80V ONYX - How It Works

Introduction

This post explains how electricity flows through an 80V ONYX at a practical, system level. Instead of treating voltage and current as abstract ideas, we trace how energy moves through the bike’s real components and how that directly determines acceleration, torque, efficiency, heat, charging behavior, and top speed.

We start with a simple overview, then move into progressively more technical detail covering:

• How the battery pack produces high power from many low-voltage cells
• How the controller converts DC into three-phase AC
• How phase current creates torque in the motor
• The DC-DC converter and 12 V accessories
• Regenerative braking
• AC charging and DC conversion
• Why voltage limits speed and current limits torque

Simple overview

At its core, the ONYX RCR 80V works like this:

• The battery stores energy using hundreds of lithium cells.
• The controller converts battery DC into precisely timed three-phase AC.
• The motor uses phase current to generate magnetic fields and torque.
• The DC-DC converter powers the 12 V system.
• The charger converts wall AC into high-voltage DC to refill the battery.
• During braking, energy flows back into the battery through regeneration.

Everything else on the bike depends on this energy path.

Electrical paths inside the bike

There are three main electrical paths operating simultaneously.

High-voltage drivetrain:

Battery -> Controller -> Motor -> Rear wheel

Low-voltage accessory system:

Battery -> DC-DC converter -> 12 V accessories

Charging path:

Wall outlet (AC) -> Charger -> Battery

Core electrical quantities

Ohm’s law on the RCR

Every conductive part of the bike follows:

Why this matters:

• High current magnifies even small resistance
• Resistance turns power into heat
• Low-resistance wiring and connectors directly improve efficiency and reliability

How the battery produces high power from low-voltage cells

Each lithium-ion cell in the battery operates over a narrow voltage range:

• Fully charged: ~4.2 V
• Nominal: ~3.6-3.7 V
• Near empty: ~3.0 V

By itself, one cell cannot power a motorcycle. The pack becomes powerful through series and parallel connections.

Series connections (voltage)

Cells are stacked end-to-end:

• 22 cells × ~3.6 V ≈ ~80 V nominal

This creates the high system voltage required for speed.

Parallel connections (current)

Multiple series strings are connected side-by-side:

• Each parallel group shares the current load
• This multiplies how many amps the pack can safely deliver

Why small voltage changes still deliver huge power

Electrical power is:

Even when voltage falls from 4.2 V to 3.0 V per cell:

• Pack voltage only drops modestly
• Available current remains high
• Total power stays large

This is why the bike can still deliver strong acceleration at 70% or 40% state-of-charge, but begins to feel weaker near empty due to voltage sag and current limits.

The motor controller (DC to AC inverter)

Control algorithms inside the controller

Beyond simple switching, modern ONYX controllers run real-time control software that decides exactly when and how long each MOSFET is turned on.

Common elements include:

• Rotor position estimation using Hall sensors or back-EMF sensing
• Field-oriented control (FOC) to align current with the rotor’s magnetic field
• Current control loops that regulate phase current thousands of times per second
• Torque commands derived from throttle input
• Voltage and temperature limiting to protect the battery and electronics

Its core job:

• Convert steady DC from the battery into three precisely timed AC waveforms

How DC becomes three-phase AC

Inside the controller:

• High-power MOSFETs rapidly switch the battery on and off (thousands of times per second)
• Pulse-width modulation (PWM) shapes these pulses into smooth currents
• Six switching channels generate three phase pairs (A, B, C)

The result:

• A rotating magnetic field inside the motor
• Speed controlled by electrical frequency
• Torque controlled by current amplitude

Electrically, the controller behaves like a continuously adjustable electronic transformer and variable resistor combined into one device.

Hall sensors vs encoders (rotor position feedback)

For the controller to produce smooth torque, it must know the rotor’s exact position. That angle information is used by the control algorithm to time the phase currents and align the magnetic fields inside the motor.

There are two main ways this position is measured: Hall sensors and encoders.

The short version

• Hall sensors are used on almost all e-bikes. They are simple, reliable, inexpensive, and work extremely well in real riding.
• Encoders are high-precision sensors common in industrial and robotics motors. They are more accurate, but far more complex and rarely practical for hub motors.

Hall sensors (standard on e-bikes)

Hall sensors are small magnetic sensors built into the motor. They report rotor position in coarse steps, which is sufficient for smooth control.

In practice this provides:

• Smooth starts from a stop
• Strong low-speed torque
• Predictable throttle response
• Broad controller compatibility (FarDriver, QS, stock ONYX, etc.)

