Alternator Repair Manual - Stator, Rectifier, Field
For 10Si and 15Si Series Alternators, Type 116 and 136

repair manual testing rectifier diodes
Figure 9 - Testing the Bridge Rectifier

alternator grounded stator test
Figure 10 - Testing the Bridge Rectifier


10Si and 15Si Series Alternator

This is an alternator repair manual for Delco's 10Si and 15Si, type 116 and 136 series alternators. On this page we will cover testing of several crucial components. First the rectifier, which is the component that converts AC voltage to the DC voltage used by your vehicle's battery. Then the stator, which is a large coil where the AC voltage is generated. Finally, we test the field connections, mainly the voltage regulator and brush holder assembly. The field voltage powers the inner rotor, which induces a current in the stator.

Checking Bridge Rectifier Diodes

Note that the rectifier bridge has a grounded heat sink and an insulted heat sink connected to the alternator output terminal.

To check the rectifier bridge, connect the ohmmeter to the grounded heat sink and one of the three terminals (Fig. 9).

Important: Connect ohmmeter pressing down very firmly onto flat metal connector, then reverse the lead connections to the grounded heat sing and same terminal. If both readings are the same, replace the rectifier bridge. A good rectifier bridge will give one high and one low reading. Repeat this same test between the grounded heat sink and the other two terminals, and between the insulated heat sink and each of the three terminals. This makes a total of six checks, with two readings taken each check.

The ohmmeter check of the rectifier bridge, and of the diode trio as previously covered, is a valid and accurate check. DO NOT replace either unit unless at least on pair of readings is the same. Caution: Do not use high voltage to check these units, such as a 110-volt test lamp.

To replace the rectifier bridge, remove the attaching screws and disconnect the capacitor lead.

Checking the Stator for Grounds and Shorts

The stator windings may be checked with a 110-volt test lamp or an ohmmeter. If the lamp lights, or if the meter reading is low when connected from any stator lead to the frame, the windings are grounded. If the lamp fails to light, or if the meter reading is high when successively connected between each pair of stator leads, the windings are open (Fig. 10). Note: Ohmmeter or test light checks for opens can be made only on "Y" stators, visually identified by the three stator leads crimped together. Delta windings cannot be checked for opens with an ohmmeter or test light. Usually laboratory equipment is required to check Delta windings.

A short circuit in the alternator stator windings is difficult to locate without laboratory test equipment due to the low resistance of the windings. However, if all other electrical checks are normal and the generator fails to supply rated output, a shorted stator winding or an open Delta winding is indicated. Also, a shorted stator can cause the indicator lamp to be on with the engine at low speed. Check the regulator in the next section before replacing stator.

Checking Field Parts, Voltage Regulator and Brush Holder

To determine if the regulator in the alternator is defective, an approved regulator tester must be used.

After removing the three attaching nuts, the stator, and diode trio screw (Fig. 9), the brush holder and regulator may be replaced by removing the two remaining screws. Not the two insulators located over the top of the brush clips in Figure 7, and that these two screws have special insulating sleeves over the screw body above the threads. The third mounting screw may or may not have an insulating sleeve. If not, this screw must not be interchanged with either one of the other two screws, as a ground may result, casing no output or uncontrolled generator output. Regulators may vary in appearance but are completely interchangeable in these generators.