How to check a 1 phase motor?
The scheme for checking it looks like this:
- Turn on the device in Ohm units and measure the resistance of the collector lamellas in pairs.
- Then measure the resistance between the armature housing and the commutator.
- Check the stator windings.
- Measure the resistance between the housing and the stator terminals.
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Checking the motor windings. Malfunctions and test methods
Ideally, in order to check the windings of an electric motor, it is necessary to have special instruments designed for this, which cost a lot of money.
Surely not everyone has them in their home. Therefore, it is easier for such purposes to learn how to use a tester, which has another name: a multimeter. Almost every self-respecting home owner has such a device. Electric motors are manufactured in various versions and modifications, and their malfunctions are also very different. Of course, not every fault can be diagnosed with a simple multimeter, but most often checking the motor windings with such a simple device is quite possible.
Any type of repair always begins with an inspection of the device: the presence of moisture, whether parts are broken, the presence of a burning smell from the insulation and other obvious signs of malfunction. Most often, the burnt winding is visible. Then no checks and measurements are needed. Such equipment is immediately sent for repair. But there are times when there are no external signs of failure, and a thorough check of the motor windings is required.
Types of windings
If you don’t go into details, the motor winding can be imagined as a piece of conductor that is wound in a certain way in the motor housing, and it seems that nothing should break in it.
However, the situation is much more complicated, since the electric motor winding has its own characteristics:
- The material of the winding wire must be uniform along its entire length.
- The shape and cross-sectional area of the wire must have a certain accuracy.
- In industrial conditions, a layer of insulation in the form of varnish must be applied to the wire intended for winding, which must have certain properties: strength, elasticity, good dielectric properties, etc.
- The winding wire must provide strong contact when connected.
If there is any violation of these requirements, then the electric current will flow under completely different conditions, and the electric motor will deteriorate its performance, that is, the power, speed will decrease, and may not work at all.
Checking the motor windings of a 3-phase motor . First of all, disconnect it from the circuit. The majority of existing electric motors have windings connected in star or delta configurations.
The ends of these windings are usually connected to blocks with terminals that have the appropriate markings: “K” - end, “N” - beginning. There are options for internal connections, the nodes are located inside the motor housing, and different markings (numbers) are used on the terminals.
The stator of a 3-phase electric motor uses windings that have equal characteristics and properties, and the same resistance. When measuring the winding resistances with a multimeter, it may turn out that they have different values. This already makes it possible to assume that there is a malfunction in the electric motor.
Possible faults
It is not always possible to visually determine the condition of the windings, since access to them is limited by the design features of the engine. In practice, you can check the winding of an electric motor using its electrical characteristics, since all motor breakdowns are mainly detected:
- A break, when the wire is broken or burnt out, no current will pass through it.
- A short circuit caused by damaged insulation between the input and output turns.
- A short circuit between turns, with the insulation damaged between adjacent turns. As a result, damaged turns are self-excluded from operation. Electric current flows through the winding, which does not involve damaged turns that do not work.
- By breaking through the insulation between the stator housing and the winding.
Methods
Checking the motor windings for open circuits
This is the simplest type of verification. The malfunction is diagnosed by simply measuring the wire resistance value. If the multimeter shows very high resistance, then this means that there is a wire break with the formation of air space.
Checking the motor windings for short circuits
If there is a short circuit in the motor, its power will be cut off by the installed short circuit protection. This happens in a very short time. However, even in such a short period of time, a visible defect in the winding may occur in the form of carbon deposits and metal melting.
If you measure the winding resistance with instruments, you get a small value that approaches zero, since a piece of the winding is excluded from the measurement due to a short circuit.
Checking the motor windings for interturn short circuits
This is the most difficult task in identifying and troubleshooting. To check the motor winding, several measurement and diagnostic methods are used.
Checking the motor windings using an ohmmeter
This device operates on direct current and measures active resistance. During operation, the winding forms, in addition to active resistance, a significant inductive resistance value.
If one turn is closed, then the active resistance will practically not change, and it is difficult to determine it with an ohmmeter. Of course, you can accurately calibrate the device, carefully measure all windings for resistance, and compare them. However, even in this case it is very difficult to detect shorted turns.
The results are much more accurately produced by the bridge method, which measures active resistance. This method is used in a laboratory environment, so ordinary electricians do not use it.
