How to check the angle grinder armature for inter-turn short circuit

What burns most often in an angle grinder.Signs of rotor burn

As Shakespeare said, “Nothing lasts forever under the moon. Household appliances, alas, are no exception. It happens that even the most reliable mechanism fails. And you should be ready to meet this fact without panic, with the firm belief that there is no such a thing as a hopeless situation. How is the angle grinder arranged, what can be malfunctions, how to check the motor anchor, determine the cause of failure and fix the problem? Knowledge of the device of the main nodes of the power tool will allow the master with his own hands to diagnose and repair the angle grinder.

Factors that cause the stator to fail:

Signs by which you can tell that the stator is defective:

  • The smell of burning insulation appears.
  • The housing overheats.
  • Smoke is visible.
  • The shaft rotation slows down or stops.
  • The shaft spontaneously unwinds, the tool suddenly reaches maximum speed.

Winding wires are coated with a protective layer of insulating varnish. Overheating can cause the stator to burn out and break down. This causes a short circuit of the windings. The lacquer emits a specific smell. Short circuit of just one of the wires completely destroys the angle grinder.

Rules to avoid overheating of the angle grinder motor:

  • Turn off the device after working at lower speeds, not immediately, but after about one minute.
  • Take frequent breaks when working under load at low revolutions.

Often a defective stator can be avoided by rewinding. Rewinding a damaged stator coil of an angle grinder can be done with your own hands, but it is still recommended to have this work done by a specialist.

Rotor malfunctions

if used optimally, the rotor will not wear out. Routine work is done with the replacement of brushes when they are worn out. But over time, with heavy loads, the stator will become hot and burn. The most common mechanical failure is bearing wear or misalignment.

The angle grinder will work, but the plates will quickly wear out, and over time the motor will break. To avoid breakdowns, it is necessary to check the tool and maintain normal operating conditions.

Moisture on the metal causes the formation of rust. The friction force increases, more current is required for work. There is considerable heating of contact groups, solder, there is a strong spark.

Malfunctions of the rotor

In the case of optimum use, the rotor will not wear out. Routine maintenance with replacement of brushes when worn out. But over time, with heavy loads, the stator heats up and builds up fouling. The most frequent mechanical breakdown is wear or misalignment of the bearings.

The angle grinder will work, but the plates will wear out quickly and the motor will break over time. To avoid breakdowns, it is necessary to check the tool and maintain normal service conditions.

Moisture striking metal causes rusting. The friction force increases, more current is required to work. Significant heating of contact groups, solder, strong sparks.

Repair of angle grinder with their own hands: the principle and structure of the device

To repair the angle grinder is not a simple thing, you need to know all the details and causes for which the unit can fail. For example, repair of an asynchronous motor or sparking collector, it is not always under the power of an ordinary person. And then you have to go to the master. To understand what is the device of the angle grinder, you need to know how this technique works. With the help of electricity runs the motor, which transmits the rotation to the shaft thanks to the gear. At the end of the shaft there is a circle of cutting or grinding type.

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The quality of the angle grinder depends on the number of revolutions per minute. A professional tool is capable of reaching speeds of 1000 rpm.

The first thing to do in case of failure is to disassemble the machine and clean it, in most cases the angle grinder begins to work.

If this does not happen, you need to figure out exactly where the breakdown occurred. The composition of the angle grinder may differ depending on the model, but the main parts they have the same.

At disassembly we can see 4 components:

The motor makes the gearwheel move, which in turn drives the cutting element.

Oddly enough, in most cases, breakdowns occur because of dust accumulation and as a result of a loose trigger. So first you need to determine the integrity of the electric drill, its lamellae and the battery. All this is not so difficult, enough to know how the machine is constructed. If you’ve ever studied the structure of a vacuum cleaner or washing machine, it will seem like a small thing, but a special video can help you.

Interturn fault in the stator

Often, a faulty motor has an interturn fault. First check the stator winding for resistance. This is an unreliable method, because the multimeter can not always accurately display the result of measurement. It also depends on the technology of rewinding the motor, the age of the iron.

