SECTION 4 - HYDRAULICS
4-6 – JLG Lift – 3121166
4.7 PUMP/MOTOR
Theory of Operation
The Power Module (see Figure 3-32., Sevcon Power Mod-
ule Location on page 3-38) 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 Ter-
minal 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 available
Battery Voltage will be applied to the pump motor. Simi-
larly, 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 approximately +24V (referenced to -B)
when the pump is static. The P Terminal will be approxi-
mately at +1V (referenced to -B) when the pump is run-
ning at full speed (Lift Up from Ground Mode).
-B
P
+B
Series DC
Pump Motor
24V
Line Contactor
Power Module
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