11.1V 6.6Ah standby battery design scheme of optical fusion splicer

Foreword: optical fusion splicer is widely used on optical cable engineering, line maintenance, emergency repair, manufacture and test for optical fiber devices and research teaching of scientific research institutions in telecom operators, engineering company, enterprise and public institution. The device melts two ends of the optical fiber by electric arc and achieves coupling of fiber-mode by collimation principle. In order to be convenient for construction, market has invented handheld optical fusion splicer, ribbon fiber fusion splicer to splice ribbon fiber, optical cable to splice leather cable, leather cable fusion splicer with jumper wire, etc. Portable optical fusion splicer becomes the important tool for site test. It is the essential assurance for long-term fieldwork to provide efficient, portable, light weight and abundant backup power supply solution for optical fusion splicer. Due to its special advantages, 18650 lithium ion battery has become the first choice of back-up source of high-tech test instrument.

Design requirements:

I. Standby battery design scheme of optical fusion splicer:

Standby battery of optical fusion splicer needs to have automatically temperature protective function at 70℃. The device requires large instant starting current. Peak current is 15-20A and normal current is 2-3A. it has strict requirements on battery continuous working hour, so Large Electronics applies imported SANYO battery in standby battery of optical fusion splicer. SANYO battery has advantages of high specific energy, small size, long cycle life, good safety performance, high voltage and good consistency. Lithium ion battery pack designs output overcurrent protective value is 25A, continuous working current is 7A, and battery capacity is 6600mAh, which are fully meet power demand of the device. The concrete design parameters are as follow:

1）The design requirement of lithium ion battery type: 18650-3S3P/6.6Ah/11.1V

2）The design requirement of electric circuit:

1、Over-charged protection voltage of single battery: 4.35±0.25V

2、Over-charged recovery voltage of single battery: 4.15±0.50V

3、Over-discharged protection voltage of single battery: 2.40±0.08V

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

5、Over-discharge cut-off current of battery pack (10ms): 20~30A

6、Over temperature protection value of battery pack (restorable): 70±5℃

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

3）The design requirements of battery cycle life: 300~500 times (national charging and discharging standard)

4）Design requirements of battery dimension: refer to battery case

II Standby battery design scheme of optical fusion splicer

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 70±5℃ due to any issues, the temperature switch begins to protect the battery.

4）18650 lithium ion battery/18650/2200mAh/3.7V Li-ion cell（SANYO）

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）Battery capsulation (housing)