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Choosing an Electric Bicycle (EBike)

What to know when choosing an electric bike?

First you need to know all the various features electric bike manufacturers offer for their models and evaluate which suits your needs. The bike that meets your needs best is the best electric bicycle for you.

Price should not affect your buying decision. A higher price doesn’t mean it’s a better electric bicycle. As we mentioned above the bike that meets your needs best is the best electric bicycle for you.

  1. What are the regulations governing the use of electric bicycles in your municipality (age requirements, license requirements, insurance requirements, helmet requirements, area restrictions?
  2. You need to evaluate your priorities when choosing an electric bike. Is it for recreational reasons or for commuting?
  3. What kind of terrain are your traveling – hilly, bumpy, gravel roads or flat asphalt roads?
  4. How far do you need to travel on a single charge of the battery?
  5. Do you like to pedal or always use electric power?
  6. Is the size and weight of the bike a factor to consider when storing or transporting your electric bike?
  7. Is range an issue when purchasing your electric bicycle?
  8. Is the bike tough enough withstand the local environment in your area?
  9. Is easy mounting and dismounting an issue when purchasing an electric bike?
  10. Is a folding electric bike an necessary for your electric bike?
  11. How long will the battery last before I have to buy a new one?

WEIGHT: The weight of an electric bike is essential to its performance, there are also legal limits for weight(see Rules & Regulations). The heaviest parts of an electric bike is the battery, the frame, and the motor.
Manufacturers have been busy reducing the weight of these parts, and if life was ever straight forward then the lighter bikes would be the best, however, life not being so easy, there are of course swings and roundabouts. Did you expect it any other way?

Frame: Lightweight frames are always good, unless you plan to do serious off-roading where a light weight frame sometimes sacrifices flexibility and strength.

Battery: Lightweight batteries are really coming along and in the more expensive bikes will usually provide power equivalent to the uncompromising heavy batteries. Beware though as cheaper models do sacrifice power in order to reduce weight.
I explain more about batteries in a dedicated section.

Motor: Through continuous improvement and increased investment (thanks to you) motors are becoming smaller but like any of the latest technology the best ones are more expensive. Better motors will have lighter more durable materials and sometimes they will be smaller in size and weight while still offering the same power output. Lesser motors will sacrifice power to reduce weight.
The pros and cons of the most frequently used battery technologies. All batteries are recyclable.

Sealed Lead Acid (SLA)

Pros: high energy density, maintenance free, tried and tested on electric bikes, cheap.
Cons: heavy, battery cells age and eventually die, no fast charge option.

Like a car battery your lead acid battery takes a few cycles to get to peak performance, once there it should be topped up as often as possible. The reason you get a 3 year warranty with many car batteries is that they are being charged every time you run the engine and this means they rarely experience 'deep discharges'. The less full cycles you do the longer your SLA battery will last so top up when you can.

Nickel-Metal-Hydride (NiMH)

Pros: High energy density, fast charge the norm, lightweight, low toxicity.
Cons: Need interval discharges, can suffer from memory effect, performance reduced in cold weather.

NiCd and NiMh batteries are tremendously robust; they can deliver high amounts of current and be 'exercised' back to life when they start to die. As with most batteries the most important thing is to keep them topped up, however they are known to suffer from 'memory effect' or 'floating voltage'. To address this problem they need to have periodic full discharges and as they age the number of full discharges required each time increases. For a NiCd battery this period is every month and for a NiMh it is every 3 months. If a NiCd battery appears to be almost completely dead it may be brought back to health by isolating each group of cells and charging with very high currents, this should be left to someone qualified for the task.

Lithium-ion (Li-ion)

Pros: Very lightweight, very high energy density, durable, no maintenance, fast charge.
Cons: Expensive, can be unstable, cells charge and discharge at different rates.

Lithium-Polymer (Li-Po)

Pros: Lightest battery available, highest energy density, no maintenance, fast charge, proven high level of stability under extreme laboratory tests, flexible shape, low self discharge.
Cons: Most expensive,  no history of use for this application.

Lithium: No matter which type of exotic lithium chemistry is used the battery maintenance follows a simple rule: keep it topped up! A lithium battery that will perform say 500 full cycles may well perform 1,500 or 2,000 half cycles. The trick is to get a bigger battery than you need for your journey or carry the (usually small) charger with you and take advantage of 'opportunistic charging'. Reducing deep discharge cycles increase lifetime and performance over the lifetime.

THE FUTURE BATTERY

Lithium batteries are the main focus for battery R&D; there are very good reasons for this such as: high energy density (energy/litre or Kg), low weight, flexibility of application, reduced internal resistance, longer life cycle etc.

