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There are various types of electric bike motors available on the market. Two main types which should be distinguished are hub motors and central crank drives. There are significant differences between the hub motor and the crank drives.
Crank Drive Systems
Crank drive is located in the middle of the bike frame, where the bottom bracket normally sits. Crank drives propel the bike through the chain with the use of the rear wheel gears. It is therefore a very efficient system, because it can increase its own torque through the use of wheel’s cassette. To put it simple, it can allow the bicycle to climb up very steep hills.
But the system has some disadvantages as well. The main disadvantage is its weight, which is very often quite high, and a lack of a throttle. Crank drives are normally built as a pedelec, which means that the electric assistance works only when the rider keeps pedalling by rotating the cranks. Crank drive system are also equipped with a torque sensor, which identifies when the rider puts more effort on the cranks. The higher the rider’s effort on the cranks, the more power is supplied by the motor and the faster the bike goes. To sum up, the crank drive systems are very efficient and are great for hill climbing. But because they work as a pedelec only, the rider need to keep pedalling to make the assistance work, and they need to pedall quite hard to be able to ride fast or uphill.
It is a completely different drive type from the crank central drive bikes. The motor is located inside the hub, which propels the whole wheel independently from the bike chain or cassette. Hub motor bikes can be powered by both a pedelec mode and a throttle only, which means that no pedalling by the rider is required, in contrast to the crank drive systems where pedalling is needed for the electric assistance to work. Hub motors provide a great solution for those who would like to take a break from pedalling but still want their bike to keep moving, and those who want to use electric assistance while pedalling but don't want to pedal as hard as in the crank drive system to make the bike go fast. Hub motors are suitable for different styles of cycling as users can change the mode from throttle only to pedelec mode at any time.
There are different types of hub motors, with the main types being direct drive only, and the ones using an internal gearing system:
Direct drive hub motors
The direct drive hub motors are very reliable and quiet but on the negative side they are usually quite large and heavy. The direct drive motors need to be big in order to generate sufficient amount of torque.
Geared hub motors
The geared hub motors have a different construction. The hub shell is a lot smaller and the motors weight less, comparing to the direct drive ones. The electric motor inside is a lot smaller but it is assisted by the internal gearing system that allows to generate higher torque. Low weight and a small size work as an dvantage of the geared hub motors. On the negative side, it is normal for geared motors to generate some noise. The level of noise can vary, with steel gears motors being usually quite loud, and Teflon gears ones being very quiet.
Hub motors -conclusion
So which system is better? Considering all pros and cons, it's probably the geared motors that win the battle. Weight in electric bicycles is crucial and geared motors from reputable manufacturers like 8FUN not only have low weigh, but also offer a great performance and reliability.
Brushed or brushless motor?
There are also two different types of electric motors - brushed and brushless. Generally, brushed motors are less reliable than the brushless ones. They need to be replaced after being used for some time, whereas brushless motors can often run for years without the need for any maintenance. Brushless motors are generally maintenance-free and their failure rates are very low.
The battery on an electric bike is just as important as the motor. Some would even say that thay are more important, as it's usually the batteries that are more likely to go wrong. In recent years, there has been a real boom on the electric bikes' batteries market, with more new technologies being used, and better types of batteries that can imporove performance of e-bikes available.
Types of E-bike batteries
Lead acid battery - the oldest type of batteries and the worst possible choice. Approx life time of the lead acid battery is only 120 recharge cycles. These batteries are difficult to recycle and also very heavy to carry. Some of the lead acid batteries have a memory effect, which means that the battery will loose some of its capacity over time.
Lithium Ion battery - these are a lot more advanced than lead acid batteries, but still not the perfect solution for an electric bike. The advantage of lithium ion batteries is their light weight, but the life time can achieve approx 500 recharge cycles, which is much more than lead acid batteries, but not a lot, comparing to Lithium Polymer ones.
LiFePO4 - Lithium Iron Phosphate battery is also a lithium based mixture but with the addition of iron cathodes. The LiFePO4 battery has a very long lifetime but is not widely used in electric bicycles mainly because of its power density being much lower than in Li-Ion or Lithium Polymer batteries.
Lithium Polymer - LiMnCo02 - is the most advanced type of electric bike batteries. These batteries have the greatest power density and a superb light weight construction. The lifetime can achieve as many as 900 recharge cycles, which makes them the most popular choice for electric bikes.
Lithium Sulphur – this is the latest battery technology, still being tested in laboratories. The big advantage of lithium sulphur batteries is the highest energy density available, and also an extremely low weight - it is estimated that 360Wh battery pack might weight only 1kg. However, the disadvantage of this type of batteries is a low number of recharge cycles, with curently only 250 recharge cycles is achievable.
Main problems with e-bike batteries
When thinking of buying an electric bicycle, most people are not aware of potential problems associated with batteries, one of them being a high cost, if a replacement battery is required. The battery is the most expensive part of an electric bike. Currently replacement batteries cost between £250 and £600 for a new battery pack, depending on the type of the battery, its chemistry, bike model, and some other factors.
The main problem associated with batteries is the loss of memory. All batteries will have some degree of memory effect and loose their capacity with the number of recharge cycles. The loss of memory will vary in different batteries, with some poor batteries loosing as much as 50% of capacity after just six months of use, and good quality ones lasting for two years loosing only over a third of their capacity. The majority of high quality e-bike batteries should achieve around 500-700 recharge cycles before they will need to be replaced.
Another problem associated with e-bike batteries is power delivery, which is more common with cheap and unbranded bikes imported from China that have a very poor records of after sales service. The good thing is that power delivery issue is easy to identify. The motor on the bike simply cuts off when cycling uphill. During climbing the motor normally needs a higher current in order to deliver more power. Then it drains the battery with higher current and poor quality batteries are simply not able to deliver the required current for a longer period of time. It is therefore important to highlight that not every lithium battery is equal and the same. How to distinguish a good one from a poor one? Warranty on the battery is usually a good guide here - good quality batteries usually have a two year warranty. But we should always remember to ask the seller what the warrantly actually covers.
Battery Management Systems
BMS battery management system in lithium batteries has a role of a little computer that controls the battery performance. All lithium batteries in electric bikes are built up with a number of cells which are all connected. Because there are many cells in one battery, one central computer needs to control a power delivery between cells, check the cell balancing, and make sure that the battery does not overheat and delivers the allowed current. Again, it all comes down to the price, with the majority of cheap lithium batteries using a very poorly designed battery management systems. It is therefore important to ask the seller what type of battery management system is fitted into the battery. Only branded management systems from reputable companies, such as O2 Micro or Toshiba, can give the best performance in power delivery.
Controller is the type of computer responsible for power delivery between the battery and the motor. There are various types of controllers, which can be programmed in a different way. Some controllers can be programmed as e-bikes (bike operated by twist and go only) or pedelecs (require rider’s input in order to provide assistance), other controllers are much 'smarter' and can operate in both pedelec and e-bike mode. There are controllers that are re-programmable to run on a different set up, and some controllers also have a de-restriction options, which allow to increase the maximum allowable legal speed of 15.5mph (25km/h).