UPS battery capacity and discharge rate impact analysis Jinhua Battery Factory

by:Power Kingdom     2021-07-09

  Jinhua Battery Factory

   When the UPS manufacturer configures the battery, the design capacity selected is fully meets or even exceeds the power capacity and power supply time requirements of the load without power failure. However, after the UPS is put into operation, users often find that the actual time of the UPS without power failure after the mains power failure is far less than the design value. The reason for this phenomenon is not that the battery backup capacity is not enough at the initial configuration in most cases. The capacity of the battery is not used. There are many reasons for the decrease in the actual capacity of the battery, such as battery quality problems, but more problems with use and maintenance.

  (1)Battery capacity

   Lead-acid battery plate is charged and formed during the manufacturing process. The lead on the positive plate becomes lead dioxide, and the lead on the negative plate becomes spongy lead. However, the time for the manufacturer to form the electrode plate is limited, and it is impossible to convert all the materials into active materials. Therefore, the state The standard stipulates that a new battery reaches 90% capacity as qualified. Only in the subsequent daily use, the capacity gradually reaches the normal value, and it is required to reach 100% after two years of installation.

   The rated capacity of the battery pack is obtained under the specified discharge rate, discharge rate (1/H) u003d discharge current (A) / battery rated capacity (Ah) For example, one of the typical specifications of small batteries used in UPS power supplies is l2V, 6Ah/2Ohv, this specification is defined as output DC voltage l2V, nominal capacity is 6Ah, and the discharge rate condition is 20hr. The specific meaning is: the battery pack with output DC voltage l2V is discharged under the condition of 20H constant discharge rate, and the total ampere-hour measured should be 6Ah when the output voltage drops from l2V to l0.5V. .

   Industrial batteries in my country, Japan, and Germany use a 10-hour rate (expressed as C10), and the American industrial battery standard is an 8-hour rate (expressed as C8,). In actual use, its discharge rate is not equal to the discharge rate specified by the standard capacity. When the actual discharge rate is greater than the discharge rate specified by the nominal capacity, the actual output capacity is less than the nominal capacity.

   my country’s electricity, post and telecommunications standards stipulate that when a 10-hour rate battery is discharged at a 1-hour rate, its capacity is 55% of the nominal capacity, which is 0.55C10. The Japanese Industrial Standard stipulates that 2V/10 hour rate batteries have a capacity of 0.65C10 at 1 hour rate, 6V, 12V, 10 hour rate batteries, 1 hour rate capacity of 0.6C10. 20 hour rate batteries, 10 hour rate capacity of 0.93C20, The 1-hour rate capacity is 0.56C20.

   There are two ways to express the life of a battery: one is a battery for deep cycle use, and the other is a 'back-up power' battery for floating charge. The service life of the battery used in deep cycle is expressed by the number of deep cycles. The battery used in 0.8C10 deep charge and discharge cycle has a life of more than 1200 times, while the battery used in floating charge can reach 10-20 years. When the battery has only 80% capacity, it is regarded as the end of life.

   The actual service life is very different from the design service life, which mainly depends on the loss of water in the battery. The design life can be reached under the design conditions, and when the external conditions such as temperature, charging voltage, depth of discharge and other changes exceed the design requirements, the actual service life will be much lower than the design life, and the actual use capacity will also be lower than the design capacity.

  (2) The effect of discharge rate on the actual output capacity of the battery

   battery capacity C(Ah) equals the discharge current The product of (A) and the discharge time (h) when the battery voltage reaches the lower limit, and the discharge rate (1/h) is the ratio of the actual discharge current (A) to the battery's nominal capacity (Ah).

   In the actual operation of UPS, after the mains power failure, the battery inverter is required to bear the full load power. The discharge rate varies greatly depending on the backup time. For example, the standard machine is about 10min, the maintenance time is very short, the discharge rate is very large, and the long delay machine can reach 4h or 8h, and the discharge rate is very small. Therefore, the actual discharge rate of the battery is not the discharge rate defined in the battery specification. The discharge curve shown in Figure 5-1 reflects the impact of different discharge rates on the battery capacity.

  The lower the actual discharge current of the battery, the longer the battery voltage can maintain a stable time, and vice versa. For example, for a 100HR battery pack, when the discharge current is 5A, the discharge rate is 0.05C, and the output voltage remains above 12V for more than 10h. When the battery voltage drops to the critical voltage of 10.5V, the discharge time Up to 2Oh, the capacity released by the battery is basically its nominal capacity. If the discharge current is increased to 100A and the discharge rate is 1C, the output voltage will remain above 12V for less than 10min. When the battery voltage drops to the critical voltage, the discharge time can be maintained for more than 30 minutes, and the actual discharged capacity is about 58.3.M, which is much lower than the nominal capacity of 100Ah.

   The allowable discharge threshold voltage value of the battery pack and the actual available capacity (AM are closely related to the discharge current of the battery.

  The allowable discharge time of the battery is the time it takes for the battery voltage to drop from the rated value to its allowable critical voltage when the battery is discharged under the actual discharge current.

The available efficiency of a battery is the ratio of the actual maximum capacity it can release under the actual discharge current to its rated capacity.

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