Drill Does Not Gain Speed ​​And Spark Brushes

In household electrical equipment, collector motors are widely used. Small dimensions, lightness, simplicity in management caused their presence in angle grinders, rotary hammers, circular saws, screwdrivers. The main disadvantage is the increased wear of the brush-collector pair. The failure of this unit is predetermined by the arising of sparking in it.

The device of the electric motor and the principle of operation

The principle of operation of the electric motor is based on the interaction of a conductor with a current located in a magnetic field.

A magnetic field creates a stator.

The main element of its design for the DC motor is a permanent magnet, for alternating current. the excitation winding. The rotor (anchor) has its own winding, to which voltage is applied using a brush-collector assembly. The interaction of magnetic fields makes the rotor rotate.

The collector consists of a set of contacts, which are copper plates located directly on the rotor. Mikanite or mica cuffs act as insulators for each individual contact. Graphite brushes. sliding contacts pressed to the collector.


Transient windings occur in the rotor windings due to intermittent mechanical contact of the brushes with the collector plates, which causes the formation of small arcs.

Important: A fully functional engine does not exclude sparking during operation. There are other reasons that cause severe sparking and create the possibility of motor failure.

Brush wear

During prolonged use or low-quality material of the brushes, they cease to be tightly pressed to the contacts of the collector. Due to poor contact, the engine does not gain momentum or does not start immediately. A worn brush is easy to identify visually.

To correct the situation, replacing only the worn part, sometimes fails. Replace brush holder and spring.

Short circuit in the armature winding

The consequence of this defect is uneven sparking on the collector. On some plates it will be stronger than on others. Due to the presence of inter-turn circuit, the current in individual sections of the rotor winding will be stronger than in others.

Video: Drill Does Not Gain Speed ​​And Spark Brushes

Rewinding or replacing the rotor will fix the problem.

Malfunction in the stator winding

A defect similar to the closure of the rotor winding takes place for the stator winding. You can check the presence by measuring the resistance of parts of its windings. With a strong difference, it is necessary to rewind the winding or replace it.


The product of brush wear is graphite dust, it is an additional source of increased sparking. Dust accumulation occurs between the plates, which creates additional conditions for the process of sparking. Maintenance work on cleaning the collector with emery paper and cleaning the dirt between the plates will keep it clean.

Incorrectly installed brushes

If the brushes are located with a deviation from the norm to the collector surface, a significantly larger amount of graphite dust is generated during operation. The shifted brushes must be corrected.

Poor brush contact with the collector

The electric motor spends part of the operating time in overheating mode. In such conditions, carbon deposits form on the collector. Bad contact leads to an increase in sparking brushes and even more soot.

It is necessary to clean the surface of the collector with sandpaper with fine grain. Use a screwdriver to increase the stripping effect. Clamp the rotor of the engine and, at low revs, perform sandblasting with sandpaper. After you need to finally polish it on a felt circle.

Mechanical disturbances

Mechanical reasons are caused by non-compliance with the requirements of design and technological documentation. Most mechanical causes are eliminated by turning a collector on a lathe. This repair operation is entrusted to a qualified technician. Here are some types of malfunctions that may indicate a breakdown:

  1. The collector surface has irregularities;
  2. The runout of the shaft exceeds the value specified in the technical documentation;
  3. Separate collector plates favor a common level for all;
  4. Protrusion of isolation (mica);
  5. Brushes in brush holders move with jamming;
  6. On the contrary, the brushes are inserted into the brush holders with a large gap, which creates vibration during operation;
  7. Brush holders mounted far from the collector;
  8. Uneven tension of the springs, as a result of the difference in the effort of preloading the brushes.

Videos that can help solve your case:

Drill Does Not Gain Speed ​​And Spark Brushes


An increased spark indicates abnormalities in work. It is required to carry out measures to identify and eliminate deficiencies. Failure to do so will shorten the life of the engine, and possibly the entire power tool where it is involved. The best option is to use the services of a service center for the repair of household appliances.