ENGINE AR-COMPLETE 1699338 - Caterpillar

not be used to check such a rectifier up to its rated current and voltage values.If a power rectifier (1), under test does not test open or shorted with an ohmmeter and the operating characteristics of the generator indicate a faulty rectifier, it is necessary to test the questionable rectifiers dynamically to determine accurately whether the rectifier is defective or not.
FIG. 38. WIRING DIAGRAM
1. Power rectifier. A. Ammeter. V. Voltmeter.Dynamic Testing of Power Rectifiers
A-DC Ammeter 0-75 amps scaleV-DC Voltmeter 0-4 volt scaleTest rectifier installed in heat sink.
To check the forward current rating of a power rectifier, the rectifier must be installed in a heat sink with sufficient cooling to limit the case temperature.
Type S Rectifiers (35 Ampere Rating)
Adjust the DC supply voltage to obtain 35 amperes DC through meter (A). The DC voltage across meter (V) should be no more than 1.3 volts.Type T Rectifiers (50 Ampere Rating)
Adjust the DC supply voltage to obtain 50 amperes DC through meter (A). The DC voltage across meter (V) should be no more than 1.2 volts.
FIG. 39. TEST SET UP
1. Power rectifier. 2. Ammeter. 3. Voltmeter. 4. Separate DC source. 5. Hand rheostat.Installation of Power Rectifiers
See Fig. 40. Silicon stud-mounted diodes are manufactured with a variety of base and stud sizes. The use of the mounting stud accomplishes two functions; that is, electrical connection to the rectifier base and the transfer of thermal losses from the rectifier to the heat sink and cooling medium. The electrical connections are readily made with conventional screw type terminals. However, proper mounting to achieve low thermal resistance is not so readily accomplished. Consequently, take the following steps to obtain good terminal transfer of rectifier heat losses.The nut of a replacement power rectifier must be tightened to the torque specified to obtain maximum pressure of the two mating surfaces and, yet, not cause mechanical distortion of the rectifier base. Overtightening could stress the silicon crystal and cause changes in electrical characteristics or actual cracks in the crystal. A 9M6331 Pound-Inch Torque Wrench (2) (accurate in the listed torque range) should be used when tightening power rectifiers (1).1. Apply a thermally conductive lubricating film between the two mating surfaces to exclude the partially stagnant air which acts as a thermal insulating film.2. Tighten the nut on the power rectifier stud to the torque value shown in the chart.
FIG. 40. INSTALLING POWER RECTIFIERS
1. Power rectifiers. 2. Torque wrench.3. If a torque wrench is not available, tighten the rectifier stud nut finger tight against the lockwasher. Then tighten the nut an additional 60 degrees (one flat). Do not exceed this or the specified torque.Contact between the rectifier base and the heat sink (even when both are machined smooth) is actually a large number of point contacts. Between the points of contact is a thin film of dead air, which is a thermal barrier. To eliminate this thermal barrier, a thin film of thermally conductive lubricant should be applied to both mating surfaces before tightening. 4L7464 Silicone Grease (similar to