Power Draw on 6500 w/ Dual Power Supplies

[johnnylingo]

I have a 6509-E with dual 3000W power supplies.  Each is plugged in to a separate UPS, and they are the only things plugged in to those UPSes.

Something very odd I notice is that one UPS shows a 30% load, while the other only 10%.  The 6509 is configured for redundant mode.

My understanding is even in redundant mode, the power drawn by both supplies should be equal.  Is this correct? 

>show power status all

                        Power-Capacity PS-Fan Output Oper

PS   Type               Watts   A @42V Status Status State

---- ------------------ ------- ------ ------ ------ -----

1    WS-CAC-3000W       1171.38 27.89  OK     OK     on

2    WS-CAC-3000W       1171.38 27.89  OK     OK     on

[Reza Sharifi]

In redundant mode one power supply run the system while the other one is on stand-by to take over in case the first one fails. To achieve equal load sharing, you need to configure them in combined mode.

See blew:

How to Enable or Disable Power Redundancy

To disable or enable redundancy (redundancy is enabled by default) from global configuration mode, enter the power redundancy-mode combined | redundant commands. You can change the configuration of the power supplies to redundant or nonredundant at any time.

To disable redundancy, use the combinedkeyword. In a nonredundant configuration, the power available to the system is the combined power capability of both power supplies. The system powers up as many modules as the combined capacity allows. However, if one power supply fails and there is not enough power for all of the previously powered-up modules, the system powers down those modules.

Link:

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/15.0SY/configuration/guide/power.html

HTH

[johnnylingo]

That would explain what I'm seeing, but actually contradicts the documentation you linked to.  Specifically:

To enable redundancy, use the redundant keyword.  When you install and power up two power supplies, each concurrently provides approximately half of the required power to the system. Load sharing and redundancy are enabled automatically; no software configuration is required.

I interpret this to mean the power draw on both supplies should be the same.

[Reza Sharifi]

Here is a bit more info in this post

according to Edison:

In redundant mode, it's not the sum of both but up to 50% of each.

In combined mode, it's the sum of both.

https://supportforums.cisco.com/thread/207276

may be this make more sense

HTH

[johnnylingo]

Hmmm, but the issue remains - on the 6500, each power supply should be drawing half the power.  In the event of a failure, obviously then the remaining power supply does 100%.

Perhaps I just have a buggy UPS.  I'll do some more tests.

[johnnylingo]

Ah, I have a theory on the issue.  In that thread you linked to:

found out that there 6000W power supplies provide 6000W only if both of  the input circuits are at 220V! If either of them drops, it will lower  the output to 2900W (that is yours 2671.20W in the log)

Something else that's odd is even though the UPSes are rated for 2200W, system power total only reports 1171W.  This may explain it.  I'll have to look more closely on how they are hooked up.