Section 7

DIAGNOSTIC TESTS

7.Inspect the slip rings.

a.If slip rings appear dull or tarnished they may be cleaned and polished with fine sandpaper. DO NOT USE ANY METALLIC GRIT TO CLEAN SLIP RINGS. (A 400 grit wet sandpaper is rec- ommended).

b.After cleaning slip rings, blow away any sandpa- per residue.

RESULTS:

1.Replace bad brushes. Clean slip rings, if necessary.

2.If brushes and rings are good, go to Test 11.

2.If Rotor checks good, perform “Insulation Resistance Test,” on Page 14.

TEST 11- CHECK ROTOR ASSEMBLY

DISCUSSION:

During the “Fixed Excitation Test” (Test 4), if AC out- put voltage did not come up to about one-half rated volts, one possible cause might be a defective Rotor. The Rotor can be tested for an open or shorted condi- tion using a volt-ohm-milliammeter (VOM).

Also see Chapter Three, “INSULATION RESIS-

TANCE TESTS”.

PROCEDURE:

Gain access to the brushes and slip rings. Disconnect Wire 4 and Wire OF from their respective brushes and remove the brush holder. Then, test the Rotor as follows:

1.Set a VOM to its “Rx1” scale and zero the meter.

2.Connect the positive (+) meter test lead to the positive (+) slip ring (nearest the Rotor bearing). Connect the common (-) test lead to the negative (-) slip ring. Read the resistance of the Rotor windings, in OHMS.

ROTOR RESISTANCE *

MODEL:

OHMS

QP55 4702/4703

14.88Ω

QP65 4704/4705

10.81Ω

QP75 4706/4707

14.50Ω − 16.0Ω

*Resistance values In ohms at 20° C. (68° F.). Actual readings may vary depending on ambient temperature. A tolerance of plus or minus 5% is allowed.

3.Set the VOM to its “Rx1 K” or “Rx10,000” scale and zero the meter.

4.Connect the positive (+) meter test lead to the positive (+) slip ring, the common (-) test lead to a clean frame ground (such as the Rotor shaft). The meter should read “Infinity”.

RESULTS:

1. Replace the Rotor if it fails the test.

Figure 7-8. – Rotor Assembly

TEST 12 - CHECK MAIN CIRCUIT BREAKER

DISCUSSION:

The main circuit breaker on the generator panel must be closed or no output to the load will be available. A defective breaker may not be able to pass current even though it is in the “ON” position.

Figure 7-9. – Main Breaker (Typical)

PROCEDURE:

Set the coach main breaker to it’s “OFF” position. Check that the appropriate main breaker on the gen- erator panel is set to its “ON” (closed) position. Set a VOM to measure resistance and use it to check for continuity across the breaker terminals.

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Generac Power Systems 75, 55, 65 Test 11- Check Rotor Assembly, Test 12 Check Main Circuit Breaker, Tance Tests Procedure
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65, 75, 55 specifications

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