E-bike : a motor-assisted bicycle
Many cyclists dream of always having a tailwind, the electro-assist bike helps to realise this dream. People who haven't sat on a bike for years, have ridden again, with this new type of recreational bicycle. Making a trip with a full battery, gives extra help for more strenuous routes with hills or headwinds.
The auxiliary motor gives support up to a speed of 25 km/h. There are also more powerful motor versions, with a speed of 45 km/h, but like a moped require the use of a helmet and need insurance ; but these more powerful and more expensive electro-assist bikes are less popular.
The speed of an E-bike is little different from an ordinary bicycle, but additional features such as disc brakes and suspension are common.
But the E-bike unfortunately has some technical limitations, that one should know and accept ! Bike dealers don't always explain how fragile and expensive the batteries can be. Dealers just want to sell bicycles ; so honest information can be scarce. It is normal that a battery (costing € 500 or € 1000) will need to be replaced after three years of use. Only with very careful use, can a battery life of four or five years be reached.
Many people put their bike in a shed in October, and don't get it out again until April for a first spring trip. If the battery is not charged in the interim, it will probably have been destroyed ; as a total discharged condition is very harmful for a rechargeable battery. To prevent this, the battery shouldn't be left without recharging for more than six months, or the battery will be seriously damaged.....
The dark bars in FIG.1 show the performance of 6 different kinds of lithium-ion battery, with an energy-density of between 80 Wh/kg and 250 Wh/kg ; each type has its own advantages and disadvantages. The abbreviations indicate the various battery types, and are explained in some more detail below.
The traditional car-accumulator was based on lead (Pb). The first versions of the E-bike had a Nickel-Cadmium (NiCd) battery ; but fortunately these have since disappeared. Then came the Nickel-Metal Hydride (NiMH) rechargeable batteries, which could be frequently recharged, were lighter, and more environmentally friendly.
Nowadays, lithium-ion (sometimes called "Lion") batteries have replaced previous types of batteries ; especially because they have more energy per kilogram of battery weight. The energy-density is expressed in Watt-hours per kilogram (Wh/kg) ; the higher this number, the more energy is available, per kg of battery weight.
The total energy content (in Wh) of the battery is the product of the voltage and the specified number of Ampere-Hour (Ah) of the battery (electrical power is measured in Watts, which is the Amps multiplied by the Volts). E-bikes have the few hundred Wh, in "normal" mode of use, under average conditions, this results in a range of about 12 km per 100 Wh. Unfortunately batteries often lose efficiency in cold weather conditions, so in winter the range of an E-bike can be halved, strong headwinds can also be a extra load too.
The battery packs are available in a combination of cells, usually providing 24 or 36 volts of electricity. Of course, the battery selected is related to the choice of motor used ; in general, there has been a shift toward higher voltages over the years
FIG.1 showing 9 different types of battery, and their energy-densities (Wh/kg)
A scheme showing 6 different types of lithium rechargeable batteries, and their characteristics can be found here.
The LCO type of battery is not used in E-bikes ; it is mainly found in mobile phones and laptop computers, it is fairly expensive and is temperature sensitive.
The LMO type of battery isn't used for E-bikes, unfortunately the number of recharging cycles is limited. The advantage of this battery is that he can deliver relatively high currents, so it is widely used in cordless electric DIY drills, etc.
The NMC type of battery is popular with E-bikes and electric cars, and is often used.
The LFP type of battery is often used in modern E-bikes, as it is a reliable and stable battery, the only drawback is that it quickly loses power, and needs to be regularly recharged !
The NCA type of battery can be used in E-bikes, but there are some disadvantages ; the number of recharge cycles is limited, and the battery is temperature-sensitive. But there is plenty of current ; so Tesla has used it in its luxury electric cars.
The LTO type of battery is not used for E-bikes, as the LTO battery performs relatively poorly when it comes to the number of Wh per kilo. An advantage of this type of battery is that it can be charged very often. Therefore, in electric or hybrid cars, a LTO battery can be used to store electricity generated from braking energy. This type of battery is very stable at different temperatures, is good at absorbing energy, and gives a smooth power output, but it is expensive and has a lower capacity for its size.
Many bicycle sellers do not even know what is in the battery of E-bikes !
It is important to realise that a good battery charger is more than just a simple power supply, there are sophisticated electronics which monitor and control the recharging process, with a limit on the recharging rate, and which automatically switch off when the battery is fully charged. E-bike suppliers therefore specify their own brand of batteries and chargers, which is important for warranty claims.
A few simple rules, for getting the most from a lithium rechargeable E-bike battery :
* Batteries will last the longest if they remain at room temperature.
* Never completely discharge them, this is really important to remember !
* It isn't necessary to fully charge them up to 100 % capacity, 98 % charging is enough.
* It is also preferable to only slowly and gently to discharge them and recharge them.
* The more roughly they are treated the shorter their life will be, and the faster their performance will deteriorate !
It is clear that some of these ideal rules are broken regularly, so an E-bike battery is unlikely to last even for 5 years unfortunately.
When we read the newspaper, every other month someone has a new idea. Most of these breaktroughs will never be in production. But in 2019 Tesla bought the firm Maxwell. They had advanced new types of dry batteries in pre-production. The expectation is that Tesla can devellop and massproduce batteries within a few years with 500Wh/kg, a fast loading rate, and with double number of recharges. The environmental issues are smaller for they use no solvents , have a double lifetime and don't use cobalt (expensive, poisonous). They even will be cheaper !
The valuable source for knowledge: http://batteryuniversity.com/learn