# How to generate electric power by a Brushless DC motor?



## major (Apr 4, 2008)

Scania said:


> how to make this (http://www.alibaba.com/product-gs/202230554/electric_bicycle_motor.html) motor to be a generate to produce a DC current?
> 
> a normal BLDC motor like RC plane & electric bike


Hi scania,

Your English seems a little broken. So I'm not quite sure what it is you want. But here goes.

Any motor can be used as a generator, or vice versa, if properly excited. Your link shows a brushless PM (permanent magnet) motor. So the PM sets the excitation. Therefore such a motor will generate simply by driving it with mechanical power (turning the shaft). The phase leads will output an alternating voltage. If you hook an electrical load to the phase leads, it will produce an alternating current. The magnitude will be proportional to the speed at which you drive the shaft.

If you need a DC output, you can simply rectify and filter the output. But this gives you an electrical source dependent on the speed at which you drive the shaft. In other words, the only regulation you have is mechanical. If you need further regulation, you need an "active" rectifier. Which would be the controller which was used for the BrushLess DC (BLDC) motor in the first place. This assumes that such a BLDC controller is capable of regeneration.

Hope that helps you.

major


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## Scania (Jul 22, 2009)

how about this?

because it is my final year project, only buy & install will have low marks, I want to build more by myself.


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## major (Apr 4, 2008)

Scania said:


> how about this?


Looks like it to me. But speed will have to be high enough to get generated voltage above battery voltage and diodes will only conduct when it is. And you have no way to regulate voltage or current except for controlling the speed. Give it a shot 

major


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## Scania (Jul 22, 2009)

if I want to put a Capacitor on the circuit to store the curren, how should I put?

How to calculate how much F I'll need?


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## major (Apr 4, 2008)

Scania said:


> if I want to put a Capacitor on the circuit to store the curren, how should I put?
> 
> How to calculate how much F I'll need?


If only used with the battery, I don't think you need capacitor filter.


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## Sunking (Aug 10, 2009)

Scania said:


> if I want to put a Capacitor on the circuit to store the curren, how should I put?


You do not need a capacitor, the battery in effect is a capacitor.


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## Scania (Jul 22, 2009)

But will it damage the battery if always charge & recharge the battery?

it is a KER-System of my bike, it still have a control circuit to drive the motor.


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## major (Apr 4, 2008)

Scania said:


> it is a KER-System of my bike, it still have a control circuit to drive the motor.


Ahhh! Formula 1 teams spend $millions for KERS. And you want the answers for free here  I wish I had them for you kid. 

This equipment isn't all that expensive for a bike. I suggest you just wire the thing up and start experimenting. Even if you can't get an F1 perfect system, you'll learn a lot and can do a good report for a grade (or mark as you call it).



> But will it damage the battery if always charge & recharge the battery?


You're talking the ripple? I don't think so. But I have no idea what type battery you have. Is battery management important? You bet. Will ripple current hurt it? I doubt it. In fact for Pb-acid, ripple may help.

I hope you can understand this and it is helpful. I have worked with students my entire career. And don't mind throwing a few facts or ideas your way. But ultimately it is your project and you have to do the work.

Good luck and keep us posted.

major


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