AGV car early use lead-acid battery, but lead acid battery volume, low specific energy, resulting in a short range AGV car. The new type of lithium battery has the advantages of high specific energy, same power reserve, small size, light weight, long cycle life, no environmental pollution and so on. Thus AGV car more and more widely used lithium battery instead of lead-acid battery. Our company combined with the characteristics of the industry and customer needs, customized design of 24V AGV lithium battery and 36V AGV lithium battery for customers are selected high energy ratio cell, design of lithium battery solution supporting customer AGV car products, the battery can continue to work with high current, protection plate using imported IC and MOS tube control management, Thus protect AGV quick charge lithium battery safe and reliable use.



Design requirements:



I. Design requirements of AGV car lithium battery:



The design of the battery uses special lithium iron phosphate cylindrical lithium battery, the cell has the characteristics of high safety, high rate, large current discharge, fast charging (4C charging). The AGV has strong power and can be fully charged in 30 minutes with the maximum current. Charging for 15 minutes can work for 2 hours. Due to the short charging time, AGV can basically work all day long. The battery design conforms to the national standard QC/T743-2006, with long cycle life, high power, high current discharge performance.



The shell is made of metal stamping process, the electric core combination is fixed and isolated by special bracket, and the protective plate is made of imported chips. AGV car lithium battery overall structure to achieve shock resistance, impact resistance, with high safety, high reliability, long life and other characteristics. The main features of the design are as follows:

1) Cell specification characteristics:



Cylindrical lithium iron phosphate: 26650-3.2V 3000mAh



Discharge rate: 4C up to 12A



Charging rate: 4C up to 12A

2) Structural design:



The shell adopts the stamping process of pulling gold pieces, the combination of electric core adopts the special bracket, and the connector adopts the aviation plug.

3) Circuit design requirements: accurate power management + accurate LED power display. SBS intelligent battery management system is adopted to effectively manage the battery's remaining power. The precise LED electric quantity display can effectively display the remaining electric quantity of the battery to the user in the form of LED light with an accurate percentage, so as to achieve the purpose of high efficiency and intuition.



Ii. AGV car lithium battery circuit design scheme:

1) protection board (PCM) : according to the chemical characteristics of lithium battery itself and the work characteristics of forklift, the design of the specific protection circuit, in addition to overcharge, over discharge, over current, short circuit protection function, such as protection board design also give full consideration to high-power radiator and the balance of the whole battery problem, the whole protection plate aluminum alloy for heat dissipation substrate, temperature rise of less than 20 degrees.

2) Protection circuit: imported IC and MOS tubes are used to carry out online real-time monitoring of functions such as overcharge, overdischarge, overcurrent and short circuit of the cell, so that the cell can work in a safe, stable and efficient range.

3) Overcurrent fuse: it is mainly designed for the protection of the battery management system of lithium battery itself. Due to the high power battery USES the larger capacity batteries, although the battery management system has over current and short circuit protection, if abnormal will result in failure protection function, in the case of output short circuit will produce very big current, lead to danger happening, so plan incorporating over-current fuse, when an exception occurs in case of short circuit fuse disconnect circuit, and irreversible, Achieve the purpose of abnormal protection.



4) Cell: Panasonic NCR18650B/3.6V/3400mAh lithium cell, the cell's maximum charging rate can reach 1C, the maximum discharge rate can reach 1.5C, the cell itself has multiple safety protection functions. The cell has a built-in thermistor (PTC), and the unit structure is isolated by PTC to prevent the occurrence of incurrent.

5) Battery parameters: 46.8V/ 40.8AH (usually nominal: 48V40Ah). Normal operating current 30A, maximum operating current up to 58A.

6) The internal resistance balance is adopted in the battery pack, which can effectively make up for the reduction of capacity caused by the difference of single cell and prolong the service life of the battery to the maximum extent.



7) Battery parallel unit: PTC isolation is adopted to avoid inrush current safety problems caused by large capacity.

8) The main circuit of the battery adopts copper strip as the current collector, and tries to make the discharge current of the single battery close to each other.

9) The battery pack adopts plastic bracket to isolate and fix the battery, which is more conducive to the heat dissipation and safe use of the battery.