Alternator stator testing

Testing the correctness of the stator winding of the alternator is performed visually and by measuring the resistance. The visual inspection looks for changes in color or damage to the windings. Often due to excessive heat, parts of the winding insulation are deformed. A quick check of the condition of a suspicious part of the winding is to scrape the winding with a knife blade. If the varnish falls off, the winding insulation is damaged. In the same way, the connections on the stator are also checked. Any signs of damage indicate that the stator is faulty.

Alternator stator

If the stator passes the visual inspection, it is approached testing of windings for open-circuit, and short to ground. The electrical check is done with an ohmmeter. As the stator has three windings connected in a star, there are three leads (a, b, and c). Resistance measurement is performed between two leads in each combination (a-b, a-c, and b-c). The measured coil resistance should be less than 0.5 Ω. If infinite resistance is measured between any two terminals, the winding is broken and the stator is replaced.

Testing windings for open-circuit (A) and short-to-ground (B)

An ohmmeter is connected between the stator housing and the winding terminal to test for a short-to-ground. With good winding insulation, the ohmmeter shows infinite resistance across all three windings. If at least one winding shows some resistance, the insulation of that winding has broken, it is short-to-ground and the stator is replaced.

To perform an alternator stator winding test, follow these steps:

Visual inspection

Perform a visual inspection of the state of the stator winding and its insulation. In case of a noticeable color change, overheating, or burning of the winding, replace the stator. If in doubt about the condition of the insulation, scratch the insulation with a knife blade. If it falls off, the winding insulation is defective, and replace the stator.

Testing windings for open-circuit

Read the required stator winding resistance value from the information system. Set the resistance measurement on the multimeter. Connect the measuring pipettes between the two leads of the stator. Repeat the measurement two more times between each combination of leads. If at least one measurement shows infinite resistance, replace the stator.

Testing windings for short to ground

Place one measuring pipette of the ohmmeter on the stator housing, and the other on each output of the stator winding. The measured resistance should be infinite. If any resistance value is measured, the winding insulation has broken, and the stator needs to be replaced.