Starter Motors

Starter Motors

Estimated study time 30 Minutes.

Starter motors are very high current devices, they are the only device on board that can be connected directly to a battery with no fuse. A thorough understanding of the mechanism of and the wiring to your starter motor can get you out of a few tricky situations at sea, and help you spot problems before they become serious.

Most problems with starting circuits emanate from a lack of maintenance to the:

  1. Batteries
  2. Battery terminals
  3. Engine Negative connection (sometimes, misleadingly this is called the engine ground, or engine earth)

As mentioned earlier in the course, all connections between the start battery and the starter motor, must be periodically checked, cleaned and coated with dielectric grease, do not use vaseline!

Problems can arise from low battery state of charge that can cause the starter to stick.

The lesson below covers how the starter motor works, how its wired and how to find and repair common faults with your engine starting system. But prevention is much better, in all but a handful of cases a faulty starting system is due to a lack of maintenance and periodic testing, most faults can be pre-empted. Knowing your boat is the best tool for diagnosing potential problems, does it take longer to start, does the starting sound different than usual, if so carry out the tests as shown in the video lesson below. At this stage you should be familiar with batteries, relays, solenoids, cleaning and testing connections, and using the multimeter, and clamp meter, if not please complete those sections first.

The Engine Starting Process.

Each time you press the start button you initiate a cascade of events.

  1. The start button connects power to the start relay
  2. The start relay connects the power to the start solenoid
  3. The start solenoid connects power to the starter motor

Each of the above processes should be thought of as stand alone circuits, that can be tested individually, the first process is simply a start button powering an electromagnetic coil in a relay, nothing complicated. The second process is simply another circuit powering a solenoid, and the third is yet another circuit providing power to the starter motor. Diagnosing and testing requires us to reduce seemingly complex wiring down to the lowest denominator, ultimately even the most complex of wiring boils down to a collection of very simple single circuits.