2 Follow the procedure listed in After working inside your system.Power supply unitsThe power supply unit (PSU) is an internal hardware component which supplies power to the components in the system.Your system supports one of the following:• Two 1600 W, 1100 W, 750 W, or 495 W AC PSUs• Two 1100 W DC PSUs• Two 1100 W or 750 W Mixed Mode HVDC PSUsNOTE: For more information, see the Technical specificationssection.CAUTION: If two PSUs are installed, both the PSUs must have the same type of label. For example, Extended PowerPerformance (EPP) label. Mixing PSUs from previous generations of PowerEdge servers is not supported, even if the PSUs havethe same power rating. Mixing PSUs will result in mismatch condition or failure to turn the system on.NOTE: Titanium PSU is nominally rated for 200 V AC to 240 V AC input only.NOTE: When two identical PSUs are installed, power supply redundancy (1+1 – with redundancy or 2+0 – without redundancy) isconfigured in system BIOS. In redundant mode, power is supplied to the system equally from both PSUs when Hot Spare isdisabled. When Hot Spare is enabled, one of the PSUs is put into the sleep mode when system utilization is low in order tomaximize efficiency.NOTE: If two PSUs are used, they must be of the same maximum output power.Hot spare featureYour system supports the hot spare feature that significantly reduces the power overhead associated with power supply unit (PSU)redundancy.When the hot spare feature is enabled, one of the redundant PSUs is switched to the sleep state. The active PSU supports 100 percent ofthe system load, thus operating at higher efficiency. The PSU in the sleep state monitors output voltage of the active PSU. If the outputvoltage of the active PSU drops, the PSU in the sleep state returns to an active output state.If having both PSUs active is more efficient than having one PSU in the sleep state, the active PSU can also activate the sleeping PSU.The default PSU settings are as follows:• If the load on the active PSU is more than 50 percent of PSU rated power wattage, then the redundant PSU is switched to the activestate.• If the load on the active PSU falls below 20 percent of PSU rated power wattage, then the redundant PSU is switched to the sleepstate.You can configure the hot spare feature by using the iDRAC settings. For more information, see the iDRAC User’s Guide available atDell.com/idracmanuals.Removing a power supply unit blankPrerequisitesFollow the safety guidelines listed in Safety instructions.StepsIf you are installing a second PSU, remove the PSU blank in the bay by pulling the blank outward.142 Dell EMC PowerEdge R640 Installation and Service ManualInstalling and removing system components
