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Portable Generator Familiarization & Troubleshooting Guide Section 3 • Generator Diagnostics and Adjustments Figure 3.31— Troubleshooting Flow Chart For (Brush Type) Generators With “Two-Board” Regulation 76
Portable Generator Familiarization & Troubleshooting Guide Section 3 • Generator Diagnostics and Adjustments Troubleshooting “Two Board” Regulation Generators (Brush Type) Refer to Figure 3.31. Test 1: — Check (AC) Frequency and Voltage Connect an accurate (AC) frequency meter across the two parallel blades of one of the panel 120VAC receptacles. • Start the engine and let it stabilize. Read the (AC) frequency.A frequency reading of 61-63 Hertz should be obtained. If frequency is not within specifications: • Consult the appropriate engine service manual for adjustment. With the generator engine running, connect the VOM test probes across the parallel blades of the panel 120VAC receptacles.A reading of approximately 130-140VAC should be indicated. If voltage checks as specified: • Discontinue test. If voltage reading is zero: • Go to Test 2:“Flash The Field.” If voltage reading is low: • Go to Test 7:“Check The Rotor.” Test 2: — Flash The Field In normal generator operation, upon startup there is some “residual” magnetism in the rotor to get the generating process started. Residual magnetism is the magnetism left in the rotor after the unit is shut down. When residual magnetism is lost, the unit will have an output voltage that will remain at zero. If residual magnetism is lost, it can usually be restored by “flashing the field” with a simple process involving a (DC) battery. This usually occurs if the unit is out of use for a long period of time. If the unit is equipped with a voltage regulator or a bridge rectifier, flash the field as follows: • Obtain a 12VDC battery. • Get two jumper leads that can go from the battery to the brushes. (Wires with alligator clips work well.) • Find the brushes inside the alternator portion of the unit. • Start the engine and get it up to running speed. • Connect the battery positive (+), to the positive brush, which will be the brush closest to the rotor bearing. • Connect the battery negative (-), to the negative brush, which is the brush farthest away from the rotor bearing (Refer to Figure 3.32). Figure 3.32 — Restoring Residual Magnetism • After about five seconds, disconnect the battery wires from the brushes and check for proper (AC) output voltage. • Shut the engine down. Restart the unit and check once again for proper (AC) output voltage. NOTE: Some units are equipped with “FIELD BOOST” and should never lose residual magnetism unless a field boost failure has occurred. Field boost current flashes the field on every startup (see “Field Boost” on page 45). Refer to the appropriate electric schematic and/or wiring diagram to determine if a unit has field boost. 77
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