For 48V battery packs, ternary lithium batteries generally use 13 strings or 14 strings, and lithium iron phosphate batteries generally use 15 strings or 16 strings. Today, let's talk about the difference between the number of strings of ternary lithium batteries.
1. Operating voltage range
The ternary lithium battery cell has a voltage range of 4.2V-2.75V. After 13 strings, the voltage range is 54.6V-35.75V; after 14 strings, the voltage range is 58.8V-38.5V. The voltage of the battery pack after 14 strings will be too high, and the load needs to be able to withstand this voltage range (power products are motors; energy storage products, the loads are generally UPS, inverters, equipment control boards, etc.), if 14 strings Exceeding the working voltage range of the load, only 13 strings of low-voltage battery packs can be selected.
2. Impact on load
For power products, after 13 strings become 14 strings, the voltage becomes higher, the speed of the motor of the same power will become faster, and the acceleration of uphill or starting will increase significantly. The overall line current becomes smaller, and the loss also becomes smaller. After energy storage products become 14 strings, the voltage increases, the load power remains unchanged, the current will decrease, and the line loss will also decrease.
For example, the load power is 1000W.
The nominal voltage of the 13 battery pack is 3.6V*13=46.8V, and the current is 1000W/46.8V=21.37A (excluding loss and conversion rate);
The nominal voltage of the 14-string battery pack is 3.6V*14=50.4V, and the current is 1000W/50.4V=19.84A (excluding loss and conversion rate).
As the voltage increases, the current will decrease.
The capacity of the battery pack remains the same, the voltage increases, the power also increases, and the power supply time to the load becomes longer. For example, a 15Ah battery pack,
The power of 13 strings is 46.8V*15Ah=702Wh. Power supply time 702Wh/1000W=0.702 hours (excluding loss and conversion rate);
The power of 14 strings is 50.4V*15Ah=756Wh. Power supply time 756Wh/1000W=0.756 hours (excluding loss and conversion rate). The power supply time of the 14-string battery pack becomes longer.
3. Specification and size
One string has been added from 13 strings with 5 parallels to 14 strings with 5 parallels. The size of a row of 5 cells has been increased, and the size of the bracket has also been increased accordingly. The size of the BMS will not change much. Generally, 14-string and 13-string BMS can share a base plate. As the size of the internal battery cell arrangement increases, the size of the outer box will increase accordingly.
4. Cost price
From 13 series 5 parallel to 14 series 5 parallel, 5PCS is added to the battery cell, and a series of management protection is added to the BMS line, the cost will increase, and the cost of nickel belts, brackets, and other auxiliary materials will also increase correspondingly.
The cost of matching chargers has also increased accordingly. The 13-string battery pack charger voltage is 54.6V; the 14-string battery pack charger voltage is 58.8V. If you use a 5A charger, there is a 21W difference in charger power. The greater the power, the more expensive the cost. So the cost of the charger has also increased.
In summary, the 48V battery pack and 14-series ternary lithium battery pack have a higher charging voltage and discharge cut-off voltage than the 13-series battery pack. The load capacity is strengthened and the power supply time becomes longer, but the size and cost price have also increased.