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Use pliers also to measure resistance and current. Sometimes they check by the sound of running motor if the bearings are good, lubricated and drive reducer is in good working order. Also check the inter-turn short circuit with an oscilloscope, but they have a high cost, not everyone has this device.

Visually inspect motor. There should be no traces of oil, leakage, odor. Measured by phase current, should be the same. Use a good tester to check windings for resistance. At a difference in the measurements of more than 10% there is a possibility of short circuit turns of windings.

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Interturn faults

This type of short circuit is a connection of turns inside the winding due to damage to the insulation of winding wires. The most common causes of inter-turn short circuits are when the insulation of the conductors is damaged during straightening and settling of the coils, during winding laying, due to solder or shavings between coils, when the winding breaks on the housing, due to crossing wires in the slot in a bulk winding and the like.

Intersection closures may occur in one or more armature sections or between sections due to shorting of adjacent collector plates. When closing between the ends of a section or between the collector plates, or when individual turns of a section are joined together, closed loops are formed in the armature winding.

In a loop winding, a short circuit between two adjacent plates causes only the section connected to those plates to be short-circuited, and the number of winding turns acting in the winding is reduced by the number of turns contained in one section.

In a wave winding, a short circuit between two adjacent plates causes a series of sections which are enclosed in one complete loop around the armature. Their number is equal to the number of pole pairs of the machine.

In short-circuited circuits, as they rotate in the magnetic field, an electromotive force (EMF) is induced, which causes high short-circuit currents due to the low resistance of these circuits. Short-circuited turns appearing during machine operation are strongly heated by the current flowing through the winding and usually burn out.

How to determine if a motor has a short circuit? In wave winded armatures, and also in windings with equalizing connections with a large number of closed sections, it is impossible to detect a shorted branch by the heating, since the whole armature is heated. Sometimes the location of the short circuits may be found on external inspection by looking at the charred and burned-out insulation of a section of the winding.

The simplest and most frequently occurring cases (e.g. winding faults in one winding section, between adjacent collector plates or between adjacent sections in the same winding layer) can be identified by voltage drop, listening and other methods.

A technique for determining faults by voltage drop

This method (figure 3) is as follows. To the pair of collector plates 1 a direct current is brought with the help of probes 3. Use probe 2 to measure the voltage drop across the same pair of plates. If there is a short circuit in the section connected to the pair of plates being tested, the voltage drop across the same current is less than that across the other pair of plates which are not short-circuited. The more short-circuited the turns, the less voltage drop. The smallest voltage drop (or equal to zero) will be at the short circuit between the collector plates themselves.

The whole armature is checked in this way and the measurements are compared. The armature should be checked with the brushes up. The circuit parameters are the same as in figure 2, a.

To prevent damage to the millivoltmeter (Figure 3), first touch the probe 3 to the collector, and then touch probe 2; remove the probe in reverse order.

This method gives good results when determining short circuits between turns in a section with a small number of turns (bar windings). In the multi-winding sections when one or two turns are shorted the difference in millivoltmeter readings on the collector plates of the serviceable section and the damaged one can be negligible.

Figure 4 shows circuits for determining the inter-turn circuits with the phone and a steel plate. The test setup consists of an electromagnet 1 supplied with alternating current of increased frequency. Anchor 3 is placed over the electromagnet. If there is an inter-turn short circuit in any section, there will be a high current in that section, which is detected by the heating. With the aid of the telephone 2 and electromagnet 4 the damaged section can be quickly identified. If the winding sections are intact, a faint sound of equal strength can be heard in the telephone 2. If one of the sections has a short circuit, the sound in the phone is noticeably amplified.

Checking the Armature for a Short Circuit. a. by telephone; b. by steel plate

For a complete check of the winding you need to move the electromagnet 4 on the teeth of the armature until the last will not be bypassed in a circle. If the teeth of the core, which covers the faulty section, bring a thin steel plate 5 (Fig. 4, b), then it will rattle. This method detects a short circuit on the adjacent collector plates, which causes the same phenomena as an inter-turn short circuit.

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The circuit shown in Figure 2, c, can be used to detect inter-turn closures. To do this, connect the second conductor not to the shaft, as shown in the figure, but to the collector plate. Wires from the telephone 1 are connected to the two adjacent plates.

