Foreword: based on customer’s requirements of power drive of military equipment, Large Electronics chooses the design scheme of lithium iron phosphate battery with high rate to replace the military equipment power system using nickel-cadmium/nickel-metal hydride battery as power battery in the earlier. Lithium ion battery of military equipment power system decreases the size of military equipment and deduces the total weight of the equipment. It also makes the military equipment have stronger grade ability and wonderful explosiveness due to good charging and discharging performance of lithium ion battery with high rate. The battery management system adopts imported chip and MOS tube, which has real-time communication capability sharing information with host machine, and helps operator to know the battery status at any time.
Based on the special environment, the requirements are as follow: 1. The battery needs to have over 700 times cycle life, large rate discharging, small size, 2C normal discharging current, 4C maximum discharging current and 6C instantaneous current. 2. It must have communicating function, which can read the battery application information at any time by customer’s host machine so as to make sure normal operation of the whole machine. 3. The battery can support two electric machines with total power at 800W and provide instant impulse current of grade ability.
I. Military power battery design scheme of unmanned tank
1）Guard plate (PCM): it is protective circuit of lithium iron phosphate battery pack. Because of the chemical characteristics of lithium ion battery, it not only has protective function of overcharging, over-discharging, overcurrent, short circuit, over temperature, etc., but also provides battery capacity measurement and balancing function of the whole battery pack.
2）Protective circuit: it adopts imported IC and MOS, and has on line monitoring for battery functions of overcharging, over-discharging, overcurrent, short circuit, etc., which helps battery works under safe, stable and efficient circumstance.
3）Overcurrent fuse: it is designed for secondary defense. The battery pack applies large power cell with large capacity. Although battery management system has protection of overcurrent and short circuit, it still leads in protection failure when abnormal circumstance occurs. Large current is produced under output short circuit and results in danger. Therefore, there is overcurrent fuse in the scheme, so that the fuse will cut off the circuit irretrievably for abnormity protection when short circuit occurs.
4）Battery: apply LARGE26650/3.2V/2500mAh lithium iron phosphate battery. The maximum charge rate of the battery is 5C, and maximum discharge rate is 15C.
5）The normal working current of the whole battery pack is 35A, maximum working current is 60A, and instant starting current is 100A.
6）Battery pack: adopting dynamic balancing mode inside can remedy the capacity reduction led by difference between single batteries during application, and expand the cycle life as much as possible.
7）PCM: it has SMB US communication function. Host machine can read the voltage, capacity, remaining capacity, temperature, etc. by the communication interface at any time.
8）The battery pack adopts plastic holder to isolate and fix the battery, which does good to heat dissipation and safety application of the battery.
Schematic diagram of the design scheme