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    Calculating Power Requirements for MX104 Routers

    The information in this topic helps you determine which power supplies are suitable for various configurations, as well as which power supplies are not suitable because output power is exceeded. You determine suitability by subtracting the total power draw from the maximum output of the power supplies. Afterward, the required input power is calculated. Finally, you calculate the thermal output. A sample configuration is provided in Table 1.

    We recommend that you provision power according to the maximum input current listed in the power supply electrical specifications (see MX104 AC Power Specifications and MX104 DC Power Specifications).

    Use the following procedures to calculate the power requirement:

    1. Calculate the power requirement.
    2. Evaluate the power budget.
    3. Calculate input power.
    4. Calculate thermal output (BTUs) for cooling requirements.

    The following sample configuration shows an MX104 router with:

    • Two (redundant) power supplies
    • Two (redundant) Routing Engines
    • Two 20-port Gigabit Ethernet MICs with SFP
    • Cooling system (standard fan tray and air filter)

    To calculate the power requirements:

    1. Calculate the power requirements (usage) using the values in Power Requirements for MX104 Components as shown in Table 1.

      Table 1: Sample Power Requirements for an MX104 Router

      Chassis Component

      Part Number

      Power Requirement

      Base system


      350 W

      MIC 0


      37 W

      MIC 1


      37 W

      Total output power

      424 W

      Note: The power consumed by an MX104 router as shown in Table 1, may differ slightly, due the power conversion losses in the power supply.

    2. Evaluate the power budget. In this step, we check the total output power against the maximum output power of available power supply options.
    3. Calculate input power. In this step, the input power requirements for the example configuration are calculated. To do this, calculate the total input power including the MICs as shown in Table 2.

      Table 2: Calculating Input Power Example



      Total input power requirement (maximum)

      625 W

      AC/DC power supply efficiency

      91 %

      Sum of MIC power requirements

      37 W + 37 W = 74 W

      Additional power supply conversion losses, due to added MICs

      (Sum of MIC power requirements) * (efficiency) - (Sum of MIC power requirements)

      (74 W) * 91 % – (74 W) = 7.3 W

      Input power to base system (includes power conversion losses in power supplies)

      350 W

      Total calculated input power requirement with MICs

      (Sum of MIC power requirements) + (Additional power supply conversion losses) + (Input power to base system)

      74 W + 7.3 W + 350 W= 431.3 W

    4. Calculate thermal output (BTUs). To calculate this, multiply the input power requirement (in watts) by 3.41.

      Table 3: Calculating Thermal Output

      Power Supply

      Thermal Output (BTUs per hour)

      MX104 power supply (as shown in the example)

      431.3 W * 3.41 = 1471 BTU/hr

      MX104 power supply (maximum)

      625 * 3.41 = 2131 BTU/hr

    Published: 2014-02-13