Auto Service World
Feature   January 1, 2008   by Mohammad Samii

Start it up: How the humble starter has changed;Electrical Starters;Electrical Starters

Today's starters and alternators are complex mechanisms. A review of their new designs will help one keep on top of what to pay attention for during servicing

The great advances in electronics that have drastically changed the ignition, fuel and engine control systems of modern automobiles have also affected the design and performance of rotating electrical components. Starters and alternators have been through major changes and transformations in performance and power output, and today have very little resemblance to the same units made in the 80’s or even the 90’s.

An understanding of the new features is a must for technicians who have to diagnose and repair issues that come up with these technologies.


What will be readily apparent to a technician when comparing today’s starters with older models is today’s systems are made to be lightweight, demand less cranking amps and provide equivalent power with better efficiency.

Current automotive and light truck starters have a few common traits which one should be aware of, especially as they require careful handling in order to prevent any damage to the complex mechanisms:

• Permanent Magnet Fields There are hardly any copper field windings used anymore. A majority of today’s modern starters have a permanent magnet field that is powerful as well as light weight. Handling these newer generation starters requires additional care as permanent magnet field shoes are highly brittle and susceptible to cracking in the case of accidental drops or intentional hammering.

• Reduction Gear Mechanism

There are rarely any direct drive starters anymore, as most new starters are of reduction gear design. That is to say, the rotational speed of a fast turning armature is entered into a reduction gear mechanism where its speed is reduced and the torque is increased and delivered to the flywheel via the starter drive.

The reduction gear mechanism can be either of planetary or offset type. Regardless of the type, they provide an approximate reduction ratio of 4-to-1 to decrease the armatures speed and increase the torque. This means the armatures are built to stand a very high RPM. (Fig. 1)

• Crimped-Cap Solenoids

Almost all newer starters use a crimped cap solenoid which does not allow taking the cap off to inspect or service the contacts. However, this is not a common service anymore. Rebuilding such solenoids is still feasible and as an electrical rebuilder we do rebuild most brands, but they require a special fixture for disassembly and recrimping the new caps in place.

Most of the features described above are also seen in medium-and to a lesser extent-in the heavy duty and diesel applications. Reduced weight has made handling of such lighter weight starters easier for the truck technicians.


One of the most prominent changes in the design of new alternators is perhaps the increased output. Where 0.5 – 0.7KW alternators were common for late 70’s or early 80’s cars, they have consistently grown in output where 1.5 – 2.0KW alternators are nearly common place. Of course this increased output from 40 -50 amps to nearly 150 amps had required changes in the sizes of the output cable and control circuits (fusible links) that differ from the older and simpler systems.

Some of the design changes seen in newer alternators are:

Dual Internal Cooling Fans

Additional heat, a byproduct of increased output, has drastic effect on sensitive electronics which requires efficient cooling methods. Thus it is common to see alternators with dual internal fans that can displace a lot more air for cooling of the mass, windings, rotors and electronics. (Fig. 2)

Lighter Weight

The output to weight ratio has decreased. Comparatively speaking, modern alternators weigh less than the older designs, but they can produce more power at this lighter weight. A typical GM CS-130 alternator weighs about five kg, but generates an output of more than 100 amps due to more efficient design.

Multi-Grooved Pulleys

The common V-belts that were used for many years have practically disappeared from the scene. Now almost all modern alternators require a serpentine belt to be driven. The higher alternator output and using a single belt concept to drive all driven accessories is the reason for the use today of multi-grooved belts and automatic spring-loaded belt tensioners that keep a consistent belt tension for all the accessories.

Overruning Clutch Pulleys and Decouplers

Another recent feature in modern alternators is the use of what is generally known as clutch pulley or decouplers. These newly designed pulleys allow the alternator’s rotor to free-run (decouple) from the drive belt when the rotor mass speeds up and for the belt to re-engage with the alternator’s rotor during rapid deceleration. This eliminates opposing forces on the belt, reduces the vibration and belt squeak, and prolongs the life of the belt and belt tensioner.

