E-bike Controller: the newest ‘essential’ component

The e-bike controller is a new addition to the group of core components making up the modern bike.

Traditional bikes don’t have them—but all the rest do. And controllers are central to making e-bikes work the way they are intended, or simply work at all!

E-bikes vs EVs and “M”-bikes

Speaking generally, as the EV revolution unfolds we see a contrast between electric cars on one hand and their two-wheel counterparts on the other.

Electric cars are way simpler than the combustion machines they’ve replaced in the sense that they incorporate fewer moving parts.

Bikes have become more complicated, not so much because of the slight increase in the number of components and the high-tech nature of those components.

Bike frames are durable and reliable (unless they’re carbon and you crash them); hubs keep on going (as long as you choose a decent wheel set); headsets are easy enough to service or replace.

The big change is that, in the growing numbers of mid-drive powered e-bikes, you no longer have a bottom bracket (which takes care of the press fit vs threaded debate once and for all). You have, rather, a motor module where the crank bearings and spindle now reside, a module that often includes a transmission which, in turn, eliminates both front and rear derailleurs. 

The key additions to the component set in sum are the a battery, the motor—and the controller. 

E-bike Controller – General Issues

At the most basic level, a controller takes the input from the battery and the input from the rider and determines the level of power to input to the motor.

If the e-bike controller is one amongst several equally important components, there is a case to be made that it is the most significant.

This is because an e-bike is an electrical system and thus requires a device to regulate how much current is allocated to each component and for what duration of time.

Calling it the “brain” of the e-bike which many in the industry do, is probably going a bit far. Yet it does posses brain-like functions in the form of algorithmic (think of them as ‘neural’) processes that regulate vital functions in the electrical system.

Types of Controllers 

A common model is the standard battery-mounted controller that includes a circuit board and a bunch of Metal Oxide Semiconductor Field Effect Transistors (Mosfet for short).

Another common controller is the ‘box’ type which is typically used for a hub motor. 

Mid-drive motors incorporate their controllers into the body of the motor itself.

Function of the e-bike controller

How does an e-bike controller actually work?

For most of us, even seasoned bike mechanics, the controller is a black box—you don’t need to know exactly how it works in order to deploy it, unlike many components on a conventional bike, the derailleurs for one.

Briefly, then, inside a controller is a circuit board. Sensors and firmware match voltage and amperage input and output and then distribute that current to the various components such as the motor.

Where there’s a throttle, turning the throttle sends voltage to the controller and then on to the motor. Input from the brakes is also important here since applying the brakes cuts the power, a function coordinated by the controller.

Let’s take a close look at an early controller developed at First Components to get a better idea.

The FIRST Components Controller

This particular controller was developed to work with a front or rear hub motor and includes an optional bottom bracket that enables calculation of torque. 

In other words, like all controllers, it was designed to work in a certain context and includes a limited range of functions that are designed to be fit to purpose—that is to work with whatever hub motor a manufacturer or authorized electrical technician will fit, retro-fit, or replace in a particular e-bike.

Knowing what you are doing gives an end-user or a bike shop the ability to mix and max components, which comes with a warning though.

Over the decades it’s been possible to substitute branded components for own-branded or alternative brand parts (which has been a large part of FIRST Components’ business over the years). 

Mismatch amongst components is a matter of mechanical incompatibility where often the worst that can happen is perhaps a little clunky shifting. Compatibility of electronic components, though, is crucial because the potential for fire. The point is that the level of knowledge and experience is a good deal higher for e-bikes compared with m-bikes where knowing which combination of components belong together is paramount.

Looking at this controller’s functions from top to bottom, there’s firstly the throttle control or “handlebar mounted speed adjustment” as we label it on the internal documentation.

Because this controller is designed to accommodate a hub drive, the handlebar throttle is an essential component. The speed sensor on the bottom bracket does allow for a pedal assist function as is standard with mid-drive motors. The optional accessory is the brake signal that activates during braking. 

The control panel connector allows linking to a display unit of some kind—any kind of hub motor and display unit or ‘computer’ can be connected. This unit originally shipped with a basic display (which would still be fine on entry-level models). But given the rapid advances in display design, function, and battery life, adding a third party’s unit is probably the best idea.

The BLDC Hall Sensor lets a controller know the position of the motor’s rotor in BLDC motors which lack brushes. It’s a solid state unit, highly resistant to extremes of humidity, dust, temperature and vibration. Without getting into the nitty-gritty of electrical engineering, the data it provides is essential for a brushless motor to run.

Does a controller determine an e-bike’s performance?

Not the controller by itself, although it is certainly a key component—performance is determined by the interrelation amongst a number of variables.

The two key variables in e-bike performance are power and torque. Power is defined as energy over time and is measured in watts, a measurement further subdivided into continuous and peak power output. 

A key classification of an e-bike motor is the wattage with motors ranging from 250 watts, 350, 500, 750, and even 1000. It is what the motor can continuously sustain without overheating. Watts are the product of volts and amps. Most e-bike motors are 36, 48, or 52 volts, with 48 and 52 being the most common.

Peak power is the voltage of an e-bike multiplied by the amps of a controller; most controllers are 15-20 amps.

Torque is the level of rotational force when power is applied and is measured in newton-meters.

The way to calculate peak power is to multiply the voltage of an ebike by the amps of the motor controller. Although most e-bike brands don’t make the number of amps of their motor controller clear, most will be around 15-20 amps. Doing the math, a 36 volt e-bike with a 15 amp controller will deliver 540 watts of peak power. If the controller is 20 amp, then peak power will be 720 watts.

A controller only determines an e-bike’s performance insofar as it coordinates all these variables—the outcome of that coordination is what we refer to as “performance”.

Remove or Replace Controller

Whether or not this is possible depends on the type of controller your system is running and how complex that system is. 

The key theme of this article is that when it comes to e-bike electronics, you need to know what you are doing and be confident in your level of knowledge. Otherwise, leave it to your e-bike shop professional.

A controller such as FIRST Components’ controller is straight-forward: ensure that the connections are reconnected in the order they were disconnected.

Before you remove the controller, take some images and even record the removal on video as well. That way you can be sure of which plugs go together and you can simply reverse the order of disassembly.