Generac Power Systems IM Series - Manual (Page 24)

4. Set a VOM to its "Rx1" scale and zero the meter.
Connect VOM test leads across wire ends of Wires 11
and 22 and note the resistance reading, in ohms. Resis­
tance should be as follows (plus or minus 10%);
NP45G Units = 0.4 ohms
NP55G Units = 0.3 ohms
NP65G Units = 0.2 ohms
5. Connect VOM test leads across wire ends of Wires 33
and 44. Again, note the resistance. Resistance should
be the same as in Item 4 above.
6. Set VOM to its "Rxl 0,000” scale and zero the meter.
Connect one VOM test lead to Wire 11 and the second
test lead to frame ground. The VOM needle should not
move upscale (infinity). Now, connect one test lead to
Wire 33 and the second lead to frame ground. Meter
should indicate infinity.
Test Results:
A. Power Windings check GOOD: Go to Step 9.
B. Power Windings check BAD: Replace Stator Assemb­
ly-
Step 9 - Check Rotor (Field) Circuit
Test Procedure: Use a VOM to test Wire 4, between
Electronic Voltage Regulator and Choke Module for open
or shorted condition. Wire 4 between Choke Module and
Brushes was previously tested in Step 6. Then, inspect
brushes and slip rings and test Rotor as follows:
1. Remove Wires 4 and 0 from Brushes, then remove
Brush Holder. Inspect Brushes and Brush Holder.
Replace if cracked, damaged, worn excessively, etc.
Inspect Slip Rings. If they are dull or tarnished, polish
with fine sandpaper. DO NOT USE ANY METALLIC
GRIT TO CLEAN SLIP RINGS. Use low pressure air (25
psi or less) to blow away cleaning residue.
2. Set a VOM to its "Rxl: scale and zero the meter.
Connect VOM positive (+) test lead to the positive (■<-) Slip
Ring (nearest the Rotor bearing). Connect negative (-)
VOM test lead to the negative (-) Slip Ring. Meter should
indicate the following resistance (plus or minus 10%) at
20°C (68®F).
NP45G Units =13.9 ohms
NP55G Units = 15.5 ohms
NP65G Units = 11.1 ohms
3. Reassemble Brushes and Brush Holder, retain Brush
Holder and Wires. Make sure Brushes are properly
seated in Brush Holder and are contacting the Slip Rings
properly. Rotate Rotor several times to seat Brushes
against Slip Rings.
Test Results:
A. Rotor circuit checks GOOD: Go to Step 10.
B. Rotor circuit tests BAD: Repair or replace defective
wire(s) or brushes. Replace defective Rotor Assembly.
Step 10 - Check Voltage Regulator Sensing
NOTE: Sensing signals to the Electronic Voltage
Regulator are delivered via Wires 11 and 22. Loss of
these sensing signals to the Regulator due to an
open or shorted condition (in a non-compensated
Regulator) normally means a "Full Field" condition
and resultant high a-c voltage output. However, the
NP series generators are equipped with a VoHage
Regulator
that provides automatic protection
against an open sensing circuit and the resultant
high voltage condition. Should sensing wires 11 or
22 open, Voltage Regulator action will automatically
open the Excitation circuit to the Rotor and a-c
output voltage will drop dramatically. Total a-c volt­
age output from the Stator a-c power windings will
be a result of residual Rotor magnetism only.
Test Procedure: Recheck Wires 11 and 22, between the
Electronic Voitage Regulator and the Stator, as outlined
in Step 8.
Test Results:
A. Wires 11 and/or 22 indicate open or shorted condition:
Repair or replace wires as necessary.
B. Wires 11 and 22 check GOOD: Go to Step 11.
Step 11- Check/Adjust Voltage Regulator
Test Procedure: Refer to ADJUSTMENTS section.
With correct a-c frequency indicated, try adjusting the
Voltage Regulator. Frequency and voltage must both be
within the specified limits.
Test Results:
A. Frequency GOOD, cannot adjust in the correct volt­
age: Replace the Voltage Regulator, adjust and test unit.
B. Frequency and Voltage both GOOD: STOP tests.
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