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2-2 Technologies MN770
DC SCR Control NEMA Type C designation of electrical power source equipment for adjustable speed
drives.
Series 19H DC SCR (not used in elevator applications)
Series 20H DC SCR (Line Regenerative)
DC SCR controls are used in elevator applications where speeds range from 50 to over
1000 FPM. The Baldor DC SCR (Thyristor) control is a three phase, full wave rectified,
DC motor armature and field (where applicable) control. The SCR bridge converts three
phase AC to DC power. This rectified DC provides power to the DC motor armature, and
the reference transformer to operate power supplies and other circuits.
Armature or encoder feedback may be used with either control. DC tachometer or
resolver feedback is available with the optional expansion board. A Series 20H control
can be configured to check for torque output (torque proving) before a holding brake is
released.
20H Control The Series 20H is a standard line regenerative control. Regenerated power is applied
back to the incoming power lines. External filters can improve the Total Harmonic
Distortion (THD) of the AC waveform. This control is not designed for regenerative use
with stabilized shunt or compound wound DC motors. If stabilized shunt or compound
wound motors are to be used, the series field must be isolated and not connected.
Contact the motor manufacturer for motor derating under these conditions.
Regulation from the Series 20H, using armature feedback, will be 2% of base speed.
With DC tachometer feedback, the regulation will be 1% of set speed. Use of encoder or
resolver feedback will provide 0.1% regulation.