How To Determine Which Type of Electric Bike to Buy?When you go to buy a bike, you will find that you have a choice between mountain bikes, road bikes or hybrids. But which bike makes the most sense for you?
Decide what you want to do with the bike. Where do you want to ride? How often? Is comfort a top priority, or is performance more important?
Buy a mountain bike if you want to ride off road. Mountain bikes also make great city bikes. If you don"t plan to ride off road, simply switch to smoother tires.
Buy a road bike if you want to go fast, and if you only ride on the pavement. Road bikes are light and efficient, but people who don"t ride very often generally find them uncomfortable.
Buy a hybrid if you want the upright, comfortable riding position of a mountain bike, and the efficiency of a road bike. Hybrids are great for city riding, commuting, and light trail riding.
Consider a one-speed cruiser for a quality low-cost, low-maintenance bike. Cruisers are great for running errands and getting around a college campus. But watch out for long hills!
Buying Guide For Electric Bikes
There are so many electric bikes on the market now that it can be difficult to choose between different brands and different models. To add to the confusion many of the electric bike brands have bikes that look identical and have very similar specifications but with widely varying prices.
So how do you choose where to spend your money and ensure you get what you expect?
Most of our customers shop around before coming to us so we have learned a lot about what customers look for and what they expect. We also know that most people know what to look for in a normal bicycle and finding a good brand that can be trusted is important.
For any of you that have tried several ebikes you will no doubt have noticed that even when the specifications are identical, e.g. 200W-250w motor and 24V-36V Li-Po battery, the performance of each model can be a world apart. There are straight forward reasons for this and I hope reading this guide will answer all of your questions.
Electric bike brands are still relatively young and although established in the industry have yet to creep into consumer awareness, as for example Barracuda or The Classis normal bicycles have in the UK.
So for you THE CUSTOMER, it is important to learn a little about the important features of an electric bicycle.
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.
Our Manufacturers and Us 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 lightweight 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.
BATTERIES OK now you have found the honey pot! The electric bike industry has been waiting for your interest to become significant enough to allow more effective battery technologies to be offered at reasonable prices. That is starting to filter through and the following are the main 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.
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.
Pros: Very lightweight, very high energy density, durable, no maintenance, fast charge.
Cons: Expensive, can be unstable, cells charge and discharge at different rates.
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.
HOW TO GET THE BEST FROM YOUR BATTERY
SLA: 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: 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: 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 a node, 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 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 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 ( BDC )
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 ( BDC ) usually provide more torque (turning force – quite useful for a bike!) at these lower speeds.
The motor is coupled through the gearbox to a freewheel 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 ( BLDC )
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 ( BLDC ) 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 ( BLDC )better able to cope with higher speeds and torque requirements and the brushless motor ( BLDC ) 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 ( BLDC ) 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.
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.