All about the marine-diesel-engine motor-starters

Motor-Starters - The Types

There are several types of starters in use, the most common being the overrunning clutch starter, and inertia-engagement Bendix drive is now less common. There are four basic groups of starters:

Pre-engaged (Direct) Drive Starters

The most common type of starter motors are the solenoid-operated direct drive unit and the operating principles are the same for all solenoid-shifted motor-starters. When the ignition switch is placed in the Start position, the control circuit energizes the pull-in and hold-in windings of the solenoid. The solenoid plunger moves and pivots the shift lever, which in turn locates the drive pinion gear into mesh with the engine flywheel. When the solenoid plunger is moved all the way, the contact disc closes the circuit from the battery to the starter motor. Current now flows through the field coils and the armature. This develops the magnetic fields that cause the armature to rotate, thus turning the engine.

Gear Reduction Motor-Starters

Some manufacturers use a gear reduction starter to provide increased torque. The gear reduction starter differs from most other designs in that the armature does not drive the pinion directly. In this design, the armature drives a small gear that is in constant mesh with a larger gear. Depending on the application, the ratio between these two gears is between 2:1 and 3.5:1. The additional reduction allows a small motor to turn at higher speeds and greater torque with less current draw. The solenoid operation is similar to that of the solenoid-shifted direct drive starter in that the solenoid moves the plunger, which engages the starter drive

Sliding Gear Drive Motor-Starters

These two stage starters have either mechanical or electrical pinion rotation. The electrical units have a two-stage electrical pinion-engaging drive. The first stage allows meshing of the starter pinion without cranking the engine over. The second stage starts when the pion fully travels and meshes and then allows full excitation and current flow to the starter motor. The First stage of mechanical units has a solenoid switch, which pushes forward the pinion engaging drive via a lever. When pinion meshing occurs current is applied to the starter via the solenoid switch.

Bendix Drive Inertia Motor-Starters

The Bendix friction-clutch mechanism drive was developed in the early 20th century. They use a drive friction clutch, which has a drive pinion mounted on a spiral-threaded sleeve. The sleeve rotates within the pinion, and moves the pinion outwards to mesh with the flywheel ring gear, and the impact of this meshing action is absorbed by the friction clutch. The engine once started then turns at a higher speed and drives the Bendix gear at a higher speed than the starter motor. The pinion then rotates in the opposite direction to the spiral shaft and then disengages. The drive pinion being thrown out of mesh and then stopping is a common fault.

Always wait several seconds before attempting to restart as the drive mechanism may be damaged. Another fault is when the pinion does not engage after the starting motor is energized, and a high-pitched whine is emitted from the starter. Turn off the ignition immediately as the unloaded DC starter motor will overspeed and be seriously damaged. Problems can be minimized by ensuring that the sleeve and pinion threads are clean and lubricated so that the pinion engages and disengages freely. The Bendix gear, shaft, bearings and end plates can be cleaned of dried grease with WD40 and oiled with a fine sewing machine 3 in 1 oil.

Motor-starters - Installation, Maintenance and Troubleshooting.

Starter installation is generally limited to two factors. The first is being mechanically secure, and the second is that the attached cables are of the correct rating and that terminal nuts are properly torques up so that they do not work loose. In addition, the negative cable should also be attached as close as practicable to the starter. Starter motor design is generally robust as it must withstand the shocks of meshing, engine vibration, salt and moisture laden air, water, oil, temperature extremes, high levels of overload etc. Preventive maintenance is essential to ensuring reliability:

Shaft Corrosion. A common problem especially on idle vessels is the buildup of surface corrosion, or accumulated dirt on the shaft and pinion gear assembly, and lack of lubrication causes seizure or failure to engage. It is good practice to remove the starter every 12 months, clean, and lightly oil the components according to makers' recommendations.

Starter-Motors Maintenance. Problems often occur with seized brushes, and this is primarily caused by lack of use. Always manually check that brushes are moving freely in the brush-holders, and that the commutator is clean. Remove all dust and particles using a vacuum cleaner. Wash out with a quality spray electrical cleaner if badly soiled. Follow the DC motor maintenance procedures. Under no circumstances clean and polish the commutator with any abrasive materials.

Motor-Starters Troubleshooting. Many are familiar with the silence and loud click when the start solenoid operates but the starter fails to turn over. The main causes are due to bad negative connection, bad positive connection caused by loose or dirty connections, or a solenoid plunger sticking and not closing fully preventing the main contacts from closing. Motor-starters require looking after, and if they are, troubleshooting will be a rare requirement

All about motor-starters and a lot more about engine electrical systems