ONYX Superpower BMS (Setup and Behavior)

This page is part of the ONYX Battery Guide

Intro

SuperPower BMS is a battery management system with a built-in Bluetooth app interface used on ONYX 72V 45A and 80V 45A battery platforms. It provides real-time visibility into pack behavior along with control over protection and balancing.

Think of SuperPower BMS as the battery’s protection and visibility layer, not a performance controller.

The BMS is not controlling your bike, it is only managing and protecting the battery. The motor controller still decides how much power gets pulled, and that mismatch is where most real-world issues originate.

All behavior described here is based on real ONYX load conditions, not nominal specifications.

SuperPower BMS App

• SuperPower BMS - iOS
• SuperPower BMS - Android

Summary

• Integrated BMS system with Bluetooth monitoring and configuration
• Real-time visibility into cell and pack behavior
• Protection-based system, not a performance controller
• No coordination with motor controller demand
• Voltage sag under load is the primary source of shutdown issues
• Weakest cell defines overall system reliability
• Behavior must be evaluated under load, not at rest

System Overview

Behavior Overview

Under real ONYX riding conditions, battery behavior looks very different from what you see at rest.

• Voltage drops quickly under throttle
• Cell differences show up under load, not at idle
• Weak cells typically show up during acceleration
• Temperature increases with sustained current draw
• The BMS reacts after limits are hit, not before

This is why the battery can look healthy when idle but behave very differently once you start riding.

Bluetooth behavior:

• Requires close proximity
• Disconnects are normal while moving
• Not suitable for real-time riding feedback

Setup and Connection

1. Power the battery and ensure the BMS is active
2. Open the SuperPower BMS app
3. Connect via Bluetooth
4. Verify:
   • total voltage
   • individual cell voltages
   • temperature readings

Notes:

• iOS and Android behavior is similar
• Connection stability depends on enclosure and interference
• Always confirm values before changing configuration

Technical Fundamentals

Protection System

The BMS enforces:

• Overvoltage protection (OV)
• Undervoltage protection (UV)
• Overcurrent protection
• Temperature protection

These are hard cutoffs. When triggered, power is immediately disconnected. There is no gradual reduction, it is an immediate stop.

MOSFET Control

• Charge and discharge paths are controlled internally
• When a limit is exceeded, the BMS opens the circuit
• This results in instant loss of power to the system

This is why shutdowns feel abrupt rather than gradual.

Balancing

• Passive balancing only
• Removes energy from higher cells
• Active near full charge
• Cannot correct large imbalances

What the BMS Cannot See

The BMS only sees what is happening inside the battery.

It does not see:

• motor demand before it happens
• throttle input
• controller behavior

This is why shutdowns can feel sudden. The system demand happens first, and the BMS reacts after limits are exceeded.

72V 45A Systems (Typical 20S)

Focus:

• Stability under acceleration
• Preventing cutoff from transient sag

80V 45A Systems (Typical 22S)

Focus:

• Managing higher voltage stress
• Avoiding false trips during regen
• Accounting for stronger sag under load

Current Behavior

The BMS rating does not reflect actual ONYX demand.

• Acceleration spikes exceed nominal current
• Controller demand is not limited by BMS rating
• The BMS only reacts after limits are exceeded

This is why the system can feel stable at low power but shut down instantly under heavy acceleration.

Recommendations:

• Do not set overcurrent protection too close to nominal
• Allow buffer for short spikes
• Avoid removing protection entirely

Voltage Sag and Weak Cells

Most real-world shutdown issues come down to voltage sag.

What happens:

1. You apply throttle
2. Current demand increases
3. Voltage drops across the pack
4. One cell drops faster than the others under load
5. UV protection is triggered
6. The BMS cuts power

Key points:

• Pack voltage alone is misleading
• The lowest cell determines shutdown
• Sag must be evaluated under load, not at rest

This is the exact moment where most riders experience sudden power loss.

Recommendations:

• Watch cell voltages during acceleration
• Identify the lowest cell under load
• Adjust UV thresholds carefully

Voltage Sag Reference

Voltage sag is the drop between resting voltage and voltage under load. It happens instantly when throttle is applied, and the harder the acceleration, the larger the sag.

Severe sag is what causes most unexpected shutdowns.

These ranges are typical for ONYX 72V and 80V systems under moderate to high load and should be treated as guidelines, not exact limits.

Cell Delta Under Load

These values should be evaluated under load, as cell differences are often minimal at rest and only become visible during real demand.

Balancing Behavior

Passive balancing has limits, but it is always active when conditions are met.

• Balancing is fully automatic on these systems
• No manual control is required
• The BMS handles it internally

Balancing only becomes effective near the top of the charge range under normal conditions.

• Typically begins around 80 percent charge and above
• Most active close to full charge
• Below that range, little to no balancing occurs

This means:

• The battery needs to be charged high enough for balancing to happen
• Letting the battery sit at a higher state of charge allows the system to correct small differences between cells

This is why partial charging over long periods can slowly increase imbalance.

The app is useful here:

• It shows state of charge
• It shows cell voltages
• It lets you confirm when balancing conditions are met

Practical behavior:

• Small imbalances often correct themselves over time
• Repeated full or near-full charges help maintain balance
• If the pack is slightly out of balance, letting it sit at high charge can improve it

Limitations:

• Balancing is slow
• Only active near the top of charge
• Cannot fix a degraded or failing cell

Warning:

If one cell consistently deviates, the issue is not balancing. It is a problem cell.

Diagnostics

If you experience shutdown under acceleration:

1. Open the app and monitor live data
2. Apply throttle and observe cell voltages
3. Identify the lowest cell
4. Compare delta against other cells
5. Adjust UV threshold or inspect pack
6. Repeat under consistent throttle conditions for accurate comparison

The goal is to reproduce the issue under controlled conditions, not guess based on idle readings.

Use the app for:

• Identifying weak cells
• Observing sag patterns
• Tracking imbalance over time
• Verifying protection events

State of charge is an estimate based on voltage and becomes less accurate under load.

Do not use the app for:

• Real-time riding decisions
• Accurate state of charge
• Absolute measurements without validation

Regenerative Behavior

Regenerative braking can trigger overvoltage protection.

• Occurs during downhill or aggressive deceleration
• More noticeable at higher pack voltages
• Can cause sudden cutoff if limits are too tight

Recommendations:

• Leave headroom in OV settings
• Test behavior after configuration changes

Hardware and Thermal Considerations

ONYX battery compartments are enclosed.

Effects:

• Heat buildup under load
• Reduced efficiency of internal components
• Increased chance of thermal shutdown

Heat builds gradually, but shutdowns happen instantly.

Recommendations:

• Improve airflow where possible
• Do not raise temperature limits to compensate
• Treat thermal issues as system design problems

Final Advice

• The BMS protects the battery, it does not control the bike itself
• Configuration must match real load behavior
• The weakest cell defines reliability
• Voltage sag under load is the critical factor
• Always validate behavior under real riding conditions

Always treat BMS limits as protection boundaries, not operating targets.

Correct setup results in:

• Stable acceleration
• No unexpected shutdowns
• Predictable performance

Incorrect setup results in:

• Sudden power loss
• Misleading battery readings
• Long-term pack degradation