SECTION 3 - CHASSIS & SCISSOR ARMS
3-2
31215074
3.2
PUMP/MOTOR - THEORY OF OPERATION
The Power Module (see Figure 3-18., ZAPI Power Module
Location on page 3-26) is essentially a "low-side" switch
for the pump motor. The positive terminal of the pump
is tied to Battery Positive after the Line Contactor. The
negative terminal of the pump connects to the P Termi
-
nal of the Power Module, which switches current
through MOSFET transistors to the Battery Negative.
For variable speed pump operation, the MOSFET transis
-
tors switch On and Off at high frequencies (16kHz). The
Duty Cycle is varied to control the voltage applied to the
pump motor. When the MOSFET's spend 50% of the
period On and 50% Off, approximately ½ of the avail
-
able Battery Voltage will be applied to the pump motor.
Similarly, the MOSFET are On continuously (100% Duty
Cycle) to apply all available Battery Voltage to the pump
motor (as in Lift Up at full speed).
When the Control System is energized, the voltage at
the P Terminal will be approxi24V (referenced
to -B) when the pump is static. The P Terminal will be
approximately at +1V (referenced to -B) when the pump
is running at full speed (Lift Up from Ground Mode).
Pump Motor Electrical Evaluation
Several basic electrical tests can be performed on the
Pump Motor. Failure of one of these evaluations is signif
-
icant and may indicate that the device is physically dam
-
aged.
Refer to Figure 7-2., Resistance Measurement. Make all
measurements with a voltmeter set to resistance scale
(Ohms). Disconnect the Main Battery Disconnect and all
pump motor cables during this analysis.
•
Resistance < 5 Ohms between Motor Termninals.
The internal windings are very low impedance and
should appear to be a short-circuit for an ordinary
voltmeter (other tests can determine if the windings
are truly shorted). High resistance can signal worn
brushes, a faulty commutator, or open windings.
•
Resistance > 1 MegaOhms between Motor Termi
-
nals and Motor Housing.
The internal windings
should be electrically isolated from the motor hous
-
ing. Low resistance may be an indication of a broken
motor terminal, damaged brush, faulty commutator,
or burned winding.
Common Difficulties
The following difficulties can be examined using the JLG
Analyzer, a voltmeter, and simple hand tools. Unless other
-
wise noted, the Control System shall be energized in
Ground Mode during testing. For a convenient Ground
Reference, place the black meter lead on the negative post
of the left battery in the left-side battery compartment.
The vehicle should be placed on a firm, level surface for all
analysis.
-B
P
+B
Series DC
Pump Motor
24V
Line Contactor
Power Module
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