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:
- Calculate the power requirement.
- Evaluate the power budget.
- Calculate input power.
- 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 |
|
DC power to upper half of MX2020 components | Upper (zone 1) | PDM 2 and 3 | PSM 9 through 17 |
|
| 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
- 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
Component
Model Number
Power Requirement (Watts) with 91% Efficiency
Base chassis
CHAS-BP-MX2020
Fan trays (upper and lower)
MX2000-FANTRAY
1700 W * 4 = 6800 W
MPC
MPC-3D-16XGE-SFPP
440 W * 20 = 8800 W
ADC
ADC
150 W * 20 = 3000 W
CB-RE
RE-MX2000-1800X4
250 W * 2 = 500 W
SFB—slots 0 through 7
MX2000-SFB
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.
- 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)
2100
37,800
MX2020 DC PSM 80 A (feed to each input)
2500
45,000
- 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
91%
2100
2307
MX2020 DC PSM 80 A
91%
2500
2747
- 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.
