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# Power calculation

Posted on 2007-07-30
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Please advice on how to calculate the power/ amps for Rack requirement in datacenter. Example have 5 servers each with 2Amps and 500Watts.
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Question by:michael0820

LVL 8

Assisted Solution

Its simple  P=VA* .8  if you have power ratings and amps then follow the formula, where 0.8 is the power factor

For Eg the 2 Amps for 230 Power

2*230=460*0.8= 368 Watts for 5 servers you need to have  1840 Watts of power

Cheers

Yasir
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LVL 4

Accepted Solution

The equation is Power(in W) = Voltage(in V)*Current(in Amps). And he said he knew the wattage, which is the Power. The only thing in this case that would be left to find is the voltage. And where did you get the .8 powerfactor? He never mentioned the current being out of phase with the voltage. So for 5 servers of 500W and 2A, the total power needed would be 2500W peak and ~1767.5W RMS(or Avg Power). RMS is just .707*Power.
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LVL 27

Assisted Solution

APC has a "Rack Configurator" you can use.  It will allow you to enter the specific servers (& etc) you have.  If they don't have those specs listed, you can enter the specs listed on the servers you have.   They will then calculate the requirements for you.
http://configurator.apcc.com/products/powerstruxure/configurator/PSX_ChooseRackTool.cfm?cc=US&startCfg=rack&ConID=Guest

This is a link to APC's product selector main page:
http://www.apc.com/sizing/selectors.cfm
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LVL 14

Assisted Solution

And yes, its not truly an "Expert" answer, but in this type of calculation it is always better to have higher estimates.

The electricians are mostly interested in how many amps you're going to pull and what size the breakers should be, they are not going to be concerned about the power factor and rms.

If the 2 am draw is at the local voltage (be careful since most devices have different draw for different voltage)  Then all the electrician cares about is that you have 5 devices using 2 amps, and he will want to know what type of connectors to install.  (Sometimes servers use twistlock connectors to try and prevent someone from accidentally unplugging them.)

So, for the average calculations just add the number of amps used by each device, simple.
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