Three Cases of Fault Repair of Locomotive Electric Starter

First, after the start switch is turned on, only a sound of a “click” from the starter is heard, but it does not turn the failure analysis and maintenance: under normal circumstances, the electric starter can effectively control the power under the control of the electromagnetic switch. The main contact of the starter is forced to close to ensure that the large current required by the electric starter passes smoothly. Due to the frequent start-up, between the electromagnetic switch and the main contact, not only through a large current, but also to withstand a strong impact, a long time, it will inevitably cause severe erosion and wear of its contact surface, so this A fault is a relatively common fault in electromagnetically actuated start systems. After analysis, a “click” sound from the electric starter at the start-up is actually the sound produced by the contact plate and the main contact at the instant of closing. It can be seen that the electromagnetic switch has completed the basic process of coil magnetization and iron core movement. The engagement of the electromagnetic switch has been completed, but the electric starter does not turn, it can be initially determined that the contact surface of the electromagnetic switch contact plate and the main contact surface is severely ablated. In order to confirm the above inference, the short-circuit test of the electromagnetic switch battery connection post and the magnetic field connection post using a screwdriver resulted in the normal operation of the electrical starter, which indicates that the failure occurred inside the electromagnetic switch. The electromagnetic switch was disassembled for inspection and it was found that the contact surface of the contact plate and the main contact had severe ablation. Turn the contact plate upside down, and then grind the two contacts flatly, install the test, and troubleshoot. Second, the start switch is placed in the starting position, the electric starter does not rotate, and the electromagnetic switch emits a slight “click” sound. Failure analysis and repair: In the troubleshooting of this fault, initially considered to be due to insufficient battery power supply, but to replace one Only after the battery with the same specifications as the battery has been fully charged, the failure has not been eliminated. It is inferred that the fault should come from the electric starter or starter relay. From the analysis of the fault phenomenon, when the start switch is turned on, the active iron core of the electromagnetic switch has a sound of action, indicating that the holding coil and the attraction coil have a 12V current, but the electric starter does not rotate, so it can be concluded that the fault originates from the electric starter and its Related parts. The reasons are: (1) There is a partial short-circuit fault in the attracting coil and the holding coil of the electromagnetic switch, which cannot generate enough electromagnetic force to close the contact plate and the contacts. (2) The magnetic core of the electromagnetic switch is hindered by oil stains or scale, and the stroke of the movable stroke is shortened, and the contact plate and the contact cannot be engaged. (3) The contact surface of the contact plate and the contact is severely oxidized and ablated, and the contact resistance increases. The cranking of the engine crankshaft cannot be driven by the electric starter by the normal operating current. (4) Electric starter Excitation windings, brushes, or armature windings, etc., are open circuited so that the electric starter cannot rotate. (5) The electric starter shaft and the shaft sleeve are locked and the electric starter cannot be rotated. During inspection and repair, in order to find out whether the fault originates from the DC motor or the electromagnetic switch, first use a screwdriver to short-circuit the power supply terminal of the electric starter and the magnetic field connection. As a result, not only does the electric starter operate normally, but it also drives the crankshaft of the engine. Obviously fault in the electromagnetic switch, replace a new electromagnetic switch, try again, troubleshooting. Decomposition of the electromagnetic switch, found that the coil has a partial short-circuit black mark, but it is not serious. After the cleaning, dipping, drying and shaping treatments are completed and tested, the electromagnetic switch works normally and can continue to be used. Third, turn on the start switch, hear the starter relay constantly "click" sound, electrical starter rotation power failure analysis and repair: from the start relay contact intermittent opening and closing action sound judgment, it is likely that the relay itself is faulty Therefore, the inspection should focus on the starter relay. Remove the starter relay to the electromagnetic switch connection wire, put the start switch in the starting position, measure the DC voltage of the starter relay S with the multimeter voltage block is about 10V, suspect that the internal contacts of the starter relay is not closed tightly, resulting in the supply voltage decline. Then measure the voltage between the “+B” and “SW” columns, which is also about 10V, and it seems that the battery power supply is insufficient. Upon examination, it was found that the density of the electrolyte in a battery cell in the battery dropped significantly, indicating that there was a serious self-discharge failure between the positive and negative plates of this cell. Replace a normal battery of the same specification and try again. If the fault persists, the engine cannot be started. After analysis, the main reasons for this failure are: (1) The contact plate is in poor contact with the main contacts, and the resistance increases. This not only results in ablation of contact points due to overheating, but also mainly impedes a strong starting current. by. (2) The surface of the commutator has oil contamination, excessive brush wear or insufficient spring elasticity, which increases the contact resistance between the brush and the commutator. (3) There is a local open circuit fault in the electrical starting armature winding or the excitation winding. The short-circuit test of the battery post of the electromagnetic switch and the magnetic field connection column with a screwdriver resulted in that the electric starter was still unable to operate. It can be assumed that the fault is due to the DC motor. The DC motor was disassembled and after careful inspection, it was found that the brush end cap lacked an insulating brush. After installing a brush, try again and troubleshoot. Because the electric starter armature winding and the excitation winding are in series with each other, the relationship between the two insulated brushes and the two ground brushes determines the characteristics of their circuit. When an insulated brush is lost, just a branch of the armature winding and the excitation winding is cut off. This not only weakens the strength of the magnetic field but also weakens the torque of the armature windings, thus creating the above-mentioned failure. Author: Agricultural Machinery Bureau of Huachuan County, Heilongjiang Province, from: "Use and Maintenance of Agricultural Machinery"

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