DIY engine anchor repair

In detail: DIY repair of an engine anchor from a real master for the site my.housecope.com.

In many household devices and home-made structures, low-power electric machines are used as a drive. Despite the high reliability of electric motors, their failure for a number of reasons is not uncommon. Given the relatively high cost of these devices, it is more practical to repair them rather than replace them. We suggest considering the possibility of rewinding electric motors at home.

As a rule, collector DC motors and brushless AC induction motors are used in everyday life. It is the repair of these drives that we will consider. Information on the principle of operation and design features of asynchronous and collector machines can be found on our website.

As for synchronous drives, they are practically not used in everyday life, therefore this topic is not touched upon in this publication.

Any type of engine problem can be mechanical or electrical. In the first case, strong vibration and characteristic noise may indicate a malfunction, as a rule, this indicates problems with the bearing (usually in the end cover). If the malfunction is not eliminated in time, the shaft can jam, which will inevitably lead to failure of the stator windings. In this case, the thermal protection of the circuit breaker may not have time to trip.

Video (click to play).

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"Burnt" stator winding wires

Based on practice, in 90% of failure of asynchronous machines, problems arise with the stator winding (open circuit, turn-to-turn circuit, short circuit to the case). In this case, the short-circuited armature, as a rule, remains in working condition. Therefore, even with a mechanical nature of the damage, it is necessary to check the electrical part.

In most cases, the problem can be detected by its appearance and characteristic odor (see Fig. 1). If it is not possible to establish a malfunction empirically, we proceed to diagnostics, which begins with a continuity call. If found, the engine is disassembled (this process will be described separately) and the connections are carefully inspected. When the defect is not found, it is possible to ascertain a break in one of the coils, which requires rewinding.

If the continuity does not show an open circuit, you should proceed to measuring the resistance of the windings, while taking into account the following nuances:

  • the insulation resistance of the coils to the case should tend to infinity;
  • for a three-phase drive, the windings must show the same resistance;
  • for single-phase machines, the resistance of the starting coils exceeds the given indications of the working windings.

In addition, it should be borne in mind that the resistance of the stator coils is quite low, so it makes no sense to use devices with a low accuracy class to measure it, most multimeters belong to those. The situation can be corrected by collecting a simple circuit on a potentiometer with the addition of an additional power source, for example, a car battery.

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Circuit for measuring winding resistance

The measurement technique is as follows:

  1. The drive coil is connected to the diagram presented above.
  2. The potentiometer sets the current to 1 A.
  3. The coil resistance is calculated according to the following formula: where RTO and UPETE were described in Figure 2.R is the resistance of the potentiometer, is the voltage drop across the measured coil (shown by the voltmeter in the diagram).

It is also worth talking about the technique that allows you to determine the location of the turn-to-turn closure. This is done as follows:

The stator, freed from the rotor, is connected through a transformer to a reduced power supply, after placing a steel ball on it (for example, from a bearing). If the coils are working, the ball will cyclically move along the inner surface without stopping. If there is a turn-to-turn short circuit, it "sticks" to this place.

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Steel ball testing

This type of electric machine is more likely to experience mechanical failures. For example, the wiping of brushes or clogging of the collector contacts. In such situations, repairs are reduced to cleaning the contact mechanism or replacing the graphite brushes.

Testing the electrical part is reduced to checking the resistance of the armature winding. In this case, the probes of the device to two adjacent contacts (lamellas) of the collector, after taking the readings, the measurement is made further in a circle.

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Checking the armature winding of the collector motor

The displayed resistance should be approximately the same (taking into account the instrument error). If a serious deviation is observed, then this indicates that there is an inter-turn short circuit or an open circuit, therefore, rewinding is necessary.

This is a reference data, so the most reliable way to get this information is to consult the appropriate sources. These data can also be given in the passport for the product.

On the net you can find tips in which it is recommended to manually recalculate the turns and measure the diameter of the wire when rewinding. It's a waste of time. It is much easier and more reliable for marking the engine to find all the necessary information, which will indicate the following parameters:

  • rated performance (voltage, power, current consumption, speed, etc.);
  • number of wires for one slot;
  • Ø wire (as a rule, insulation is not taken into account in this indicator);
  • information about the outer and inner diameter of the stator;
  • number of grooves;
  • with what step the winding is performed;
  • rotor dimensions, etc.

Below is a fragment of a table with winding data for type 5A electric machines.

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Example of a table with winding data

It is necessary to immediately warn that without special equipment and work skills, rewinding the coils will most likely be a useless exercise. On the other hand, a negative experience is also an experience. Understanding the complexity of a process is the best explanation for its cost.

We give an algorithm of actions for asynchronous machines, it is as follows:

  1. Disconnect the drive from the mains (380 or 220 V).
  2. We dismantle the electric motor from the structure where it was installed.
  3. Remove the rear cooling fan shroud.
  4. We dismantle the impeller.
  5. We unscrew the fastening of the end caps, and then remove them. It is advisable to start from the front part; after dismantling it, the rotor will easily "come out" from the rear cover.
  6. We take out the rotor.

This process can be greatly facilitated if you use a special device - a puller. With its help, it is easy to free the motor shaft from the pulley or gear, and also to remove the end covers.

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Dismantling puller

We will not give instructions for disassembling a collector motor, since it is not particularly different. The structure of this type of electric machine can be found on our website.

The sequence of actions is as follows:

  1. Using a knife, remove the bandage fasteners and the insulating coating from the wire connections. Some instructions recommend fixing the wiring diagram, for example by taking a photo. There is no particular point in doing this, since this is a reference information and it is not a problem to recognize it by the make of the engine.
  2. Using a chisel, we knock down the tops of the wires from each end of the stator.
  3. We release the grooves using a punch of the appropriate diameter.
  4. We clean the stator from dirt, soot, impregnation varnish.

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Stator free from winding

At this stage, we recommend that you stop, take the case and take it to the specialists. Self-dismantling will reduce the cost of restoration work. As mentioned above, it is quite difficult to rewind the coils with high quality without special equipment. To understand the complexity of the process, we will describe its technology, which will facilitate the choice.

The process consists of the following steps:

  1. Installation of insulators in each groove (sleeve).
  2. The thickness of the material and its characteristics are selected according to the reference book.
  3. The winding data is determined by the brand of the motor.
  4. On a special machine, the required number of turns of the random coils is wound. On the network you can find photos and parameters of homemade hand-held machines, but the quality of their work is rather questionable. Image - DIY engine anchor repairLoose winding machine
  5. The coil groups are placed in the grooves, after which they are strapped and connected. These processes are quite complex and manual.
  6. Impregnation is in progress. For this, the body is heated to a temperature of 45 ° C - 55 ° C and is completely immersed in a container with impregnating varnish. It makes no sense to fill the wires with varnish, since in this case there will still be voids left.
  7. After impregnation, the body is placed in a special chamber, where it is dried at a temperature of 130-135 ° C.
  8. Final testing of the coils with an ohmmeter.
  9. Assembly and test run (if only the body was transferred for repair, and the rest of the parts and fasteners).

If only the case was handed over for restoration, we recommend checking the coils before turning on the motor.

The process of replacing the winding of a collector motor is somewhat similar, with the exception of small nuances associated with the design feature. For example, the anchor is sent for rewinding, and not the case, provided that the problem did not arise with the excitation coils. In addition, there are the following differences:

  • A special machine of a more complex configuration is used for winding.
  • It is imperative to groove, balance the armature (in the final part of the process), as well as clean and grind it.
  • Using a special milling machine, the collector is cut.

These processes require special equipment, without it, rewinding of electric motors is a waste of time.

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