High Energy Density/Low Weight:  The honey pot of honey pots! A number of companies and universities around the world are claiming that they can increase the energy density of Lithium based chemistry by over 10 times....that would truly speed up this pending transport revolution. Prof' Peter Bruce of the University of St Andrews in Scotland is one of the people claiming success in this area.

Fast Charging: Many companies have now demonstrated technology for rapidly charging batteries, especially lithium batteries. There are products available on the market already and there are batteries designed to cope with the high currents required. Altair Nano and Toshiba have developed lithium batteries capable of taking huge currents without thermal overload. The key is the low internal resistance and without getting too technical, both companies achieve this by eliminating graphite in the porous separator and using nano particles to absorb the lithium ions.
Long Life: a bonus of low internal resistance is that an increase in longevity occurs. Battery life spans are normally related to the number of full charge and discharge cycles a battery can do before it loses 30 to 40% of it's capacity. Altairs Nano Titanate battery has now achieved over 20,000 cycles and Toshiba's has achieved 9,000. In the future you may well have to include your batteries in your will!

What exactly is an electric vehicle (EV) battery?

An electric vehicle battery is a high current battery. This is very different from most consumer electronics batteries. And the EV battery is much larger, with much more energy stored. (Do NOT test EV batteries by putting your tongue on the contacts! And do not short the terminals to see if you get a spark!)

Keep in mind that good EV batteries have enough energy to carry a 90 kg man over hill and dale for close to 20 miles. That is a LOT of energy!

A battery is not just one solid piece, but a collection of “cells". The cells are one complete unit of anode, cathode, separator, and electrolyte that produce electricity from a chemical reaction in the cell.

Each cell type (also called a cell's “metallurgy”) has a nominal voltage. For example, NiMH (Nickel Metal Hydride) is about 1.2 volts per cell and thus we need to combine a bunch of cells to get the voltage we use in an electric motor. So 30 cells gives us 36 volts (not exactly – but you get the idea) and we have a useful voltage. For comparison, Pb (Lead Acid) is 1.5 volts per cell.
How do you measure a battery's capability?

Usually, when people ask about a battery's capability, they want to know two big things:

The amount of energy stored in the battery's cells. (How far can I go?)

At what rate the cells discharge electricity. (How much power and speed?)
 
Amp Hours are the most common way to describe the amount of electricity in the cells – and all that talk about “watt hours” is really the same thing, times the voltage (Volts x Amp hours = Watt Hours). The capacity of one cell in Amp Hours is also the capacity of the entire battery in Amp Hours. One 7 amp cell is 7 AH at 1.2 volts. If you need 30 of them to get your required voltage, you still only have 7 Ah in usable energy – at that voltage.

To put this another way: More Amp Hours means you can go farther, at higher speeds and up bigger hills. But more Amp Hours usually costs more money, and weighs more.

Max current means essentially “How fast can the cell discharge energy?” Think of it as a can full of water. The can is the cell, the water is the electricity – the larger the cell, the larger the amount of water – and the water flows out of a hole in the can. The larger the hole, the faster the water can come out. In terms of a battery, if the discharge (the hole) is not big enough, then the motor may not be able to get enough energy (the water) to function at max performance.

You could also think of the max current as “how big the fuel line is".

Some people will describe max current in terms of max amperage that the cell can endure and for how long. Another way is to describe it in terms of “C”, or “at what rate can the battery be discharged for one hour = 1C. An example is: If a battery can be discharged at a 10 amp draw and will last for one hour, than it is a 10Ah battery at 1C.

What are some problems with battery construction?

Most consumer electronics battery applications use a tiny handful of cells. For example, a cell phone battery could be 3.6 volt, three NiMH cells in a battery inside a plastic case. In EVs, there are usually more than 30 or more combined cells. Each cell is connected to another with a small tab of metal called a “connector.” Each connector is a potential point of mechanical failure, and a small resistor.

Large packages of cells also create heat problems. A cell buried inside of several layers of other cells has no way to easily shed heat developed during charging or discharging. Heat leads to failure, diminished performance and longer charging times.
 
What are the solutions?

Each battery type has different capabilities, needs, and limitations. So, very careful engineering tailored to the type of battery being used is needed.

There is a trade off in terms of cost, weight, capacity, system complexity, and safety involved in all battery engineering choices. All of these factors must be brought in line with one another to create a safe, sound solution.

A big part of preventing catastrophic failures (like the kind that burn down houses) is a “battery management system". This BMS component is what prevents the cells from over-discharging, overheating, charging incorrectly, and other things that could cause problems. The BMS also manages cell charge and discharge to get optimal performance and life from the battery package. Physically, this is a printed circuit board with a complex and often IC-controlled circuit.

