How to Remove the BMS Board from an SX3 Main Battery

By askUncategorised

How to Safely Remove and Desolder the BMS Board from an SX3 Main Battery

⚠️ Important Safety Notice

  • Only attempt this if you are experienced with high-voltage lithium battery packs.
  • Always wear protective gear (gloves, goggles).
  • Work in a fire-safe, ventilated environment.
  • Do not short any terminals or expose cells to heat or moisture.
  • Do not use or keep any conductive tools (e.g., metal tweezers, screwdrivers) near the battery during the procedure.
  • Keep your desk clean and free of unnecessary tools or objects.
  • Ensure there are no liquids on or near the work area.

Required Tools & Materials

  • Insulated screwdriver set
  • T25 Torx bit (to remove the main battery)
  • Soldering iron (with fine tip)
  • Multimeter
  • Heat-resistant gloves
  • Safety glasses
  • Kapton tape (optional)
  • Plastic spudger (non-metallic prying tool)

Step-by-Step Instructions

1. Preparation

  • Disconnect the battery from any bike system (here is how to do it).
  • Place the battery on a non-conductive, fireproof surface.

2. Open the Battery Case

  • Remove the battery from the bike using using a T25 Torx bit.
  • (optional) Discharge the battery partially to around 30–40% for safety (34v).
  • Use the multimeter to confirm voltage on main output terminals: VG (negative) and VP (positive).
  • Carefully pry open the battery casing. Avoid using force near connector areas.
  • Take a photo of the BMS wiring layout for reference.

3. Locate the BMS Board

4. Disconnect Low-Voltage Wires

  • Carefully unplug balance connector, free up temperature sensors.

5. Disconnect Main Power Leads

  • This is the most dangerous step.
  • Desolder the negative terminal first (VG / black), then the positive (VP, red).
  • Use a high-power soldering iron to melt the thick solder from ends of the battery pack (not from BMS).

6. Remove the BMS Board

  • Gently lift the board using a plastic/wood spudger.
  • Avoid bending or stressing the board during removal.

Final Notes

  • Double-check that no wires or terminals are left exposed.
  • Store the removed BMS in an antistatic bag.
  • Document the wiring for future installation or replacement.