device behavior upon startup is clearly shown.
Good luck to you in your affairs and concerns.

Who wants to strain, spend their money and time on re-equipment of devices and mechanisms that already work perfectly? As practice shows, many do. Although not everyone in life encounters industrial equipment equipped with powerful electric motors, they constantly encounter, albeit not so voracious and powerful, electric motors in everyday life. Well, everyone probably used the elevator.

Electric motors and loads - a problem?

The fact is that virtually any electric motor, at the moment of starting or stopping the rotor, experiences enormous loads. The more powerful the engine and the equipment it drives, the greater the costs of starting it.

Probably the most significant load placed on the engine at the time of start-up is a multiple, albeit short-term, excess of the rated operating current of the unit. After just a few seconds of operation, when the electric motor reaches its normal speed, the current consumed by it will also return to normal levels. To ensure the necessary power supply have to increase the power of electrical equipment and conductive lines, which leads to their rise in price.

When starting a powerful electric motor, due to its high consumption, the supply voltage “drops”, which can lead to failures or failure of equipment powered from the same line. In addition, the service life of power supply equipment is reduced.

If emergency situations occur that result in engine burnout or severe overheating, properties of transformer steel may change so much so that after repair the engine will lose up to thirty percent of its power. Under such circumstances, it is no longer suitable for further use and requires replacement, which is also not cheap.

Why do you need a soft start?

It would seem that everything is correct, and the equipment is designed for this. But there is always a “but”. In our case there are several of them:

• at the moment of starting the electric motor, the supply current can exceed the rated one by four and a half to five times, which leads to significant heating of the windings, and this is not very good;
• starting the engine by direct switching leads to jerks, which primarily affect the density of the same windings, increasing the friction of the conductors during operation, accelerates the destruction of their insulation and, over time, can lead to an interturn short circuit;
• the aforementioned jerks and vibrations are transmitted to the entire driven unit. This is already completely unhealthy, because may cause damage to its moving parts: gear systems, drive belts, conveyor belts, or just imagine yourself riding in a jerking elevator. In the case of pumps and fans, this is the risk of deformation and destruction of turbines and blades;
• We should also not forget about the products that may be on the production line. They may fall, crumble or break due to such a jerk;
• Well, and probably the last point that deserves attention is the cost of operating such equipment. We are talking not only about expensive repairs associated with frequent critical loads, but also about a significant amount of inefficiently spent electricity.

It would seem that all of the above operating difficulties are inherent only in powerful and bulky industrial equipment, however, this is not so. All this can become a headache for any average person. This primarily applies to power tools.

The specific use of such units as jigsaws, drills, grinders and the like require multiple start and stop cycles over a relatively short period of time. This operating mode affects their durability and energy consumption to the same extent as their industrial counterparts. With all this, do not forget that soft start systems cannot regulate engine speed or reverse their direction. It is also impossible to increase the starting torque or reduce the current below that required to start rotating the motor rotor.

Video: Soft start, adjustment and protection of the commutator. engine

Options for soft start systems for electric motors

Star-delta system

One of the most widely used starting systems for industrial asynchronous motors. Its main advantage is simplicity. The engine starts when the windings of the star system are switched, after which, when the normal speed is reached, it automatically switches to delta switching. This is the starting option allows you to achieve a current almost a third lower than when starting an electric motor directly.

However, this method is not suitable for mechanisms with low rotational inertia. These, for example, include fans and small pumps, due to the small size and weight of their turbines. At the moment of transition from the “star” to the “triangle” configuration, they will sharply reduce the speed or stop altogether. As a result, after switching, the electric motor essentially starts again. That is, in the end, you will not only not achieve savings in engine life, but also, most likely, you will end up with excessive energy consumption.

Video: Connecting a three-phase asynchronous electric motor with a star or triangle

Electronic motor soft start system

A smooth start of the engine can be done using triacs connected to the control circuit. There are three schemes for such connection: single-phase, two-phase and three-phase. Each of them differs in its functionality and final cost, respectively.

With such schemes, usually it is possible to reduce the starting current up to two or three nominal. In addition, it is possible to reduce the significant heating inherent in the aforementioned star-delta system, which helps to increase the service life of electric motors. Due to the fact that the engine starting is controlled by reducing the voltage, the rotor accelerates smoothly and not abruptly, as with other circuits.

In general, engine soft start systems are assigned several key tasks:

• the main one is to reduce the starting current to three to four rated ones;
• reducing the motor supply voltage, if appropriate power and wiring are available;
• improvement of starting and braking parameters;
• emergency network protection against current overloads.

Single-phase starting circuit

This circuit is designed to start electric motors with a power of no more than eleven kilowatts. This option is used if it is necessary to soften the shock at startup, and braking, soft starting and reducing the starting current do not matter. Primarily due to the impossibility of organizing the latter in such a scheme. But due to the cheaper production of semiconductors, including triacs, they have been discontinued and are rarely seen;

Two-phase starting circuit

This circuit is designed to regulate and start motors with a power of up to two hundred and fifty watts. Such soft start systems sometimes equipped with a bypass contactor to reduce the cost of the device, however, this does not solve the problem of phase supply asymmetry, which can lead to overheating;

Three-phase starting circuit

This circuit is the most reliable and universal soft start system for electric motors. The maximum power of motors controlled by such a device is limited solely by the maximum temperature and electrical endurance of the triacs used. His versatility allows you to implement a lot of functions, such as: dynamic brake, flyback pickup or balancing of magnetic field and current limiting.

An important element of the last of the mentioned circuits is the bypass contactor, which was mentioned earlier. He allows you to ensure the correct thermal conditions of the electric motor soft start system, after the engine reaches normal operating speed, preventing it from overheating.

The soft start devices for electric motors that exist today, in addition to the above properties, are designed to work together with various controllers and automation systems. They have the ability to be activated by command from the operator or the global control system. Under such circumstances, when the loads are turned on, interference may appear that can lead to malfunctions in the automation, and therefore it is worth taking care of protection systems. The use of soft start circuits can significantly reduce their influence.

Do-it-yourself soft start

Most of the systems listed above are actually not applicable in domestic conditions. Primarily for the reason that at home we extremely rarely use three-phase asynchronous motors. But there are more than enough commutator single-phase motors.

There are many schemes for smooth starting of engines. The choice of a specific one depends entirely on you, but in principle, having a certain knowledge of radio engineering, skillful hands and desire, it is quite you can assemble a decent homemade starter, which will extend the life of your power tools and household appliances for many years.