How To Sovle 48v20ah Lifepo4 Battery Pack Problem?

- Feb 23, 2019-

How to Sovle 48v20ah Lifepo4 battery pack Problem?

First of all, 48v 20ah lifepo4 battery pack is composed by two 10A batteries which are connected in parallel, and then 16 batteries are formed to form 48V/20A batteries. Make sure the appearance of battery pack is normal, and the connector, protective board and wiring are normal. when we found the total voltage of the battery pack is 54.7V, but the output voltage is only 36V. What's the problem?

Detection method: 

how to test whic part problems? Use multimeter to check battery voltage one by one.

Test results: 

It was found that one battery voltage was 2.55V, and the other battery voltage was about 3.5V. Charge the battery again until it stops automatically. At this time, the other groups are measured at about 3.65V, the low voltage group is only 2.75V, and the corresponding indicator on the equalization protection board is not on. The heat sink has been heated, indicating that the protective plate has begun to balance the voltage of each battery group. At this time, the total output voltage is 57.41V. It is suspected that the battery group with low voltage or the balanced protective plate is abnormal.

Reason analysis: 

The fault was caused by the low voltage battery. The main reason is that the inconsistency of lithium-iron batteries is serious. In the long-term use, the voltage of that group of batteries is gradually lower than that of other batteries, and the battery is not well balanced by normal charging, resulting in the voltage of that group of batteries becoming lower and lower than that of other batteries.

In use, the protection panel will cut off the power supply of the whole battery group to protect the battery because the group of batteries first reaches the undervoltage protection threshold of 2.5V. According to the barrel principle, the capacity of the whole battery pack depends on the lowest battery pack. When charging, because the capacity and voltage of other batteries are much higher than those of low-voltage batteries, when the capacity of low-voltage batteries is far from full, the voltage of other batteries has reached the turn-off voltage of the protective board, so the charging of the whole batteries is cut off. Such a vicious cycle, resulting in low-voltage packs not charged, resulting in the capacity of the whole battery pack is getting lower and lower, which is reflected in the use of shorter and shorter riding distance.

Supplementary Description: 

The main characteristics of the equalization protection board for lithium iron phosphate batteries: when charging, when the voltage of any battery group reaches 3.7V, the protection board cuts off the charging circuit to prevent the battery from overcharging; when discharging, when the voltage of any battery group is less than 2.5V, the protection board cuts off the external power supply to prevent the battery from overcharging (the author has pushed several cars home). 。 When the battery voltage of the corresponding group is higher than 3.5V, the protective plate begins to balance.

The disadvantage of the old balanced protection board: 

although the battery has a balanced protection board, the balanced effect is very limited. Its principle is: discharging the battery pack with over-set voltage, after reaching the set voltage, then turning on the charging circuit to charge the whole battery pack, so that the "backward" battery pack has the opportunity to achieve the same voltage as other batteries. However, the discharge current can not be very large, otherwise the calorific value and device life become a problem.

What can SINOLI BATTERY do for you?

SINOLI battery is a professional lithium ion battery pack manufacturer in China. SINOLI battery was established with a mission to solve the problem of high price and poor quality lithium ion battery. we are mean to improve battery quality with technique and reduce the cost and risk of batteries for our customers. SINOLI invented a new blanace protective board to make sure each group of batteries are balanced during operation.