Desktop POS Terminal 12V Rechargeable Standby Battery Design Solution

The 12V hot-swappable backup battery for desktop POS machines is specifically developed for industrial mainboards powered by 12V mains electricity, catering to outdoor use of portable devices. This solution integrates charging circuits, buck-boost converters, and input/output conversion circuits to enable simultaneous charging and discharging through a single port, eliminating the need for separate charging and discharging operations. It supports maximum power requirements up to 100W for industrial mainboards.

 

Design Requirements

Design Requirements for 12V Plug-and-Play Backup Battery in Desktop POS Machine:  

This 12V plug-and-play backup battery is specifically developed for industrial mainboards powered by 12V mains supply and designed for outdoor use. It integrates charging circuits, buck-boost circuits, and input/output conversion circuits to achieve simultaneous charging and discharging through a single port, eliminating the need for separate charging and discharging operations.

 

1) Lithium Battery Pack Specifications: 18650-4S/2.6Ah/14.8V configuration must sustain a 25W industrial mainboards for at least one hour of operation.

 

2) Input / Output Characteristics: Shared port for both input and output, featuring automatic input/output switching functionality.

 

1. Input Characteristics: When mains power (DC: 12V/5A) is available, it simultaneously charges both the mainboards and the lithium battery pack.

2. Output Characteristics: In the absence of mains power, the battery automatically outputs 12V/3A to supply the mainboards.

3. Status Characteristics: Input/output states switch automatically via conversion circuits, preventing mainboards shutdowns or reboots due to delays.

 

3) Charge/Discharge Indication:  Adjustable indicator quantity per customer requirements, providing charge/discharge process monitoring, battery full charge status, and low voltage alarm indication.

 

4) Basic Characteristics of Protection Board

1. Single-cell overcharge protection voltage: 4.35±0.25V

2. Single-cell overcharge recovery voltage: 4.10±0.10V

3. Single-cell over-discharge protection voltage: 2.40±0.08V

4. Single-cell over-discharge recovery voltage: 3.00 ± 0.10V

5. Battery pack overcurrent protection threshold (10ms): 8~12A

6. Battery pack over-temperature protection threshold (recoverable): 70 ± 5℃

7. The finished battery pack also features short-circuit protection.

 

5) Battery cycle life design requirement: 300–500 cycles (per national standard charging/discharging specifications)

 

6) Battery external dimensions design requirement: Refer to actual battery casing dimensions.

 

Desktop POS Terminal 12V Rechargeable Standby Battery Design Solution:

1) Smart Buck-Boost Module Circuit: Primarily converts the adapter's 12V/5A input via DC-to-DC conversion into a charging mode suitable for a dual-series  lithium battery’s  CC/CV phase,  while simultaneously stepping down the dual-series lithium battery to a regulated 12V/2.5A output. This circuit also enables automatic input/output state switching.

 

2) Protection Board (PCM): Primarily implements protection circuitry for the rechargeable lithium battery pack. Due to lithium batteries' inherent chemical properties, it provides intelligent capacity calculation and safeguards against overcharge, over-discharge, short circuits, and overcurrent to prevent hazards such as combustion or explosion.

 

3) Protection IC: The primary protection function chip in the design scheme, providing real-time online monitoring of the battery cell for overcharge, over-discharge, overcurrent, and short-circuit conditions, ensuring the cell operates within a safe, stable, and efficient range.

 

4) Thermal Switch: Primarily designed for temperature protection. When the battery's internal temperature reaches 70±5°C due to other abnormal issues, the thermal switch activates to initiate temperature protection.

 

5) 18650 Lithium-ion Cell / 18650 / 2600mAh / 3.7V Li-ion cell (SANYO).

 

6) Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET): The MOSFET acts as a switch in the protection circuit, ensuring the voltage across the load remains constant—neither increasing nor decreasing—to guarantee voltage stability.

 

7) Connector: Facilitates input and output of the lithium battery status for the medical infusion pump.

 

8) Battery Housing: Meets medical product fire safety standards and forms the overall shape of the battery assembly.