With the development of lithium-ion battery materials, the advantages of lithium-ion battery such as fast charging at any time and long service life are becoming more and more prominent. More and more forklift manufacturers also choose lithium batteries as their endurance experts.
1. Design requirements of forklift lithium battery
In the early days of electric forklift, lead-acid batteries were mostly used, but the lead-acid batteries were large in volume, low in specific energy and easy to pollute the environment. The new type of lithium battery has high specific energy, the same power / capacity, small volume, light weight and long cycle life. Nowadays, the logistics forklift truck generally begins to use lithium battery instead of lead-acid battery. Combined with the industry characteristics and customer needs, our company chooses LiFePO4 battery solution to support customers' electric forklift products. The battery can work continuously with high current. The protection board adopts imported IC and MOS tube for control management, and its service life is 3-5 times that of lead-acid battery.
The battery design is applied to the supporting use of the logistics forklift, which requires small volume and long working time, and can drive two motors: one is to drive the vehicle, the other is to drive the lifting objects. Our lithium iron phosphate battery electric forklift has a total power of 800W, instantaneous power of 1000W, moisture-proof appearance, long cycle life, high power and high current discharge performance, and the whole product is suitable for indoor environment with low temperature rise.
2. Design scheme of forklift lithium battery
1) Protection board (PCM): according to the chemical characteristics of LiFePO4 battery and the working characteristics of forklift truck, the protection circuit is designed specifically. In addition to the functions of overcharge, over discharge, overcurrent and short circuit protection, the design of protection board also fully considers the problems of high-power heat dissipation and the balance of the whole battery. The whole protection board uses aluminum alloy as the heat dissipation substrate, and the temperature rise is less than 20 ℃.
2) Protection circuit: the imported IC and MOS tube are used for on-line real-time monitoring of overcharge, over discharge, over-current, short circuit and other functions of the cell, so that the cell can work in a safe, stable and efficient range.
3) Over current fuse: mainly for lithium battery itself battery management system protection failure design. Because the battery pack uses high-power cells with large capacity, although the battery management system has over-current and short-circuit protection, if there is abnormal, it will also lead to the failure of the protection function. In the case of output short-circuit, it will produce a very large current, leading to danger. Therefore, the scheme adds an over-current fuse. When there is an abnormal short-circuit, the fuse will open the circuit, and cannot be replaced Recovery, to achieve the purpose of abnormal protection.
4) Cell: ifr26650 / 3.2v/3000mah lithium iron phosphate cell is adopted. The maximum charge rate of the cell can reach 1c and the maximum discharge rate can reach 2C. The cell has multiple safety protection functions. The cell has a built-in thermistor (PTC), and the cell structure also adopts PTC isolation to prevent the occurrence of surge current.
5) Parameters of the whole battery: 25.6v/80ah (usually nominal: 24v80ah). The normal working current is 30a, the maximum working current is 50a, and the instantaneous starting current is 120a.
6) The internal battery pack adopts resistance balance, which can effectively make up for the capacity reduction caused by the difference of single cell during use, and maximize the service life of the battery.
7) Battery parallel unit: PTC isolation is adopted to avoid inrush current safety problems caused by large capacity.
8) The high current main circuit of the battery uses copper strip as current collector to make the discharge current of the single battery as close as possible.
9) The battery pack adopts a plastic bracket to isolate and fix the battery cells, which is more conducive to the heat dissipation and safe use of the battery.