Generac Power Systems 20 kW LP, 10 kW LP manual Test 6 Check Field Boost 12-20 kW, Reconnect Wire

Section 2.4

Diagnostic tests

Part 2

AC generators

Test 6 – Check Field Boost (12-20 kW)

DISCUSSION:

See “Field Boost Circuit” in Section 2.2. Field boost current (from the circuit board) is available to the rotor only while the engine is cranking. Loss of field boost output to the rotor may or may not affect power winding AC output voltage. The following facts apply:

•A small amount of voltage must be induced into the

DPE winding to turn the voltage regulator on.

•If rotor residual magnetism is sufficient to induce a voltage into the DPE winding that is high enough to turn the voltage regulator on, regulator excitation current will be supplied even if field boost has failed. Normal AC output voltage will then be supplied.

6. Reconnect Wire 4.

RESULTS:

1.If normal field boost voltage is indicated in Step 6, replace the voltage regulator.

2.If normal field boost voltage is NOT indicated in Step 6, check Wire 4 (between regulator and circuit board) for open or shorted condition. If wire is good, replace the circuit board.

Test 7 – Testing The Stator With A Vom

(12-20 kW)

•If rotor residual magnetism has been lost or is not sufficient to turn the regulator on, and field boost has also been lost, excitation current will not be supplied to the rotor. Generator AC output voltage will then drop to zero or nearly zero.

5.54 VDC

DISCUSSION:

A Volt-OHM-Milliammmeter (VOM) can be used to test the stator windings for the following faults:

•An open circuit condition

•A “short-to-ground” condition

•A short circuit between windings

Note: The resistance of stator windings is very low. Some meters will not read such a low resis- tance, and will simply indicate CONTINUITY. Recommended is a high quality, digital type meter capable of reading very low resistances.

LINELOAD

WIRE 44 TEST POINT

WIRE 11 TEST POINT

Figure 3. Field Boost Test Points

PROCEDURE:

1.Disconnect Wire 4 from the voltage regulator, third terminal from the top (see Figure 3).

2.Set a VOM to read DC volts.

3.Connect the positive (+) VOM test probe to the terminal end of disconnected Wire 4.

4.Connect the common (-) VOM test probe to the grounding lug.

5.Crank the engine while observing the VOM reading. While the engine is cranking, the VOM should read approximately 4-6 Volts DC. When engine is not crank- ing, VOM should indicate “zero” volts (see Figure 3).

Figure 4. Test 7 Test Points

PROCEDURE:

1.Isolate the generator from the transfer switch by dis- connecting the load wires from the main breaker inside the generator.

2.Disconnect Stator Leads 22 and 33 from the neutral connection and separate the leads.

3.Disconnect and isolate Wires 2 and 6 and Wires 11 and 22 from the voltage regulator.

4.Make sure all of the disconnected leads are isolated from each other and are not touching the frame during the test.

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