How an E-bike Works - Simplified
History & Background:
The most common wheeled transports worldwide are bicycles, both electric and non-electric, with almost a billion sitting and rolling across the globe. Annual worldwide sales exceed 50 million e-bikes, and in the United Sates, annual electric bicycle sales are approaching 1 million. Why not ride with a motor?
Since the late nineteenth century, bicycles have provided two-wheel mobility that allows the rider to “get there” quickly and easily. Compared to feeding and caring for a horse, the bicycle cost was less than 10% of the cost to feed the horse. The bicycle replaced the stagecoach as the popular transport, resulting in mobility for the masses. Preceding the bicycle was the three wheeled trike, first invented clear back in the 1700’s.
Many innovations in transportation have occurred from bicycle roots, including ball bearings, spoked wheels, pneumatic tires, and others. Bicycles proceeded automobiles, providing technology to another newer mobility family member. Electric motors proceeded their gas-powered cousins by fifty years (1830’s vs. 1880’s). The total battery weight that powered the motors held back early electric transport growth.
Today’s popular electric bikes are equipped with the electric motor, battery, controller (CPU) and display. Most of the other components are the same or similar to a non-motorized bicycle. Brakes on an e-bike may have a slightly larger rotor to assist with braking performance, since a higher average speed and overall bike weight is common on an e-bike. The additional bike weight is easily overcome by the motor that propels the bike and rider forward.
Bikes and trikes today are used for both work and play - recreational rides, athletic training, commuting to work, delivery tasks, and more.
At the heart of current electric transport technology are the batteries. Energy stored in the battery cells powers the motor(s) that turns the wheels. Today’s lithium-Ion battery cells offer a very good cycle life, leading power to weight ratios, and have proven safe in contained environments (battery cases). That is why Li-ion batteries are the most commonly used batteries for e-bikes and electric cars, with a very high energy density per pound and self-discharge rate much lower than many other battery types,
Lithium-ion is in its golden age. The cells do not require maintenance and are free from the “memory effect” that goes with lead-acid batteries. Li-ion battery packs are usually monitored by a battery management system (BMS) that takes care of ensuring long battery life, balancing voltage between different Li-ion cells, and protecting the battery from over-charging, over-discharging and over-temperature conditions. The BMS is a small circuit board inside the battery cell case. Research activity on new battery technology is at a fervent pace, with promising developments that will deliver range and lifespan improvements.
Battery capacity on e-bikes is typically rated in Amp hours, where volts times amp / hours yield a watt hour rating. As an example, a 48-volt e-bike with a 15-amp hour rating will yield a 620-watt hour battery. A conservative user of power riding an e-bike will consume roughly 20-watt hours per mile, so this battery size would yield a 31-mile range. Longer ranges are possible using more leg power, running the motor on lower assist levels and with less throttle, or even riding a while with no assist. Many e-bikes have larger capacity cases optionally available, or the rider can carry a second battery on the bike rack to double their range. Electric cars haul more weight, and their battery packs are rated in 1000's of watt hours (kilowatt hours). For instance, the Chevrolet Bolt has a 65 kilowatt hour rating and an estimated range over 200 miles.
Electric E-bike motors power the bike and move it forward. Electric motors have been around since the 1800’s. They are rated in watts – typically the more watts the more power. Larger vehicles, such as electric cars and motorcycles, again rate their power in kilowatts (1000 watts). E-bikes have motors from a variety of worldwide suppliers in various wattages, and are either hub motors or mid-drive motors. E-bike wattage sizes in the U.S. vary, but are commonly, but not exclusively, 250, 350, 500, 750, and 1000 watts. Electric motorcycles have larger wattage motors, starting at 1500 watts, and the aforementioned Chevy Bolt - 150 kilowatts.
Many states adopt a system that may limit e-bike motor sizes when in use on bike lanes, paths, and streets. It is currently a 3-class system, with 750 watts being the highest motor size allowed. Imagine if they limited the motor size and speed on autos, rather than placing the responsibility on the driver. Imagine ...
There are two primary types of e-bike motors — hub-drive motors and mid-drive motors. Hub drive motors are typically located on the rear wheel hub, while mid-drive motors turn the crank arm on the crank set. On three-wheeled electric trikes, the motor is typically placed in the front hub. Which is better, hub or mid-drive? Both have a place, feel slightly different, and have different characteristics, with pros and cons for both. Most riders become accustomed to whichever they have.
Electric Motor Assist:
E-bike motors can be activated in two ways — with a throttle or by pedaling. A throttle mode e-bike works similarly to motorcycles and scooters — it has a little throttle mounted on the handlebar. Think of the throttle as a connector between you and the bicycle electronics. When you activate the throttle, it drives power and moves the bike forward, without you needing to pedal. There are three types of throttles: twist, thumb, and push button. They all get the same work done; the only difference is the way you engage with it.
A throttle makes it easier to get the bike moving from a standstill, such as at an intersection with a traffic light. You can cruise along your route without the need to pedal. The downside of a throttle in conjunction with a powerful motor is that they can be legally classified as mopeds or motorcycles, thus needing a license plate, compulsory insurance and the rider wearing a helmet (based on state and city requirements).