7.4V 2.2Ah Backup Battery Design Solution of Special Portable video Recorder

Foreword: (keyword: individual combat reserve battery) individual combat system is an electronic device originally used for soldiers to carry in order to improve the level of individual equipment. The portable video equipment for individual combat is an important tool for military and police officers to carry out reconnaissance of forward combat and data and evidence collection of crime scene. Because of the particularity of users and environments, the backup battery of individual combat needs to meet the special requirements of long-term complicated environment, which assures to charge continuously for individual combat video recorder stably for a long time.

1) Backup battery design requirements of individual combat

This scheme uses low temperature 18650 cell with high energy density ratio. The outer shell is encapsulated by UL-94V0 fire rating shell. Batteries have IPX1 waterproof level to make battery work in 40 ℃ to + 70 ℃ environment.

1. Model number design requirement of lithium ion battery pack: 18650-2S1P/2.2Ah/7.4V

2. Design requirements of circuit section

• Over-charged protection voltage of single battery: 4.28±0.25V

• Over-charged recovery voltage of single battery: 4.10±0.50V

• Over-discharged protective voltage of single battery: 2.80±0.08V

• Over-discharged recovery voltage of single battery: 3.00±0.10V

• Over-discharge cut-off current of battery pack (10ms)：4~8A

• Over temperature protective value (restorable) of battery pack: 75±5℃

• The finished product has protective function of short circuit and reverse-charging.

• Design requirement of cycle life: 300~500 times (national standard of charging and discharging)

• Design requirements of battery dimension: refer to battery housing and can custom according to customer’s requirements

2) Backup battery design solution of individual combat

1. Guard plate (PCM): it is protective circuit of rechargeable lithium ion battery pack. Because of the chemical characteristics of lithium ion battery, it needs protective function of intelligent capacity calculation, overcharging, over-discharging, short circuit, overcurrent, etc. so as to avoid combustion, explosion, etc.

2. Protection IC: it is the chip has main protective function in the design scheme. The chip monitors the cell on the functions of overcharging, over-discharging, overcurrent, short circuit, etc. at any time, which helps the battery works under safe, stable and efficient circumstance.

3. Temperature switch: it is designed for temperature protection. When the battery is heated up to 75±5℃ due to any issues, the temperature switch will begin to open temperature protection.

4. Lithium ion battery: 18650/2200mAh/3.7V  Li-ion cell

5. MOSFET: it works as the switch in protective circuit to make sure that the voltages of two ends won’t be up and down, so that the voltage will be stable.

6. The capsulation of battery pack: housing

7. Backup battery design schematic diagram of individual combat