What a technician needs to keep in mind is that these pulleys and decouplers fall into two major categories: Overruning Alternator Pulley (OAP) and Overruning Alternator Decoupler (OAD). The latter, in addition to a one-way clutch, incorporates a specially designed spring that is designed to match the vibration characteristics of a particular engine. It reduces the vibration and belt bounce by its continuous compression and decompression of the spring inside the OAD mechanism, causing a very smooth transition between different speeds and electrical load changes. (Fig. 3)

Reduced EMI

The design of the newer generation of alternators incorporate features to reduce electromagnetic interference to allow other electronic modules such as PCM, BCM, VCM and a host of others to work in an environment that is less affected by such factors. The effect of unintentional voltage spikes and an interfering magnetic field is not desirable, and has to be minimized for proper operation of other electronic devices.

Avalanche Diodes

There has been a gradual but consistent move by alternator manufacturers to incorporate what are known as avalanche diodes in the design of the modern alternators. Avalanche diodes, which are basically Zener diodes used in a power application, are a type of diode that allows the voltage one way but blocks that voltage the opposite way … very much like any other diode. However, avalanche diodes have the added ability to allow the current flow in a reverse biased mode when the voltage exceeds a certain threshold, named the avalanche voltage setting. What this does is to clip any signal (spike) that is larger than the avalanche setting, which is normally between 24 to 28 volts. That is to say if during a normal operation a stray signal is created by an inductive load, that signal’s level (amplitude) will be contained by the alternator diodes within a 24 -28V range preventing any damage to the mechanism.

Smaller slip rings

Almost all internal fan alternators use rotors with slip rings that are about 15mm or less in diameter. Combined with specially formulated brushes, this slip ring and brush combination easily provide a 200,000 KM service life, given they do not become contaminated with leaking coolant, oil or power steering fluids, for example. Technicians should pay particular attention to these kinds of contaminations in order to prevent any problems with the alternators.

Voltage Regulators

Electronic voltage regulators introduced since the 1970’s have also become very sophisticated. Not only do they perform their intended function of providing a set po
int for the charging system and control the alternator output in regards to the load demand, in some designs they interface with the PCM to convey load information and receive variable voltage set point instruction. Some of the features of the new voltage regulators are:

Activation by PCM

Where the older designs were activated by warning light circuit, most new regulators are activated by a signal from the PCM. This signal is normally pulled low by the electronics of the regulator and as soon as it detects the alternator is charging properly, raises the activation voltage to the applied level which is then interpreted by PCM as a normal condition which requires the warning light to be turned off.

Digital Operation

Where the early electronic regulators were designed with analog circuits, most new regulators work on the basis of digital designs and circuits. Digital regulators switch the field current at a fixed frequency (400Hz in GM Delphi alternators, as an example), so the field current is a PWM (Pulse-Width Modulated) signal which its duration (pulse-width) varies with the load and RPM. Built on digital principle, they can easily interface with vehicle’s PCM or other related electronics.

Feedback Circuits

Most new regulators have a feedback feature to convey to the PCM how hard they are working, conveying to the PCM the duration of the applied field current in order to provide the necessary load information. These types of regulators have terminal identified by letters “F,” “FR,” “DFM”… etc.

Light Circuit Driver

Even though the activation of the regulator is normally done by the PCM, some regulators have a transistorized light driver circuit to turn the warning light off when they feel the alternator is charging properly. (Fig. 4)

There are other associated features of the new regulators such as Soft Start Delay (SSD), Lead Response Curve (LRC), and Temperature Compensation Curve (TCC) that is beyond the scope of this article; but suffice to say that the modern automotive charging/starting system has not been immune to advances in electronics and computers.

Mohammad Samii owns and operates Sammy’s Auto Eclectic Service, Inc. in Champaign, Illinois. He is also an educator, a columnist, and Automotive Parts Remanufacturers Association’s (APRA) Coordinator of Electrical Training. His monthly column “Auto Electric Corner” appears in APRA’s Global Connection Magazine.

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