# Help understanding PWM....



## Dalardan (Jul 4, 2008)

Well, it doesn't have any effect on your acceleration if you floor the pedal...

PWM is a way to apply partial power to your motor. It works by switching the motor on and off at a really fast speed (over 20 thousand times per second if you don't want to hear it singing...). The way it modulates power is by staying on for a relative percent of time. If it is on 50% on the time, you get half power. If it is on 75% of time, you get 75 % of power and so on.

You can see your motor like a small fan through witch you would blow air. If you blow small high power pulses of air but at a high frequency, you'll be able to make it turn as fast as if you would blow a continuous stream of air but with less power. This way you get a higher torque (like with the small high power pulses) but can go at a lower speed.

This is not really technical, but it works like that. So it shoudn't affect your acceleration.

Dalardan


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## Qer (May 7, 2008)

Dalardan said:


> (over 20 thousand times per second if you don't want to hear it singing...)


Actually it seems that most controllers run PWM at around 15-16 kHz because it seems to be a frequency that's practical because of several reasons. I don't think any controller runs at over 20 kHz and I've still only heard people complain about noise from Curtis controllers and that's because they drop down at 1.5 kHz when you start the car.

Besides that your explanation is ok.


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## Bowser330 (Jun 15, 2008)

Thank you...

By "power" you mean Voltage? or Voltage AND Amperage?

So if I floor the pedal it will be at 100% on...? right?

Meaning 100% voltage and Amperage at 0rpm-XXXXrpm

(of course considering the amps will drop as motor rpm increases)


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## Dalardan (Jul 4, 2008)

By flooring the pedal, you get full voltage 100% of the time, thus you get the maximal current your controller and your battery pack can flow through your motor for a given RPM.

This way, you get 100% of the power available for this point of operation, like if you would have connected directly you battery pack to your motor (DO NOT DO THIS! It's only a way explain how it works. I did neglect the effect of the current limiter of the controller that limits the maximal current to a safe limit for itself.)

Dalardan


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## Bowser330 (Jun 15, 2008)

Dalardan said:


> By flooring the pedal, you get full voltage 100% of the time, thus you get the maximal current your controller and your battery pack can flow through your motor for a given RPM.
> 
> This way, you get 100% of the power available for this point of operation, like if you would have connected directly you battery pack to your motor (DO NOT DO THIS! It's only a way explain how it works. I did neglect the effect of the current limiter of the controller that limits the maximal current to a safe limit for itself.)
> 
> Dalardan


Thank you very much that is exactly what I needed to know...


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