Lesson 3/Learning Event 2
The coarse load control is located directly below the ammeter. This is part of the load bank
controls. The control has eight positions and an OFF position. During a 24-volt load operation,
each position adds 12.5 amperes of load when the knob is turned to the right. If the tester is being
used for a 12-volt load operation, each position from 2 to 8 adds 6.5 amperes of load. (Position 1
of the coarse load control has no control during the 12-volt load operation.) The load bank also
has a fine load control located to the right of the coarse load control. This is used when you want
an amperage load between the 12.5-ampere positions for 24 volts. It can also be used for the 12-
volt load operation.
The field rheostat control, located in the lower right of the tester, is a variable resistor. It is used to
change the generator output. This control should be left in the open position when the field
rheostat is not being used.
The voltmeter in the upper right of the tester has two scales, four rows of numbers, and four
ranges that can measure from 0 to 50 volts. The 0 to 10 scale is also used as an accurate 0- to 1-
volt scale or range. The voltmeter has a range selector switch located to its lower left. The switch
to the left of the voltmeter dial is used to turn the load bank on or off and should be left in the
OFF position when not in use.
The compartment along the right-hand side of the tester is used to store test leads. There are
seven separate leads and an external shunt. The leads consist of four 16-gage (light) leads (three
black and one red), two 6-gage heavy leads (one black and one red), and one black jumper lead.
The 16-gage leads are used to connect the voltmeter to a circuit and to connect the field rheostat to
a generating circuit. The two 6-gage leads are used to connect the adjustable load bank, ammeter,
and the fixed resistor to a circuit. The black jumper lead can be used anywhere it is needed in a
circuit with low amperage. The external shunt consists of two large and two small leads. It is used
when measuring loads from -150 amperes to +500 amperes.
The area above the ammeter and voltmeter has long slots cut in the metal. These slots allow air to
circulate through the LVCT for cooling. It is very important, when the meter is in use, that they
are not covered in any way.