What is the difference between battery in series and parallel?

Introduction

Due to the limited voltage and capacity of single batteries, it is necessary to combine series and parallel in actual use to obtain higher voltage and capacity to meet the actual power supply requirements of the equipment. In this passage, we will talk about what is the difference between batteries in series and parallel.

Definition of lithium battery in series and parallel

Lithium battery in series means that the voltage is added, the capacity remains unchanged, and the internal resistance increases. Whereas lithium batteries in parallel means the voltage remains the same, the capacity is added, the internal resistance is reduced, and the power supply time is prolonged.

And what do we do if we want to increase both voltage and capacity? Here comes the lithium battery series and parallel to realize it, there are both parallel combinations and series combinations in the middle of the battery pack, which increases the voltage and capacity.

In practice, for series voltage, 3.7V single cells can be assembled into a battery pack with a voltage of 3.7*(N)V according to needs (N: number of single cells), such as 7.4V, 12V, 24V, 36V, 48V, 60V, 72V, etc. For, parallel capacity, a 2000mAh single battery can be assembled into a battery pack with a capacity of 2*(N)Ah (N: number of single batteries), such as 4000mAh, 6000mAh, 8000mAh, 5Ah, 10Ah, 20Ah, 30Ah, 50Ah, 100Ah, etc.

Lithium battery packs of battery in series and parallel

What is a battery pack?

Lithium battery PACK refers to the processing, assembly, and packaging of lithium battery packs. The process of assembling lithium batteries into groups is called PACK, which can be a single battery or a lithium battery pack connected in series and parallel. The lithium battery pack is usually composed of a plastic case, a protective plate, a battery cell, an output electrode, a connecting tab, and another insulating tape, double-sided tape, etc.

Composition of a battery pack:

1. Lithium battery: the core part of the finished battery

2. Protection board: play overcharge, over-discharge, over current, short circuit, NTC temperature control intelligent protection, and other functions.

3. Plastic shell: the support frame of the entire battery; the positioning and fixing of the protective plate; carrying and limiting all other non-shell components.

4. Terminal lead: It can provide various terminal line charging and discharging interfaces for various electronic products, energy storage products, and backup power supplies.

Calculation of series and parallel connection of lithium battery packs

We all know that when the series voltage of lithium batteries increases, the parallel capacity increases. So how to calculate the number of strings and parallels of a lithium battery pack, and how many cells are composed of it? Before performing calculations, we need to know what specifications of cells are used for the assembly of this lithium battery pack, because different cells have different voltages and capacities, and the number of series and parallels required to assemble into a specific specification of the lithium battery pack is different.

Common types of lithium batteries on the market are 3.7V for lithium cobaltate, 3.6V for ternary, 3.2V for lithium iron phosphate, and 2.4V for lithium titanate. The capacity varies depending on the size, material, and manufacturer of the battery.

Take a 48V 20Ah lithium battery pack as an example:

Assuming that the specification of the single–cell used is 18650, 3.7V, 2000mAh

Number of cells in parallel: 20Ah/2Ah=10 or 10 parallel (10 cells in parallel)

The whole set of batteries is 13 strings × 10 batteries = 130 batteries

Precautions for lithium batteries in series and parallel

1. Lithium batteries of different voltages are connected in series

Due to the consistency problem of lithium batteries, they are connected in series under the same system (such as ternary or iron-lithium). It is also necessary to select groups with the same voltage, internal resistance, and capacity. If different voltage platforms and batteries with different internal resistances are used in series, it will cause the battery to be fully charged and discharged after each cycle. If there is a protection board and does not fail, the capacity of the entire group will be reduced. If there is no protection board, it is bound to be causing the battery to be overcharged or over-discharged and cause damage.

2. Lithium batteries of different capacities are connected in parallel

If you mix new and old lithium batteries with different capacities or use them together, leakage and zero voltage may occur. This is because during the charging process, the capacity difference causes some batteries to be overcharged and some batteries are not fully charged. During discharging, some batteries with high capacity are not fully discharged, and batteries with low capacity are over-discharged. In such a vicious circle, the battery is damaged and leaks or has low (zero) voltage.

Precautions

It is easy to tell the difference between battery in series and parallel base on this passage, moreover, here are the precautions in summary for you to get more information about the battery pack.

1. Do not use batteries of different brands together.

2. Do not use batteries of different voltages together.

3. Do not mix lithium batteries of different capacities or use new and old batteries together.

4. Batteries of different chemical materials cannot be mixed, such as nickel-hydrogen and lithium batteries.

5. When the battery power is low, replace all the batteries.

6. Use the lithium battery protection board with corresponding parameters.

7. Choose batteries with the same performance. Generally, lithium batteries need to be paired in series and parallel. Matching standards: voltage difference ≤10mV, internal resistance difference ≤5mΩ, capacity difference ≤20mA