Detailed operation – Rockwell Automation 20A PowerFlex 70EC/700VC User Manual

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Stop Modes

Detailed operation

Mode

Description

Coast to Stop

Coast is selected by setting [Stop Mode A/B] to a value of “0.” When in Coast to Stop, the drive acknowledges the Stop
command by shutting off the drive output and releasing control of the motor. The load and motor will coast until the kinetic
energy is dissipated.

DC Brake to Stop

This method uses DC injection of the motor to Stop and/or hold the load. DC Brake is selected by setting [Stop Mode A/B]
to a value of “3.” The amount of time that braking will be applied is programmed in [DC Brake Time] and the magnitude of
the current used for braking is programmed in and [DC Brake Level]. This mode of braking will generate up to 40% of rated
motor torque for braking and is typically used for low inertia loads with infrequent Stop cycles.
1. On Stop, 3 phase drive output goes to zero (off)
2. Drive outputs DC voltage on the last used phase at the level programmed in [DC Brake Level], parameter 158. This

voltage causes a “stopping” brake torque. If the voltage is applied for a time that is longer than the actual possible
stopping time, the remaining time will be used to attempt to hold the motor at zero speed (decel profile “B” on the
diagram above).

3. DC voltage to the motor continues for the amount of time programmed in [DC Brake Time], parameter 159. Braking

ceases after this time expires.

4. After the DC Braking ceases, no further power is supplied to the motor. The motor/load may or may not be stopped. The

drive has released control of the motor/load (decel profile “A” on the diagram above).

5. The motor, if rotating, will coast from its present speed for a time that is dependent on the remaining kinetic energy and

the mechanics of the system (inertia, friction, etc.).

6. Excess motor current and/or applied duration, could cause motor damage. The user is also cautioned that motor

voltage can exist long after the Stop command is issued. The right combination of Brake Level and Brake Time must be
determined to provide the safest, most efficient stop (decel profile “C” on the diagram above).

Coast Time is load dependent

Stop

Command

Time

Output Voltage

Bus Voltage

Output Current

Motor Speed

Command Speed

Stop

Command

DC Brake Time

(A)

(C)

(B)