Tech behind Electric Bikes

Electric bikes are now common. That's nice from a consumer’s point of view, but with so many machines available, it can be difficult to choose the right model.

Most consumers want an e-bike that will accommodate its motor without being too cumbersome and will remain stable in spite of its electronic components. Some consumers want only the most basic of e-bike features, including lights, a cargo rack/basket, and a water bottle holder. Others are focused more heavily on safety features, such as brake type. And still others are concerned with convenience and portability.

Advantages of Electric Bikes

An electric bike can be a godsend in many situations:

• Electric bikes provide a convenient mode of transportation for busy people who are towing a buggy full of children or picking up a few grocery items.
• Electric bikes are a green alternative to driving a vehicle. Studies show that the average car speed in rush hour traffic can be as low as 18 to 20 mph. Electric bike speed can be as high as 15 mph. With an electric bike, you can reduce pollution, improve fitness, and still arrive at the same time as your car-bound colleagues.
• Electric bikes offer the chance for those with low lung capacity (the people who suffer from asthma, for example), or a reduced fitness level to get out and enjoy the countryside. Even those who are moderately fit can appreciate some assistance when going up hills.

The economic advantages of owning an electric-bike should be considered too. The annual cost of driving a new family car is about $9,000 per year, on average. Running an electric bike costs around $400 per year. And while filling a gas tank costs around $30, recharging an electric bike battery costs only about 50 cents. A tank of gas may get you further, but not 60 times further!

How does an electric bike work?

The basics of an electric bicycle are simple. The electric motor propels it, the power is supplied by a battery, and speed is controlled by a throttle. Although not all electric bikes have a throttle. The difference lies in the arrangement of the components and what assistance they give.

The first electric bike was just a normal bicycle with an electric motor and a battery fitted to it. Kits are still available today that allow you to create this configuration. As electric-bikes became more popular, dedicated models were developed. Most of them still look very much like ordinary bicycles, but now they're built with the motor and battery as an integral part. Today’s electric bicycles are better balanced and more efficient than ever before.

The Technology: The motor

There are three different types of e-bike motors available: brush motors, brush-less motors, and friction drive motors.

Brush and Brush-less electric-bike motors

Brush motors are common because they're durable and rather inexpensive to produce. However, modern brush-less motors are lighter, smaller, and more powerful than brush motors, and they can be almost silent. E-bikes with brush motors cost more, but they require no maintenance. As a result, most electric bikes now have a brush motor.

Friction drive e-bike motors

In a friction drive motor, a small, solid wheel rotates against the side of the tire in order to drive it. The first motorcycles used the same concept, with a motor mounted above the front wheel. The drive rubs at the side of the tire is problematic. It's inefficient, and it quickly wears the sidewall away. Tires need to be replaced every couple hundred miles. For this reason, electric-bikes with this type of motors are not seen anymore, or rarely seen.

Location of the Motor on an Electric-bike

An electric bike’s motor is fitted to one of three places: the front hub, the crank, or the rear hub.

Though rear-wheel versions are available, most e-bike conversion kits are for the front wheel. They are easier to fit. However, they do change the balance of the bike, and brakes should also be up-rated to cope with the additional weight.

Mid-mounted crank drives produce the most bicycle-like feel, because the pedal crank turns and drives the chain, just like when you pedal. Crank drives are efficient at transmitting power, which makes them popular, especially for fast, off-road electric bikes.

Rear hub motors are also popular. Some owners suggest they make the back of the bike feel a bit heavy, but balance is still good. In many ways, this is rear-wheel drive like you get with a scooter or motorbike. The rear hub looks larger than usual, but in profile, it looks much like an ordinary bike.

Electric-bike Motor Power

Motor power varies and can be restricted depending on whether it's used on- or off-road. A typical electric motor for a road bike will deliver between 250 and 600 watts.

Torque is a consideration, but actual figures are rarely quoted by electric-bike makers. Owners will frequently comment on whether their electric bike offers plenty of torque or lacks it, but these comments need to be taken in context. Road conditions, as well as the weight of the rider, have a big impact.

The Technology: The battery

Lithium-ion batteries are almost invariably used in e-bikes. Though they cost more than nickel-cadmium batteries, they produce more power from the same size unit and remain efficient for longer.

Around 90% of electric bikes are powered by standard lithium-ion batteries, but there have been further developments in the technology. These developments include lithium-ion polymer batteries, lithium manganese batteries, and lithium cobalt batteries.

• Lithium-ion polymer batteries have the same electrical properties as standard Li-ion batteries, but the material can be shaped more easily. There's the potential for some interesting designs, though we've yet to see them.
• Lithium manganese batteries are used in the latest Nissan Leaf electric car. It's claimed they generate more power and last longer. The new Leaf has double the range of its predecessor, but we've seen these batteries in very few (and very expensive) e-bikes so far.
• Lithium cobalt batteries are said to be lightweight while offering a great range, though they are not commonly used.

