Connecting a three-phase compressor in compliance with phasing

How to connect a 380 compressor to the network

It should be understood that the engine power with such a connection, no matter how hard you try, will drop noticeably.
Thus, a delta connection uses only 70% of the engine power, and a star connection uses even less - only 50%. In this regard, it is advisable to have a more powerful engine. When connecting the motor, be extremely careful. Take your time. When changing the circuit, turn off the power supply and discharge the capacitor with an electric lamp. Work with at least two people.

So, in any connection scheme, capacitors are used. In essence, they act as the third phase. Thanks to it, the phase to which one terminal of the capacitor is connected shifts exactly as much as necessary to simulate the third phase. Moreover, to operate the engine, one capacity is used (working), and for starting, another (starting) is used in parallel with the working one. Although this is not always necessary.

For example, for a lawn mower with a blade in the form of a sharpened blade, a 1 kW unit and only working capacitors will be sufficient, without the need for containers for starting. This is due to the fact that the engine is idling when starting and it has enough energy to spin the shaft.

If you take a circular saw, a hood or another device that puts an initial load on the shaft, then you cannot do without additional banks of capacitors for starting. Someone may say: “why not connect the maximum capacity so that there is not enough?” But it's not that simple. With such a connection, the motor will overheat and may fail. Don't risk your equipment.

Whatever the capacitance of the capacitors, their operating voltage must be at least 400V, otherwise they will not work for a long time and may explode.

How to connect and configure a pressure switch?

In the general circuit diagram of a compressor installation, the pressure switch is located between the unloader valve and the secondary engine control circuit. Typically the pressure switch is equipped with four threaded heads. One of them is intended for connecting the device to the receiver, and the second is for connecting a control pressure gauge. One of the remaining connectors can be used to install a safety valve, and the remaining one can be fitted with a regular ¼-inch threaded plug. The presence of a free connector allows you to install the control pressure gauge in a place convenient for the user.

The pressure switch is connected in the following sequence:

Connect the device to the unloading valve of the receiver.
Install a control pressure gauge (if it is not necessary, then the threaded inlet is also plugged).
Connect the terminals of the electric motor control circuit to the contacts (taking into account the selected connection diagram - to normally open or normally closed contacts). When the voltage in the network fluctuates, the connection is made not directly, but through a surge protector. This is also required when the power for which the contacts are designed exceeds the motor load current.
If necessary, use the adjusting screws to adjust the relay to the required compressed air pressure values.

When connecting, you need to check whether the network voltage corresponds to the factory settings of the compressor pressure switch.
For example, in a three-phase network with a voltage of 380 V, the relay must have a three-contact group (two phases + zero), and for a voltage of 220 V - a two-contact group. The adjustment is made when the receiver is at least two-thirds full. To perform this operation, the relay is disconnected from the power supply, and, by removing the top cover, the compression of the two springs is changed. The adjusting screw, on which the axis of the larger diameter spring is mounted, is responsible for the upper limit of the working pressure. On the board next to it, the generally accepted pressure symbol (P - pressure) is usually indicated, and the direction of rotation of the screw by which this pressure is reduced or increased is also indicated. The second, smaller adjustment screw is responsible for setting the required pressure range (difference). It is marked with the symbol ΔР, and is also equipped with an indicator of the direction of rotation.

Let's first consider how a three-phase motor is connected to a 380V network.

Three-phase motors come with either three terminals - for connection to a star only - or with six connections, with the ability to select a circuit - star or delta. The classic scheme can be seen in the figure. Here in the picture on the left there is a star connection. The photo on the right shows how it looks on a real engine frame.

It can be seen that for this it is necessary to install special jumpers on the required pins. These jumpers come with the motor. In the case where there are only 3 terminals, the star connection is already made inside the motor housing. In this case, it is simply impossible to change the winding connection diagram.

Some say that they did this to prevent workers from stealing units from home for their own needs. Be that as it may, such engine options can be successfully used for garage purposes, but their power will be noticeably lower than those connected by a triangle.