The section that has a coil closure is usually replaced with a new one. the reinsulating of the short circuit can be limited only in the case of incomplete contact in the short circuit place, and that in the absence of other damage to the insulation.

If necessary (as a temporary measure) with a small number of collector plates, disconnect the damaged sections from operation. Switching off one section has no noticeable effect on the machine’s commutation.

Checking and repairing the armature of the angle grinder

What the diligent owner of the house wants to see in his “luggage” of power tools? To this question, everyone, without hesitating for a second, will answer. a drill. And immediately adds. and, of course, the angle grinder! After all, it will help to cut metal, ceramic, brick, concrete, asphalt, stone or wood; perform work on the arrangement of niches, arched and doorways. With the help of this power tool, you can clean surfaces from rust, scorch marks and deposits, get rid of welds or just polish the metal to a shine. angle grinder will be an indispensable assistant in other types of home repair.

Whatever the angle grinder (angle grinder) has a robust design, during operation, some of the nodes and parts fail. Failure of the armature, operating under relatively harsh conditions, is often the cause of the drive not functioning properly. In this article, the master plumber will consider how to repair or replace the angle grinder anchor.

The motor armature of an angle grinder is a conducting coil and a magnet wire, into which the rotating shaft is pressed. It has a pinion at one end and a manifold with blades at the other. The magnetic circuit consists of slots and soft plates coated with varnish to insulate one from another.

Two conductors of the anchor winding are placed in the grooves according to a special scheme. Each conductor makes up half of the coil, the ends of which are connected to the lamellae in pairs. The beginning of the first coil and the end of the last coil are in the same groove, so they are closed to one lamella.

When you buy a power tool, not many people think about the fact that someday it will break down. Breakdowns can happen with any power tool, regardless of the price and manufacturer.

  • Breakage of conductors.
  • Intertwin short circuit.
  • Isolation breakdown to ground. is the winding short circuit to the metal body of the rotor. Occurs due to destruction of the insulation.
  • Disconnection of collector terminals.
  • Uneven wear of the collector.

The main causes of breakdowns of bolsters, including their anchors, can be considered:

  • Mechanical wear. brushes suffer most often.
  • Failure to maintain “nameplate” operating conditions. armature and stator.
  • Overloads and voltage peaks in the mains. stator and rotor.
  • Failure of small parts. bearings, retainers, nuts, washers, etc.
  • Dropping, knocking or other rough handling of the angle grinder. housing breakage.
  • Lack of preventive cleaning. gearbox malfunction or breakage of the on/off button./off.

If armature is defective, motor overheats, winding insulation melts and windings short-circuit. The contacts between the armature winding and the collector plates are unsoldered. Current supply is interrupted and the motor stops working.

A good diagnosis of rotor damage can determine the extent of repair work. The specifics of the formation of defects, which most appear when overheating the angle grinder during prolonged work at high loads, allows you to determine them visually.

Standard diagnostics involves a visual analysis of the device. It is necessary to analyze the integrity of the wire and the current supply to the collector of the motor. The angle grinder should be inspected from the inside if the power supply is normal. It is not very difficult to disassemble the device. It is best to photograph the location of the main modules of the device during disassembly. After disassembly, conduct a visual inspection of the armature for such properties:

Causes of the malfunction and typical signs

The main factors that affect stator failure are as follows:

Characteristic signs of stator malfunction are as follows:

  • there is a persistent smell of burnt insulation of the winding wires;
  • the temperature of the body parts of the angle grinder rises noticeably;
  • the electric drive of the angle grinder buzzes stronger than normal;
  • it is quite possible the appearance of smoke;
  • The spindle starts to rotate more slowly, or may even stop altogether;
  • The opposite extreme of the previous case is also possible. the spindle runs at high revolution speeds and runs at a breakdown.

