# Electro generation in Hub motor



## kalsi27nov (6 mo ago)

Since I am building an electric motorbike for the first time, I have a question. For example: when the vehicle is in motion, we do not ride at a constant speed since there are many other vehicles that are on the road running at different speeds, therefore, the throttle is adjusted as required. And many times the throttle is at zero but the vehicle is moving. 
My question is:
At zero throttle and vehicle moving, the hub or a mid-drive tends to rotate because the wheels are rotating and there is no freewheel like a bicycle. During that zero throttle duration, the motor produces energy just like a generator. 
Q1 Is that energy utilized to charge back the battery or does it go waste?
Q2 If it is recovered then is that feature available in the motor controller?


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## _GonZo_ (Mar 23, 2009)

kalsi27nov said:


> At zero throttle and vehicle moving, the hub or a mid-drive tends to rotate ...
> Q1 Is that energy utilized to charge back the battery or does it go waste?


Movement is NOT energy.
So unless you brake with the motor, reducing the speed of the vehicle there will no energy generation.



kalsi27nov said:


> Q2 If it is recovered then is that feature available in the motor controller?


Most motor controllers have the function of generative braking.
So yes when the vehicle decelerates using generative braking most of that energy (60-90%) generated by the deceleration is returned to the battery.


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## brian_ (Feb 7, 2017)

Movement is energy, so energy is put into the motor to spin it faster, and is returned by the motor when it slows down (like any flywheel), but that kinetic energy of motor rotation is not important. But _GonZo_ is correct that the motor won't absorb mechanical energy and generate electricity unless the controller makes it do that, just as it doesn't produce mechanical energy by using electricity unless you use the "throttle" to tell the controller to make it do that.


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## ishiwgao (May 5, 2011)

The first sentence of OP's post feels like this thread is going in the direction of:

_"zero throttle vehicle moving to recharge energy, then use recharge energy to move vehicle, equals no need batteries anymore!"_


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## remy_martian (Feb 4, 2019)




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## _GonZo_ (Mar 23, 2009)

Maybe I expressed wrong: Any object will remain at uniform motion unless compelled to change its state by the action of an external force (energy)
In other words, unless there is an add of energy (positive or negative) the motion by itself has no energy.
Only accelerations or decelerations of the object will absorb or generate energy.


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## remy_martian (Feb 4, 2019)

Incorrect.

Basic high school physics: motion has inertial energy

E = 1/2 m * v * v

m is mass

v is velocity

The equation clearly shows you change the energy if you change the mass or the velocity.

What you state, acceleration or deceleration, produces a force:

F = m * a


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## _GonZo_ (Mar 23, 2009)

Inertial energy is a potential energy, meaning that it is there but it is not available unless you change the motion with and acceleration or deceleration.


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## remy_martian (Feb 4, 2019)

It is not a lossless process.


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## kennybobby (Aug 10, 2012)

The OP has probably left the scene due to the lack of a simple answer.



kalsi27nov said:


> ...
> During that zero throttle duration, the motor produces energy just like a generator.
> 
> Q1 Is that energy utilized to charge back the battery or does it go waste?
> ...


The simple answer is that yes it can be sent back to charge the battery, known as regeneration braking, if the motor controller has the regeneration feature. If it does not, then the energy goes to waste as heat.

The regeneration braking can be adjusted to be greater or lesser by the amount of charge sent back to the battery; when high regen braking is active it can feel as strong as pulling the brake lever. It is quite fun in a car.


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## remy_martian (Feb 4, 2019)

A fan sail and roller skates is a much easier build than a bike -- I think he's changed projects.


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