Battery charging and battery life expectancy

Charging an e-bike battery is simple; it requires nothing more than a household outlet.

The time or distance an electric bike battery will run between charging is hard to judge with much accuracy. There are too many variables: terrain, speed, rider weight, bike load, and more. However, it can be made a few generalizations about an e-bike’s recharge time and overall working life. These generalizations should be used for comparison purposes only.

• Cheap batteries are available, but they can take six hours or more to charge and have a life of around 500 charges.

• High-quality batteries charge in two to four hours and can last through approximately 1,000 charging cycle.

The Technology: The Throttle

A few electric-bikes use levers much like you'd find on some lawn movers. Some just have a button, but most use motorcycle-style twist grips. These give a positive feel and more precise control.

Notably, quite a few electric bikes have no throttle at all. Instead, sensors judge the effort required for pedaling and, at a predetermined level, the motor kicks in. The important thing to note is that these are “assisted pedaling e-bikes,” also known as pedelecs. They help you out when the going gets tough, but they do not supply constant power.

Choosing your electric bike

No e-bike is perfect for every situation, so you need to think about what you'll use it for most of the time. Will you use your e-bike for commuting and/or shopping? Leisure rides? Serious off-road?

You'll also want to ask yourself a few other questions. How far do you plan to travel on your e-bike? Will you transport it to a destination in your vehicle, or will your trips always begin at home?

Do you hope to get some exercise with your e-bike, or do you want a full-time electric drive? And do you want to buy an e-bike that provides trip information and journey feedback?

How far can you go on an e-bike?

In terms of how far you can go, there's a big difference between a pedelec (pedal-assisted electric bike) and full-time electric bike. If you're prepared to pedal and only need help on hills, you could get anywhere from 50 to 100 miles on a single charge with the former.

If you're going for a full-time electric bike, the distance you travel on a single charge will be reduced considerably, though it's difficult to offer precise figures. Manufacturers will quote anywhere from 20 to 40 miles while simultaneously using phrases like "in ideal conditions."

Whether the terrain is flat or hilly impacts the distance you can travel, as does the weight of the bike, your own weight, the gearing available on the bike, and how much juice you give it. We suggest that a distance of 10 to 20 miles is a realistic expectation. Of course, if you're prepared to do at least some pedaling, you can extend that dramatically.

A Note about Regenerative  Braking

A few electric bikes incorporate a technology that started in race cars: regenerative braking. When you brake, you create energy. That energy can be harvested and fed back into the battery, prolonging its life. Regenerative braking is only just being introduced to e-bikes, but it's certainly something to watch out for.

Which e-bike features matter most?

There are e-bike styles to suit all tastes, and it's nice to have a lot of choices when shopping. Here are a few features you might wish to consider when selecting an electric bike.

• Gears: An electric bike with multiple gears is easier to pedal and can reduce the drain on the battery.
• Size: Some electric bikes look a little small, but if you're going to drive to the edge of the city and ride the last couple of miles, a light, folding model that you can easily throw in the trunk has definite advantages.
• Foldability: Not all folding e-bikes are small. Some full-size electric bikes with standard 26-inch or 27.5-inch wheels can be folded to fit into compact spaces. Make sure you’re aware of a folding bike’s weight before you buy it, though. “Foldable” doesn't always mean light.
• Frame: Bike frames are usually made of a lightweight aluminum alloy, but magnesium alloy and carbon-fiber composites are available (though not common). Reduced weight helps extend range.
• Seat: What is the seat like? If you're going to spend much time on your electric bike, a good seat with padding and springing adds comfort.
• Trip Computers: A trip computer gives you all kinds of feedback, from speed and distance traveled to battery status.

• Riding position: You also may wish to check out an e-bike’s riding position before investing in it. For short trips, the riding position might not make much difference, but for long journeys, the upright "Dutch" style with pulled-back handlebars is very comfortable – particularly for tall riders. The same goes for mountain bike styles, though these bikes are not often designed to actually go off-road.

• Brakes: Caliper brakes (the type found on ordinary bicycles) are common on e-bikes, but disk brakes offer better stopping power. In wet conditions, however, initial braking can be slowed as you first clear water from the disk. It's a minor thing, and you soon get used to it.

• Batteries: Battery packs can be fitted in all kinds of different positions, but often, they are fixed to a rack behind the rider. If you plan on carrying anything, this configuration could be problematic.

• Lights: Good e-bikes integrate lights into the power circuit so you don't have to worry about separate batteries.

• Tires: Some e-bike tires are reinforced. They last longer and reduce the chance of a flat.

• Weight capacity: Most electric bikes quote a maximum weight capacity. This is important if you are larger than average.

Source: Orlando Sentinel