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Chapter 3. Replacing controller unit components 45
Power supply
The controller unit power system consists of two power supplies. The power supplies slide
into either of the two slots on the back of the controller unit. The power supplies provide
power to the internal components by converting incoming ac voltage to dc voltage. The
power supplies are interchangeable and redundant. Each power supply uses one power
cord. You can plug both power cords into a common power source or plug each cord into a
separate circuit for power redundancy. One power supply can maintain electrical power to
the controller unit if the other power supply is turned off or malfunctions.
Servicing notes
Consider the following when servicing the power supplies:
• Each power supply has a built-in sensor that detects the following conditions:
– Overvoltage
– Overcurrent
– Overtemperature
If any of these conditions occur, one or both power supplies enter shutdown mode. All
power remains off until one of the following occurs:
– You cycle the power switches (turn off the power switches, wait at least 30 seconds,
then turn on the power switches). For more information, see "Overtemperature
condition and power supply shutdown" on page 22 .
– The power supplies automatically resume operation when the ambient air
temperature cools to below 70º C (158° F). When the power supplies automatically
resume operation, the controller also resumes operation.
After you manually cycle the power off then on, or when the power supplies
automatically resume operation, an automatic restart resets the controllers, attempts to
spin up the drives (which has no effect on the drives if they are already running), and
returns the controller unit to normal operation without operator intervention.
• You can hot swap (replace) a power supply because the two power supplies provide
redundancy.
• Both power supplies have built-in temperature sensors designed to prevent the power
supplies from overheating. If a temperature sensor detects an ambient air temperature
greater than 70
º
C (158
º
F), the “overheated” power supply automatically shuts down.
The second power supply remains on as long as its temperature remains below 70
º
C
(158
º
F). If the second power supply overheats, it turns off all power to the controller
unit.
Note: There is a serious problem if the air temperature inside the cabinet is hot enough
to cause the power supplies to shut down.