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 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 been riding 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.
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 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. New and high grade E-bikes will have 48V nowadays.


There are 6 different types of lithium rechargeable batteries.

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.

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 loses some 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 charge ; so Tesla has used it in its luxury electric cars, but the cheaper models are using LFP now.

Many bicycle sellers do not even know what is in the battery of their 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. In 2019 Tesla had about 250Wh/kg energy density; Tesla bought the firm Maxwell that year. 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 !

Another Tesla devellopment is the NMC/graphite battery. This should have 5000 load cycles , and only 10% decay over that period, so 1.600.000km use. Then the battery could be used as home energy storage for years  http://jes.ecsdl.org/content/166/13/A3031.full   But it still uses cobalt and maybe recycling can offer a good way to diminish the use and waste of this expensive and poisenous stuff; they are working on it  https://www.youtube.com/watch?v=LAssX6hAyKs 

  And then there are new types like Lithum-Sulphur, Sodium-ion (Natrium),  Aluminum-Air batteries and many others....  By 2030 we will reach around 800Wh/kg.

   Those batteries could last 400.000km; even when you ride 5000km a year, you can use it 80 years, for most people and bikes a lifetime.


The folding bike of FIG.1 is a typical example of the E-bikes around €1000. The Chinese manufacturer Bafang is a big player in that part of the E-bike sector. A disadvantage of frontwheeldrives, are unexpected steering reactions.

Hub motors are the easiest to mount in a bicycle, and therefore are somewhat cheaper than a motor near the bracket (a so called mid-motor).

The motor of this bike is specificly made for 20 inch wheels; the rev's of the wheel get higher when the wheels are smaller. The gearing of the motor must be adapted.. 

This Bafang motor is 36 Volts; we see a shift in the market toward 48 Volts in the newer and more expensive models.

A mid-motor has less variation in rev's, that is good for electromotors. Almost all expensive E-bikes have a mid-motor, and in the higher segment of the market, there are more manufacturers  offering a wider choise of models.


                   FIG.1 Folding E-bike with Bafang frontwheel hub drive.






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