The whole truth about e-bike recuperation


Ah, that magic word is recuperation! A fairly significant part of people who have thought about buying an electric bike, having heard about the recuperation function — returning part of the movement energy back to the battery — begin to dream of huge e-bike runs, often without understanding the essence of the issue.

What could be the reason for such interest in the recuperation function? People’s tendency to embellish reality?

Probably many remember how they were popular in Soviet times

Nowadays dynamos are still on sale, for example, on Aliexpress they are found as

If you do not go to Aliexpress, you will notice that such a large manufacturer of bicycle components as Shimano also produces hubs with a built-in generator.

And it would seem that you can use this generator to charge an e-bike battery! But let’s turn to mathematics, which will unbiasedly put everything in its place.

The power of the generator built into the hub is 3 W at a voltage of 6 V. The most common battery capacity for an e-bike is 10 Ah. With a nominal battery voltage of 36 volts, the absolute capacity is 360 Wh. Thus, even if we do not take into account the voltage conversion losses from 6 V to 36 V, we need 360 Wh / 3 W = to charge the battery.

But, of course, the advocates of recuperation are not talking about such bicycle generators! After all, why install an additional generator on an electric bike when it already has a generator — this is

Recently, at one well-known forum about electric transport, I

This is the method of charging the battery using recuperation that most people dream about when they come to buy an e-bike with the question «Does this e-bike support recuperation?»

I am forced to upset such dreamers — in this mode, it is unlikely that the battery can be charged, even partially, since for charging it is necessary to provide

First, a sufficient rotational speed of the motor-wheel is needed, that is, it is necessary to drive at a speed of at least 20 km / h.

Secondly, the operation of the motor in generator mode will create resistance to movement, as if you are driving uphill, and with a rather serious bias. And while maintaining a speed of 20 km / h for a sufficiently long time is almost unrealistic.

Another, more realistic way of recharging the battery using recuperation, many consider

But here too there are

Secondly, battery charging is an inertial process, as it depends on chemical processes, which reduces the efficiency of recharging.

Third, underweight. If in the case of electric trains and electric vehicles the weight of the vehicle is quite significant, then in the case of an electric bike the inertia force is no longer enough.

As a result, taking into account the losses for the conversion of kinetic energy of movement into electrical energy, and then into chemical energy of the battery, the real efficiency of recuperation on an electric bike is about

And now

Thanks to the use of an overrunning clutch and design features, gear motors up to

Thus, you can use a direct drive motor and, due to recuperation, increase the mileage on a single charge by 3-5%, or you can use a gear motor and achieve an increase in mileage of up to 30% (relative to a direct drive motor).

In fact, these motors have different purposes: a direct drive motor is advisable if you want to travel at a speed of more than 50 km / h in a heavy vehicle with a large battery, and you are not worried about the increased energy consumption.

And it is reasonable to use a geared motor in the case when low weight is important for you, efficient use of battery energy (including through the use of the assistant mode) and will suit a travel speed of 25-60 km / h. It looks more like

Direct drive motors are cheaper due to the simplicity of the design, for this they are loved by DIYers, but they also weigh many times more. And geared motors are used more by manufacturers of high-quality and, as a result, more expensive electric bicycles, such as

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