Generac Power Systems 53187 - Manual (Page 43)

P A R T I
THE REVOLVING FIELD AC GENERATOR
1 SECTION 1.7- TROUBLESHOOTING
(UNITS WITH 10 INCH STATOR)
Diagnostic Tests (Continued)
TEST 3- DO A FIXED EXCITATION TEST:
Discussion: This test w ill help you narrow the
possible causes of zero, residual or low AC output
voltage dow n to Just a few possible causes.
The test consists of disdonnectlng regulated exci­
tation current flow to the Rotor, but leaving the field
boost circuit to the Rotor Intact. W ith regulated excita­
tion current disconnected, the generator’s AC output
voltage w ill be com m ensurate w ith Rotor residual m ag­
netism plus field boost.
Procedure: Disconnect W ires No. 1 and 4 from the
Voltage Regulator term inals, so that regulated excita­
tion current Is not available to the Rotor. Connect an
AC Voltm eter across the generator AC output leads
(T1, T2, T3). Start the engine, let It stabilize and w arm
up. The AC voltage reading should be com m ensurate
w ith Rotor residual m agnetism plus field boost, as
follow s:
1. Une-to-neutral voltage should be approxim ately 25-
40 volts AC.
2. Line-to-Une voltage should be approxim ately 50-80
volts AC.
Results:
1. If line-to-neutral voltage is low er than 25-40 VAC, go
to Test 10. if line-to-line voltage is less than 50-80 VAC,
go to Test 10.
2. If 25-40 VAC line-to-neutral voltage is indicated (or
50-80 VAC line-to-line), go to Test 4.
If sensing (actual voltage) signals to the Regulator
should be lost, the Regulator w ould interpret such a
loss as ‘’zero* actual volts. Regulator action w ould then
increase excitation current flow to the Rotor until a ‘full
field' condition existed. The result w ould be a high
voltage condition. How ever, the Part No. 81918 Regu­
lator w ill shut dow n autom atically on loss of sensing
voltage. W ith the Regulator shut dow n, excitation cur­
rent to the Rotor w ill term inate and AC output voltage
w ill drop to a value com m ensurate w ith the Rotor's
residual m agnetism plus field boost.
Procedure: Inspect W ires No. 11 and 22, betw een
the Voltage Regulator and the engine control circuit
board. These are the sensing (actual voltage) leads.
Use a VOM to test the w ires for "continuity*.
Results:
1. Reconnect, repair or replace bad w ire(s) as required.
2. If the sensing circuit is good, go on to test 5.
TEST 5- TEST THERM AL PROTECTOR:
Discussion: You m ay w ish to review “ THERMAL
PRO TECT OPT on Page 1.3-7.
Procedure: To test the therm al protector, proceed
as follow s:
1. in the control panel, locate (a) W ire No. 5, (b) W ire
No. 2, and (c) W ire No. 6. W ire No. 5 is unconnected
and has a w ire nut at its end. W ire No. 2 connects to
the excitation circuit breaker. W ire No. 6 attaches to the
Voltage Regulator plug.
2. Set a VOM to its "Rxl ‘ scale and zero the m eter.
3. Disconnect W ire No. 2 from the excitation circuit
breaker. Unplug the Voltage Regulator plug. Rem ove
the w ire nut from W ire No. 5.
4. Connect one VOM test probe to W ire No. 5 and the
other end to Pin 2 of the Regulator plug, to w hich W ire
No. 6 attaches. The m eter should read the resistance
of the excitation w inding (about 1.00 ohm ).
5. Now , connect the VOM test probes across W ire No.
2 and W ire No. 6. Again, excitation w inding resistance
should be read.
Results:
1. If excitation w inding resistance is indicated in Step
4, but not in Step 5, the therm al protector is open and
m ust be bypassed.
2. If excitation w inding resistance is indicated in both
Steps 4 and 5, go on to Test 6.
TEST 4- CHECK REGULATOR SENSING CIRCUIT:
Discussion: The sensing circuit is the Regulator's
ACTUAL voltage signal. The Regulator electronically
com pares the actual voltage w ith a pre-set REFER­
ENCE voltage. If ACTUAL voltage is less than REFER­
ENCE voltage, the Regulator w ill increase excitation
current flow to the Rotor. If ACTUAL voltage is greater
than REFERENCE voltage, it w ill decrease excitation
current flow to the Rotor. In this m anner, Rotor m ag­
netic field strength and AC voltage are regulated.
TEST 6- TEST EXCITATION CIRCUIT BREAKER:
Discussion: This test w ill determ ine if the excita­
tion circuit breaker has failed open. If the breaker is
open, loss of excitation current to the Rotor w indings
w ill result and AC output w ill drop to residual voltage.
The breaker is m ounted in the control panel.
Procedure: Disconnect W ires 2 and 2A from the
circuit breaker. Connect VOM test ieads across the tw o
breaker term inals. The VOM should read "continuity".
If not, the breaker is open and should be replaced.
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