1. Product Overview

The DALY 3S 12V 20A BMS is a battery protection system designed for three 3.6V or 3.7V lithium-ion cells or parallel cell groups connected in series.

A completed 3S lithium-ion battery pack has a nominal voltage of approximately 10.8V–11.1V and reaches 12.6V when fully charged. These batteries are commonly marketed as 12V lithium-ion battery packs.

The BMS monitors the three series-connected cell groups and protects the battery against abnormal charging, excessive discharge, overcurrent and short-circuit conditions. The product label specifies a 20A discharge-current rating and a 20A charging-current rating.

An NTC connection is also provided for temperature monitoring. This helps the BMS respond to unsafe temperature conditions when the correct sensor is installed and positioned properly.

2. Technical Specifications

Protection thresholds, balancing current, recovery delays and other parameters not printed on the product label should be confirmed using the manufacturer’s specification for the exact model.

3. Typical Connection Points

The exact connector pin order must be confirmed from the wiring diagram supplied with the BMS. Never identify balance wires only by colour or physical position.

4. Protection Functions

The DALY 3S BMS is intended to provide essential protection for compatible lithium-ion battery packs, including:

• Individual cell-group voltage monitoring
• Overcharge protection
• Over-discharge protection
• Discharge-overcurrent protection
• Charging-overcurrent protection
• Short-circuit protection
• Charge and discharge control through internal MOSFETs
• Temperature monitoring through the NTC connection
• Recovery after supported protection events
• Cell balancing only if supported by the exact model

A BMS helps protect a correctly designed battery pack, but it cannot repair damaged, mismatched or deeply discharged cells.

5. Suitable Applications

This BMS may be suitable for compatible 3S lithium-ion battery packs used in:

• Rechargeable LED lights
• Portable electronic equipment
• Bluetooth speakers
• Small robotics projects
• DIY electronics
• Battery-powered instruments
• Small backup-power devices
• Toys and hobby equipment
• CCTV and monitoring equipment
• Custom 12V-class lithium-ion battery packs
• Battery repair and replacement projects

The connected equipment’s continuous operating current and startup current must remain within the verified capability of the BMS, battery cells, wiring and connectors.

6. Battery and Charger Compatibility

Use this BMS only when:

• The battery contains exactly three series-connected lithium-ion cell groups.
• Each cell group has a nominal voltage of 3.6V or 3.7V.
• Each cell has a maximum charging voltage of 4.2V.
• The complete pack has a maximum charging voltage of 12.6V.
• The charger is designed specifically for a 3S lithium-ion battery.
• All three cell groups are at closely matched voltages before installation.
• The battery cells can safely provide the required charge and discharge current.
• The connected load’s continuous and peak current remain within the verified system limits.

Do not use this BMS with 3S LiFePO₄ cells. A 3S LiFePO₄ pack uses different charging and protection-voltage thresholds.

Do not use a 12V lead-acid charger unless its charging profile and maximum voltage have been verified as suitable for a 3S lithium-ion battery pack.

7. Installation Guidance

• Measure the voltage of all three cell groups before installation.
• Confirm the balance-connector pin sequence before making any connection.
• Connect B− to the negative terminal of the first cell group.
• Connect B1 to the junction between cell groups 1 and 2.
• Connect B2 to the junction between cell groups 2 and 3.
• Connect B+ to the positive terminal of the third cell group.
• Connect the charger and load negative through P−.
• Connect the charger and load positive to the battery-pack positive terminal.
• Install the NTC sensor where it can accurately monitor battery temperature.
• Verify the voltage between every consecutive balance wire before inserting the connector.
• Use properly sized wires and connectors for the expected current.
• Install a correctly rated fuse close to the battery’s positive terminal.
• Keep soldering time short to prevent overheating the cells and BMS.
• Insulate every exposed electrical connection.
• Mount the BMS where it cannot contact nickel strips, metal enclosures or other conductive components.
• Provide adequate heat dissipation when operating at higher current.

Incorrect connection of even one balance wire can permanently damage the BMS.

8. Important Current-Rating Note

The printed 20A BMS rating does not increase the current capability of the battery cells.

The safe current of the complete battery system is determined by the lowest-rated component, including:

• Battery cells
• BMS
• Nickel strips or busbars
• Power wires
• Connectors
• Fuse
• Charger
• Connected load

Motors, pumps, speakers and other inductive equipment may draw startup or surge currents significantly higher than their normal operating current.

Confirm both the continuous and peak-current requirements before selecting this BMS. Additional operating margin is recommended instead of continuously using the BMS at its maximum advertised rating.

9. Safety Information

• Use only with a compatible 3S lithium-ion battery pack.
• Use only a charger designed for a 12.6V 3S lithium-ion battery.
• Never reverse the battery polarity.
• Never short the battery or BMS terminals.
• Do not connect the balance wires in the wrong sequence.
• Do not insert the balance connector until every sensing voltage has been verified.
• Do not exceed the verified charging or discharge-current rating.
• Use a suitable fuse and correctly rated wiring.
• Keep the BMS away from water, conductive dust and loose metal objects.
• Do not use damaged, burnt, corroded or unusually hot components.
• Stop using the battery if any cell becomes swollen, overheated or abnormally unbalanced.
• Installation should be performed by someone familiar with lithium-ion battery wiring and safety.