This is why nearly every serious hub-motor setup uses Hall sensors. For street riding and high-power builds, they already deliver excellent control.

Encoders (high-resolution feedback)

Encoders measure rotor position with very fine resolution, often hundreds or thousands of points per rotation.

This enables:

• Near-perfect smoothness at very low speed
• Extremely precise torque control
• Cleaner field-oriented control behavior
• No stutter when creeping or starting under heavy load

This type of feedback is common in CNC machines, robotics, and industrial motion systems.

Why encoders are rare in hub motors

Despite their advantages, encoders come with major tradeoffs:

• Higher cost
• More wiring and tighter mechanical tolerances
• Limited controller support (not supported by FarDriver)
• No increase in top speed or peak power
• Improvements are mainly noticeable only at crawling speeds

On bikes like the ONYX RCR or 80 V builds, Hall sensors already provide smooth launches and strong torque. Moving to encoders would require a different controller platform and custom motor work for gains most riders would barely notice.

Bottom line

Hall sensors are the practical sweet spot for hub motors: simple, proven, and smooth where it matters.

Encoders are powerful technology, but for e-bikes they are usually overkill.

In practice the controller repeatedly performs:

• Measure motor currents and rotor angle
• Compute desired torque
• Calculate phase current targets
• Adjust PWM duty cycles to reach those targets

This is why the motor feels smooth at low speed, powerful under load, and stable at high RPM: the controller is continuously solving a fast control problem in software.

The controller is not just a “throttle box.” It is a high-power electronic inverter.

Phase current and how the motor creates torque

Why the motor must use AC

A brushless motor cannot run on steady DC because:

• Fixed DC would create a stationary magnetic field
• A stationary field would pull the rotor into alignment and then stop producing torque

Three-phase AC solves this by:

• Creating a rotating magnetic field
• Continuously pulling the rotor forward
• Allowing smooth torque at any speed

The controller adjusts:

• Phase angle to keep fields aligned with rotor magnets
• Phase current magnitude to set torque
• Electrical frequency to set speed

This electronic rotation replaces mechanical brushes and commutators used in older DC motors, giving higher efficiency, longer life, and precise torque control. The hub motor contains:

• Stator windings (electromagnets)
• Rotor magnets (permanent magnets)

When three-phase current flows:

• Magnetic fields rotate around the stator
• The rotor is pulled along by these fields
• Mechanical torque is produced at the wheel

Key relationships:

Important distinction:

• Battery current ≠ phase current
• Phase current is often several times higher than battery current due to voltage conversion inside the controller

This is how moderate battery current can still create massive wheel torque at low speed.

Current, torque, and acceleration

Putting it together:

• Battery supplies power
• Controller converts voltage into phase current
• Phase current produces torque

So in practice:

Which leads to:

• Acceleration is current-limited
• Top speed is voltage-limited

Voltage and top speed

As motor speed increases, the motor generates back-EMF that opposes the battery.

Eventually:

• Motor back-EMF ≈ battery voltage
• Phase current falls
• Torque approaches zero

This defines the electrical speed ceiling of the bike.

• Higher battery voltage -> higher possible top speed
• Lower voltage -> earlier speed saturation

Power flow to the motor

Electrical input power:

Mechanical output power:

Electrical input × motor efficiency

But in practice, that power is transformed in stages, not transferred all at once:

• DC power leaves the battery
• The controller converts it into three-phase AC
• The motor turns electrical energy into magnetic field energy
• Magnetic forces create torque at the rotor
• Torque becomes motion at the wheel

Battery power, motor electrical power, and wheel power are related but not always equal:

• Battery power = battery voltage × battery current
• Motor electrical input = phase voltage × phase current
• Wheel power = torque × rotational speed

Because the controller converts voltage into phase current:

• At low speed, motor phase power can exceed battery power
• High phase current produces strong torque with moderate battery current
• At cruising speed, battery power and motor power become similar

Losses occur in:

• Controller switching and conduction
• Motor copper (I²R) losses
• Magnetic core losses
• Bearings and tire contact

Why this matters in real riding:

• Hard acceleration creates high current and heat
• High speed stresses voltage and switching losses
• Moderate cruising gives the best efficiency and range

DC-DC converter and accessories

How high-voltage DC becomes stable 12 V

The DC-DC converter is another switch-mode power supply.

