Selection of UPS power supply for weak electric room and calculation method of battery capacity

- Oct 28, 2018-

The UPS, that is, the uninterruptible power supply, is a system device that connects a battery (mostly a lead-acid maintenance-free battery) to a host computer and converts the direct current into a commercial power through a module circuit such as a host inverter.

It is mainly used to provide stable and uninterrupted power supply to a single computer, computernetwork system or other power electronic equipment such as solenoid valves, pressure transmitters, etc. When the mains input is normal, the UPS will supply the mains to the load for use. The UPS is an AC-type voltage regulator, and it also charges the battery inside the unit; when the mains is interrupted (accident blackout) At the same time, the UPS immediately supplies the 220V AC power to the load through the inverter switching method, so that the load maintains normal operation and protects the load from soft and hardware. UPS devices typically provide protection against excessive voltage or low voltage.

UPS and DC power supply are important power supply protection devices for enterprises. It can guarantee that the computer system will continue to work for a period of time after power failure, so that users can save the disk urgently, so that users will not affect the work or lose data due to power outage.

The UPS power system consists of five parts: main circuit, bypass, battery and other power input circuits, AC/DC converter rectifier (REC), DC/AC conversion inverter (INV), inverter and bypass output. Switch circuits and energy storage batteries.

The main advantage of the uninterruptible power supply is its uninterrupted power supply capability. When the mains AC input is normal, the UPS rectifies the AC power into DC power, and then inverts the DC power into a stable and impurity-free AC power for use in the rear stage load. Once the mains AC input is abnormal, such as undervoltage or power failure or the frequency is abnormal, the UPS will activate the backup energy-battery, and the UPS rectifier circuit will be turned off. Correspondingly, the battery's DC current will be inverted to a stable state. The alternating current of impurities continues to be used for the rear stage load. This is the origin of the UPS's uninterrupted power supply capability.

Of course, the uninterrupted power supply time of the UPS is not unlimited. This time is limited by the amount of energy stored in the battery itself. In the event of an AC power outage, what you need to do during the precious time of the UPS's battery supply is to quickly restore the AC.


Teach you how to calculate the number of batteries in the UPS configuration

The length of time that can be supplied is determined by the capacity of the battery. The calculation method of UPS battery configuration is introduced as follows:

First, the following factors affect the standby time:

  1. The total load power P(t)(W), taking into account the power factor of the UPS, can be calculated directly in units of P(t) volt-amperes (VA).

  2. V (low) is the termination voltage (V) after the battery is discharged, 2V (battery) V (low) = 1.7V; 12V (battery) V (low) = 10.2V

  3. V (float) is the float voltage (V) of the battery, 2V (battery) V (float) = 2.3V; 12V (battery) V (float) = 13.8V

  4. Kh is the battery capacity conversion factor (Ct/C10), 10Hr discharge rate is 1, 5Hr discharge rate is 0.9, 3Hr discharge rate is 0.75, and 1Hr discharge rate is 0.6.

  5. I is the battery operating current (A), T is the continuous discharge time (H), and V is the DC supply voltage of the external battery of the UPS (V)

Second, the calculation method:

  1. The number of 12V single cells N: N = V ÷ 122V The number of single cells is 6N

  2. Battery operating current I: I=P(t)÷V

  3. Actual battery capacity C: C = I × T÷Kh

  4. For example: power supply standby time of 1KVA is 4 hours, V=36V of UPS is selected, then 1N=36V÷12V=3 sections 2I=1000VA÷36V=28A 2C=24A×4H÷0.9=124AH 3 The capacity of the battery can be The selection of 100AH group 3 sections, or 65AH 2 group 6 sections, the results of the selection are deviated, depending on the user's needs and cost considerations. Note: The common capacity specifications for 12V batteries are 7Ah, 17Ah, 24Ah, 38Ah, 65Ah, 100Ah, and 200Ah.

Battery calculation method:

For example, a mountain 40KVA UPS power supply, DC voltage is 384V, each group is 32V for 12V battery. If the backup time requires 2 hours, calculate the battery capacity: 40000VA*2H/(0.7*384V)=297AH, so choose 3 groups. 100AH battery, a total of 96 knots.

The current of the battery pack is 40KVA/384V=104A, so the battery connection is 50mm2 cable.

Total number of batteries = (power / DC voltage * hours) / each block of security * number of blocks per block

The power is the power of the UPS, the DC voltage is the voltage required for the power supply of the UPS battery, and the DC voltage of the UPS of different powers is different. The number of blocks in each group is the minimum number of blocks required. When the battery is generally configured, it must be the number of blocks per group. Integer multiple, the common UPS DC voltage and the number of blocks per group are as follows (the battery is calculated based on 12V): For example, configure a 5KVA UPS with a delay of 8 hours, its power is 5000, and the DC voltage is 96V. There are 8 batteries in each group, and 100AH batteries are configured. The total number of batteries required is: (5000/96*8)/100*8=32 blocks.

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