How do controllers work?

[mattwilkinson]

Hi guys

Sorry for just a general question... I am doing a school project build on an electric bike and can barely find any information on how the controller actually works.
The electric motor is an external motor 24v with controller and throttle.

My basic understanding is there is a potentiometer in the throttle with sends a voltage of 1-4 volts down to the controller and then something in the controller regulates how much current to send to the motor?

Any help appreciated

Thanks

 

[amberwolf]

Sorry I couldn't help.


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[flat tire]

Most people here use brushless motors and controllers which work a little differently from your DC brushed motor and controller so keep that in mind.

PWM is how the controller regulates amps to the motor. Brushless motors use this method too, they just have 3 conductors instead of 2 and constantly vary the polarity. your controller just uses 2 conductors with fixed polarity. Wiki link: https://en.wikipedia.org/wiki/Pulse-width_modulation

 

[Drunkskunk]

Your brushed controller will work much like a brushless controller. The basic principles are the same.

Inside that controller are a few basic parts. A computer chip, a voltage divider that supplies the 5 volts for the chip and throttle, a current sensor, and a group of MOSFETs that handle actually feeding power to the motor.

When you turn the throttle to start the motor moving, the chip sees the rise in voltage. it then begins sending pulses of voltage to the MOSFETs, turning them off and on very quickly. Like 16khz quickly. This is called Pulse Width Modulation (PWM). A long explanation can be found here: electronics-tutorials.ws/blog/pulse-width-modulation. But to sum it up, The length of the time each pulse is on compared to the time each pulse is off acts just the same as variable voltage. For example. if you sent all pulses on, the controller would act like it was sending full 24 volts to the motor. If you send half of them off, the controller acts like it's sending 12 volts to the motor. For this reason, you can't use a Digital Volt Meter on the controller to read the output. You need an analog meter for a brushed controller.

The MOSFETs are just a fancy transistor that are very good at being switched on and off very fast. These actually feed power to the motor.

The current sensor works to keep the current from going over at a set maximum. A motor under load will try to draw as much current as it can. The chip is monitoring this current level all the time, and when it goes above a set limit, the chip will over ride the throttle input and back off the power it sends to the motor, holding it at the limit.

 

[mattwilkinson]

Thanks everyone it is much appreciated