Foreword: (keyword: 18650 lithium ion battery) as the rapid development of society and deficiency of water resource, monitoring and protecting water resource have become a global heated discussion. Portable field water quality monitor is the essential tool of field scientific research, while an efficient, portable, light weight and sufficient backup power supply solution of detector is the important assurance for long-term field work. Because of its advantages, 18650 lithium ion battery pack has become the first choice of backup power supply of high-tech testing instruments.
Ⅰ. Battery design requirements of field water quality monitor:
Field water quality monitor is a portable water detecting instrument that can test on the quality of water resource for pollution state. The instrument mainly constitutes by small electric pump, blender, heating device, sensor, display parts, etc. The device requires large instant starting current, 20A peak current, 4~5A nominal working current and continuous working hour, so that Large Power adopts imported Sanyo battery with high specific energy, light weight, small size, long cycle life, good security and nice voltage consistency. Current protection value is 30A, continuous working current is 7A, and capacity is 20Ah, which fully meets the requirements of device. The concrete design requirements are as follow:
1）Design requirement of lithium ion battery pack model No. : 18650-3S8P/20Ah/11.1V
2）Design requirements of electric circuit:
• Over-charged protection voltage of single battery: 4.35±0.025V
• Over-charged recovery voltage of single battery: 4.15±0.050V
• Over-discharged protection voltage of single battery: 2.40±0.08V
• Over-discharged recovery voltage of single battery: 3.00±0.10V
• Over-discharge cut-off current of battery pack (10ms): 30~35A
• Over temperature protection value of battery pack (restorable): 70±5℃
• The finished product has protective function of short circuit and reverse-charging.
3）Design requirement of cycle life: 300~500 times (national standard of charging and discharging)
4）Design requirement of housing dimension
Ⅱ. Battery design scheme of field water quality monitor:
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/18650/2500mAh/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.