Vehicular Charging Systems Part I By Frank Oropeza Editor’s Note: Although manufacturing abilities and components have evolved since this series was first published in 1984, electrical parameters of alternators have remained virtually unchanged. Even the 10SI remains popular because of its economical retrofit possibilities. The advent of alternators as the elec- trical generating method of maintaining a charged system in a vehicle coupled with an electronic voltage regulator has resulted in improved performance and reliability. The alternator is the power source for operating electrical acces- sories and charging the storage battery. It is also important that the alternator output be maintained at the proper volt- age level with varying load changes throughout the entire speed range of the vehicle to prevent battery problems. The basic alternator remains un- changed with the exception of new alter- nator models featuring higher amperage to accommodate higher demand. Recent improvements in charging systems are reflected primarily in voltage regulator technology, and this is evidenced by growing demand for these new concepts. The pull-in problem that relates to exces- sive air gap in a rotor/stator pair has been resolved by the new stator excited regu- lators. Also, the effects of leaky rectifiers are of no consequence, in some of the new concepts, because a capacitor is used to couple the stator signal to the regulator, hence, the effects of leaky rec- tifiers is precluded. Alternators An alternator is an alternating current source excited by a battery that also func- tions to store the generated electrical energy. Essentially, an alternator converts mechanical energy to electrical energy to maintain a charged condition in the RECTIFIER ASSY. P+ FILTER CAP a ROTOR IIE [> ~ Figure 1 BRUSH ASSEMBLY Basic Alternator battery in order to supply the various load requirements. This electrical energy is a result of rotating an electro-magnet (rotor) inside a three-phase stator assem- bly. The alternating current and voltage is next converted to direct current and voltage by a three-phase rectifier assem- bly and the output functions to charge the battery. Additionally, by using a voltage regulator we establish how much charge to divert to the battery. Alternators are still theoretically the same, however, the additional imports, Japanese and European varieties, further complicate the rebuilding industry. When one considers the voltage regulators nec- essary to complement the vast assort- ment it is difficult to keep up with all the variations and parts necessary to service them. Regardless of origin, the basic alter- nator still functions the same and utilizes basic components (Figure 1) such as: ¢ Rotor ¢ Stator ¢ Rectifier assembly ¢ Housing assembly ¢ Brush assembly ¢ Filter capacitor Any functional part that we add to the above is incidental because that alters the basic alternator for a particular applica- tion. Such functional changes are typically: ¢ Diode trio ¢ Isolation diode ¢ Excitation resistor ¢ Field relay ¢ Voltage regulator Component Characteristics Rotors Most rotors look alike and if you use a 1ODN rotor in a 10SI alternator with a Delco original regulator you will get questionable results. Incidentally, this is a viable concept, but you need to select your voltage regulator source and antici- pate about five to 10 percent degradation on system rated output. Measurement of rotors can be accom- plished with the current draw technique or with a multimeter. The resistance range is between 2 to 5 ohms for 12 volt rotors. Stators The two types of stator connections commonly used in alternators are the “Y” (Wye) and the Delta connection (Figure 2). The “Y” stator is found pri- marily in applications with lower power requirements as compared to the Delta stator. Additionally, the “Y”’ stator pull-in characteristic is considerably earlier— typically 1,500 rpm and the Delta is typ- ically 2,000 rpm. This data is supported by Figure 3, (page 5), which shows that at lower rpm, the Wye stator has a higher power output and the Delta stator is slow in pull-in, but exhibits a higher power characteristic at higher rpm. This fact is further support- ed when an OEM stator is changed out for a higher amperage stator, the pull-in characteristic on a self-excited one wire system application is adversely affected. The Delta wound stator application is more common today because of the con- tinuing demand for higher electrical loads. The most effective stator test is to use a stator tester such as is available from JIMCO or Crumbliss wherein a current source is utilized to determine current rating. When testing stators one must recognize that the current variance between windings should not exceed three amperes. A resistance measure- ment is not recommended for this test due to the low resistance value of the DELTA Figure 2 CONNECTION – Delta and Wye Alternators CONNECTION AMPS oR AC Figure 3 ALT RPM (X 1000) Wye vs. Del