Filter
Top Products
© 2012 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information. Page 9 of 17
“show env power all”
SW PID Serial# Status Sys Pwr PoE Pwr Watts
1A NG3K-PWR-1100WAC LIT1337057T OK Good Good 1100/0
1B No Input Power Bad N/A 235/0
2A NG3K-PWR-1100WAC LIT13370597 OK Good Good 1100/0
2B NG3K-PWR-715WAC LIT133705CC OK Good Good 715/0
Intelligent Power Management
Placing all of the available power in a single pool has advantages: a load (the switches in the power stack and
their respective power-able devices) is applied to the pooled power, making an efficient use of the power
resources of the stack. An administrator may conclude that there is too much power available in one stack and
may decide to take a power supply offline or pull it out and deploy it somewhere else.
A traditional power supply reaches around 80 percent efficiency when the applied load reaches around 60 percent
and tops out at a load of perhaps 80 percent; therefore, to make the best possible use of power, it is a good idea
to apply all of the load to a single power supply to reach higher efficiency more quickly before powering up a
second power supply and so on. Figure 7 shows the efficiency curve of three switches compared to the efficiency
curve of one switch with an optimal load.
Figure 7. Efficiency Curves
These efficiency curves belong to three different switches, each drawing different loads from their power supply
and none of them reaching 60 percent load, which increases the amount of energy wasted.
A more energy-efficient scenario could involve the same three switches drawing power from the same source, as
in a power stack. Three switches have a higher chance to reach the optimal load on the power supply, so the
maximum efficiency can be reached sooner, translating into energy savings and more intelligent use of power.
Note that Cisco IOS Software has the knobs to take a power supply offline and place it back online as required,
and the Cisco StackPower feature has the instrumentation to provide the information needed to take an action, but
off-lining a power supply requires administrator intervention.