Bryant ASPAS1BBA015 - Manual (Page 38)

Page 38
SECTION 2.4
DIAGNOSTIC TESTS
PART 2
AC GENERATORS
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
11 and Wire 22.
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 Char t on previous page : “Results - Fixed
Excitation Test/Rotor Amp Draw Test.”.
TEST 5: WIRE CONTINUITY
DISCUSSION:
The voltage regulator receives unregulated
alternating 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
11 and 22. The regulator rectifies the AC from the
excitation winding and based on the sensing signals,
regulates the DC current flow to the rotor. The
rectified 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.
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
terminal 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 6 - 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
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.
• 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.
PROCEDURE:
1. Locate Wire 4 that is routed from the circuit board and
connects to the voltage regulator terminal, third from the
top (see Figure 3). Disconnect that wire from the voltage
regulator terminal.
2. Set a VOM to read DC volts. Disconnect Connector C2
from the control panel (C2 is the closest to the back
panel).
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 9-10 volts DC. When engine is not
cranking, VOM should indicate "zero" volts (see Figure 4).
RESULTS:
1. If normal field boost voltage is indicated in Step 5,
replace the voltage regulator.
2. If normal field boost voltage is NOT indicated in Step 5,
check Wire 4 (between regulator and circuit board) for
open or shorted condition. If wire is good, replace the
circuit board.