Motor starters are usually fitted with a trip device which deals

with overcurrents from just above normal running current of the motor

to the stall current. The aim should be for the device to match the

characteristics of the motor so that full advantage may be taken of

any overload capacity. Equally, the trip device must open the starter

contactor before there is any danger of permanent damage to the


Contactors are not normally designed to cope with the clearance of

short-circuit conditions, and it is therefore usual for the contactor

to be backed up by HRC fuses or by circuit-breaker.

The arrival on the scene of very compact motor starters and the need

to provide proper back-up protection to them has posed a problem. BS

EN 60947-4-1 (1992) (previously BS 4941) ‘Motor starters’,

describes three types of co-ordination, the most onerous condition

(type C) requiring that under fault conditions there shall be no

damage to the starter or to the overload relay. The usual back-up

device will be the HRC fuse. It is important that the user check with

the manufacturer's catalogue to ensure that the correct fuse is

used to secure this co-ordination.

The starter motor

in your automobile is a DC motor. If you were to accidentally reverse

the battery polarity, the DC motor would still rotate in the same

direction. Reversing polarity of the battery will not cause the motor

to rotate in the opposite direction.

To reverse the direction of rotation of this type of motor, either

the current through the stator winding or the current through the

armature must be reversed. Reversing both of them will result in the

same magnetic polarities between the armature and the stator poles.

This results in the same direction of rotation.

The industry's standard for reversing the direction of rotation

of a DC motor is to reverse the direction of the current through the

armature. When a DC motor has more than one set of windings, shunt

and series, as well as interpoles, the currents through all the

stator windings would need to be reversed in order to change

direction of rotation. This is far more complicated than merely

reversing armature current.

All engines require a toyota starter motor to turn them

over before firing. In conventional vehicles, this is a

straightforward, but powerful, direct-current electric motor. When

the starter switch is activated by the driver, current flows to a

solenoid attached to the starter motor. This current moves a lever

into the solenoid that then causes a cogwheel of the motor to mesh

with the teeth on the circumference of the flywheel. At the same

time, an electrical contact is closed to allow a large current to

flow and rotate the starter motor as well as the engaged flywheel.

Typically, currents of hundreds of amperes are required to start the

engine and are provided by the battery, which is generally a 12-V

lead–acid module. The battery is recharged by the alternator–

rectifier combination when the engine is running. Automotive

batteries have improved enormously over the years and have far longer

lives than formerly, even though they may be called upon to power

many more functions. Although guarantees may be for two or three

years, in practice batteries often operate for eight years or longer

before failing. Moreover, modern car batteries no longer require

periodic ‘topping-up’ with de-ionized water. Further information on

the evolution of the lead–acid battery is given in Section 7.4,

Chapter 7.

A starter motor is required to run the internal combustion engine up

to a speed sufficient to produce satisfactory carburation.

The starter motor is mounted on the engine casing and a pinion on the

end of the BMW starter motor shaft engages with the flywheel teeth.

The gear ratio between pinion and flywheel is about 10:1. A machine

capable of developing its maximum torque at zero speed is required.

The series wound motor has speed and torque characteristics ideal for

this purpose.

The engagement of the pinion with the flywheel is effected in

different ways. Perhaps the two most commonly used are the inertia

engaged pinion and the pre-engaged pinion methods.

In inertia engagement the drive pinion is mounted freely on a

helically threaded sleeve on the armature motor shaft. When the

starter switch is operated, the armature shaft revolves, causing the

pinion, owing to its inertia, to revolve more slowly than the shaft.

Consequently, the pinion is propelled along the shaft by the thread

into mesh with the flywheel ring gear. Torque is then transmitted

from the shaft to the sleeve and pinion through a heavy torsion

spring, which takes up the initial shock of engagement. As soon as

the engine fires, the load on the pinion teeth is reversed and the

pinion tends to be thrown out of engagement. Inertia drives are

usually inboard, i.e. the pinion moves inward towards the starter

motor to engage with the ring gear; an inboard is lighter and cheaper

than an outboard starter.

To obtain maximum lock torque (i.e. turning effort at zero speed),

the flux and armature current must be at a maximum, so resistance in

the starter circuit (windings, cables, switch and all connections)

must be a minimum; any additional resistance will reduce the starting

torque. Generally, the inertia engaged

mercedes starter motor is energised via a solenoid

switch, permitting the use of a shorter starter cable and assuring

firm closing of the main starter-switch contacts, with consequent

reduction in voltage drop. The use of graphite brushes with a high

metallic content also assists in minimising loss of voltage.

While inertia drive has been the most popular method of pinion

engagement for British petrol-engined vehicles, the use of outboard

pre-engaged drive is increasing. The pre-engaged starter is essential

on all vehicles exported to cold climates and for compression

ignition engines which need a prolonged starting period.

The simplest pre-engaged type of drive is the overrunning clutch

type. In this drive, the pinion is pushed into mesh by a forked lever

when the starter switch is operated, the lever often being operated

by the plunger of a solenoid switch mounted on the motor casing.

Motor current is automatically switched on after a set distance of

lever movement. The pinion is retained in mesh until the starter

switch is released, when a spring returns it. To overcome edge-to-

edge tooth contact and ensure meshing, spring pressure or a rotating

motion is applied to the pinion. An overrunning clutch carried by the

pinion prevents the motor armature from being driven by the flywheel

after the engine has fired. Various refinements may be incorporated,

especially in heavy-duty starters. Among these are: a slip device in

the overrunning clutch to protect the motor against overload; a

solenoid switch carrying a series closing coil and a shunt hold-on

coil; an armature braking or other device to reduce the possibility

of re-engagement while the armature and drive are still rotating; a

two-stage solenoid switch to ensure full engagement of the starter

pinion into the flywheel teeth before maximum torque is developed

(Figure 44.15).

The engine may be started either by an electric

honda starter motor
or by compressed air. 

An increasing used form of motor starter is known as “soft start”.

Soft starters utilise sold state technology, typically thyristors, to

supply the motor.

In a “soft starter” voltage and frequency of supply to the motor is

varied in a controlled way in order to provide the required torque as

the speed increases up to full load.

Soft starts can be arranged to provide up to 200% full load torque at

starting, whilst limiting the current drawn from the supply to

perhaps 350% rather than the 600% typically experienced from direct

on line. Other parameters and facilities including kick start

ability, ramp time to full speed and low load energy saving are

available depending upon supplier.

Soft starters are available for the largest 400/600 volt motors. By

specifying soft starters the specification of the associated supply

system can be relaxed since large starting currents and resultant

voltage drops will not occur.

Some users are specifying speed control inverters for motor starting

even when full speed control facilities are not needed. So used

inverters provide a soft starter capability, have good motor control,

protection and diagnostic facilities as well as providing an energy

saving function, if needed.

The engine starting quality is strongly influenced by the


starter motor
and the injection strategy. Indeed, an

insufficient amount of kinetic energy initially provided to the

system will not compensate for the energy loss caused by the DMF

resonance. An adequate starter motor must be carefully chosen to

fulfil this requirement, even under critical conditions with low

battery voltage or corroded components of the starter system.

Moreover, the engine should not be fired too soon during the starting

phase before the starter motor reaches a stationary speed.

  • Created: 27-10-21
  • Last Login: 27-10-21

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