What is an eBike Speed Controller? and How Does it Work

EBike rider’s look at the handlebar display and think that it is the “controller” for an eBike. Unfortunately that’s not the case. The display is exactly that – it just shows you what’s happening with the bike.

In short, the speed controller, also called the “controller” or “motor controller”, is the brain of your ebike power distribution. The primary function is to control the electric power flowing from the battery to the motor. The controller also connects the other features of an eBike like the brakes, throttle, pedal assist, speed sensor, lights and various other sensors together and is basically the heart of the eBike.

What is a Speed Controller on an eBike?

A speed controller on an eBike is an electric circuit that controls the electric motor speed and serves as a dynamic brake. The controller uses power from a battery pack and drives it to the motor. Different speed controllers are used based on motor type. On an adaptive eBike, conversion kits are used, and the speed controller is the main component.

The speed controller sends signals to the eBike’s motor in various voltages. The signals detect the direction of the rotor relative to the starter coil. Purpose-built eBikes use Hall effect sensors to help detect the orientation of the rotor. In an adaptive eBike without such sensors, the electromotive force of the undriven coil is calculated so the sensors can detect the orientation of the rotor. (Source)

Some controllers can even be adjusted with the aid of a USB connection and a computer. You can adjust the limit on speed, torque, disable or enable pedal assist, and configure the power limits.

What are the Main Features of a Speed Controller?

As mentioned above, the main function of the speed controller is to tie all the electrical components of the eBike together into one cohesive unit. The speed controller also offers protection in several aspects. It can protect battery voltage by continuous monitoring. It will shut down the motor when the voltage sags to the cutoff level, which protects the battery from over-discharge.

The speed controller also protects against over-voltage. It will shut down when the battery reaches full charge. Temperature protection is also a feature of the speed controller in that it will monitor the temperature and shut down the motor when it becomes too hot. Brake protection is also a feature. The speed controller will always prioritize the brake, so if you push the brake and throttle simultaneously, it will perform the braking function.

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What Are the Different Types of Speed Controllers?

There are 3 different eBike Speed controllers: DC Motor Controller, brushless DC Motor controller, and BLDC motor controller with Hall sensors.

Brushed DC motor controllers

Feature permanent magnets that aid the controller. These controllers have a simpler design in that a set of keys change the current supplied to the motor. This type of controller is most common on smaller electric vehicles like bikes, scooters, and pedalecs.

Brushless DC motor controllers

Often abbreviated BLDC motor controllers, are used on brushless motor setups. These feature permanent magnets are reliable and efficient controllers. This type of controller uses a set of keys and 2 or more transistors per phase (most have 3 phases).

BLDC controllers for motors with Hall sensors

The final type of speed controller. A Hall Effect sensor is based on the Hall Effect, which determines the position of the rotor according to a stator. The stator is a fixed part of the motor while the rotor is the rotating portion. It determines speed and other attributes very efficiently and accurately.

Because the Hall Effect Sensors are for brushless motors, they serve to ascertain when to move the rotor again after a rotation.

How Do I Choose an eBike Speed Controller?

Several factors should be considered when deciding on a speed controller for your eBike. First, check the controller voltage and power. You will want to make sure the speed controller works with the battery and motor.

If you purchase a non-programmable controller, you must ensure the control voltage matches the motor voltage. The power of the controller should be the same or slightly higher than the motor power. For example, if the motor voltage is 24-volts, the speed controller voltage should also be 24-volts.

If you have a programmable speed controller, the power can be limited as needed, so you can match the voltage of the controller to the motor and battery voltage.

You also want to check the controller’s current rating. It should be lower than the battery output current. Ensure the phase and battery current of the speed controller. The phase current connects to the motor and can be higher than the battery current. (Source)

One of the best options for your eBike is to purchase the controller as part of a kit, if you are adding the setup to a bike. This way, the controller comes with the motor and is already set up for use with that motor. This is the preferred method for beginners as it is much less confusing.

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What is a Good eBike Controller to Buy?

As mentioned, you can take the guesswork out of buying a speed controller if you buy a conversion motor kit. One of the best on the market is the Bafang 750-Watt Mid-Drive Kit.

If you’re building from a Bafang kit the controller is located inside the motor housing. This make for a nice clean installation on your bike.

If you simply need a controller for your existing motor, you will need to do some research on what is compatible with your motor and battery setup. Amazon is a pretty good source for finding a controller for most eBike kits. Remember to check the motor model, voltage and wattage.

Finishing Up

As we have learned, the speed controller, or simply controller, is the heart and brain of the eBike. You want to ensure your speed controller operates seamlessly with your motor and battery’s capabilities. The best option to ensure this is to buy a kit with the motor and controller already together. This will ensure they work together well, and you have the best experience.

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