Electric scooter controller: what it is, how it works, and how to choose one

On electric scooters, we often talk about the battery and the motor. However, a third, less visible component plays a crucial role in almost everything: the controller. It is responsible for regulating the energy that the battery sends to the motor at every moment. Acceleration, electric braking, maximum speed, overheating, and a significant portion of malfunctions are all related to it.

This guide explains what a controller does, how to understand its specifications without being misled, and the order in which you should think before replacing it.

The role of the controller, in a single image

A battery provides direct current: two wires, a positive and a negative, with a relatively stable voltage. A scooter motor, on the other hand, is a three-wire "brushless" motor, which are referred to as the three phases. To make it rotate, current must be circulated through these three wires in sequence, at the right time and with the correct intensity, thousands of times per second.

The controller performs precisely this function. Inside, electronic switches open and close very rapidly to cut the current from the battery and distribute it among the three phases. A small computer controls these switches based on what you request from the throttle, the motor's position, and everything else the controller monitors.

By the way, the controller also performs other functions:

• Electric braking: This system uses the motor like a generator, which slows down the wheel and sends a small amount of energy back to the battery;
• Protections: It reduces or cuts off power if the temperature of the motor, the battery voltage, or any other parameter exceeds the predefined limits;
• Communication with the display: Speed, battery level, riding modes, and error codes are displayed on it.

The numbers that matter, and how to interpret them

The voltage: that of a fully charged battery

A scooter battery is made up of lithium cells connected in series. Each cell has an average voltage of approximately 3.6V and reaches 4.2V when fully charged. The battery is typically identified by its average, or nominal, voltage, but it is the fully charged voltage that the controller must handle.

Furthermore, a safety margin is essential: during electric braking, the voltage rises above the battery's voltage. For example, a controller rated for 100V can accept a 72V battery (84V at full charge) with some margin. A controller specified as "72V" without further clarification should be verified: does it actually support 84V and the voltage spikes that occur during braking?

Two different types of current: battery current and phase current

This is the point that most specifications get wrong. A controller has two current limits:

• The battery current is the current drawn from the battery. When multiplied by the voltage, it gives the actual power consumed
• The phase current is the current it sends to the motor. This current is what generates torque, which provides the force for starting and climbing hills.

Why aren't these two currents equal? At low speeds, the motor only needs a small voltage, but a high current to produce torque. The controller then acts like a transformer: it exchanges voltage for current. At startup, the phase current can therefore be much higher than the battery current, without the battery providing more power. This is what allows for strong acceleration without immediately draining the battery.

For example, our RageLink X400 Dual controllers are rated for 400 amps of phase current and 250 amps of battery current per motor: the first number indicates the power output, while the second indicates the amount of current the battery must be able to deliver.

Watts: A calculation, not a guarantee

The electrical power drawn from the battery is simply calculated as: battery voltage multiplied by battery current. A controller limited to 50A on a 72V battery will consume a maximum of 72 x 50 = 3600W. On a scooter with two motors and two controllers, you add the power consumption of both.

This calculation often provides a more meaningful understanding than the wattage figure printed on the motor, which generally indicates the continuous power output – the power the motor can sustain for a long time without overheating – rather than the peak power.

Square wave or sine wave

There are two main ways to operate a brushless motor. The first, known as square wave (or trapezoidal) control, powers the phases in steps: it's simple and robust, but the motor is noisier and slightly less smooth at low speeds. The second, often called vector control or FOC (for "Field Oriented Control"), continuously varies the current in a sinusoidal manner. The motor is quieter, smoother, and generally has better efficiency.

Modern performance controllers almost all operate using Field-Oriented Control (FOC). For a rider, the difference is most noticeable in the smoothness of acceleration and the precision of the throttle response.

Sensors or no sensors?

To deliver power at the right time, the controller needs to know the position of the motor's rotor. There are two solutions:

• with sensors: Most scooter motors have three sensors called "Hall effect" sensors (five thin wires next to the three thicker phase wires). The controller knows the position of the motor even when it's stopped, which provides a smooth and jerk-free start
• Sensorless: The controller determines the motor's position based on the voltage it produces while rotating. This is very effective when riding, but can be more challenging when starting from a complete standstill.

A faulty sensor or a poorly seated connector can cause typical symptoms: the motor may stutter, hesitate when starting, or only start if the scooter is pushed.

Should I use one or two controllers?

A dual-motor scooter often has two controllers, one for the front wheel and one for the rear wheel, which manufacturers sometimes distinguish with a letter (controller A and controller B). They are not always interchangeable: one may have the connection to the display, while the other does not.

There are also dual controllers, which control two motors within a single housing, such as the RageLink X400 Dual. This means only one unit to mount, wire, and configure, while both wheels are managed together.

How to choose a controller, in order of priority

It's tempting to change controllers to gain performance. However, the controller is only one component: it can't draw more current from a battery than it provides, nor can it send more power to a motor than it can handle without overheating. The workshop's approach is as follows.

1. Battery voltage. The controller must accept the full-charge voltage, with some margin.
2. What the battery can deliver. The maximum current of its battery management system (BMS) and the quality of the cells determine the limit. Beyond that, the battery will shut down or degrade quickly. See our electric scooter batteries, including our Performance versions, which are designed to deliver higher currents.
3. **What the motor can handle.** The phase current is converted into torque, but also into heat within the motor. A larger or better-cooled motor can handle more. See our electric scooter motors.
4. Placement and Cooling. A controller that overheats will reduce its power to protect itself. It must be mounted on a surface that dissipates heat.
5. Connections. Motor sensors, throttle, brake, display: each pin must correspond correctly, or be properly adapted.
6. Adjustment. An adjustable controller allows you to adapt the current settings to the battery and motor. However, you need to know how to do it.

And we must not forget the rest of the machine: more power requires adequate brakes and tires to match.

Failures that are (or appear to be) caused by the controller

• The scooter cuts out when accelerating quickly: Most often, this is because the battery (or its BMS - Battery Management System) is protecting itself from being overloaded, rather than the controller.
• The motor stutters or jerks: This could be due to a faulty Hall sensor, a poorly seated sensor connector, or a damaged phase wire.
• Power decreases after a few minutes: This could be due to thermal protection of the controller or the motor.
• An error code is displayed: This indicates a family of faults (motor, sensor, voltage, communication), which must be interpreted according to the display manufacturer.
• The controller has actually burned out: This could be due to water damage, a short circuit in the phases, or electric braking with a fully charged battery on a controller that doesn't have sufficient voltage headroom.

Speed and the Law: What You Need to Know

In France, an electric scooter that operates on public roads must be limited by design to a maximum speed of 25 km/h. A more powerful controller does not change this rule: on the road, the scooter remains speed-limited. Performance is measured on a closed track or on private property, where our racing team operates.

Our RageLink controllers

We are developing our own line of controllers: RageLink. Designed by our engineering team in Lyon and manufactured in our workshops in France, they range from 400 to 2000 amps of phase current, at 100V, and can be configured, updated, and locked via a mobile application. They are not yet available for sale: you can sign up for the waiting list to be notified first.