UPS Power Configuration Scheme for Small and Medium Computer Rooms: How to Calculate Power and Endurance

1. calculate the total load power to avoid mismatch.

The first step in configuring UPS is to completely count the sum of rated power of all devices that need to be connected to UPS. Common 

computer room loads include servers, switches, routers, monitoring hosts, firewalls, etc. The rated power will be marked on the nameplate 

of the equipment, and the basic total power can be obtained by adding them one by one. When accounting, IT is necessary to distinguish 

the load types: IT equipment such as servers and network equipment are mostly resistive loads, which can be directly accumulated accor-

ding to the nominal power; If the inductive load such as precision air conditioning and motor is connected to the computer room, the peak 

current will be 2-3 times when the equipment is started, so the power should be reserved at least 2 times of the nominal power to avoid tr-

iggering UPS overload protection at the moment of starting. To give a simple example: 8 servers with a single 300W, plus switches and mo-

nitoring equipment, totaling 400W, the total power of resistive load is 300× 8+400 = 2800 W.

2. UPS host power reserve 20%-30% margin.

After calculating the total load power, the UPS host with the same power cannot be directly selected. Long-term full-load operation of UPS 

will accelerate the aging of internal IGBT, capacitor and other components, greatly shorten the service life, and can not meet the needs of 

temporary capacity expansion of subsequent loads. For conventional computer room scenarios, it is recommended to reserve 20%-30% 

power margin. The core calculation formula is: rated apparent power of UPS = total active power of load ÷(0.7~0.8). For example, for the 

above-mentioned load of 2800W, 2800÷0.7=4000VA, it is most suitable to choose 4KVA online UPS host. We should also pay attention to 

the power factor parameters of UPS when selecting the type. The power factor of conventional industrial-grade online UPS is mostly 0.8, 

which should be based on the actual active power on load, not just the apparent power value to avoid falling into the parameter misund-

erstanding.

3. Match the battery capacity according to the target battery life.

The battery life is the core index of UPS configuration, which is directly determined by the total battery capacity. The general estimation 

formula is: total battery capacity (Ah)=(UPS rated power× power factor× target battery life) ÷ (DC bus voltage× battery discharge effici-

ency). Taking 4KVA UPS, DC bus voltage of 192V, and target battery life of 2 hours as an example, substituting the formula to calculate: 

(4000× 0.8× 2) ≈ (192× 0.9) ≈ 37 ah, and actually selecting 16 batteries of 12V 65Ah in series, the battery life requirement of more than 

2 hours can be stably met. In the actual configuration, it is suggested to reserve an extra 10% capacity margin. Low ambient temperatu-

re and aging and attenuation of the battery will lead to the decrease of the actual available capacity, and the reserved margin can ensure 

the battery life to reach the standard in the whole life cycle.

Concluding summary

Generally speaking, the UPS configuration of small and medium-sized computer rooms can avoid most of the selection errors by follow-

ing the three-step method of "accounting load, reserving margin and matching battery life". For the core data room, it is recommended 

to give priority to online UPS, which can realize zero-sensing switching during power failure, and at the same time, it has the ability of 

voltage-stabilizing filtering and surge protection to protect equipment safety in all directions.

If you need type selection and transformation, you can consult Baoweite for the scheme. Thank you for browsing. You can collect official 

website of Shenzhen Baoweite Power Supply Co., Ltd.