Types of breakdowns in angle grinders

Typical minor malfunctions

In the case of a malfunction, you must first rule out elementary breakdowns:

  • The angle grinder does not turn on. The angle grinder suddenly became faulty. it stopped turning on. In that case, you need to check the serviceability of the socket, then plug and power cord, perhaps the drive simply does not work due to the fact that the product does not get the current.
  • the cable and plug are intact, but the drive does not work. The start button must be checked. Angle grinder switch is easier to repair by buying a new button and replacing it. Because it is rarely repairable. mostly the plastic switch rod is broken inside. If you want to experiment, you can disassemble it, numbering the contacts, and reassemble everything in its place, so that after reassembly there is no short circuit.
  • The above parts are intact, but the angle grinder doesn’t want to work. then it’s time to check the brushes. It may be time in the angle grinder to change them. Brushes are constantly warmed by work, so they wear out quickly and need to be replaced more often than other parts, and in pairs.
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Significant defects

Having excluded all minor breakages, it is necessary to understand why the tool does not want to turn on, and how to repair it. Most likely, the faults are serious and require additional knowledge. This occurs in cases where:

  • The housing is deformed;
  • One of the bearings is jammed;
  • The armature or stator is not working;
  • The gear teeth of the chainwheel are broken or worn;
  • The manifold is out of order;
  • the sensor of the control electronics shows no signs of life.

If it is determined that the malfunction has occurred in the mechanical part of the angle grinder, then it is necessary to pay attention to the condition of the big gear that is on the shaft, and the bushings. If the teeth are worn or wobble, they need to be replaced immediately.

The most common faults

Malfunctions of the angle grinder are quite common. Everyone who works with this tool knows about it. What fails most often?

The spindle locking button is broken.

Just one awkward press on the spindle locking button while the disc is rotating causes it to break. It can sometimes be broken if it is used to remove a jammed disc. To prevent this from happening, use a wrench inserted into the openings beside the blade locking pin.

Breakage of the gear teeth

It usually occurs when a gearwheel jams. If you can hear a rattle in the gearbox, it is a sign of this malfunction. When the pinion has more than one tooth broken, the angle grinder will not be able to cut the desired material.

In order for the tool to continue to work, you need to change gears, all of them, and even the bevel wheel. Before you go to the store for parts, remember the manufacturer, model and power of the product.

The electric motor doesn’t work.

This type of failure occurs with angle grinders, which work in places where there is a lot of dust, and when they are given a rest, they are left on the ground. Dust that gets inside spoils the winding. High loads, especially for a small power angle grinder, will break the motor.

If the angle grinder is used to cut materials that create a lot of dust, it is advisable to cover the ventilation holes with something.

The bearing fell out

The weakest link, and not only at bolsters, are bearings. High speed rotation quickly wears out the mechanism. The good news is that it is easy to replace the bearing. Replacing the sprinkled bearing in the angle grinder, should be done in time, so as not to happen a breakdown that can not be corrected already.

Stator malfunction

This failure is easy to identify when the angle grinder turned on, but the disc speed is too intense and different from normal operation. then there is a winding fault in the stator. Stator failure is considered to be the most serious, requiring special skills to rectify. When in doubt, it is better to call in professionals, so you do not have to buy a new tool.

If the decision to repair yourself is made, it begins with cutting off the front parts of the winding, the remains are all removed. The next step is to make a new winding according to the template. It must be identical in the number of turns, with the same density and made of wire of the same thickness as the previous.


angle grinder, the power of which is less than 1100 W are usually equipped with spur gears. They are located on the stator. Greater power drills have helical gears. Each of the variants is cone-shaped, the gear rod of the angle grinder is crossed with the stator shaft at an angle.

Angle grinder gearbox repair mainly consists of replacing the gears. If the disc gear is broken, it is difficult to replace it, because it is very firmly fixed. It’s not hard to disassemble the gearbox:

  • You need to unscrew the nut on its side;
  • gently grip the rotor housing in a vise and lightly tap out the gear housing;
  • change the position of the clamped rotor and knock out through a wooden board the bearing;
  • unscrew the pinion from the shaft.

Speed regulator

Not all bandsaw models have a speed regulator. When the angle grinder is used for cutting, in principle, it is not necessary, but if grinding is carried out, it is simply necessary. If it suddenly stopped working, then most likely the board is burned out, which should be removed and buy the same one in a power tool store for further replacement.

Self-repair angle grinder is not always feasible. If something suddenly does not come out or not everything is clear, it is better to apply to the service center.

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