Bidirectional UPS Module, compatible with 2S Lithium, 9–10V

The compact UPS module is an efficient solution for maintaining continuous power to electrical equipment in the event of a mains voltage failure. The 2S version is designed for Li-Ion batteries with two cells in series (7.4 - 8.4V), with supported capacity between 2 and 15Ah, compatible with 18650, 21700, 26650, 32650 or polymer-type batteries. The module operates on a bidirectional charge-discharge principle with the same port, eliminating the need for complex connections.

The integrated charging chip charges the 2S battery up to 8.2 - 8.4V, with a default charging current of 1.2 - 1.4A. Two LED indicators provide real-time monitoring: the discharge LED lights dimly at loads above 50 - 100mA, becomes brighter above 0.5 - 1A, and reaches maximum brightness above 2A, while the charging LED is on when charging is in progress (IN > BAT by 0.5V), off when charging is complete, and flashes in case of an anomaly. Multiple protections include overcharge, over-discharge, overload, and short circuit through the integrated fuse. The input does not support reverse polarity.

When an external source is connected, the module simultaneously powers the connected equipment and charges the battery. When the input voltage is interrupted, switching to battery power happens automatically. The output voltage is isobaric, equal to the battery voltage in battery mode, with no boost or stabilization, decreasing gradually as the battery discharges. The output path loss in battery mode is approximately 80 milliohms, which means a drop of about 0.1V at 2A. The rated output power is 50W (4A continuous, 6A peak, recommended load under 4A). The module is compatible with equipment that accepts variable DC voltage within the range of the battery used, including projects based on Raspberry Pi, ESP32, Arduino, or other embedded platforms that require stable power and protection against voltage drops.

Multiple modules can be connected in parallel to increase available power or for redundancy. There are two methods of parallel connection:

- The first method (common) involves physically stacking the boards one on top of another using copper pins, then connecting the power source and battery. This method is mainly used to stack power, with stacking efficiency of about 80%. For example, two 2S modules connected this way provide a rated current of 4A x 2 x 0.8 = 6.4A, equivalent to about 57W. The recommended limit is a maximum of 3 modules in parallel, with two being sufficient for general use.

- The second method involves connecting the modules in parallel on the power bus, being suitable for increasing runtime and redundancy. If one module or battery fails, the others continue to power the equipment.

The low weight of 6.20g and compact dimensions of 50 x 20 mm make integration into enclosures or panels easy.

Note: if the powered equipment does not support variable voltage, it is recommended to add a DC-DC module (buck for step-down or boost for step-up) after the output terminals. For example, a 2S/3S-5V/3A buck module for 5V power supply or a 2S/3S-12V/2A boost module for 12V power supply. When connecting motors or electromagnetic loads, it is recommended to connect a capacitor of a few hundred microfarads in parallel across the IN terminals to reduce interference generated by electrical sparks.

Specifications:

Version: 2S (7.4 - 8.4V)

Recommended input voltage: DC 9 - 10V (accepts 9 - 15V)

Maximum input current: 6A

Output voltage: equal to battery voltage (isobaric, unregulated)

2S battery voltage: 7.4 - 8.4V (charging up to 8.2 - 8.4V)

Supported battery capacity: 2 - 15Ah

Compatible battery types: Li-Ion, LiPo, 18650, 21700, 26650, 32650

Output current: 4A continuous, 6A peak (recommended under 4A)

Maximum power: 50W

Default charging current: 1.2 - 1.4A

Protections: Overcharge, over-discharge, overload

Input reverse polarity protection: Not available

Discharge path loss: ~80 milliohms (approx. -0.1V at 2A)

Idle consumption: 0.3 - 0.5mA

Discharge LED indicator: Dimly lit >50mA, bright >0.5A, maximum >2A

Charging LED indicator: On = charging in progress, off = fully charged, flashing = anomaly

Parallel connection: Yes, max 3 modules (2 recommended), efficiency ~80%

UPS switching: Automatic

Dimensions: 50 x 20 mm

Weight: 6.20g

Usage:

Select a 2S Li-Ion battery (7.4 - 8.4V) with a capacity between 2 and 15Ah, of type 18650, 21700, 26650 or polymer. Use of a BMS and balancing board is recommended.

Connect the battery to terminals B+ and B-, strictly observing polarity.

Connect the external power supply (recommended 9 - 10V DC, minimum 6A) to terminals IN+ and IN-. Warning: do not reverse polarity.

Connect the powered equipment to terminals IN+ and IN-, in parallel with the power supply.

Check all connections before applying voltage. Use short cables with sufficient cross-section.

Monitor the charging LED: on = battery is charging, off = fully charged, flashing = anomaly.

Monitor the discharge LED to estimate the load current in real time.

In the event of an external power failure, the module automatically switches to battery power. The output voltage will gradually decrease as the battery discharges.

When the input voltage returns, the module automatically resumes charging the battery.

For parallel connection (method 1 — stacking): physically stack the modules using copper pins, then connect the power supply and battery. Do not exceed 3 modules in parallel.

For parallel connection (method 2 — redundancy): connect the modules independently on the same power bus, each with its own battery. The modules can be placed anywhere in the network.

If the equipment does not support variable voltage, add a DC-DC module after the output terminals to stabilize the voltage.

Usage example:

Dimension diagram: