In this page I explain how an electric bicycle is made and how it works using mine as an example
In the picture above I have circled the three most important parts of the bike:
- Battery and controller case
Let’s start with the handlebar
Here you see:
- A. Ebike computer. It gives me several information about the bicycle like battery voltage, external temperature and temperature of the battery, speed and distance travelled. I describe the computer in this posts: https://jacklithium.wordpress.com/2012/07/12/e-bicycle-computer/ and https://jacklithium.wordpress.com/2012/07/19/electric-bicycle-computer-version-2-0/ . An alternative with similar functionalities to what I am building is already commercially available (and has been for a few years) and it’s called Cycle Analyst.
- B. Throttle and state of charge indicator. This is how I accelerate the bicycle giving the input to the motor to move forward. In the photo above, the state of charge indicator is off because the motor controller is off. The state of charge is just an approximate way to determine if the battery needs to be recharged or not. This is the indicator with the controller turned on:
- C. Watt meter. This is a meter that gives me several informations. I can see the battery voltage and the instant Amps drawn from the battery. But most importantly It displays the AmpsHours and WattHours used. This means being able to calculate or to have a rough idea of the energy/range left on the battery. At the moment I am using the Watt meter as a reference for my bicycle computer.
- D. Li-ion battery used to power my e-bike computer.
Next is the battery and controller case:
- Battery. This battery is made with 120 Li-Ion “18650” laptop cells. I’ve build this battery myself using dead laptop batteries. You can find out more about the battery building and a video on these pages: https://jacklithium.wordpress.com/2012/08/08/dead-laptop-batteries-to-e-bike-battery-video/ and https://jacklithium.wordpress.com/2012/05/17/transform-dead-laptop-batteries-into-a-reliable-e-bike-battery/. The battery is 36v 24Ah nominal.
- Controller.The controller’s main task is to transfer power from the battery to the motor using the signal provided by the throttle. Controllers generally have many other features like LVC ,Regenerative Braking and Cruise Control. LVC means low voltage cutoff; if your battery drops under a certain voltage the controller stops working in order to protect your battery from being over discharged. Regenerative braking is the possibility to recover the kinetic energy of the motor and put it back into the batteries. This function is not available for geared motors (like the one I am using on my bicycle) due to its mechanical characteristics. The controller I am using is rated 36v 30A (but it can take up to about 60V due to the capacitors that are rated for 63v max). In my case I am using a small amount of power and the controller gets barely warm after a ride. If you plan to “stress” the controller using a lot of power it’s strongly suggested to keep it outside the battery box where it can get fresh air and cool down quickly if necessary.
- Key Switch. I used a key switch to turn the controller (and the whole system consequently) on. This is a feature that is implemented on most e-bike controllers. I could have used a simple lever switch but that would have made the bike available and ready for anyone who wanted to steal it.
And lastly the motor!
I am using a brushless rear hub geared motor. This means that the motor is in the wheel and uses a planetary system (good explanation and images here: http://en.wikipedia.org/wiki/Epicyclic_gearing), also the motor is without “brushes” and this reduces the maintenance of the motor to a bare minimum.
Hub motors are very simple to install and save a lot of room being inside the wheel and not on the bicycle frame.
In this image you see the wires coming out on the right side of the axle.
Details of the axle and motor wires
The wires go into the battery and controller case and are connected to the controller.
Some technical data:
|Motor||Bafang geared hub 500W brushless|
|Controller||36v 30A sensored with sensorless option|
|Battery||Li-ion 10s12p – 36v 24Ah|
|Max speed||32 kph / 20mph|
|Range||50 to 70 km – 30 to 45 miles|