Strong sparking under the brushes of the collector motor of low power direct current most often indicates a violation of electrical contact in the switching zone or displacement of the neutral, which requires immediate diagnosis in order to avoid burnout of lamellae. If you observe a bright arc flying out from under the brush holders, this indicates that the process of switching the anchor windings occurs with a delay or excessive energy, destroying the copper-graphite node. Ignoring this symptom leads to blackening of the collector, the appearance of sodium and, ultimately, to a short circuit of the turns of the anchor.
To effectively combat the problem, it is necessary to understand the physical nature of the phenomenon: under ideal conditions, the current in the short-circuited section should change direction smoothly, without breaking the chain and forming a spark. But in the real world collector-machine low power, such as starters, windows or wiper drives, this is hampered by the inductance of the windings and the resistance of contact. The main task during repair is to minimize the additional switching current, which causes arc formation between the outgoing brush and the collector plate.
The first step in analysis is always a visual assessment of the nature of the sparking and the state of the friction surfaces. Depending on the intensity of the glow and its localization, it is possible to determine whether the cause is mechanical wear, electrical overload or improper installation of the brush machine. It is important to note at once that weak sparking (classification 1-11⁄4 according to GOST) is permissible when working, but the appearance of a circular fire or a stable arc requires intervention.
Mechanical causes of unstable operation of the node
The most common cause of increased sparking are mechanical defects of the surface of the collector or the brushes themselves. If the copper plates are produced, beat or contaminated with oil, the contact area is sharply reduced, which leads to local overheating and breakdown of the air gap. The uneven surface does not allow graphite brush fit tightly to the collector, creating microgaps, in which the arc flashes when the chain is broken.
Also critical parameter is the pressure of the brushes on the collector. Too little pressing increases the transient resistance, causing sparkling under the back edge of the brush, whereas excessive pressure leads to accelerated mechanical wear and heating of the unit. In low-power engines, spring mechanisms are often used, which eventually lose elasticity or, conversely, catch up, violating the design mode of operation.
⚠️ Attention: The use of incorrect stiffness brushes can cause rapid wear of the collector. Always choose the marking of graphite according to the product passport.
To eliminate mechanical causes, a number of actions must be performed to restore the geometry and purity of surfaces. Often it is enough to grind the collector and grind the brushes to achieve a tight fit.
- 🔧 Checking the beating of the collector with the indicator head and eliminating the production by grinding.
- 🔧 Assessment of the condition of the brush springs and replacement of those whose force differs from the norm by more than 20%.
- 🔧 Cleaning the surface of the collector from oil stains, sodium and oxides with special solvents.
- 🔧 Control of the gap between the brush and the wall of the brush holder (should be within 0.1-0.3 mm).
How to properly wipe brushes
For high-quality laundry, use a glass skin (not sandpaper!), superimposed on the collector. Move the anchor back and forth, avoiding rotation so that the brushes take the shape of a surface.
Electrical factors and neutralization
If the mechanical part is in good working order but the sparking persists, the problem lies in the electrical switching processes. The key parameter here is the position of the brushes relative to the magnetic neutral of the machine. When the brushes are displaced from the neutral zone, a reactive EMF is induced in them, which prevents the current from quickly changing direction, causing sparking under the front or back edge depending on the direction of rotation.
In DC machines of low power, the position of the brushes is often fixed constructively, but in some models the possibility of turning the traverse is provided. Displacement can occur due to vibrations, loosening of fasteners or poor quality previous repairs. For precise installation, neutrals use the three-point method or oscilloscope, achieving a minimum spark when reversing the direction of rotation.
Another electrical factor is the state of the interlamellan connections and anchor windings. A circuit between the collector plates or a turn-on circuit in the winding violates the symmetry of the magnetic field and the distribution of currents. This causes the switching current to become too large in individual sections, causing a strong spark that can develop into a circular fire throughout the collector.
To diagnose electrical faults, the method of voltage drop between lamellae is used or the PJA device (checking anchors) is used. Detection of a defective section allows you to localize the problem and avoid replacing the entire node if repair is possible.
Effects of working conditions and load
The mode of operation directly affects the intensity of spark formation. The operation of the engine in the overload mode, when the anchor current exceeds the nominal value, is always accompanied by increased sparking. This is because the energy stored in the magnetic field of the short-circuited coil is proportional to the square of the current, and when overloaded, it becomes sufficient to break through the air gap.
Also negatively affected by frequent starts and reverses, characteristic of servo drives and actuators. At these moments, the currents of transient processes are many times higher than the working values. If the control system does not have proper protection or smooth start, the brushes are subjected to extreme heat and electrical stress, which leads to their rapid destruction.
The temperature of the machine also plays a role. When overheating, the properties of graphite change, the resistance of contact increases, and the oxidation of copper plates occurs more intensively. In turn, work at too low temperatures can lead to the formation of condensation on the collector, causing sparking and even breakdown.
⚠️ Warning: Prolonged engine operation with sparking above the permissible class leads to irreversible damage to the manifold and requires its replacement or professional rewiring.