What can be redone

Low-power 380 Volt electric motors are suitable for conversion: up to 3 kW. Theoretically, powerful motors are also reconnected. But this will additionally entail the installation of a separate circuit breaker in the electrical panel and special wiring. And this work becomes meaningless if it suddenly turns out that the input cable cannot carry such a load.

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Even if your network carries high loads, and you managed to convert a 3 kW motor from 380 to 220 Volts, you will be upset the first time you put it into operation. The launch will be difficult. You will decide that the work was in vain. Therefore, if you redo it, then it will be low-power models.

Connection diagram for a 3-phase motor in a 220V network connected by a star.

As you can see, the 220V voltage is distributed over two series-connected windings, where each is designed for such a voltage. Therefore, the power is lost almost twice, but such an engine can be used in many low-power devices.

The maximum power of a 380V motor in a 220V network can only be achieved using a delta connection. In addition to minimal power losses, the engine speed also remains unchanged. Here, each winding is used for its own operating voltage, hence the power. The connection diagram for such an electric motor is shown in Figure 1.

Fig. 2 shows a terminal with a 6-pin terminal for delta connection. The three resulting outputs are supplied with: phase, zero and one terminal of the capacitor. The direction of rotation of the electric motor depends on where the second terminal of the capacitor is connected - phase or zero.

In the photo: an electric motor with only working capacitors and no capacitors for starting.

How to connect and configure a pressure switch?

The pressure switch is connected in the following sequence:

Connect the device to the unloading valve of the receiver.
Install a control pressure gauge (if it is not necessary, then the threaded inlet is also plugged).
Connect the terminals of the electric motor control circuit to the contacts (taking into account the selected connection diagram - to normally open or normally closed contacts). When the voltage in the network fluctuates, the connection is made not directly, but through a surge protector. This is also required when the power for which the contacts are designed exceeds the motor load current.
If necessary, use the adjusting screws to adjust the relay to the required compressed air pressure values.

To reduce setup time, in some designs the adjusting screw for changing the upper pressure limit is moved outside the pressure switch housing. The result is monitored using the pressure gauge readings.

Using a magnetic starter

The good thing about using a 380 electric motor connection diagram is that it can be started remotely. The advantage of a starter over a switch (or other device) is that the starter can be placed in a cabinet, and the controls can be placed in the work area; the voltage and currents are minimal, therefore, the wires are suitable for a smaller cross-section.

In addition, connection using a starter ensures safety in the event that the voltage “disappears,” since this opens the power contacts, and when the voltage appears again, the starter will not supply it to the equipment without pressing the start button.

Connection diagram for a 380V electric asynchronous motor starter:

At contacts 1,2,3 and start button 1 (open), voltage is present at the initial moment. Then it is supplied through the closed contacts of this button (when you press “Start”) to the contacts of the coil starter K2, closing it. The coil creates a magnetic field, the core is attracted, the contacts of the starter close, driving the motor.

At the same time, the NO contact closes, from which the phase is supplied to the coil through the “Stop” button. It turns out that when the “Start” button is released, the coil circuit remains closed, as do the power contacts.

By pressing “Stop”, the circuit is broken, returning the power contacts to open. The voltage disappears from the conductors and NO supplying the engine.

Video: Connecting an asynchronous motor. Determination of engine type.

If you have a three-phase electric motor, you know it doesn't come cheap. Therefore, if you need to use a single-phase motor, the thought of buying new equipment will only come to you when you do not know how to make an electric motor at home. We will tell you how to convert an electric motor from 380 to 220 Volts with your own hands.

How to select capacitors for a three-phase motor using it in a 220V network.

The first thing you need to know is that the capacitors must be non-polar, that is, not electrolytic. It is best to use containers of the brand ― MBGO. They were successfully used in the USSR and in our time. They perfectly withstand voltage, current surges and the damaging effects of the environment.

They also have mounting eyes that help you easily place them at any point on the device’s body. Unfortunately, getting them now is problematic, but there are many other modern capacitors that are no worse than the first ones. The main thing is that, as mentioned above, their operating voltage is not less than 400V.

Calculation of capacitors. Working capacitor capacity.

