Foreword: (keyword: lithium ion battery pack) traditional field ground penetrating radar tester applies lead-acid battery as mobile backup power. Lead-acid battery cannot meet the requirements of backup power of modern portable industrial instruments because it has low energy density, heavy weight, low discharging rate and non-environmental. On the contrary, lithium ion battery has advantages of high energy density, light weight, small size, long cycle life, good safety performance, high voltage and good consistency, so it becomes the first choice to replace lead-acid battery in industrial instrument area.
I. Backup power requirements of ground penetrating radar tester
Ground penetrating radar tester has requirements on high working voltage, long-term and special environment temperature. It applies domestic top one brand BAK lithium ion battery with long cycle life. Connect 6 batteries in series and 8 in parallel to meet the related parameters of customers’ requirements. As for protective circuit of lithium ion battery, apply 6 batteries in series for protective circuit of precise hardware and 6 batteries in series for charging balanced circuit, so that the maximum overcurrent of finished product is 25A, continuous discharging current is 8A, and charging balanced current is 300mA. As for related working environment, apply upscale white waterproof case to meet customers’ requirement for waterproof environment. The concrete parameters of the compounding finished battery are as follow:
1）The design requirement of lithium ion battery pack type: 18650-6S8P/16Ah/22.2V
2）Parts of the design requirements of electric circuit
• Over-charged protection voltage of single battery: 4.35±0.25V
• Over-charged recovery voltage of single battery: 4.15±0.50V
• Over-discharged protection voltage of single battery: 2.70±0.08V
• Over-discharged recovery voltage of single battery: 3.00±0.10V
• Over-discharge cut-off current of battery pack (10ms): 30~35A
• Charging balanced current: 300±50mA
• Charging balanced voltage: 4.20±25mV
• Battery over temperature protective value (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 requirements of battery dimension: Refer to battery case
II. Backup power design solution of ground penetrating radar tester
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) Charging balanced module: balance the voltage difference of all batteries during charging process and strengthen the consistency of battery voltage so as to expand cycle life of the compounding battery pack.
4）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.
5）18650 lithium ion battery/18650/2000mAh/3.7V BAK cell (long lifespan battery)
6）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.