Technical Documentation
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Calculating Power Requirements for MX960 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 current 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 Electrical Specifications for the MX960 AC Power Supply and Electrical Specifications for the MX960 DC Power Supply).
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.
Both normal-capacity and high-capacity MX960 chassis with DC power supplies and MX960 chassis with high-capacity AC power supplies are zoned. MX960 chassis with normal-capacity AC power supplies have one overall zone. Zoning means that certain components are powered by specific power supplies (see Table 1 for information on zoning). When calculating power requirements, be sure that there is adequate power for each zone.
Three AC power supplies are mandatory for MX960 chassis with normal-capacity AC power supplies.
Table 1: MX960 Zoning
Chassis Power Configuration | Zone | Power Supply (PEM) | Components Receiving Power |
|---|---|---|---|
MX960 DC (normal-capacity and high-capacity power supplies); MX960 AC (high-capacity power supplies) | Zone 0 | PEM 0 or 2 |
|
MX960 DC (normal-capacity and high-capacity power supplies); MX960 AC (high-capacity power supplies) | Zone 1 | PEM 1 or 3 |
|
The following sample configuration shows an MX960 chassis with:
- Four high-capacity AC power supplies (using two feeds for each power supply); two supplies are active, two are redundant
- Six 16 port 10 GbE MPC with SFP+ interfaces (slots 0 through 5)
- Two SCBs with two (redundant) RE-1800x2 routing engines (SCB slot 0 and SCBslot 1)
- SCB (SCB slot 6)
- Five 16 port 10 GbE MPC with SFP+ interfaces (slots 7 through 11)
- High-capacity cooling system (upper and lower fan trays)
Note: The high-capacity cooling system satisfies cooling requirements of MPCs, and must be used for proper cooling.
- Calculate the power requirements (usage) using the values
in Power Requirements for an MX960 Router as shown in Table 2.
Table 2: Sample Power Requirements for an MX960 Router
Chassis Component
Part Number
Power Requirement
Zone
Base system
MX960BASE-AC-HIGH
50 W1
—
High-capacity cooling system
FFANTRAY-MX960-HC
320 W * 2 = 640 W
Zone 0 (lower fan tray) and Zone 1 (upper fan tray)
MPC - slots 0 through 5
MPC-3D-16XGE-SFPP
440 W * 6 = 2640 W
Zone 1
MPC - slots 7 through 11
MPC-3D-16XGE-SFPP
440 W * 5 = 2200 W
Zone 0
SCB 0
SCB-MX960 with
RE-S-1800X2-8G
150 W
90 W
Zone 1
SCB 1
SCB-MX960 with
RE-S-1800X2-8G
150 W
90 W
Zone 0
SCB 2 - slot 6
SCB-MX960
150 W
Zone 0
MX960 normal-capacity AC (not zoned)
Zone 0 total output power
Zone 1 total output power
6160 W
2935 W
3225 W
1 Divided equally between zone 0 and zone 1.
- Evaluate the power budget, including the budget for each
zone if applicable. In this step, we check the required power against
the maximum output power of available power supply options.
Table 3 lists the power supplies, their maximum output power, and unused power (or a power deficit).
Table 3: Calculating Power Budget
Power Supply
Maximum Output Power of Power Supply
Maximum Output Power for System
Nonzoned Unused Power
Zone 0 Unused Power1
Zone 1 Unused Power2
MX960 AC normal-capacity
1700 W
5100 W
Power exceeded (non-zoned; 5100 W - 6160 = power exceeded)
–
–
MX960 AC high-capacity
1700 W (one feed)
4100 W (two feeds)
3400 W (one feed)
8200 W (two feeds)
–
Power exceeded
1165 W
Power exceeded
875 W
MX960 DC normal-capacity
2800 W
5600 W
–
Power exceeded
Power exceeded
MX960 DC high-capacity
1700 W (one feed)
4100 W (two feeds)
3400 W (one feed)
8200 W (two feeds)
–
Power exceeded
1165 W
Power exceeded
875 W
1 For this configuration, output power is 2935 W.
2 For this configuration, output power is 3225 W.
- Calculate input power. In this step, the input power requirements
for the example configuration are calculated. To do this, divide the
total output requirement by the efficiency of the power supply as
shown in Table 4.
Note: MX960 AC and MX960 DC normal-capacity power supplies are not included in the following table, because their power budget was exceeded in the sample configuration.
Table 4: Calculating Input Power
Power Supply
Power Supply Efficiency1
Input Power Requirement2
MX960 AC high-capacity
~88 %
3335 W3
MX960 DC high-capacity
86 %
3413 W3
1 These values are at full load and nominal voltage.
2 For this configuration, total power for zone 0 is 2935 W. The calculation method for zone 1 is the same as zone 0.
3 Zone 0 requirement.
- Calculate thermal output (BTUs). To calculate this, multiply
the input power requirement (in watts) by 3.41 as shown in Table 5.
Table 5: Calculating Thermal Output
Power Supply
Thermal Output (BTUs per hour)
MX960 AC high-capacity
3335 * 3.41 = 11,372 BTU/hr1
MX960 DC high-capacity
3413 * 3.41 = 11,638 BTU/hr1
1 Zone 0 output. The calculation method for zone 1 is the same as for zone 0.