In order not to resort to long formulas and torture your brain, there is a simple way to calculate a capacitor for a 380V motor. For every 100 W (0.1 kW) 7 µF is taken. For example, if the motor is 1 kW, then we calculate it like this: 7 * 10 = 70 µF. It is extremely difficult to find such a capacity in one jar, and it is also expensive. Therefore, most often the containers are connected in parallel, gaining the required capacity.

Starting capacitor capacity.

This value is taken at the rate of 2-3 times greater than the capacity of the working capacitor. It should be taken into account that this capacity is taken in total with the working capacity, that is, for a 1 kW motor, the working capacity is equal to 70 μF, multiply it by 2 or 3, and get the required value. This is 70-140 µF of additional capacitance - starting. At the moment of switching on, it is connected to the working one and the total is 140-210 µF.

Features of the selection of capacitors.

Capacitors, both working and starting, can be selected using the method from smallest to largest. Having thus selected the average capacity, you can gradually add and monitor the operating mode of the engine so that it does not overheat and has enough power on the shaft. Also, the starting capacitor is selected by adding until it starts smoothly without delays.

In addition to the above type of capacitor - MBGO, you can use the type - MBGCh, MBGP, KGB and the like.

Let's summarize.

Sometimes it becomes necessary to change the direction of rotation of the electric motor. This option is also available for 380V motors used in a single-phase network. To do this, you need to make sure that the end of the capacitor connected to a separate winding remains unbroken, and the other can be transferred from one winding, where the “zero” is connected, to the other, where the “phase” is connected.

This operation can be performed by a two-position switch, the central contact of which is connected to the output from the capacitor, and to the two outer terminals from “phase” and “zero”.

More details can be seen in the figure.

There are three-phase electric motors for 220V. Each winding of them is designed for 127V and when connected to a single-phase network in a delta circuit, the motor will simply burn out. To prevent this from happening, such a motor should be connected to a single-phase network only according to the “star” circuit.

Air relay connection diagrams

The compressor pressure switch is manufactured for connection to electrical circuits of different loads. In accordance with the rating of the power supply line, the appropriate model of the relay unit is selected.

Option #1: to a network with a nominal value of 220 V

If the drive motor is a single-phase device, then a 220 V relay with two groups of contacts is installed.

Option #2: to a three-phase network with a voltage of 380 V

For a three-phase load of a 380 V circuit, one of the options can be used: a modification of the relay for 220 V or 380 V, with three contact lines, to simultaneously disconnect all three phases.

Both methods have different schemes. Let's consider the first option:

By choosing the second method, power is supplied from one phase (zero) and in this case the relay rating should be 220 V. For more details, see the following diagram:

After connecting to the power supply, you need to understand the additional capabilities provided in the air blocks for ejectors.

Adjustment and commissioning process

Factory set parameters do not always meet consumer requirements. In most cases, this is due to insufficient compression force at the highest point of disassembly.

The operating range of the pressure switch may also not be suitable. In this case, independent adjustment of the actuator will be relevant.

To begin setting the operating compression value, you will need to inspect the engraved plate, which indicates the parameters of the electric motor and compressor.

We only need the largest value that the device produces. This indicator indicates the maximum pressure force that can be set on the relay for the correct operation of the entire pneumatic system.

If you set the specified value (in the figure 4.2 atm), then taking into account all factors - differences in power supply, exhaustion of the service life of parts, etc. - the compressor may not reach the maximum pressure, and accordingly it will not turn off.

In this mode, the working elements of the equipment will begin to overheat, then deform and eventually melt.

Complete set of compressor automation unit

The relay design is a small-sized block equipped with receiving pipes, a sensing element (spring) and a membrane. Mandatory subassemblies include an unloading valve and a mechanical switch.

The pressure switch sensing unit is made up of a spring mechanism, the compression force of which is changed by a screw. According to the factory standardized settings, the elasticity coefficient is set to a pressure in the pneumatic chain of 4-6 at, as reported in the instructions for the device.

The degree of rigidity and flexibility of the spring elements is subject to the temperature of the environment, therefore absolutely all models of industrial devices are designed for stable operation in an environment from -5 to +80 ºC.

The reservoir membrane is connected to the relay switch. During movement, it turns the pressure switch on and off.

