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Most often, a single-phase 220 V network is connected to our houses, plots, garages. Therefore, equipment and all homemade products are made so that they work from this power source. In this article, we will consider how to properly connect a single-phase motor.
Asynchronous or collector: how to distinguish
In general, you can distinguish the type of engine by the nameplate – on which its data and type are written. But this is only if it has not been repaired. After all, under the casing can be anything. So if you’re not sure, it’s best to determine the type yourself.
How collector engines are arranged
It is possible to distinguish between asynchronous and collector motors by structure. Collectors must have brushes. They are located near the collector. Another obligatory attribute of this type of engine is the presence of a copper drum divided into sections.
Such motors are produced only single-phase, they are often installed in household appliances, as they allow you to get a large number of revolutions at the start and after acceleration. They are also convenient in that they easily allow you to change the direction of rotation – you just need to change the polarity. It is also easy to organize a change in the rotation speed – by changing the amplitude of the supply voltage or its cutoff angle. Therefore, such engines are used in most household and construction equipment.
The disadvantages of collector motors are the high noise of operation at high speeds. Remember a drill, a grinder, a vacuum cleaner, a washing machine, etc. The noise during their work is decent. At low speeds, collector motors are not so noisy (washing machine), but not all tools work in this mode.
The second unpleasant moment – the presence of brushes and constant friction leads to the need for regular maintenance. If the current collector is not cleaned, graphite contamination (from wearable brushes) can cause adjacent sections in the drum to connect, the motor simply stops working.
Asynchronous
An asynchronous motor has a stator and a rotor, it can be single or three-phase. In this article, we consider the connection of single-phase motors, because we will only talk about them.
Asynchronous motors are distinguished by a low level of noise during operation, therefore they are installed in equipment whose operation noise is critical. These are air conditioners, split systems, refrigerators.
There are two types of single-phase asynchronous motors – bifilar (with a starting winding) and capacitor. The whole difference is that in bifilar single-phase motors, the starting winding only works until the motor accelerates. After that, it is turned off by a special device – a centrifugal switch or a start-up relay (in refrigerators). This is necessary, because after overclocking, it only reduces efficiency.
In capacitor single-phase motors, the capacitor winding operates all the time. Two windings – main and auxiliary – are offset relative to each other by 90 °. This makes it possible to change the direction of rotation. The capacitor on such engines is usually attached to the case and is easy to identify by this sign.
To more accurately determine the bifilar or capacitor motor in front of you, you can use winding resistance measurements. If the resistance of the auxiliary winding is twice as large (the difference can be even more significant), most likely it is a bifilar motor and this auxiliary winding is a starting one, which means that a switch or a starting relay must be present in the circuit. In capacitor motors, both windings are constantly in operation and the connection of a single-phase motor is possible through a conventional button, toggle switch, automatic machine.
Wiring diagrams for single-phase asynchronous motors
With start winding
To connect a motor with a starting winding, you will need a button, in which one of the contacts opens after switching on. These opening contacts will need to be connected to the starting winding. In stores there is such a button – this is PNVS. Her middle contact closes for the holding time, and the two extreme ones remain in the closed state.
First, using measurements, we determine which winding is working, which is starting. Usually the output from the motor has three or four wires.
Consider the option with three wires. In this case, the two windings are already combined, that is, one of the wires is common. We take a tester, measure the resistance between all three pairs. The working one has the smallest resistance, the average value is the starting winding, and the largest is the total output (the resistance of two windings connected in series is measured).
If there are four leads, they are called in pairs. Find two pairs. The one in which the resistance is less – working, in which more – starting. After that, we connect one wire from the starting and working windings, we output a common wire. In total, three wires remain (as in the first option):
- one from the working winding – working;
- from the starting winding;
- common.
With these three wires, we work further – we use it to connect a single-phase motor.
With all these
- Connection of a single-phase motor with a starting winding through the PNVS button
connection of a single-phase motor
We connect all three wires to the button. It also has three contacts. Be sure to start the wire “we put on the middle contact (which closes only during start-up), the other two are extremeie (optional). We connect a power cable (from 220 V) to the extreme input contacts of the PNVS, connect the middle contact with a jumper to the working one (note! not with common). That’s the whole circuit for switching on a single-phase motor with a starting winding (bifilar) through a button.
Condenser
When connecting a single-phase capacitor motor, there are options: there are three connection schemes and all with capacitors. Without them, the motor hums, but does not start (if you connect it according to the scheme described above).
The first circuit – with a capacitor in the power supply circuit of the starting winding – starts up well, but during operation, the power is given out far from the nominal, but much lower. The switching circuit with a capacitor in the working winding connection circuit has the opposite effect: not very good start-up performance, but good performance. Accordingly, the first scheme is used in devices with a hard start (concrete mixers, for example), and with a working condenser – if good performance is needed.
Circuit with two capacitors
There is a third option for connecting a single-phase motor (asynchronous) – install both capacitors. It turns out something in between the options described above. This scheme is implemented most often. It is in the picture above in the middle or in the photo below in more detail. When organizing this circuit, a button of the PNVS type is also needed, which will connect the capacitor only not at the start time, until the motor “accelerates”. Then two windings will remain connected, and the auxiliary winding through the capacitor.
When implementing other circuits – with one capacitor – you will need a regular button, automatic machine or toggle switch. Everything just connects there.
Selection of capacitors
There is a rather complicated formula by which you can accurately calculate the required capacity, but it is quite possible to get by with recommendations that are derived from many experiments:
- a working capacitor is taken at the rate of 70-80 microfarads per 1 kW of engine power;
- launcher – 2-3 times more.
The operating voltage of these capacitors should be 1,5 times higher than the mains voltage, that is, for a 220 volt network, we take capacities with an operating voltage of 330 V and higher. And to make the start easier, look for a special capacitor for the starting circuit. They have the words Start or Starting in the marking, but you can take the usual ones.
Changing the direction of the motor
If, after connecting, the motor works, but the shaft rotates in the wrong direction that you need, you can change this direction. This is done by changing the windings of the auxiliary winding. When the circuit was assembled, one of the wires was applied to the button, the second was connected to the wire from the working winding and a common one was brought out. This is where you need to throw the conductors.