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    Calculating DC Power Requirements for MX2020 Routers

    The information in this topic helps you determine which PSMs are suitable for various configurations, as well as which PSMs are not suitable because output power is exceeded. You determine suitability by subtracting the total power draw from the maximum output of the PSMs. Afterward, you calculate the required input current. 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 subsystem electrical specifications (see MX2000 Router DC Power Subsystem Electrical 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 MX2020 DC power subsystem is made up of two sub zones where each sub zone provides power to half of the FRUs in the chassis (see Table 1 for information on power zoning). Each power subsystem is made up of two DC PDMs, nine PSMs, twenty MPCs (ten MPCs powered by one power zone and the remaining ten MPCs powered by the second power zone), two fan trays within the same power zone and one fan tray powered by the other power zone, eight SFBs, and two Control Board and Routing Engines (CB-REs).

    When calculating power requirements, be sure that there is adequate power for each zone.

    Note: Four DC PSMs per zone are mandatory for the MX2020 router with DC PDMs.

    Table 1: MX2020 DC Power Zoning

    Chassis Power Configuration

    Power Zone

    Power Distribution Module (PDM)

    Power Supply Module (PSM)

    Components Receiving Power

    DC power to lower half of MX2020 components

    Lower (zone 0)

    PDM 0 and 1

    PSM slots 0 through 8

    • MPC slots 0 through 9
    • CB-RE slot 0 and slot 1
    • SFB slots 0 through 7
    • Fan tray 0, 1, 2

    DC power to upper half of MX2020 components

    Upper (zone 1)

    PDM 2 and 3

    PSM 9 through 17

    • MPC slots 10 through 19
    • CB-RE slot 0 through slot 1
    • SFB slot 0 through 7
    • Fan tray 0, 2, 3

    Note: When a PSM is switch off, the software will indicate that the PSM is present, but not turned on.

    The following sample configuration shows an MX2020 chassis with:

    • Four DC PDMs
    • Twenty 16-port 10GbE MPCs with SFP+ interfaces (slots 0 through 19)
    • Two CB-REs (with one redundant CB-RE) (CB-RE slot 0 and CB-RE slot 1)
    • Eight SFBs (with one redundant SFB) (SFB slots 0 through 7)
    • Twenty ADCs (slots 0 through 19)
    • Four fan trays
    1. Calculate the power requirements (usage) using the values in MX2020 DC Power Requirements as shown in Table 2.

      Table 2: Typical DC Power Requirements for MX2020 Router


      Model Number

      Power Requirement (Watts) with 91% Efficiency

      Base chassis



      Fan trays (upper and lower)


      1700 W * 4 = 6800 W



      440 W * 20 = 8800 W



      150 W * 20 = 3000 W



      250 W * 2 = 500 W

      SFB—slots 0 through 7


      220 W * 8 = 1760 W

      MX2020 DC power subsystem (upper and lower half of chassis, 60 A feeds to each PDM input)

      MX2020 DC power subsystem (upper and lower half of chassis, 80 A feeds to each PDM input)

      2100 W * 8 PSMs=16,800 W (+ 1 PSM@2100 W redundant capacity)

      2500 W * 8 PSMs=20,000 W (+ 1 PSM@2500 W redundant capacity)

      Note: The power reservation for the critical FRUs was 7360 W. With power droop-sharing between the two zones, the power reservation for critical FRUs is reduced to 5662 W. This number is considering 70/30% load on the power zones when droop sharing is enabled.

    2. Evaluate the power budget, including the budget for each configuration if applicable, and check the required power against the maximum output power of available PDM options.

      Table 3 lists the PSMs, their maximum output power, and unused power (or a power deficit).

      Table 3: Calculating DC Power Budget

      Power Supply Module

      Maximum Output Power of Power Supply Module (Watt)

      Maximum Output Power for System (Watt)—including redundant capacity

      MX2020 DC PSM 60 A (feed to each input)



      MX2020 DC PSM 80 A (feed to each input)



    3. Calculate input power. Divide the total output requirement by the efficiency of the PSM as shown in Table 4.

      Table 4: Calculating DC Input Power

      Power Supply Module

      Power Supply Module Efficiency

      Output Power Requirement (Watt)—per PSM

      Input Power Requirement (Watt)—per PSM

      MX2020 DC PSM 60 A




      MX2020 DC PSM 80 A




    4. Calculate thermal output (BTUs). Multiply the input power requirement (in watts) by 3.41 as shown in Table 5.

      Table 5: Calculating DC Thermal Output

      Power Distribution Module

      Thermal Output (BTUs per hour)

      MX2020 DC PDM

      34.5 KW divided by 0.91 * 3.41 = 129,280 BTU/hr (Zone 0 output. The calculation method for Zone 1 is the same as for Zone 0).

      34.5 KW of output power consumed by the chassis. This is the maximum output the chassis can consume in a redundant configuration. The input power is 34.5 divided by 0.91 = 37.9 KW.

    Modified: 2016-09-08