Section 8 Component Testing And Adjustment; Theory Of Operation; Separate Excitation - Kohler 20EORZD Manual

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Table of Contents

8.1 Theory of Operation

These generator sets utilize a rotating-field alternator to

produce AC voltage. Upon activation of the generator

master switch, DC current from the battery magnetizes

the rotor (field). When the magnetized rotor rotates

within the stator windings, an electrical voltage develops

within the stator. As engine speed and generator output

increase, the SCR module feeds rectified stator output

current to the rotor through the exciter (or brushes/slip

rings) to increase the strength of the rotor field. As the

rotor field increases in strength, generator output also

increases.

The ADC 2100 monitors the generator

output voltage through leads 11 and 44 and adjusts the

DC current from the SCR module to the rotor to meet

load requirements. See Figure 8-1.

8.2 Separate Excitation

To determine the cause of no- or low-AC output, refer to

the troubleshooting flowchart in Figure 8-2.

beginning the test procedures, read all of the safety

precautions at the beginning of this manual. Many of the

test procedures include additional safety precautions.

Check the condition of the alternator fuse before

performing the separate excitation procedure. The fuse

is located on the fuse panel. See Figure 1-2. If the fuse

is not blown, use the following procedure to separately

excite the generator using an external voltage source (a

12-volt automotive battery).

Separately exciting the generator can identify faulty

voltage regulation by the ADC 2100 or reveal a running

fault in the rotor and/or stator. An external power source

duplicates the role of the voltage regulator and excites

the generator field (rotor). A generator component that

appears to be in good condition while stationary may

exhibit a running open or short circuit while moving.

Short circuits can be caused by centrifugal forces acting

on the windings during rotation or insulation breakdown

as temperatures increase.

TP-6359 7/08