The Battery and BMS part in a VESC build is a tricky one. Here is where safety really comes into play as a typical VESC board battery has enough power to cause considerable damage and bodily harm when not made properly or used incorrectly. The consequences can be dire!
DISCLAIMER: The VESC Bible is currently being republished and rewritten to encompass all necessary beginner guides. All guides with a beta tag are still preliminary and need to be vetted and reviewed by VESC experts.
Battery selection is crucial in a VESC build, influencing performance and range. Key factors include:
- Voltage: Represented in series cell count (“S”). Higher voltage (more cells in series) delivers more power, directly impacting top speed and acceleration. However, it requires a compatible VESC controller and can pose higher risks. Beginners often start with stock battery voltage (15S) before considering higher voltage options.
- Capacity: Represented in Amp-hours (“Ah”). Higher capacity means storing more energy, translating to longer range. Capacity choice depends on desired ride time and the physical space within the build.
- Cell Type: Cells come in various chemistries and form factors. Popular choices include:
- 18650 Cells: Smaller and typically offer lower capacity and discharge rates than 21700 cells.
- 21700 Cells: Larger, providing higher capacity and discharge rates. Common models include P42a, P45b, and 50s.
- Discharge Rate: Measured in Amps (“A”). A higher discharge rate is crucial for safely delivering the current demanded by the VESC and motor under heavy loads.
Understanding Battery Ratings:
- “P” followed by a number (e.g., P28a) denotes the cell model, often indicating its discharge rate and capacity.
- Always refer to reputable sources like Mooch’s battery tests to confirm accurate cell ratings before choosing a battery.
Link to Mooch battery tests: ///tbc
BMS (Battery Management System)
A BMS is vital for protecting and managing the battery pack. It monitors individual cell voltages and prevents overcharging, over-discharging, and other potentially dangerous conditions. There are two main types:
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Smart BMS: Offer advanced features like:
- Bluetooth or CAN connectivity for monitoring cell voltages, temperatures, and other parameters via dedicated apps or VESC Tool.
- Configurable settings like charge/discharge current limits and balance thresholds.
- Active balancing, which actively transfers energy between cells for more efficient balancing.
Examples of smart BMS include Ennoid X-Lite V3 and V4.
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Dumb BMS: Simpler and often more affordable. They primarily protect the battery through basic overcharge/discharge protection and passive balancing, which bleeds off excess energy from higher voltage cells.
Examples of dumb BMS include PickleBMS, ZBMS, and Maxxgo.
Charge-Only BMS Setups
In charge-only BMS setups, the BMS only manages the charging process. The VESC controller handles discharge and low-voltage cutoff. This configuration is common in DIY VESC builds, providing flexibility and potentially lower cost. However, it requires careful VESC configuration to ensure safe discharge limits.
Choosing the Right Battery and BMS
- Desired Performance: Higher voltage batteries provide more power. Consider your desired riding style and whether you prioritise speed, torque, or range.
- Onewheel Model and Enclosure: Different Onewheel models and enclosures have varying space limitations. Ensure the chosen battery pack physically fits and has the necessary connectors for the build.
- Budget: Smart BMS generally cost more than dumb BMS. Factor in the cost of the battery, BMS, and any required breakout boards or wiring harnesses.
- DIY Skill Level: Smart BMS offer more control and monitoring capabilities but require a deeper understanding of VESC configuration. If you’re new to DIY electronics, a dumb BMS with a charge-only setup might be a simpler starting point.
Battery Balancing
Battery balancing is essential for maintaining battery health and performance. Over time, individual cells within a pack can develop slight voltage differences, leading to reduced capacity and potentially damaging overcharge or over-discharge of individual cells. Balancing mitigates this issue:
- Passive Balancing: Used by most dumb BMS and some smart BMS. It slowly discharges higher-voltage cells through a resistor to bring them closer to the pack’s average voltage.
- Active Balancing: Featured in some smart BMS. Actively transfers energy from higher-voltage cells to lower-voltage cells, resulting in a faster and more efficient balancing process.
Regularly checking cell voltages and ensuring your BMS is functioning correctly can significantly extend the lifespan of your battery pack and maintain consistent performance.
Note: While the sources provide information on various BMS options, the specific wiring and configuration may vary depending on the chosen components and Onewheel model. Refer to detailed build guides and the documentation provided by your BMS manufacturer for accurate instructions.