cisco 6500 switch power in combined mode

Answered Question
Jan 24th, 2009
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Hi every body!

Let me quote from the following link


javascript:newWin('http://en.wikipedia.org/wiki/Catalyst_6500#6503')


[edit] Combined Mode


"In combined mode, each power supply provides approximately 83% of its capacity to the chassis. This allows for greater utilisation of the power supplies and potentially increased PoE densities."


Here is my problem


Suppose we have 6500 switch with power supplies ,p1=100 watts(max), p2=100 watts(max), both power supplies are in combined mode. The total load on the switch is 100 watts.

My question is how much each power supply power? . Based on the above excerpt from the link, each power supply provides 83% of its capacity to the chassis. It means P1=83 watts( 83% of 100 watt), P2= 83 watts(83 % of 100)

So the total watts avaialable is P1+P2=83+83=166 watts. But the total load is 100 watts why we are supplying more watts than necessary?


Take another case, this time the load is 200 watts. But 6500 switch operating in combined mode , can not handle this load because each power supply can provide 83% of its capacity, so total power avaiable is 166 watts. Switch has to power down the modules to bring the total load from 200 to 166 or less.

My question is both power supply can handle this load of 200 watts easily but combined mode causes them to supply only 83% of their capacities


Thanks a lot!

Correct Answer by Edison Ortiz about 8 years 6 months ago

My question is how much each power supply power?


Hard to predict as the power consumption and output from each power supply won't be even.


One power supplying will be providing 60% of the load while the other power supply will be providing 40% of the load.


This amount will shift if you inspect carefully.


In general practice, combined mode is something we don't recommend so it's rare you will find this type of design.


But the total load is 100 watts why we are supplying more watts than necessary?


The power is provided based on demand. 83% isn't a fixed number. It's up to 83% power capacity, it can be less if the modules don't need it.


My question is both power supply can handle this load of 200 watts easily but combined mode causes them to supply only 83% of their capacities


I understand your confusion. 2 Power Supplies classified as 100W each should provide 200W of energy but that's not the case.


__


Edison.



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Correct Answer
Edison Ortiz Sat, 01/24/2009 - 10:51
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My question is how much each power supply power?


Hard to predict as the power consumption and output from each power supply won't be even.


One power supplying will be providing 60% of the load while the other power supply will be providing 40% of the load.


This amount will shift if you inspect carefully.


In general practice, combined mode is something we don't recommend so it's rare you will find this type of design.


But the total load is 100 watts why we are supplying more watts than necessary?


The power is provided based on demand. 83% isn't a fixed number. It's up to 83% power capacity, it can be less if the modules don't need it.


My question is both power supply can handle this load of 200 watts easily but combined mode causes them to supply only 83% of their capacities


I understand your confusion. 2 Power Supplies classified as 100W each should provide 200W of energy but that's not the case.


__


Edison.



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