It's been almost 10 years since E bikes started arriving on our streets. Those particular bikes are quite useful, they offer a modular pedal assist to ride at reasonable speed without too much effort on your end, even in the steepest hills. They're aimed at people who ride their bike to school or work everyday, the commuters. But you're curious and you're asking yourself "how do those bikes work and what are the differences between them?"
Let's have a look at the basic operation of an E bike. The main architecture of an electric bike is made of a battery, a motor, a control unit, sensors (pedal sensor, brake sensor...) and a user interface (LCD screen, control button...)
Basic connexions diagram:
The battery gives energy to the control unit (red arrow), the latter will distribute it according to the needs. The battery also sends data regarding its level of charge. The control button will allow to select between levels of assistance (eco, normal, turbo...), the control unit will then adapt power sent to the motor to reach the corresponding speed. The data loop coming from the motor allows to actively adapt speed. When the pedal sensor is activated, the motor is on; when the brake sensor is activated, the motor is off. A torque sensor can also be found on some bikes, it allows to adapt power delivered by the motor in regard of the power transmitted through the pedals by the cyclist. In the same way, a speed sensor (located mostly on the wheel) detects the speed at which the bike goes and restrains the assistance to go under 25 km/h. Finally, the LCD screen will display data such as the level of assistance you're in, the level of charge left, speed...
The legislation regarding E bikes' power and max speed is different between each country. In France, speed is allowed up to 25 km/h with a 250W motor. In Europe, some countries allow the speed to go up to 45km/h and with a power over 250W. However in France, such bikes are considered as mopeds and require a licence plate and insurance.
different types of motors:
- In the rear hub, with the option to activate the assistance without pedaling. The wheel is directly spun by the motor.
- In the front hub, based on the same principle as the rear hub motor. This system is less common however.
- Mid drive, in the bottom bracket area, the most common. The pedal sensor is directly integrated in the motor unit and the assistance is necessarily activated while pedaling. The motor shaft is linked to the cranks, which then transmits power to the chainring and to the chain and finally to the wheel. Among the biggest motor manufacturers:Bosch, Panasonic, Bafang, Shimano or Yamaha.
The battery is mostly hidden in the downtube and can be removed or not, to ease charging. A removable battery allows you to leave your bike in the garage while you go upstairs to charge the battery. A fixed battery grants more security; it'll be harder to steal or deteriorate. It's characterized by its energy (the power it can deliver during a certain time), in Wh (Watt hour). A battery with an important capacity (bigger capacity=longer autonomy) will have an energy around 400 Wh; a battery with around 200 Wh will not last as long. However, the autonomy of a bike is fairly dependant on the way you use it. For instance, a 200 Wh battery can last as long as a 400 Wh one if you ride in a low assistance setting as well as on flat terrain.
If you don't own an E bike, it's possible to convert your bike in an electric machine. Numerous conversion kits are available, they contain all the necessary elements (battery, motor...). The integration will not be as sleek as if your bike was originally electric.
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