# What IS a controller?!



## major (Apr 4, 2008)

Lars! said:


> Okay so can anyone explain to me exactly what a controller does?


Hi Lars,

The EV uses an electric motor to drive the wheels, right? Electric motors at a fixed voltage are essentially constant speed machines. The battery in the EV is essentially a fixed voltage power source. So, if you want to be able to drive the EV at various speeds, you need to be able to have the electric motor operate at a desired speed. Variable speed vehicle needs a variable speed motor.

The way to vary the speed of the motor is to vary the voltage applied to it. A controller is the device of choice to do that. The controller is connected to the fixed voltage battery and can reduce that battery voltage for the motor, thereby causing the motor to run at reduced speed.

The primary function of the controller is to control motor speed.

The secondary function of the controller is to limit current. This is necessary because when the motor is started from a standstill, it will draw tremendous current. This produces a very large torque which is uncomfortable and damaging. The high inrush current is also damaging to the electrical system.

Basically, yes, you need some type of controller.

Hope that helps.

major


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## tj4fa (May 25, 2008)

I found this website article informative:

http://www.4qdtec.com/pwm-01.html#intro

http://www.4qd.co.uk/fea/index.html


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## Lars! (Sep 12, 2009)

Thanks to both of you for the answers!

So the controller manages the voltage and current given to the motor..

So I'm planning to build an electric moped, so this is how it would work?:

Throttle gives signal to controller, which controls the voltage and current to the motor? But for the throttle to give a signal, it needs energy.. So does the battery first go through the throttle, and is then connected to the controller, and then to the motor? I'm a little confused 


Edit:
One more question!

Would it be possible to program the controller so it doesn't allow more than x amperes? That way I could have my electric moped go at maximum 45 kmh or 60 (not sure which one yet)


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## major (Apr 4, 2008)

Lars! said:


> Throttle gives signal to controller, which controls the voltage and current to the motor? But for the throttle to give a signal, it needs energy.. So does the battery first go through the throttle, and is then connected to the controller, and then to the motor?


No, the controller is basically two sections. A power converter and a signal processor or logic section. The power section handles all the high voltage and current from the battery and to the motor. The signal section handles the management of the power section and the inputs from the operator, ie the throttle. The throttle is typically a variable resistor using a few volts and milliamps supplied from the controller logic section. This way, the driver doesn't have to have the high voltage or current under his foot or in his hand.



> Would it be possible to program the controller so it doesn't allow more than x amperes?


That's what the current limit function does. All controllers have a current limit. A lot of them have this feature which is adjustable by the user.

Regards,

major


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## Lars! (Sep 12, 2009)

Ohhh yeah, that makes a lot more sense! 

I think I get it now.. Basically the throttle controls the power section through the logic section.. Thanks again for helping me! It's been very helpful


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