BMS 2S 20A Balance Protection Board

2S 20A Lithium Battery BMS Protection Board Balance Version

Battery Li-ion 18650 8.4V

Suitable for 2 lithium cells in series. It does not charge batteries. It is for battery protection.

     This board is a balanced BMS protection board for 2 cell series (2S, 7.4V nominal, 8.4V full) lithium ion and lithium polymer battery packs. It is used with 18650, 26650 and polymer lithium cells. It protects the cells against overcharge, overdischarge, overcurrent and short circuit; it is rated for up to 20A continuous discharge and 10A continuous charge current. The 4 MOSFETs on the board cut the current, and 2 pieces of 43ohm (430) balance resistors help both cells charge equally by burning the excess energy as heat when the cell voltage reaches about 4.2V.

     A BMS board is not a charger; it does not limit the charging current, it only protects the cells. The pack must be charged with a current limited lithium charger with 8.4V output (constant current / constant voltage). The charging voltage range given by sellers is 8.4V - 9.0V; however, a voltage above 8.4V fills the cells up to the overcharge protection threshold, and since balancing starts at 4.2V, an 8.4V charger is recommended. The charging current should be about 1/10 - 2/10 of the battery capacity; very high current charging or discharging saves time but reduces battery life. The board measures 48mm x 20mm x 3.4mm and weighs about 4gr, so it fits beside or on top of the battery pack.

Key features:

     Balanced version: When the cell voltage reaches about 4.17V - 4.2V balancing starts; with about 100mA balance current both cells charge to the same level.

     20A continuous discharge: The power stage with 4 MOSFETs delivers up to 20A continuous discharge current; overcurrent protection activates at about 25A.

     Four protections together: Overcharge, overdischarge, overcurrent and short circuit protections are on the same board.

     Labeled connection points: The 0V, 4.2V and 8.4V battery points are printed on the board; wires are soldered directly.

     Thin and light board: With 48mm x 20mm x 3.4mm size and about 4gr weight it is added to the battery pack.

Features:

• Product type: 2S lithium battery BMS protection board, balanced version
• Cell count: 2 lithium ion / lithium polymer cells in series (2S)
• Suitable cells: 18650, 26650 and polymer lithium cells
• Pack voltage: 7.4V nominal, 8.4V full
• Charging voltage: 8.4V - 9.0V (recommended: 8.4V constant current / constant voltage lithium charger)
• Continuous discharge current: up to 20A (reduce load current if cooling is poor)
• Overcurrent protection: about 25A
• Continuous charge current: up to 10A
• Overcharge protection voltage: about 4.25V - 4.35V per cell
• Overdischarge protection voltage: about 2.3V - 3.0V per cell (varies by batch)
• Balance start voltage: about 4.17V - 4.2V
• Balance current: about 100mA (2 pieces of 43ohm balance resistors)
• Protections: overcharge, overdischarge, overcurrent, short circuit
• Power stage: 4 MOSFETs
• Internal resistance: below about 7mΩ
• Connection points: 0V (battery negative), 4.2V (junction of the two cells), 8.4V (battery positive) and P- (load / charger negative)
• Color: green circuit board
• Dimensions: 48mm x 20mm x 3.4mm
• Weight: about 4gr

Usage information:

• Connection order: first solder the negative of cell 1 to the 0V point, then the junction of the two cells to the 4.2V point, and last the positive of cell 2 to the 8.4V point. Connect the negative of the load and charger to the P- point and the positive to the battery pack positive (8.4V).
• If the pack voltage is not measured between P- and battery positive after connection, the board is in protection mode; activate it by connecting the charger briefly.
• Heating of the balance resistors during charging is normal. If the resistors heat up while not charging there is a wiring error; disconnect the battery immediately.
• Load limit (seller information, approximate): drills below 50W with starting current below 25A, or resistive loads below 168W.

Application areas:

•  2S 18650 battery packs (7.4V)
•  Cordless drill and screwdriver battery packs
•  Portable Bluetooth speakers and amplifiers
•  Flashlights and camping lamps
•  Powerbanks and portable power supplies
•  RC car, boat and model vehicle batteries
•  Robot and mobile platform power packs
•  LED lighting and LED strip power
•  Small solar energy storage systems

Precautions:

•  This board does not charge batteries, it is only for battery protection. Use a current limited 8.4V (constant current / constant voltage) lithium charger; charging without current control reduces battery life. Overcharge protection is a backup safety, it is not meant to end the charge.
•  The board is only for 2 cells in series (2S); do not use it with 1S, 3S or larger packs.
•  Follow the connection order; wrong order or reverse connection can damage the board and the cells.
•  The capacity and internal resistance of the two cells should be as close as possible; the balance current is small (about 100mA) and cannot equalize very different cells.
•  At continuous current close to 20A the MOSFETs heat up; place the board in a ventilated spot and reduce the load current if needed.

Package contents:

•  1 Piece 2S 20A BMS Balance Protection Board
•  Note: Cells, wires and charger are not included in the package.