1. Product Overview

The DALY 4S 12V 30A BMS is a battery protection system designed for four LiFePO₄ cells or parallel cell groups connected in series.

A 4S LiFePO₄ battery pack has a nominal voltage of approximately 12.8V and reaches 14.6V when fully charged. Such batteries are commonly marketed as 12V LiFePO₄ battery packs.

This BMS monitors the four series-connected cell groups and helps protect the battery against unsafe charging, excessive discharge, overcurrent and short-circuit conditions.

The product label specifies a 30A discharge-current rating, 15A charging-current rating, common-port configuration and cell-balancing support. A temperature-sensor lead is also visible in the supplied configuration.

2. Technical Specifications

Protection thresholds, balancing current, delay times and recovery behaviour not printed on the label should be confirmed from the manufacturer’s specification for this exact model.

3. Typical Connection Points

The exact balance-wire sequence must be confirmed using the manufacturer’s wiring diagram. Do not identify connections only by wire colour or physical position.

4. Protection Functions

The DALY 4S BMS is designed to provide important protection functions for compatible LiFePO₄ battery packs, including:

• Individual cell-group voltage monitoring
• Overcharge protection
• Over-discharge protection
• Discharge-overcurrent protection
• Short-circuit protection
• Temperature monitoring through the supplied sensor lead
• Cell balancing
• Charge and discharge switching through internal MOSFETs
• Common-port charging and discharging
• Recovery after supported protection events

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 4S LiFePO₄ battery packs used in:

• Solar-light batteries
• Small inverter and UPS batteries
• Emergency backup-power systems
• Portable power boxes
• Robotics and automated equipment
• Rechargeable lighting systems
• Camping and recreational power systems
• DIY 12.8V LiFePO₄ battery packs
• Battery repair and replacement projects
• Low- and medium-current DC equipment

The operating and startup current of the connected equipment must remain within the verified limits of the BMS and battery pack.

6. Battery and Charger Compatibility

Use this BMS only when:

• The battery contains exactly four series-connected LiFePO₄ cell groups.
• Each cell group has a nominal voltage of approximately 3.2V.
• The completed pack has a nominal voltage of approximately 12.8V.
• The charger is specifically designed for a 4S LiFePO₄ battery.
• The charger’s maximum output voltage does not exceed 14.6V.
• The charging current does not exceed the verified 15A limit.
• The continuous and peak discharge current remain within the verified system limits.
• All four cell groups are at closely matched voltages before installation.
• The battery cells can safely supply the required charging and discharging current.

Do not use this BMS with 4S lithium-ion or lithium-polymer cells rated at 3.6V or 3.7V nominal. Those chemistries require different charging and protection voltages.

It should also not be used with lead-acid batteries.

7. Installation Guidance

• Measure all four cell-group voltages before connecting the BMS.
• Confirm the balance-wire sequence using the correct DALY wiring diagram.
• Connect B− to the battery-pack negative terminal.
• Connect the remaining sensing wires sequentially to the correct cell-group junctions.
• Connect the final positive sensing wire to battery positive as specified.
• Connect the load and charger through the common-port terminals.
• Verify the voltage between every consecutive balance wire before plugging in the connector.
• Use correctly sized cables, terminals and connectors for the required current.
• Install an appropriately rated fuse close to the battery’s positive terminal.
• Secure the temperature sensor against a representative battery cell.
• Keep soldering or terminal-heating time as short as possible.
• Insulate every exposed electrical connection.
• Mount the BMS where it has adequate ventilation and cannot contact conductive parts.

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

8. Important Current-Rating Note

The 30A 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
• Busbars or nickel strips
• Power cables
• Connectors
• Fuse
• Charger
• Connected load

Loads such as motors, pumps and inverters may draw a starting or surge current significantly higher than their normal operating current.

Confirm both continuous and peak current requirements before using this BMS. Adequate heat dissipation is also necessary when operating close to the BMS current limit.

9. Safety Information

• Use only with a 4S LiFePO₄ battery pack.
• Use only a compatible 14.6V LiFePO₄ charger.
• Never reverse the battery polarity.
• Never short the battery or BMS terminals.
• Do not connect the balance wires in the wrong order.
• Do not plug in the balance connector until every sensing voltage has been verified.
• Do not exceed the 15A charging-current rating.
• Do not exceed the verified discharge-current limit.
• Use a suitable fuse and correctly rated power cables.
• 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 LiFePO₄ battery wiring and safety.