Power problem set

Dr Peadar Grant

Data Centre Infrastructure

Attempt the following problems. Make sure to lay out your work well and give units (where relevant).

  1. Calculate the voltage developed across a 6 k resistor with 105 mA flowing through it.
  2. The current on a server PSU’s 5 V rail is measured as 4 A. What power is being delivered by the PSU?
  3. Write an expression for P using only R and I.
  4. A load consumes 60 W of power from a 12 V battery. Calculate the current.
  5. A device requires 5 A at 230 V. Determine the apparent power.
  6. A device consumes 720 W when connected to a 230 V supply. Determine the apparent power.
  7. Two devices, A and B, operate on a 230 V supply. Device A consumes 650 W and has a power factor of 0.9. Device B consumes 450 W at an unknown power factor. Determine the apparent power.
  8. An IT device has an apparent power requirement of 750 W. Its real power is 680 W. Determine:
    1. Its power factor.
    2. The reactive power component.
  9. A SAN storage array consumes 1250W at 230V:
    1. Find a suitable rackmount UPS from APC / Eaton for it.
    2. Estimate runtime of your chosen UPS from specifications.
  10. Write a script in PowerShell (or any other language) to do some / all of the following:
    1. Work out the total apparent power for a number of devices.
    2. Add in a catalogue of commonly used devices in your data centre.
    3. Select a suitable UPS from a small catalogue (e.g. 3-5).

    Test your script using some of the problems above.