Internally it:

• Chops the 80 V DC into high-frequency pulses
• Passes them through a small transformer or inductor network
• Rectifies the output back into DC
• Regulates it tightly to ~12-14 V

Key advantages:

• Electrical isolation from the high-voltage system
• Stable voltage even as battery voltage changes
• High efficiency with minimal heat

Without this conversion stage, lights and electronics would be destroyed instantly by the main battery voltage. The DC-DC converter steps ~80 V down to 12 V.

It powers:

• Headlight
• Brake light
• Turn signals
• Horn
• Display and control electronics

These loads are small compared to the motor and have minimal effect on performance or range.

Regenerative braking

During regen:

• The wheel drives the motor as a generator
• Phase currents reverse direction
• Power flows motor -> controller -> battery
• Electrical energy becomes braking torque

Effects:

Regeneration is limited by battery charge acceptance, controller settings, and motor speed.

How the charger converts AC to high-voltage DC

Household outlets provide AC power (~120 V RMS in North America). The battery requires stable DC near 90-94 V when full.

The charger is a switch-mode power supply that performs these stages:

1. Rectification

• Diodes convert AC into pulsating DC

2. Power factor correction (PFC)

• Shapes current draw
• Improves efficiency
• Reduces stress on household wiring

3. High-frequency switching

• MOSFETs chop DC into tens of kHz pulses

4. Transformer voltage conversion

• High-frequency transformer steps voltage up or down

5. Output rectification and filtering

• Converts back to smooth DC

6. Regulation

• Controls current first, then voltage
• Protects the battery from overcharge

Key takeaway:

• Voltage conversion happens after rectification using high-frequency transformers
• This allows output voltages higher or lower than the wall supply

Battery CC and CV Charging

Constant-current and constant-voltage charging (CC and CV)

Lithium batteries are charged in two main phases:

• Constant-Current (CC) phase
• Constant-Voltage (CV) phase

During the CC phase:

• The charger holds current at a fixed safe level
• Battery voltage rises steadily
• This fills the pack quickly from low state-of-charge to roughly 90-97%

When the pack reaches its maximum safe voltage, the charger switches to the Constant-Voltage phase.

That slow 97% -> 100% stretch is called the CV phase.

During CV:

• Voltage is held fixed at the pack’s maximum (about 90-94 V for an 80 V system)
• Charging current gradually tapers downward
• The final remaining energy diffuses into the cells safely
• Heat generation is minimized

This is why the last few percent takes much longer than the first half of the charge.

Trickle charging behavior

Near full charge:

• Current becomes very small
• Power input drops dramatically
• Charging appears to “crawl” toward 100%

This is often called trickle charging, but in modern lithium systems it is simply the tail end of the CV phase rather than a true continuous trickle. The charger is carefully limiting current to avoid over-voltage and cell stress.

Battery cell balancing

An 80 V pack contains hundreds of individual cells that never age or charge perfectly equally.

To keep them aligned:

• The Battery Management System (BMS) monitors each cell group
• Slightly over-charged groups are bled down through small resistors
• Weaker groups continue charging until all groups match

Balancing mainly occurs:

• Near the top of charge
• During the CV phase
• At low current levels

This is another reason full charging slows down near the end.

Without balancing:

• Some cells would over-charge
• Others would under-charge
• Pack lifespan and safety would drop dramatically

Charging and discharging

When charging:

• Charger supplies regulated DC
• Battery voltage rises gradually
• Current tapers near full

When riding:

• Voltage declines with state-of-charge
• Voltage sag appears under heavy acceleration
• Both slightly reduce torque and top speed

Where heat is generated

Primary heat sources:

• Controller switching losses
• Motor copper losses
• Battery internal resistance
• Wiring and connectors
• Charger electronics

Important scaling rule:

• Doubling current causes roughly four times the resistive heating

Why system design matters

Performance depends on the entire electrical chain:

• Battery cell chemistry and internal resistance
• Pack voltage and parallel count
• Controller phase and battery current limits
• Motor winding design
• Cable gauge and connectors
• Cooling
• Charger efficiency

Together these determine:

• Acceleration
• Sustained power
• Efficiency
• Reliability
• Top speed
• Charging speed

Final takeaway

In the 80V ONYX:

• The battery multiplies small cell voltages into high system power
• The controller converts DC into three-phase AC
• Phase current creates torque
• Voltage limits top speed
• Current limits acceleration
• Resistance determines heat and efficiency

Understanding this full chain from lithium cell chemistry to electromagnetic torque turns the bike into a transparent, predictable electrical machine rather than a black box.