A guide to safely charging lithium e-bike batteries

Charging lithium batteries is generally considered a risky process. This document outlines the risks involved and how a charging solution can reduce this risk.

May 17, 2023
Joris Koudijs

Why charging is a potential hazard

The main risk while charging lithium batteries is them catching fire. This risk can be understood by looking at the chance of a battery catching fire and the impact of such a fire.

The chance of a battery catching fire is directly affected when charging:

  • at too high temperature
  • at too high current
  • to a too high voltage
  • when a battery has been discharged too far

The impact of the fire depends on how violent the fire is. A battery fire can range from a sizzling cell to multiple complete battery packs close together setting each other on fire. Multiple factors play a role, such as the specific cell used or battery pack design. However, the two most important factors are how much the cell is charged and how close multiple packs are stored together.

A fully charged cell may reach over 500 degrees Celsius in minutes after the thermal runaway has started, while a 50% charged cell may never go beyond 200 degrees and take up to 30 minutes to reach this temperature.

Charging batteries which are densely packed creates the opportunity for one to ignite the next, causing a chain reaction and an almost unstoppable fire.

How a smart charger can improve safety

The primary function of the Battery Management System (BMS) is to protect against these fire-causing scenarios by interrupting the charge process. However, some BMSs skip some of these protections.

A charger can add a second layer of security by implementing limits for voltage and current boundaries. The charger still relies on the BMS to monitor the internal battery temperature, and since most simple chargers omit communication with the BMS, they cannot interrupt charging when temperatures become too high.

Sometimes a communication protocol between the charger and BMS is implemented using CAN or UART protocols. This can be used for redundant temperature protection or more sophisticated charge control, e.g. tailoring charge current and voltage to the battery temperature. Chargers with such functionality are commonly referred to as smart chargers.

How TILER can improve charging safety even more

Charging with TILER can decrease the risk of catching fire in different ways by implementing smart charging, minimizing movement of the battery, and not charging the batteries all on the same spot.

Limiting the battery charge

With TILER, parking means charging. As a result, bikes will be charged after every ride, only requiring the battery to be charged enough for a single trip. Through smart analysis of the battery use, TILER minimizes the battery charge while ensuring sufficient charge for every trip taken from that location. This minimizes the potential energy in the cell and the temperature it may reach in a fire event. It also slows down the reaction, leaving more time to evacuate if required. As a side catch, this charge optimization also greatly improves the battery lifetime.

Spacing batteries apart

A second benefit of charging while parking is that it ensures a minimal distance of 60cm between charging batteries. This reduces the chance of batteries igniting each other, limiting the impact of a fire significantly.

No chance of dropping

A dropped battery is always at risk of becoming unstable whether it’s related to charging or not. Some manufacturers even recommend discarding dropped batteries because of safety concerns. With TILER the battery can remain safely inside the vehicle reducing the chance of it being dropped significantly.

Early warning

The TILER system has live information about the battery vitals. This allows it to detect a thermal runaway event before it starts becoming dangerous. Using the built in internet connection it can warn local safety staff or fire department to ensure ultra-quick response to any potential battery fire.

Tiler compatibility check

Before TILER deems a bike compatible with the TILER Charge system, the bike, battery and its original charger are evaluated to ensure safety.

The charger is checked for the following:

  • charge profile
  • charge current
  • pre-charge voltage
  • end-of-charge voltage
  • maintenance charge voltage

The battery is checked for its protection types:

  • over temperature
  • under temperature
  • over voltage
  • under voltage
  • over current

In case TILER connects through the battery’s discharge path, it is checked these protections are still active to assure full redundant protection.

On bike and system level the integration is checked. This includes whether there is:

  • good interaction between the charger and battery
  • accurate SoC tracking
  • no parasitic loss causing high consumption

After these checks, the safest charging manner is determined and programmed into the charging kickstand. The final step is to design and source the correct adapter cable so the electrical connections can be made without having to cut any wires.

If you are wondering how the charging safety can be optimized in your specific situation you can reach out to us via our website.

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