Operation
Theory of Operation
326 MagneMotion
Rockwell Automation Publication MMI-UM002F-EN-P - October 2022
Electrical System
The MM LITE motors are designed to operate at a nominal +36V DC. The inverters that
power the individual blocks within the motor are enabled when the internal propulsion bus for
the motor rises above +32V DC, which allows normal motor operation. The inverters are shut
down if the voltage falls below +27V DC. The inverters are also shut down when the internal
propulsion bus reaches +42V DC to help protect internal circuitry. When recovering from this
overvoltage condition, the inverters are enabled when the voltage falls below +38V DC. The
logic circuits in the motor are designed to operate at a nominal +36V DC, but start to function
once the logic bus rises above +32V DC, which allows reporting of all motor faults.
Voltage drops in the power distribution system when the motors consume power while mov-
ing vehicles lead to fluctuations in the voltages seen at the motor power terminals. Under nor-
mal operating condition, these fluctuations are minimal and can be ignored. The power
supplies and wiring for the system must be designed to minimize these fluctuations (see Elec-
trical Wiring on page 86).
Soft Start
If the PTC used to limit inrush current heats up and goes into a high-resistance state, it does
not allow the propulsion bus to power up. To keep from overheating the internal soft start
resistor, the time between each successive turn on of the propulsion power must be a mini-
mum of 20 seconds. There must be a minimum of 10 seconds between turn off and turn on
(power cycle) as shown in Figure 6-7.
Figure 6-7: Power Cycle Timing
To make sure that the soft start circuit resets for the next turn on:
• Wait a minimum of 20 seconds from turn on to turn on.
• Wait a minimum of 10 seconds from turn off to turn on.
• Wait for the Propulsion power not ready bit in the motor fault data to be clear, indicat-
ing that the Soft Start circuit is on, before turning the propulsion power back on. See
either the Host Controller TCP/IP Communication Protocol User Manual,
MMI-UM003, or the Host Controller EtherNet/IP Communication Protocol User
Manual, MMI-UM004.
Off
20 Seconds Minimum
10 Seconds
Minimum
On
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