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 TM 55-1905-223-24-3
j. No load dc excitation test.
NOTE
The no load dc excitation test will indicate whether a generator problem is in the AVR or the generator.
(1)
Remove the AVR. Refer to step h.(1).
(2)
Temporarily insulate (tape) all of the lead terminals except X and XX that were removed from the AVR.
(3)
Using a multimeter set to measure ohms, measure the resistance between terminals X and XX at the
AVR box. Acceptable resistance values are 23.7 to 27.5 ohms.
(4)
Remove all loads that may be connected to the generator. This includes ans, coolant pumps, heaters
f
and any other equipment powered from the generator.
(5)
Open the main line circuit breaker, if the generator has one.
(6)
Start the engine and bring it up to rated speed.
NOTE
Use a dc power source or storage battery capable of producing 0.5 amp at 12 volts but not exceeding
13.2 volts to provide power to the generator X and XX leads.
(7)
Connect the power source positive (+) lead to the X terminal at the AVR box. Connect the negative (-)
lead to the XX terminal. Temporarily insulate (tape) the X and XX terminals to prevent accidental
shorting.
(8)
Check the engine speed. Engine speed should be 1797 to 1803 rpm (59.9 to 60.1 Hz). Adjust the
engine speed as necessary.
(9)
Measure the dc voltage at terminals X and XX. This voltage must be 12.0 to 13.2 volts. If it is not,
adjust the dc power supply voltage, check the battery lead connections, and connect a charger to the
battery or replace the battery with a fresh one.
(10)
Measure and record the line-to line voltage. Also record the voltage at the auxiliary terminals 2 and 3.
Use the same meter to make all checks.
(11)
The line to line voltages must all be within 1 percent of the average voltage. If there is a voltage
unbalance, recheck for any load on the generator. A load can cause a voltage unbalance condition.
(12)
If there is a voltage unbalance at no load, disconnect the power supply from X and XX, stop the engine,
remove the generator from the engine, and have it repaired orreplaced.
4-17
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