Performing a Power Budget on a PXI/PXIe System

Updated Jul 31, 2018

Reported In

Hardware

  • PXI Chassis
  • PXI Controller

Issue Details

I have a PXI chassis with a number of different modules. How do I know if the chassis will have enough power to drive all of my modules?

Solution

You will need to perform a power budget. A power budget breaks down the current and power available on each of the PXI/PXIe power rails. This way you can determine if your PXI/PXIe chassis will provide enough current on each power rail. A high level process is described in this document to provide an introduction to the process. 

National Instruments PXI/PXIe chassis have 12, -12, 5, and 3.3 V power rails. There is an excel spreadsheet attached which can serve as a template for your power budget. The steps to performing the power budget are:
  1. Determine the PXI/PXIe chassis current on each power rail. This is typically included in the chassis data sheet. If it is not in the data sheet please consult the user manual.
  2. Determine the current consumption per power rail for each of the modules in the PXI chassis. This is also typically included in the module data sheet or in the user manual.
  3. Edit the "Amps Avail" field (in the attached '1000B DC Chassis....'.xls excel spreadsheet) to reflect the current available power per rail for your PXI chassis.
  4. Edit the "Module" fields to reflect the current consumption per power rail for each of the modules. Use the maximum current consumption specification if available.
  5. Ensure that the "Available current - sum of module's current" is sufficient (positive).
  6. Ensure that the "Total Power - Power Required" is sufficient (positive).
  7. If any of the power rails share power, ensure that the total power of these rails is sufficient. For example, sometimes the 3.3 and 5 V power rails share power. So, if power is used on one rail then it will be derated from the other rail. For example, if the 3.3 V power rail consumes 1 A, the 5 V power rail would have 3.3 V*1 A=3.3 W less power. If power rails share power it will be documented in the power specification.
  8. If all power requirements are met in steps 5-7 then your chassis power requirements are met.

Additional Information

For power budgets that have a limited amount of power to pull into the chassis, also consider the amount power the chassis will draw without considering modules. Refer to the related link on the power consumption of an empty chassis.
 

The total power drawn will be equal to the power consumed by the chassis + the power draw of each module.

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