Yaskawa GPD 506/P5 Section One - Manual (Page 17)

PP.P5G5.01.Troubleshoot
Page 17
Rev. 06/11/2003
Soft Charge Resistor/Contactor
The soft charge resistor, or current-limiting resistor, works in conjunction with the soft
charge contactor to slowly charge the DC bus capacitors and minimize the inrush
current, when power is applied to the inverter. With no power applied to the inverter,
the DC bus is discharged and the contacts on the soft charge contactor are open.
The purpose of the soft charge contactor is to bypass the soft charge resistor after the
DC bus voltage has reached it’s normal operating level. When input power is applied to
the inverter, the DC bus voltage starts to increase. The contacts on the contactor are
open, so the current that is charging up the DC bus capacitors is passing through the
soft charge resistor. The soft charge resistor acts like a control valve, and allows the
DC bus capacitors to charge slowly. When the DC bus voltage has risen above the
under voltage detection point (190 VDC for 230V units, 380 VDC for 460V units and
546 VDC for 600V units), the contacts on the contactor close bypassing the soft charge
resistor. If a soft charge resistor was not used, the large inrush current would damage
the input diodes.