Improving Performance in DIY 18650 Charging Setups

Are you considering adding more charging modules to your DIY 18650 charging set-ups to improve performance? You might have noticed a few setups where people parallel connect a few 1s charging modules to charge 18650 cells. While this might sound appealing, it comes with potential challenges.

Potential Problems with Parallel Connected LiIon Chargers

When dealing with multiple Li-ion charging modules connected in parallel, there are several issues you need to be aware of:

Constant-Current Mode

At low cell voltages, the chargers operate in constant-current mode, where each module measures its own current internally. The total current is the sum of the individual module outputs. This is generally acceptable as long as the total current does not exceed the cell's specifications. However, if some cells are relatively new and others are older, the current sharing may not be even, leading to inefficiencies.

Transition to Constant-Voltage Mode

As the voltage rises, the chargers switch to constant-voltage mode. Each module has its own voltage reference and divider, so they do not all switch at the same moment. During this transition, some modules may remain in constant-current mode while others switch to constant-voltage mode, causing confusion for the constant-voltage modules.

Voltage Tolerances and Current Distribution

Even after all modules have switched to constant-voltage mode, they still have voltage tolerances. The highest-voltage module will continue to supply the current, while others will shut down due to the perceived overvoltage. This puts strain on the setup, as the modules are used in an environment they were not designed for. Moreover, the constant-current mode charge current is four times the setting of the individual modules, but none of them are aware of each other. Therefore, the last module is looking for a current drop to 50% of what it considers the initial current, which is actually 1.25 times the real initial current.

Best Practices for DIY 18650 Charging Setups

To avoid these issues and achieve optimal performance, consider the following practices:

Grouping Cells

Divide the cells into groups so that each group is connected to one charging module. This ensures that each module can communicate properly and set the current limit accurately for the number of cells being charged. This method helps prevent confusion among the modules and ensures proper charging.

Using a Single Charger with Higher Output Current Rating

Instead of using multiple chargers in parallel, consider using a single charger with a higher output current rating. This method simplifies the setup and reduces the risk of complications during the charging process.

Conclusion

Adding more charging modules to your DIY 18650 charging set-ups is not necessarily the best approach. By grouping cells and using a single high-output charger, you can ensure safe and efficient charging. Always prioritize the safety and performance of your setup to get the best results.