Motortronics
Page 3
1 About the Motortronics ABC Series
1.1 General
The ABC Series is a solid state DC injection brake for stopping three- phase AC induction motors. This full-wave
DC brake design offers smooth, low peak level braking for quiet, steady operation and optimal performance.
Designed to handle even high inertia loads, the ABC Series eliminates costly and potentially dangerous "coast-
to- stop" times. A built-in microprocessor provides system supervision that includes digital timing control for
jogging and braking.
The integral Operator Interface Module provides LED indication of the unit's operating status and easy
adjustments for quick setup. Standard features include interlocks and mechanical brake release relays, a brake
disable input and zero speed sensing with override.
1.2 Theory of Operation
Incoming AC power is fed to terminals L1 and L2 directly from the line side of the motor starter terminals and is
converted to DC within the ABC Series. Once the motor starter has been turned off (opened) and the residual
energy in the motor has dissipated, the DC current from the ABC Series is applied (injected) to starter terminals
T1 and T2 respectively. This creates a stationary magnetic field in the AC motor stator windings.
The braking torque will increase in proportion to the amount of current allowed to flow. (The DC injection level
can be adjusted using the Brake Current Potentiometer on the operator interface module. This modulates the
applied voltage based upon an "RMS" closed loop current feedback signal from the integral sensors.) The rotor
then pulls into alignment with this stationary field and brings the load to a stop faster than if it coasted to a stop.
1.3 Brake Sizing and Selection
ABC Series brakes are suitable for use in most AC motor applications where coast-to-stop times are undesirable
or unacceptable. The ABC Series is a current controlling brake, so various sizes of brake units can be applied to
various motor sizes. Because DC injection means applying power to the AC motor after turning it "Off", motor
heating (although minimal) will continue during the braking cycle and should be considered when selecting the
motor. AC motor manufacturers recommend that each braking cycle over 100% FLA be considered as an
additional starting cycle when calculating the starts- per-hour ratings for the selected motor.
If the selected ABC Series is sized to deliver 200% of motor rated current, consider each brake cycle to be 2
start cycles for these calculations (and 300% FLA = 3 "starts" per brake). Never size any DC injection brake to
exceed 400% of the motor nameplate FLA without first consulting the motor manufacturer. Additional guidelines
for applying ABC Series brakes follow:
Phone: 800.894.0412 - Fax: 888.723.4773 - Web: www.clrwtr.com - Email: [email protected]
