With the rapid development of modern society and growing shortage of water source, monitoring and protecting water source has become an internationally common topic. Portable outdoor water quality monitor has become an important instrument for outdoor researchers. Correspondingly, providing an efficient and portable emergency power supply for monitor can significantly ensure long outdoor work time. Due to unique advantage of lithium battery pack, it has become the first choice of emergency power supply for high-tech testing instruments.
1> Design requirement of battery for outdoor water quality monitor:
Outdoor water quality monitor is portable to test the water quality and pollution. It is made up of small electric water pump, stirring machine, heating device, sensor part, display part, etc. At the starting moment, peak current can reach 20A while normal working current is 4-5A, and high starting current is required. Therefore, we have adopted imported Sanyo cell, which features high specific energy, light weigh, small size, long cycle life, high safety and consistent high-voltage. Over current protection of the lithium battery pack is designed to 30A, continuous working current to 7A, and charge capacity to 20Ah, which can fully meet the power supply requirement.
Specific design parameters required as follows:
- Model: 18650-3S8P/20Ah/11.1V.
- Circuit design requirement:
- single battery overcharge protection voltage: 4.35±0.25V
- single battery overcharge recovery voltage: 4.15±0.50V
- single battery over discharge protection voltage: 2.40±0.08V
- single battery over discharge recovery voltage: 3.00±0.10V
- Combined battery over current protection (10ms):30~35A
- Battery over heat protection (recoverable): 70±5℃
- Finished battery can be protected from the harm of short circuit and reverse charge.
- Battery cycle life requirement: 300-500 times (national discharge and charge standard)
- Battery dimension design requirement:
- PCM: a protection circuit designed mainly for rechargeable lithium battery pack. Because of chemical characteristics of lithium battery, protection functions like smart capacity calculate, overcharge, over discharge, short circuit, over current, etc should be provided to avoid fire and explosion.
- Protection IC: constantly monitors cell’s overcharge, over discharge, short circuit, and over current to ensure cell’s safe, stable and efficient work.
- Temperature switch: mostly targeted for temperature protection. When battery’s temperature abnormally rises to 70±5?, temperature switch works for overheat protection whereas it automatically restores a temperature drop.
- 18650 lithium-ion cell/18650/2500mAh/3.7V Li-ion cell (SANYO)
- MOSFET: play the role of switch during circuit protection to guarantee load voltage can neither rise nor drop.
3> Diagram of design solution for backup battery of outdoor water quality monitor:
4> Picture of battery product of outdoor water quality monitor: