In the UPS power supply system, an important component is the battery pack. The battery pack is bulky and heavy, making it increasingly unsuitable for use in small computer rooms. But the battery pack is a guarantee of backup time, and a small number of batteries cannot meet daily use. The solution to this contradiction is to remove the battery pack from the computer room, but for the convenience of use and operation, UPS cannot remove it together with the battery pack. If the battery pack is far away from the UPS host, it will cause line loss on the long DC cable, which will affect the normal power supply of the system. So, what is line loss? Why does excessive line loss affect the operation of the system? How to calculate the size of line loss? This has become a crucial issue.
1. Line loss affects the normal operation of UPS power supply system
As is well known, direct current flowing through a certain length of cable causes wire loss. The line loss referred to here refers to the voltage generated by the direct current flowing through a certain length of cable, which means that the line loss to be calculated is a voltage value. Line loss has a significant impact on UPS and loads, therefore mastering the calculation method of line loss is closely related to the stable operation of the power supply system.
Taking a 12V battery as an example, its discharge starting voltage is 13.5V (determined by the floating charge voltage of UPS), and its critical discharge voltage is 10.5V (determined by the termination voltage of UPS inverter). That is to say, the terminal voltage of a single battery is only allowed to drop by about 3V. If all the 3V drop is lost on the cable, then undoubtedly, as soon as the mains power stops, the load will all go down and the battery pack will not work at all. Some users may say that the battery pack is not functioning properly and the battery is broken, but that’s not true. Blindly replacing batteries not only causes waste of manpower and resources, but also cannot solve the problem. The difference between the DC bus terminal voltage of the battery pack and the DC bus terminal voltage of the UPS is the line loss (when the UPS charger or DC input switch is turned off). Generally speaking, the line loss value should not exceed 3V.
2. Main factors affecting line loss
Of course, the smaller the line loss value, the better. There are three main factors that affect the line loss:
(1) Terminal Contact Resistance
Using high-quality power fittings (special DC terminal blocks), designing reasonable installation methods, reducing terminal connections, can significantly reduce the contact resistance of terminals.
(2) Cable Material
(3) Cable diameter and length
This is the main factor. Calculate the DC cable loss value, combined
Proper selection of wire diameter and length is the key to reduce line loss.