Common faults and solutions of generators

1. The generator's failure to generate electricity is often caused by the disappearance of residual magnetism or internal wiring errors, which can be checked using the following methods:
1) Check the tightness of the fan belt for suitability. If it is too loose, it will cause the generator speed to be insufficient, resulting in weak power generation.
2) Check the coordination between the commutator and the carbon brush. It has been proven that most generator failures occur here. Remove the dust cover and focus on checking the following aspects:
① Observe the surface condition of the commutator. If there are carbon black burn marks or oil stains that will directly affect the current output, they should be polished with "00" sandpaper and wiped clean with a clean cloth dipped in gasoline. If a glossy purple gray oxide film appears, it may not be worn out due to its good wear resistance.
② Check the binding pressure between the carbon brush and the commutator. Use your fingers or screwdriver to apply pressure to both carbon brushes. If the power generation is immediately normal, it indicates that the carbon brush spring is too soft or the carbon brush is excessively worn, and a new accessory should be replaced. If during transportation or field work, the fixed end of the carbon brush spring can be lifted with iron wire and connected to the connection screw of the carbon brush holder as a temporary remedy.
③ Check the tightness of the connection between the carbon brush and the commutator by observing the spark size between them. Control the engine above medium speed, then lap the armature and magnetic field terminal to increase the output current. At this point, there should be a weak small spark between the carbon brush and the commutator interface. If a large arc like spark occurs, it will quickly burn out the carbon brush and commutator, affecting normal power generation. At this point, the carbon brush can be pressurized with your fingers. If the spark is eliminated and the power generation is normal, it indicates that the binding pressure of the carbon brush is too low; If the spark cannot be eliminated, it indicates that the surface of the commutator is out of round, mica is protruding, or there is a short circuit, power outage, or iron collision in the armature coil.
3) If all the above checks are normal and there is still no power generation, the generator wiring and internal conditions can be checked using the wiping method. During the inspection, remove the regulator, connect the armature terminal and magnetic field terminal with a wire that collides with the battery terminal, and observe the spark situation.
There are usually four phenomena when the magnetic field wire head collides with the battery terminal: ① emitting small blue and white sparks, indicating good connection of the excitation circuit. ② No spark, indicating an open circuit in the excitation circuit. At this point, connect the magnetic field terminal to the battery terminal, then remove the terminal of the magnetic field terminal on the generator and collide with the casing. If there is a spark, it indicates that the connection is intact, but the excitation coil has broken circuit; If there is still no spark, it indicates an open circuit in the wiring. ③ If a small dark red spark is emitted, it indicates poor contact at some point in the excitation circuit. This problem is often caused by false welding Emitting a strong large spark accompanied by a loud sound indicates that the excitation circuit is colliding with iron. At this point, the magnetic field wiring terminal on the generator should be removed, and the magnetic field wiring terminal at the regulator should be collided with the battery wiring terminal again. If there is a spark, it indicates that the magnetic field coil has hit the ground.
There are also four phenomena when the wire head of the armature collides with the battery terminal:
① A large blue and white spark is emitted, indicating that the armature circuit is well connected.
② No spark, indicating an open circuit in the armature circuit. At this point, the armature wire head should be connected to the battery terminal. If the wire head on the motor armature terminal is removed and collides with the casing, if there is a spark, it indicates that the wiring is intact, and it proves that the carbon brush wire on the armature coil or its terminal is open circuit. If there is still no spark, it indicates an open circuit in the wiring.
③ A small blue and white spark emitted indicates poor contact at some point in the armature circuit.
④ Emitting a strong large white spark indicates that the armature circuit has collided with iron at some point.
