Assembling a custom electric bike battery pack often involves navigating a maze of technical specifications and best practices. For DIY enthusiasts diving into the world of Custom Electric Bikes, understanding battery components is crucial. One common question that arises when building a battery for a custom electric bike is whether it’s acceptable to mix 18650 Li-Ion cells with different milliamp-hour (mAh) ratings. Let’s delve into a real-world scenario faced by a custom e-bike builder to explore this question.
Recently, a builder working on a custom electric bike battery pack encountered a perplexing issue. Initially, they constructed a 10s2p battery pack using 18650 Li-Ion cells rated at 3.6V and 2200mAh, paired with a 10s 36V Battery Management System (BMS) rated for 15 amps. This setup functioned adequately, but the range was limited. To enhance the range of their custom electric bike, the builder decided to increase the battery capacity.
Aiming for extended rides on their custom electric bike, they added ten 18650 Li-Ion cells rated at 3.6V and 2400mAh. They reconfigured their battery pack to a 10s3p arrangement. This resulted in a battery pack composed of twenty 2200mAh cells and ten 2400mAh cells. Upon charging this modified battery pack, no immediate issues were detected; it charged to 40V and the BMS correctly cut off the charging process.
However, the problem emerged during use. When riding their custom electric bike, the battery pack discharged to below the expected 36V cutoff, reaching as low as 34.8V. This was a new behavior not observed before the introduction of the 2400mAh cells. The builder questioned whether mixing cells of different mAh ratings was the cause of this unexpected discharge behavior in their custom electric bike battery. Suspecting a potential charge imbalance due to the mixed cells, they recharged the battery, which again cut off at 40V. Now, before testing the battery further on their custom electric bike to see if the discharge cuts off at the correct 36V, they are seeking insights into whether mixing different mAh cells in a custom electric bike battery is a viable and safe practice. Online research has yielded conflicting opinions on mixing battery cells of different mAh and brands, adding to the confusion.
This real-world example highlights the uncertainty and potential issues surrounding the mixing of 18650 cells with varying mAh ratings in custom electric bike battery builds. Understanding the implications of such configurations is crucial for anyone involved in DIY custom electric bike projects, ensuring both performance and safety.
