How to Check a Drill Stator with a Multimeter

Checking the stator of the angle grinder on the intercircuit short circuit video

Signs by which you can understand that the stator is malfunctioning:

No spark?. Testing stator with multimeter

  • There is a smell of burning insulation.
  • The body overheats.
  • Smoke appears.
  • The shaft rotation slows down or stops.
  • Spontaneous shaft unwinding, tool suddenly reaches maximum speed.

The winding wires are covered with a protective layer of insulating varnish. When overheated, it burns up and breaks down. This causes a short circuit of the windings. Varnish gives off a peculiar odor. Short-circuiting just one of the wires completely knocks out the angle grinder.

check, stator, multimeter

Rules to avoid overheating of the engine angle grinder:

  • Do not switch the unit off immediately after working at reduced speed, but after about one minute.
  • Take frequent breaks when working under load at lower speeds.

Often it is possible to avoid replacing a faulty stator by rewinding it. Rewinding of a damaged stator coil of the angle grinder can be done with your own hands, but it is still recommended to entrust this work to a specialist.

Causes of inter-turn short circuits at the rotor

There are several reasons that the wiring on the turns of the rotor can short out. Among them:

Overloading of the electric motor and consequent overheating and short circuiting can occur due to improper use of the equipment by the operator. Do not exceed the load on the mechanism that is specified in the technical documentation. That’s why you should always read the manual of an electrical appliance carefully. This also happens in industrial plants, but there workers are trained before they are allowed to work with machines and other electrically powered machinery.

Other causes of overloading include damage to the armature bearings. They may seize due to manufacturing defects, wear or lack of lubrication. This would severely hamper rotation and lead to critical overloads. Dirt and solid debris, e.g., metal chips, which have entered the housing can also prevent the rotor from turning. As well as splinters of a broken part inside the motor. They can not only slow down the rotor, but also damage the winding insulation, which also leads to inter-twist short circuits.

If water gets inside the motor it is in itself dangerous, because it is an excellent conductor and can cause a short circuit. But even if this does not happen, high humidity will cause corrosion, which will prevent the rotation of the rotor. And that, as we’ve seen above, leads to overheating due to increased loads and shorting of the wires.

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You can tell if the rotor coil windings are shorted by unstable motor operation, sparking brushes and uneven heating of the housing. There are also power losses and sudden voltage spikes when switching a device with a closed rotor into the mains. You can tell by the blinking of a light bulb. It is possible that the smell of burning insulation will appear.

Check the rotor for short circuits, even if there is the slightest doubt. Otherwise, it can cause more serious damage to both the motor and the entire mechanism or machine. A single shorted section will cause overheating, breaking the insulation of adjacent coils and causing a wider short circuit. Therefore, a motor with an interturn fault on the rotor will not run for long.

Disassembling the angle grinder

How to check the stator of an angle grinder? Begin with the disassembly of the device. A screwdriver is needed to do the job.

  • Remove all unnecessary parts from the surface on which you will disassemble the angle grinder.
  • Remove the wheel.
  • Remove the screw fixing the hood.
  • Remove screws holding the plate.
  • Slide the hood toward the cord.

The stator is on the outside of the motor, on top of the rotor. To remove the stator you must first remove the brushes, then remove the gearbox, and after that pull the armature from the angle grinder body. The rotor must be removed from the stator prior to testing. Inspection is recommended to conduct in bright light. First of all, carefully inspect the winding and make sure that there are no visible breaks in it. If examination does not reveal the cause of the stator malfunction, a special stator inspection tool will be necessary.

Checking with a short circuit indicator

A winding breakage or short-circuit in the winding can be detected with the short-circuit indicator (IK). Other names are as follows: Inter-turn fault indicator or electrical machine winding fault indicator.

  • power supply unit;
  • housing with LCD display, sockets for connecting accessories;
  • connecting wires;
  • a large inductive sensor;
  • small inductive sensor.
check, stator, multimeter

The principle of operation of the indicator is based on the induction of pulse electromotive force in the tested winding. If there are short-circuited windings, the pulse of the magnetic field from the short-circuit current flowing through them is registered.