2. Inspection of abnormal generator power generation
1) Grounding ignition method: Stabilize the engine speed above medium speed, then temporarily short circuit the armature magnetic field terminal of the generator. Use a screwdriver to momentarily touch the armature terminal with the casing. If a strong blue and white large spark appears, it indicates normal power generation; If there are small dark red sparks or no sparks, it indicates that there is no power generation. At this point, tighten the fan belt a bit, remove the armature and magnetic field wiring terminals and connect them to the wire ends of the regulator. Then, try the above method again. If the spark is normal, it indicates that the belt is too loose or the armature and magnetic field wiring of the regulator collides with iron. If there is still no spark, it indicates that the generator is faulty. The grounding ignition method is simple and feasible, but it cannot accurately detect the fault of insufficient power generation of the generator.
2) No-load voltage method: First, adjust the tightness of the fan belt to a moderate level, remove the armature and magnetic field terminals leading to the regulator, and then use wires to short-circuit the armature and magnetic field terminals on the generator. In the battery positive grounding system, connect the negative probe of a DC voltmeter (5-50 V) to the armature or field terminal of the generator. Connect the positive probe to the case and observe the reading of the needle. The rotor speed of the 220 watt generator is 1250 rpm, and the voltage should be 12.5 volts. When the speed reaches 2800 rpm, it can reach 35 volts. The 150 watt generator can reach 27 volts at a speed of 1650 rpm. If the voltage value is lower than the required value by more than 3 volts, it indicates that the generator is not functioning properly.
3) Electric motor test method: Short circuit the generator armature and magnetic field terminal, connect an ammeter in series to the negative pole of the battery, and connect the positive pole of the battery to the motor casing. If inspecting on the locomotive, the three terminals of the regulator should be short circuited with wires. After the circuit is connected, the generator immediately rotates smoothly. For a 150 watt generator, the current should not exceed 6.5 amperes, and for a 220 watt generator, it should not exceed 5.5 amperes. If the generator does not rotate, it indicates an internal short circuit, disconnection, or incorrect connection within the motor; If the sound is normal and the current is high, it indicates a short circuit between the excitation coil or armature coil; If the current is normal but there is noise, it indicates that the bearing is out of oil; If the current is high and there is noise, it indicates that the bearing clearance is too large, causing friction during rotor cleaning or improper assembly of a certain part; If the sound is normal but the current is low (3-4 amperes), and there is a large spark in the commutator, it indicates a local open circuit in the armature winding. When using this method to check the fault of the generator, two points should be noted: ① The current and sound are normal, and sometimes the power cannot be generated because the magnetic pole core of the generator cannot be magnetized. When the quality of the magnetic pole iron core is poor or the magnetic molecules are severely disrupted by violent impact, the magnetic field established by the excitation coil at 12 volts cannot magnetize the iron core. In this way, the iron core will have no residual magnetism and cannot generate electricity. At this time, the magnetization voltage should be doubled The speed of the DC generator during the DC motor test is directly proportional to the power supply voltage and inversely proportional to the magnetic flux of each pole. So when the generator is running, if the magnetic field wire head is removed, the magnetic field suddenly decreases, and the motor speed will suddenly increase. At this point, due to the weak magnetic field, the back electromotive force of the motor is very low, which increases the current flowing into the armature significantly. Therefore, the magnetic field line should not be disconnected during this test.
3. The generator overheats during operation
Overheating of generators is a common and common fault, often caused by the following reasons:
1) The output current is too high. Usually, due to voltage regulation failure within the regulator, the excitation current is too high, resulting in an increase in output current. It may also be due to a short circuit in the armature and magnetic field terminals of the generator, or due to human forgetting to remove the short wiring of the armature and magnetic field.
2) Short circuit between turns of excitation coil and armature coil.
3) Due to excessive bearing clearance causing friction between the armature core and magnetic poles, it is also possible to use the wrong bearing grease. Because the rotor speed is very high, high-temperature resistant sodium based or composite calcium based lubricating grease should be used. However, ordinary lubricating grease is prone to external flow and deterioration at high temperatures, resulting in bearing heating.
4) Strong sparks between the carbon brush and the commutator can also cause overheating of the armature coil and commutator. When the temperature exceeds the melting point of the solder, the solder at the joint is melted and thrown out under the centrifugal force of high-speed rotation of the rotor.