Motortronics
Page 4
1.3.1
Standard Duty Sizing
Applying an ABC Series brake that is rated for
<
115% of the FLA (Full Load Amp) rating of the motor allows
maximum length of braking time without exceeding the thermal capacity of the stator windings. Since current is
controlled by the ABC Series throughout the braking cycle, braking torque will vary as the motor circuit
impedance decreases with speed. Braking torque will be highest at the beginning of the cycle, and can be as
much as 100% of the FLT (Full Load Torque) when set to motor FLA.
As the motor slows, the braking torque slowly decreases, reducing the mechanical stresses as much as
possible. Sizing a brake in this manner is typically good for machine tools, saws, conveyors, lumber machinery,
and most chippers where the coast-to-stop time does not exceed 5 minutes. Stop times vary greatly with load
and friction, but can be expected to be 1/2 of the coast-to-stop time or less. Keep in mind that the maximum
brake time is setting is 127 seconds. In heavily loaded, high inertia machines and long coast-to-stop times, the
Standard Duty model may not stop the load. Consider using the Extra Duty rating instead.
1.3.2
Extra Duty Sizing
For heavier machine loads such as large chippers, punch presses and other flywheel based machines, selecting
an ABC Series brake based on 200-250% of the motor nameplate FLA allows faster braking. The maximum
developed braking torque can be as much as
200% of the motor rated Full Load Torque. In this case, the load can typically stop in twice the Across-the-Line
starting time. Duty cycling of the motor is a much more important consideration in applications since additional
thermal stresses due to higher current levels are applied to the motor.
1.3.3
Custom Sizing
Extreme loads (such as overhauling conveyors or large centrifuges), or short stop times (approaching the
across-the-line starting time of the motor) may require sizing the ABC Series for 300% of the motor FLA or
greater, and should be done with careful consideration of motor heating, duty cycle, and limitations of
mechanical stress on the drive train components.
1.3.4
Emergency Stopping
An ABC Series brake used in conjunction with a mechanical brake should be considered if the stop times must
be equal to or shorter than the across-the-line start time, consider using and ABC Series brake in conjunction
with a mechanical brake.
Phone: 800.894.0412 - Fax: 888.723.4773 - Web: www.clrwtr.com - Email: [email protected]