The unloading element is located between the ejector check valve and the compression block. If the motor drive stops working, the unloading section is activated, through which excess pressure (up to 2 atm) is released from the piston compartment.

With further start or acceleration of the electric motor, a pressure is created that closes the valve. This prevents overloading of the drive and simplifies starting the device in switched off mode.

There is an unloading system with a time interval of activation. The mechanism remains in the open position when the engine starts for a specified period. This range is enough for the engine to achieve maximum torque.

A mechanical switch is required to start and stop the automatic system options. As a rule, it has two positions: “on.” and "off". The first mode turns on the drive and the compressor operates according to the established automatic principle. The second one prevents accidental starting of the engine, even when the pressure in the pneumatic system is low.

How to change the direction of rotation

If you need to change the direction only once, then this can be done at the rework stage. To do this, it is enough to swap any two stator windings. The same goal is achieved by transferring a branch of capacitors from zero to phase, or vice versa. But if you need to frequently reverse a three-phase converted motor, a switch is needed. By assembling the electric motor according to the diagram below, you will free yourself from changing the windings every time you need to set the direction of rotation of the shaft in the opposite direction.

There is nothing difficult about converting a three-phase electric motor to a single-phase network with your own hands. The greatest difficulty will be only the calculation of the capacitance of the working capacitor and the experimental selection of the capacitance from the calculated range for the starting accumulator. But this becomes easy if you haven’t lost your technical passport and have a calculator at hand.

When operating or manufacturing this or that equipment, it often becomes necessary to connect an asynchronous three-phase motor to a regular 220 V network. This is quite realistic and not even particularly difficult, the main thing is to find a way out of the following possible situations if there is no suitable single-phase motor, and a three-phase one is lying without business, and also if there is three-phase equipment, but in the workshop there is only a single-phase network.

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Diagrams for connecting the pressure switch to the compressor

The connection of the relay that controls the degree of air compression can be divided into 2 parts: the electrical connection of the relay to the unit and the connection of the relay to the compressor through the connecting flanges. Depending on which motor is installed in the compressor, 220 V or 380 V, there are different connection diagrams for the pressure switch. I am guided by these diagrams, provided that you have certain knowledge in electrical engineering, you can connect this relay with your own hands.

Connecting the relay to a 380 V network

To connect the automation to a compressor operating from a 380 V network, use a magnetic starter. Below is a diagram of connecting automation to three phases.

In the diagram, the circuit breaker is indicated by the letters “AB”, and the magnetic starter by “KM”. From this diagram it can be understood that the relay is set to a switch-on pressure of 3 atm. and shutdown - 10 atm.

Connecting the pressure switch to a 220 V network

The relay is connected to a single-phase network according to the diagrams given below.

These diagrams indicate various models of pressure switches of the RDK series, which can be connected in this way to the electrical part of the compressor.

Connecting the pressure switch to the unit

Connecting a pressure switch to a compressor is quite simple.

Screw the pressure switch onto the receiver pipe using its central threaded hole. For better thread sealing, it is recommended to use fum tape or liquid sealant. The relay can also be connected to the receiver through a reducer.
Connect a relief valve to the smallest output from the relay, if present.
The remaining outputs from the relay can be connected to either a pressure gauge or a safety relief valve. The latter is installed without fail. If a pressure gauge is not required, then the free output of the pressure switch must be plugged with a metal plug.
Next, wires from the electrical network and from the engine are connected to the sensor contacts.

After the complete connection of the pressure switch is completed, it is necessary to configure it for proper operation.

Safety precautions

Although a drill press is easy to connect and use, working with it can be dangerous without proper safety precautions. Among them it is worth highlighting the following:

Perform any repair or cleaning work only with the engine power off;
use protective clothing and glasses to protect yourself from flying chips, dust, drops of cutting fluid, and parts of the drill that break;
hide long hair under a hat, avoid working with gloves - if they get wrapped around rotating elements, they can lead to serious injuries;
Before starting work, carefully check all moving parts of the machine for defects and damage. If they are detected, it is prohibited to use the device.

To find out more about how to connect a drilling machine, contact Metaltool and they will answer your questions in detail.

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