E-Bike Repair Knowledge Base:
Fault Diagnosis, Fixes & Wiring Diagrams

FAQ

Quick answers to common e-bike questions and repairs

• Why doesn’t a replacement battery last as long as the original one?

  This situation may be caused by the following reasons:

  1. Improvements in the electric bicycle battery formulation may cause the indicator light to turn off earlier, or the resistance of the potentiometer may have changed due to prolonged use, resulting in inaccurate readings.

  2. After the e-bike’s motor has been in use for some time, the magnets may demagnetize, and the brushes and gears may wear down, thereby reducing its efficiency.

  3. After prolonged use, the charger and controller may have shifted, altering their original settings and preventing them from accurately estimating the battery’s charge level and standard voltage.

  4. The internal wiring of the battery may have been corroded over time by acid fumes released from the battery, or the connector between the battery and the controller may have overheated, thereby increasing internal resistance and causing a partial loss of battery power.

• Why does the active material in an electric bicycle battery fall off? How should you handle it?

  There are typically several scenarios in which the active material in an electric bicycle battery may fall off:

  1. The reduction of active material on the battery plates begins at the grid, which has the best conductivity. When charging begins, excessive current causes lead sulfate to reduce rapidly at this point, while lead sulfate farther away cannot undergo a chemical reaction. The internally reduced lead sulfate has poor adhesion, causing the active material to fall off.

  2. When the battery is nearing full charge, excessive current generates a large number of bubbles that violently impact the plate surface, causing the reduced lead dioxide to detach.

  3. Excessive discharge current intensifies the chemical reaction, causing the plates to warp and resulting in the detachment of the active material.

  4. During overcharging, the lead sulfate on the plates has already been reduced to lead dioxide and lead; the charging current is entirely consumed by the electrolyte, producing a small amount of gas bubbles that can also cause impact and lead to the detachment of the active material.

  For battery faults involving severe active material shedding—which generally lead to irreversible sulfation—the battery should be maintained at a charge current of 1.8 A for 10–15 hours, with the voltage maintained above 13.4 V.If there is a significant voltage difference between battery cells, discharge them to the cut-off voltage, then charge them at a current of 0.05–0.15C for 20 hours. Afterward, discharge them at a current of 1.5A until the voltage reaches 10.5V per cell. Repeat this process 1–3 times until irreversible sulfation is eliminated.

• What should be done if the battery voltage drops rapidly?

  A rapid drop in battery voltage is generally caused by low battery capacity, excessive starting current from the electric bicycle, or a short circuit resulting from poor battery connection.

  1. Low battery capacity

  After fully charging the battery, use a multimeter to check the battery voltage. If it is low, discharge and recharge the battery to ensure it maintains sufficient voltage.

  2. Excessive Starting and Operating Currents in the Electric Bicycle

  Measure the electric bicycle’s starting and operating currents. If the starting current exceeds 15A or the operating current exceeds 6A, this indicates a fault in the controller or motor. Adjust the controller’s current limit or inspect and repair the motor.

  3. Short circuit in battery connections

  Check whether the battery connections are secure. If the connectors are loose, have poor contact, or show signs of a short circuit, reconnect them to eliminate the short circuit.

  4. Meter reading does not match the battery’s actual capacity

  Compare the battery’s 2-hour rate discharge voltage with the voltage displayed on the meter. If the relationship between the displayed voltage and the battery’s capacity does not match, contact the manufacturer to have it adjusted.

• What should I do if a 24V/180W brushed electric bicycle shows no response when powered on?

  For this type of fault, first check whether the battery voltage display is normal. Then, unplug the speed controller connector, engage the door lock, and measure the speed control voltage. If the measured voltage is zero, further inspect the controller and the level lock; generally, a loose connection at the level lock connector is a common cause.Simply re-solder the connector terminals to the wires and secure them with wire clamps to resolve the issue.

• What methods are available to eliminate sulfation of electric bicycle battery plates?

  There are typically three methods to eliminate sulfation of electric bicycle battery plates: overcharging, low-current overcharging, or water treatment.

  Overcharging involves continuously overcharging the battery using the charging current from the second stage of the initial charge until the electrolyte produces a large number of bubbles and its density reaches approximately 1.28 g/cm³, thereby eliminating sulfation.

  Low-current overcharging involves discharging the battery to its cut-off voltage, draining the original electrolyte, refilling with distilled water, and continuously charging the battery using the charging current from the second stage of the initial charge. When the electrolyte density rises to approximately 1.15 g/cm3, discharge the battery to its cut-off voltage, then continue charging until the electrolyte density no longer increases,then adjust the density to 1.28 g/cm3 and discharge to the cut-off voltage. Once the battery capacity reaches 80% of the rated capacity, it is ready for use. If the capacity is insufficient, repeat this procedure until the capacity meets the required standard.

  To desulfate a battery using water treatment, first fully charge the battery, then let it stand for 10 hours until the voltage of each cell reaches 1.8 V. Drain the electrolyte and immediately add distilled water. Let it stand for 1–2 hours,then charge the battery at half the current used in the second stage of the initial charge. When the specific gravity reaches 1.12 g/cm3, reduce the current by one-fifth and continue charging. Stop charging when a large number of bubbles appear at the positive and negative terminals and the specific gravity of the electrolyte no longer rises, then discharge the battery for 1.5 to 2 hours at one-fifth of the 10-hour discharge rate.Repeat this process until the plates return to normal.

• How should you handle “imbalance” in an electric bicycle battery pack?

  “Imbalance” is a relatively common fault in series battery packs for electric bicycles. The causes of this fault are complex, ranging from manufacturing issues to problems with raw materials and usage.

  When this type of fault occurs, first perform a general maintenance charge on the batteries, then discharge them at a 2-hour rate. Continuously measure the battery voltage during discharge, identify the batteries with insufficient discharge capacity, and address them accordingly.

  For batteries with insufficient capacity, first top off with dilute sulfuric acid at a specific gravity of 1.050 g/cm³ until just enough electrolyte is visible to flow, then continue charging for 12–15 hours, ensuring the battery temperature does not exceed 50°C during charging. After charging is complete, let the battery stand for 0.5–4 hours before performing a 2-hour rate discharge.During the discharge process, measure the voltage of each cell. If the discharge time does not meet the standard, or if the cell voltage reaches 1.6 V, and the discharge time differs significantly from that of a normal cell (generally, a difference of more than 5 minutes for batteries 3 months old, more than 8 minutes for 6 months old, more than 10 minutes for 9 months old, and more than 15 minutes for 13 months old), repeat the above charge-discharge process until the requirements are met.For treated batteries, under constant-voltage charging conditions of 15 V per cell, drain all free-flowing electrolyte, wipe the battery surface clean, install the cap valves, and securely bond the panels using PVC adhesive.

  Note: If the battery still exhibits “imbalance” after following the above procedures, it indicates that a cell in the battery has a short circuit, or that the active material has severely flaked off or softened, causing irreversible sulfation, etc. In such cases, the battery must be scrapped.