Charging System Failure (Alternator, IC Regulator)
Charging system failures can roughly be classified into two types in terms of whether they involve a disabled charging (undercharge) or overcharge. Failures that involve overcharge can be localized to the alternator (including the regulator), while for failures that involve disabled charging (undercharge), not only the alternator (including the regulator) but other causes can be suspected, such as a loose belt, battery failure or a fault in the wiring system outside the alternator. The description below is limited to alternator failures. Although the regulator is built into the alternator, they will be regarded as being separate.
1. Causes of Overcharge

When the slip rings and brushes of the alternator become worn, the contact resistance between the slip rings and brushes will increase and thereby cause poor continuity. If this happens, unusual load will be applied to the power transistor of the regulator, which will cause a short-circuit condition. Then, unusual current will be carried to the rotor coil, which will in turn lead to an overcharge condition. The conditions described above could also occur when a wire breaks or terminal S is disconnected as this makes it impossible to control the alternator.

2. Causes of Disabled Charging (Undercharge)
If any of the following events occurs, charging will be disabled:

1)When due to a continuing overcharge, a short-circuit condition in the power transistor of the regulator has caused an open circuit condition;

2)When contact has been made with the frame etc. due to wire breakage or wire sheath damage in the internal wiring system of the alternator;

3)When the insulation of the rotor coil and stator coil have deteriorated causing poor insulation, or when there is a broken wire in the rotor coil; and

4)When there is a broken wire or short circuit in the rectifier.

Checking the Alternator in Isolation
If there is abnormality in the alternator, then undercharge or a regulator failure may result. Therefore, it is necessary to check for wire breakage and short circuits in the rectifier diodes, worn brushes, poor coil insulation and other defects.
(1) Checking the rectifier diodes
A typical rectifier uses eight diodes. If any of the eight diodes is disconnected or short-circuited, then the output of the alternator will decrease.

1) Visually check if there is any abnormality in soldered or caulked parts.

2) Use a tester to check each of the eight diodes for continuity. [See Photo-1]
If there is forward continuity and no reverse continuity between E and 1), 2), 3) and 4), it can be determined that the diodes are not defective.
Any defective diode must be replaced.


Raise a wire of the stator coil while taking care not to let the wire come in contact with the terminal.


Reverse the tester probes.

(2) Checking the brushes
The brushes carry current to the rotor coil. Therefore, if they are worn out, poor contact with the spring rings of the rotor will occur, which will in turn bring about an undercharge condition.

1) Check that the length of the brushes that are exposed from the brush holder is within the reference value.

2) Check if the brushes operate smoothly, by pushing them slightly with a finger.

(3) Checking the rotor coil
The rotor coil is intended to generate a magnetic force that serves as the source of power generation. Therefore, if it contains a broken wire or is grounded, an undercharge condition will result.

1)Use a tester to measure the resistance between the rotor coil and the slip rings.[See Photo-2]
If the tester shows a resistance of 2.50 ohms or more, then the rotor coil is not defective. If there is no continuity, then the rotor coil has a broken wire and needs to be replaced. If continuity is extremely low, then the rotor coil has a layer short and needs to be replaced.

2) Checking the surfaces of the slip rings
Check if the surfaces of the slip rings are smooth and have any foreign matter on them. If they are not smooth or are polluted, they need to be modified or cleaned.

3) Check if the rotor coil current is grounded via the core. Use a megohm tester to measure the insulation resistance between one slip spring and the rotor core. If the tester shows an insulation resistance of 10M ohms or more, then it can be determined that the rotor coil is not defective. [See Photo-3]
Normally, the tester should show an infinite level of insulation resistance. If there is continuity, the rotor coil is grounded and needs to be replaced.

<See Photo-2>

<See Photo-3>

(4) Checking the stator coils
The stator is a component that is to generate voltage, and is comprised of three coils.

1) Check the stator coils for continuity between terminals.
[See Photo-4]
If there is continuity between 3) and 1), 2) and 4), then the stator coils are not defective. (The resistance requirement is 1 ohm or less.)
If there is no continuity, then the stator coils contain a broken wire and therefore require a replacement.

2) Check the insulation resistance between a coil and the core that corresponds to it. Before checking, it is necessary to disassemble the unit of the alternator and separate the stator from it. Use a megohm tester to measure the insulation resistance between each coil wire and the core that corresponds to it. If the tester shows 1M ohms or more, then the status coil is not defective. If there is continuity, then the stator coil is grounded and therefore needs to be replaced.

<See Photo-4>

Conducting a Bench Test After Installing the IC Regulator
<Assemble the regulator to the alternator; then, use a test bench to conduct a performance check.>

(1) Raise engine rpm for 12 V and 24 V cars to 5000 rpm; then, measure the adjusting voltage between alternator terminals L and E (Earth).

Examples of standard values   14.6 +/- 0.3 V (12 V car)
                     28.5 +/- 0.3 V (24 V car)

(2) Raise engine rpm for 12 V and 24 V cars to 1200 rpm. Then check that 12 V and 27 V cars have 13.5 V or more and 27 V or more, respectively, at alternator terminal B.
(Checking the threshold voltage)

(3) Conduct quick acceleration and deceleration in the range between 1200 to 8000 rpm. Check if the rotor bends due to the centrifugal force of the rotor and thereby causes a layer short-circuit in the coil.
(Checking the occurrence of abnormal noise) Check the voltage between terminals L and E. Also, check the waveform using an oscilloscope or similar instrument.