Current measurement in each phase
The phase current ratio will change; if a short circuit occurs between the turns, the stator will heat up. If the engine is fully operational, then the current consumption is the same in all phases. Therefore, by measuring these currents under load, we can confidently say about the actual technical condition of the electric motor.
Checking motor windings with alternating current
It is not always possible to measure the total winding resistance and take into account the inductive reactance. For a faulty motor, you can check the winding with alternating current. For this, an ammeter, a voltmeter and a step-down transformer are used. To limit the current, a resistor or rheostat is inserted into the circuit.
To check the motor winding, a low voltage is applied and the current value is checked, which should not be higher than the nominal value. The measured voltage drop across the winding is divided by the current to obtain the total resistance. Its value is compared with other windings.
The same circuit makes it possible to determine the current-voltage properties of the windings. To do this, you need to take measurements at various current values, then write them down in a table or draw a graph. There should not be large deviations when comparing with other windings. Otherwise, there is an interturn short circuit.
Checking the motor windings with a ball
This method is based on the formation of an electromagnetic field with a rotating effect if the windings are in good condition. They are connected to a symmetrical voltage with three phases, low value. For such tests, three step-down transformers with the same data are used. They are connected separately for each phase.
To limit the load, the experiment is carried out in a short period of time.
Voltage is applied to the stator windings, and a small steel ball is immediately introduced into the magnetic field. When the windings are in good condition, the ball rotates synchronously inside the magnetic circuit.
If there is a short circuit between the turns in any winding, the ball will immediately stop where there is a short circuit. When carrying out the test, the current must not be allowed to exceed the rated value, since the ball can fly out of the stator at high speed, which is dangerous for humans.
Determining the polarity of windings using the electrical method
The stator windings have terminal markings, which sometimes may not be there for various reasons. This creates difficulties during assembly.
To determine the marking, several methods are used:
- A weak DC source and an ammeter.
- Step-down transformer and voltmeter.
The stator acts as a magnetic circuit with windings operating on the principle of a transformer.
Measuring insulation resistance with a megohmmeter
Despite the fact that the megohmmeter is considered a professional measuring device, in some cases it can also be in demand at home. For example, when you need to check the condition of electrical wiring. Using a multimeter for this purpose will not allow you to obtain the necessary data; at most, it can detect the problem, but not determine its scale. That is why measuring insulation resistance with a megohmmeter remains the most effective test method; this is described in detail in our article.
Features of testing electric motors with additional elements
Electric powertrains are often equipped with additional components designed to protect the equipment or optimize its performance. The most common elements built into the motor are:
- Thermal fuses. They are set to operate at a certain temperature in such a way as to avoid burning and destruction of the insulating material
.
The fuse is retracted under the insulation of the windings or fixed to the body of the electric motor with a steel shackle
.
In the first case, access to the pins is not difficult, and they can be checked without problems using a tester. You can also use a multimeter or a simple indicator screwdriver to determine which detachable legs the protective circuit goes to
. If the temperature fuse is in normal condition, it should indicate a short circuit when measured. - Thermal fuses can be successfully replaced by temperature relays, which can be either normally open or closed (the second type is more common). The brand of the element is affixed to its body
. Relays for various types of engines are selected in accordance with technical parameters, which can be found by reading operational documents or finding the necessary information on the Internet. - Engine speed sensors with three outputs. They are usually equipped with washing machine motors
.
The basis of the operating principle of these elements is a change in the potential difference in the plate through which a weak current passes. Power is supplied through the two outer terminals, which have low resistance and should show a short circuit when tested
.
The third pin is checked only in operating mode, when it is acted upon by a magnetic field. Do not measure the sensor's power supply when the engine is running
.
It is best to remove the power unit altogether and apply current separately to the sensor
.
To generate pulses at the sensor output, rotate the axis
. If the rotor is not equipped with a permanent magnet, you will have to install it during the test, having first removed the sensor.
This material contains all the necessary information on how to properly test an electric motor with a multimeter at home. When any electrical equipment fails, the most important thing is to ring the motor winding to eliminate its malfunction, since the power plant has the highest cost compared to other elements.
Failure to comply with the specified application standards and some exposure can cause serious problems that can be determined by using a multimeter. In order not to waste money on workshop services, you need to find out how you can independently ring an electric motor with a multimeter
. This work has quite a large number of features.
