11th May 2016

Autonomy and Watt-hour

Autonomy and Watt-hour


The unit measure of energy is Watt-hour (symbol W·h , W h or Wh) and is precisely defined as the energy necessary to develop the power of one watt for one hour. So the energy capacity of the battery is measured in Watt-hour and in case of an electric bicycle is used to estimate its autonomy and performance.

Each manufacturer is obliged to indicate the exact number of “Watt-hour” on the battery pack and mark it with a “Wh” symbol. The Infinity e-Bike is equipped with a battery of 240 Wh of extremely light weight of 1,2 kg, an optional battery of 356 Wh that weights 1,6 kg is available on request. Making a comparison with a passenger car or a motorcycle 240 Wh for an electric bicycle is the same as the amount of fuel available for a car and therefore its autonomy varies depending on our driving style as well as it happens with the cars. Moreover, electric bicycles are hybrid vehicles for which the driving component can be both muscular and electric and thus values of autonomy depend on the relation between muscular power and electric power. Making simple mathematical calculations we can understand that with the motor of 250 Watts continuously used at its maximum power and thus consuming 250 watts per hour and the Li-Ion battery of 240 Wh the motor will have an autonomy of about one hour.

At this point you are to ask how many Km you can ride with your Infinity which disposes a 240 Wh “tank”?

We all remember that distance is equal to speed multiplied by time. The speed of a cyclist riding an electric bicycle in its turn is a complex function of power (Watts), both generated by the motor and the cyclist’s muscles, and a number of other variables like road’s gradient, rider’s weight, friction tread etc …

Speaking about time the Infinity e-bike disposes several modes with constant engine power consumption, which permits to calculate for how long the battery will last. There’re 3 preset modes, namely, Economy, Tour and City Speed and a customizable Target Power mode. If for example you select the TOUR mode (limited to 80 Watts) you will have about 3 hours of riding autonomy.

So how many Km will you be able to ride?

As it was mentioned above besides the motor power it will highly depend on how many Watts you will add with your legs, but the general rule in the TOUR mode for example will be your average speed multiplied by 3 (3 here are 3 hours of riding autonomy that you get in Tour mode)!!! So at an average speed of 23Km/h you will be able to ride about 70 km!!! It is interesting to point out that in big cities like Milan, Paris, London where the average incline of the road stays in the range of [-1%;1%] and assuming that 75kg is the average weight of the cyclist, after applying the mathematical formula the above mentioned speed of 23Km/h is divided into 14Km/h generated by the motor (working in Tour mode, limited to 80 Watts) and only 9Km/h generated by the cyclist’s effort.

No doubt this is a new concept and perhaps a little bit hard to digest for those who are used to think in terms of a car autonomy, but be sure that just after several times you ride your Infinity e-bike you will become an expert!!!