Wire Continuity; Check Field Boost - Guardian 4721 Repair Manual

PREPACKAGED LIQUID
COOLED AC GENERATORS
TEST 5 RESULTS - FIXED EXCITATION TEST/ROTOR AMP DRAW TEST
Results: A
Voltage Results Above
Wire 2 & 6 60 VAC
Voltage Results Above
Wire S15 & S16 60 VAC
Static Rotor 15kW 2.2A
Amp Draw 20kW 1.5A
25kW 1.3A
Running Rotor 15kW 2.2A
Amp Draw 20kW 1.5A
25kW 1.3A
8. Set the AUTO-OFF-MANUAL switch to MANUAL. Once
the engine starts, record the AC voltage.
9. Set the AUTO-OFF-MANUAL switch to OFF. Reconnect
Wire S15 and Wire S16.
10.Set VOM to DC amperage.
11.Remove jumper lead connected to Wire 4 and Wire 15.
12.Connect one meter test lead to battery positive twelve-
volt supply Wire 15, located at the 15A fuse. Connect
the other meter test lead to Wire 4 (still disconnected
from previous tests). Measure and record static rotor
amp draw.
13.Set the AUTO-OFF-MANUAL switch to the MANUAL
position. Once the engine starts, repeat step 12.
Measure and record running rotor amp draw with the
engine running.
14.Set the AUTO-OFF-MANUAL switch to OFF. Reconnect
Wire 4 to the voltage regulator.
RESULTS:
Refer to Chart above : "Test 5 Results - Fixed Excitation
Test/Rotor Amp Draw Test.".
TEST 6 - WIRE CONTINUITY
DISCUSSION:
The voltage regulator receives unregulated alternat-
ing current from the stator excitation winding, via
Wires 2, 6, and 162. It also receives voltage sensing
from the stator AC power windings, via Wires S15
and S16. The regulator rectifies the AC from the
excitation winding and based on the sensing signals,
regulates the DC current flow to the rotor. The recti-
fied and regulated current flow is delivered to the
rotor brushes via Wires 4 (positive) and 0 (negative).
This test will verify the integrity of Wires 0 and 162.
PART 2
B C
Above Below
60 VAC 60 VAC
Below Above
60 VAC 60 VAC
2.2A 2.2A
1.5A 1.5A
1.3A 1.3A
2.2A 2.2A
1.5A 1.5A
1.3A 1.3A
MATCH RESULTS WITH LETTER AND REFER TO FLOW CHART IN SECTION 2.3 "Problem 1"
D E
Zero or Below
Residual Volts 60 VAC
Zero or Below
Residual Volts 60 VAC
Zero Above 2.2A
Current Above 1.5A
Draw Above 1.3A
Zero Above 2.2A
Current Above 1.5A
Draw Above 1.3A
PROCEDURE:
1. Set VOM to its "R x 1" scale.
2. Remove Wire 0 from the voltage regulator, 4th terminal
from the top. Also voltage regulator is labeled (-) next to
terminal.
3. Connect one test lead to Wire 0, connect the other test
lead to a clean frame ground. The meter should read
CONTINUITY.
4. Disconnect Wire 162 from the voltage regulator, 6th ter-
minal from the top. Disconnect the other end of Wire
162 from the excitation circuit breaker. Connect one
test lead to one end of Wire 162, and the other test lead
to the other end of Wire 162. The meter should read
CONTINUITY.
RESULTS:
If CONTINUITY was not measured across each wire,
repair or replace the wires as needed.
TEST 7 - CHECK FIELD BOOST
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 wind-
ing 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.
• 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.
SECTION 2.4
DIAGNOSTIC TESTS
F G
Below Above
60 VAC 60 VAC
Below Above
60 VAC 60 VAC
2.2A Zero
1.5A Zero
1.3A Zero
2.2A Zero
1.5A Zero
1.3A Zero
H
Below
60 VAC
Below
60 VAC
2.2A
1.5A
1.3A
2.2A
1.5A
1.3A
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