Rockwell Automation SB3000 High Pwr SB3000 AC Pwr Modules (RCS) - Manual (Page 67)

Theory of Operation B-7
B.3.3 Pre-charge Contactor’s Close Threshold Voltage
When control power is first turned on, the pre-charge contactor will be open. This
allows the DC bus voltage to increase to near the peak voltage of the AC line. The
pre-charge contactor’s close threshold voltage is equal to the following:
Close Threshold Voltage = 1.414 x (Peak Configured AC RMS Line Voltage) - 10%
This threshold voltage allows the SB3000 Power Module to turn on when the AC line is
up to 10% low. The pre-charge contactor will stay open until the measured DC bus
voltage reaches this threshold. When the pre-charge contactor closes, the PMI
Processor will indicate this by turning on register 201/1201, bit 12 (CHG_FB@).
B.3.4 Pre-charge Contactor’s Open Threshold Voltage
The pre-charge contactor’s open threshold voltage is the peak voltage of the
configured AC RMS line voltage, times the square root of two, minus 100 volts. The
maximum step change on the capacitor is 100 volts. If the DC bus voltage drops below
the open threshold voltage, the pre-charge contactor will be opened to protect the
capacitors and CHG_FB@ will be turned off. In this case, register 201/1201, bit 12
(CHG_FB@) will be turned off. The pre-charge contactor will remain open until the
bus voltage again reaches a steady-state voltage above the close threshold voltage.