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New Member

Power Calculator

When using the Cisco power calculator, what is the difference between 'Output Power' and 'Typical Power Used'? The numbers for the sup, fabric and line cards are not that different. But, the system fan is very different. Just trying to figure out exactly what they each mean.


New Member

It is a bit confusing indeed

It is a bit confusing indeed and can quickly get complicated, but in a nutshell, the definitions are the following:

 - Total Output Power: For a given configuration, it is the maximum power in Watts that the appliance could draw at full capacity (packets traffic, LEDs, fans et c). On NO occasion it should go any higher, therefore it always should be safely below the supply unit's nominal power (see paragraph below about Power Input)

 - Total Typical Output Power: This value is an estimation of the average power usage in Watts that the same configuration will use in "business as usual", the common range being 65-85% of processing capacity. The percentage will be automatically defined by the config itself.

Now, subtilities kick in when for example, you have to consider the facts that a Nexus appliance will reserve the typical power of several populated module slots, even if they are empty (numbers vary, but you get the idea).

Also if you mix 110V and 220V PSUs on chassis such as a Nexus 7000 with Full Mode Power Redundancy.

Last but not least, here, we talked about the power SENT by the PSU to the switch, and NOT about the power taken from the power grid to the PSU. This other value is called Power Input and can be easily calculated by dividing the Total Output Power by 0.85 (or +18%), obviously, this value should always remain below the nomal PSU's power capacity.

So, here is a very simplified example with a 6000W PSU on a Nexus 7000 with 2 Supervisors and 6 modules cards, as you know, this is for demonstration purpose only :

 - The power supply unit's nominal capacity is 6000W
 - The given config could consume a maximum of 4600W at full usage (Total Power Output)
 - At "normal everyday usage", the same config would use around 3600W (Typical Power Output)
 - Whatever happens, the PSU will always make sure to provide at least 2800W for 5 modules and 2 SUP
 - The input power can reach a maximum of 5400W from the grid to the PSU

Hopefully this clarifies everything, the good thing with Cisco Power Calculator tool is that it does the maths in real time and automatically adapts the PSU choice to the needs so the values always remain in the green.



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