To reduce the influence of regime factors, it should:
- ⚡ Control the load current with the help of an ammeter and prevent long-term operation on modes exceeding passport data.
- ⚡ Provide adequate ventilation of the engine to remove heat from the switching unit.
- ⚡ Use starters or controllers with current limitation function for reduced loads.
Diagnostics and troublesheet
Systematization of signs allows you to quickly identify the root of the problem. Below is a table that helps classify malfunctions by external signs of sparking and accompanying symptoms. Analysis of this data helps to make a decision about the method of repair: adjustment, replacement of parts or rewinding.
| The nature of sparkling | Probable cause | Action. |
|---|---|---|
| Sparkle under the back edge | Displacement of brushes against rotation | Turn the traverse in the direction of rotation |
| Sparkle under the edge | Turning displacement of brushes | Turn the traverse against rotation |
| Uniform sparking of all brushes | Overload, low voltage | Reduce the load, check the food |
| Sparking individual brushes | Bad contact, broken brush. | Replace the brush, check the pressing |
| Circular light | Closing, pollution, overload | Stop immediately, check anchor. |
The main rule: uniform sparking throughout the collector circle indicates electrical overload, and local - a mechanical defect or problem of a particular brush.
When filling out a diagnostic card, it is important to consider not only visual effects, but also temperature changes. Heating certain lamellae or brush holders may indicate a hidden defect that has not yet manifested itself as a visible arc. Using a thermal imager or a simple pyrometer greatly speeds up the search for fault in difficult cases.
Technology of replacement and selection of brushes
Replacement of brushes is the most common operation during repair, but it requires compliance with technology. You can't just insert new graphite and start the engine. Brand of brushes It must strictly correspond to the original, since different types of graphite have different resistivity and coefficient of friction. Installation of stiffer brushes can lead to abrasive wear of the collector, and softer ones to fan-shaped sparkling.
The installation process begins with a thorough cleaning of the brush holder from graphite dust and oil. The new brush should move freely, but without distortions in the clip. Particular attention is paid to the shape of the contact surface: it must repeat the curvature of the collector at least 75-80% of the area. For low-power engines, this is critical because of the small size of the assembly.
☑️ Checklist for brush replacement
After installing new elements, it is necessary to run the engine on a reduced load. This allows the brushes to finally get lost and form an oxide film on the collector, which improves switching. Abruptly reaching full power immediately after replacement can lead to local overheating and damage to newly installed parts.
Prevention and long-term operation
To minimize the risk of sparkling in the future, maintenance regulations must be followed. Regular cleaning of the engine from dust, which can be conductive, preserves the insulating properties of the units. In dusty or high humidity conditions, engines with an appropriate protection class (IP) should be used to prevent foreign particles from entering the interior.
Periodic monitoring of the state of the collector allows you to identify the initial stages of wear before they lead to an emergency. The appearance of a dark plaque or rainbow film on lamellae is often the first signal of incipient problems with switching or brush quality. Timely polishing of the collector with soft rags can extend the life of the node.
⚠️ Note: Do not use metal brushes or sandpaper to clean the collector, leaving large scratches. Apply only special wipes or glass skin zero.
It is also important to monitor the condition of the bearing units. Wear of bearings leads to radial beating of the anchor, which causes vibration of the brushes and violation of contact. Even a small vibration can destabilize the switching process in fast DC machines.
Tip: To extend the life of the collector, you can use contact aerosol cleaners, but only after the engine is completely dry and moisture residue is removed.
An integrated approach to maintenance, including mechanical inspection, electrical diagnostics and the correct selection of consumables, guarantees the stable operation of the engine. Sparkling is not just a cosmetic defect, but an indicator of the internal state of the machine, the neglect of which leads to expensive repairs.
Why do new brushes sparkle immediately after installation?
The new brushes have microscopic surface irregularities that do not coincide with the relief of the collector. The actual contact area in the first minutes of operation is less than 10%, which causes local overheating and sparkling. It is necessary to be laundred in a gentle mode (20-30% of the rated power) for 1-2 hours.
Can the collector be lubricated to reduce friction?
Absolutely not. Lubricant (oil, WD-40, solidol) has dielectric properties and dramatically increases the transient resistance of the contact, causing a strong sparkling. In addition, the lubricant collects graphite dust, forming conductive bridges between the lamellae, which leads to a short circuit.
How to distinguish sparking from overload from sparking due to displacement of brushes?
When overloading, the spark is uniform throughout the collector circle and increases with the growth of the load. When the brushes are displaced, sparking is localized under specific brushes (front or rear in the course of rotation) and can be observed even at idle. Also, the displacement often changes the nature of the sparking when the engine reverses.
Is it permissible to use brushes of another brand if there is no original?
In emergency cases, it is allowed to temporarily install brushes of a similar brand with similar current and speed characteristics, but this can reduce the life of the collector. Constant use of non-standard brushes is not recommended, as the difference in stiffness and resistance will upset the switching balance calculated by engineers for a particular engine model.