The procedure for checking the stator of the angle grinder using the IDVI device:

check, stator, multimeter
  • Inspect the short circuit indicator. Make sure there is no external damage, integrity of connecting wires and sensors.
  • Connect the power supply.
  • Press the power button and make sure that the device functions correctly.
  • If the indicator has been out in the cold for a long time, keep it at room temperature for at least two hours.
  • Switch off power supply to the angle grinder.
  • Choose the small or the big one depending on the stator size.
  • If the angle grinder’s data sheet does not specify the rated voltage per coil winding turn, it must be determined according to the formula The rated voltage of the entire coil divided by the number of turns.
  • Switch device back on.
  • Set the pulse test voltage amplitude on the display to a value higher than that obtained in the calculation.
  • Hold the probe against the coil surface and check all the slots one after the other, waiting 3-4 seconds. If a short circuit is detected, the unit will beep and the corresponding inscription will appear on the display.
  • If no short-circuited turns are found, set the next higher amplitude on the instrument and check for any winding insulation faults.
  • Switch off the device.
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With a winding fault indicator you can check the insulation condition between the stator and rotor coils as well as between the stator winding and the angle grinder housing. If you can not buy a ready-made device, you can make a simpler indicator of short circuits yourself.

An unusual test

the most accurate way is to check the stator with a metal ball and a step-down current transformer. Connect the stator to the three phase leads from the transformer. After checking the correctness of connection, switch on our circuit with undervoltage into the mains.

Throw a ball inside the stator and watch how it behaves. If it is “stuck” to one of the windings, it means that there was an inter-turn short circuit. If the ball rotates in a circle. the stator is defective. Rather unscientific, but effective method for detecting inter-turn faults in the stator.

Checking with the alternator removed

Before determining the short circuit with a multimeter, an external inspection checks the performance of the starter elements:

  • The presence of traces of abrasion of the armature surface on the lamellae.
  • Condition of collector plates for wear and soldering. On the working armature, the depth between the grooves of the collector plates must be at least 0.5 mm.
  • The clutch should only be cranked to one side, and the other side can be cranked together with the anchor shaft.
  • Inspection of the pinion, it must be without chips and wear of teeth.
  • The fork is undamaged and there is no wear on its edges where it enters the coupling.
  • Intactness of the starter reducer pinion.
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Briefly about the angle grinder

Angle grinder or angle grinder (angle grinder). used in construction operations, when you need to perform processing of solid building materials: stone, metal, wood and other.

The main detail of the angle grinder. built-in electric motor, which can operate from both a domestic AC 220 V and the battery. The electric motor consists of 2 elements: the electrostator and the rotor. The latter, rotates when the motor is running, so it is also called an anchor. In order to fix the angle grinder, you will need to check the stator and the rotor separately.

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Stator angle grinder is a fixed structure in the form of a core made of sheet electrical steel. There are slots in it, in which the winding is placed, wound in a certain way, its wires are parallel to each other, to reduce eddy currents.

408-316 Stator for Bosch GWS6-100/GWS6-115 HAMMER. 220Volt photo

The winding is necessarily coated with electrical insulation varnish in order to protect against possible short circuits between the wires. In the slots of the cores between the coils there is insulation made of electric cardboard, fiberglass tape and other similar materials. In the vast majority of models of angle grinders, the stator is tightly seated inside the body of high-strength plastic, which is the protection of the entire electrical part of the angle grinder.

Repair, replacement, rewinding

After conducting diagnostics and determining the types of rotor faults, the decision on repair methods follows. It is possible to make repairs with your own hands, which will be associated with independent rewinding of the anchor. If this option seems time-consuming and complicated, you can go on a simplified scheme and replace the burned rotor with a new one, corresponding to the model of the angle grinder. The easiest, but also the most expensive option. is to contact a special service.

When deciding to repair the anchor with their own hands to help information that is available in the articles “How to remove the anchor from the angle grinder”, “Replacing and repairing the anchor of angle grinder”, “Rewinding the anchor of angle grinder with their own hands”.

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