design requirement
1、 Design requirements for 12V charging and discharging standby battery of desktop pos:
The desktop POS machine 12V charging and discharging standby battery is specially developed for the industrial motherboard with 12V mains power supply and outdoor use. It achieves the charging and discharging function of the same port by integrating relevant charging circuits, voltage rise and fall circuits and input-output conversion circuits, without the need to separate charging and discharging.
1) Model design requirements of lithium battery pack: 18650-4s / 2.6ah/14.8v, which can meet the industrial motherboard with maximum power of 25W for at least one hour.
2) Input and output characteristics: the input and output adopt the same port, and the automatic input / output switching function is adopted.
1. Input characteristics: when there is mains power (DC: 12V / 5A), the mains power can charge the main board and lithium battery pack at the same time.
2. Output characteristics: when there is no mains power, the battery will automatically output 12V / 3A characteristics to meet the power supply of the main board.
3. Status characteristics: the input / output status is automatically switched through the conversion circuit, and there will be no shutdown or restart of the main board due to delay.
3) Charge and discharge indication: adjust the number of indicator lights according to customer requirements, and provide power maintenance, battery full or low voltage alarm indication during charge and discharge.
4) Basic characteristics of protective plate
1. Single section overcharge protection voltage: 4.35 ± 0.25V
2. Single section overcharge recovery voltage: 4.10 ± 0.10v
3. Single section over discharge protection voltage: 2.40 ± 0.08v
4. Single section over discharge recovery voltage: 3.00 ± 0.10v
5. Overcurrent protection value of combined battery (10ms): 8 ~ 12a
6. Over temperature protection value of combined battery (recoverable): 70 ± 5 ℃
7. The finished battery also has short circuit protection.
5) Design requirements for battery cycle life: 300 ~ 500 times (national standard charge and discharge standard)
6) Design requirements for external dimensions of battery: refer to the actual battery shell size.
2、 Design scheme of 12V charging and discharging standby battery for desktop pos:
1) Intelligent voltage raising and lowering module circuit: it mainly converts the adapter input 12V / 5A from DC to DC into a charging mode suitable for two series lithium batteries CC / CV, and depressurizes the two series lithium batteries into a regulated output state of 12V / 2.5A. At the same time, start the automatic switching mode of input / output state.
2) Protection board (PCM): it is mainly a protection circuit designed for rechargeable lithium battery pack. Due to the chemical characteristics of lithium battery itself, it is necessary to provide protection functions such as intelligent power calculation, overcharge, over discharge, short circuit and overcurrent, so as to avoid risks such as combustion and explosion.
3) Protection IC: the main protection function chip of the design scheme, which can monitor the functions of overcharge, over discharge, over-current and short circuit on-line, so as to make the cell work in a safe, stable and efficient range.
4) Temperature switch: mainly designed for temperature protection function. When the temperature of the battery reaches 70 ± 5 ℃ due to other abnormal problems, the temperature switch starts for temperature protection.
5) 18650 lithium ion cell/18650/2600mAh/3.7V Li-ion cell（SANYO）。
6) Field effect transistor (MOSFET): MOSFET tube plays a switching role in the protection circuit, so that the voltage at both ends of the load will never increase or decrease, so as to ensure voltage stability.
7) Connector: it plays the role of input and output of lithium battery state for medical infusion pump.
8) Battery shell: it conforms to the fire protection class of medical products and forms the mold of the overall battery.