N.B. You may have recently heard through the media of ‘exploding batteries’ on laptops and spontaneous combustion of mobility vehicles. These have been caused by instabilities in cheaply made batteries built without fire-preventative systems. If you want the benefits of a Lithium or Lithium-ion battery it is advisable that you do not try make your purchase decision on price alone. It is important that Lithium batteries are supported by a battery management system which regulates each Lithium cell individually and maintains the stability of the chemicals, charge and temperature.
You can tell if a Lithium battery has a battery management system because it will have multiple connections to the controller and will most likely slot onto the connections rather than using a cable. The management system may either be in the battery or in the charger.

ELECTRIC MOTOR

Electric motors, both AC motors and DC motors, come in many shapes and sizes. Some are standardized electric motors for general-purpose applications. Other electric motors are intended for specific tasks. In any case, electric motors should be selected to satisfy the dynamic requirements of the machines on which they are applied without exceeding rated electric motor temperature. Thus, the first and most important step in electric motor selection is determining load characteristics -- torque and speed versus time. Electric motor selection is also based on mission goals, power available, and cost.

The Brush DC Motor

The brush or standard motor is the original DC electric motor. They normally operate at higher speeds than brushless motors and therefore need internal gearing to reduce these speeds to those legally allowed for electric bicycles in the UK. Because of this the Brush motors usually provide more torque (turning force – quite useful for a bike!) at these lower speeds.
The motor is coupled through the gearbox to a free-wheel attached to the outside shell. The entire hub then rotates on roller bearings.
The bearings which a motor and gearbox run on are vital- they are going to get a lot of abuse, and no maintenance.

The Brushless Motor

These motors are usually a hybrid between an AC and a DC motor, sometimes they are referred to as ‘hall effect’ motors.

The newer brushless motors are constructed in a reverse fashion from the traditional form. The rotor contains a permanent magnet and the stator has the conducting coil of wire. By the elimination of brushes, these motors offer reduced maintenance, no spark hazard, and better speed control.

So there are advantages of each type of motor with the brush motor better able to cope with higher speeds and torque requirements and the brushless motor offering reduced maintenance and better speed control.

If that all sounds vague maybe it will help if I point out that torque is very important for electric bikes and most of the expensive electric bikes use brush motors. Brushless motors are cheaper to produce and adequate in most cases.

Why A Hub Motor?

With electric assisted and electric powered bicycles, scooters and motor cycles selling in the millions of units world wide – most of them using hub motors – hub motors have progressed from a curious way to power an electric vehicle to a mass produced drive train of considerable importance.

For electric bikes, the advantages of a hub motor are:

1. The motor is in a space that is not otherwise used in the conventional designs of bicycles.
2. The motor can be installed without significant changes in the frame or the ordinary configuration of the vehicle.
3. Hub motors are simple and self-contained, thus reducing overall cost of the vehicle by enabling the designer to use off-the-shelf parts and designs for their vehicle.
4. The motors are sealed and mostly maintenance free.
5. The motor is directly attached to the driven wheel, improving efficiency.
6. The centre of gravity is relatively low, improving balance.
7. It looks nice!

The Drawbacks of Hub Motors?

There will always be drawbacks with the design of anything.
For hub motors, the drawbacks are:
1. The cost is higher because the motor is more complicated than other kinds of electric motors.
2. Because the motor is sealed against water and dirt, getting rid of heat that the motor generates while turning can be a problem, luckily many controllers monitor motor temperature.
3. The wheel is heavier with the addition of the motor.

THE CONTROLLER

OK you will probably never have to see the controller (at least I hope you do not buy an electric bike where you need to) but it is such an important component and the performance and the longevity of the electric bike depend on it. It is best to think of it as the brain of the machine!

Simple controllers just act as a gateway for a signal between the pedals or the throttle, and the resulting supply of power from the battery to the motor.

More complex controllers carefully assess a varying array of rider and environment data to optimise the performance, increase the safety and the life of the bike’s components.

Controllers use the systems voltage and current to regulate speed and range.

Generally speaking  an electric bike with a higher voltage can supply a higher current. This means that the bike will offer more torque, acceleration and speed. However a higher current will drain the battery faster and here we really get into more swings and roundabouts: if the powerful (and more useful) electric bikes draw more current they need larger (and heavier) batteries to have a practical range.

It is a fine balancing act and the quality of the controller really does make a big difference to the performance of the electric bike. The best way to judge is to ride.

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