# Controller PWM frequencies



## Gary B (Jun 2, 2011)

Couldn't find this in other threads by searching.
With the experience I've seen on this site, I'm sure someone has checked this out. - What frequencies are "normally" (?) used in these motor controllers for the PWM? (Curtis, et. al.) - My dumb guess is that it's greater than 2 Hz and less than 500 KHz. But that leaves a lot of room. - 

Thanks for the help.
Gary B.


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## EVfun (Mar 14, 2010)

Generally around 15 kHz because it keeps the motor quiet. Low frequencies can allow motors to whine or growl. At low speeds (less than 15% throttle or over heating) the Curtis C series controllers switch at 1500 Hz and that creates an annoying whine in a number of motors (the ADC 9 inch is classic for this.)


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## Gary B (Jun 2, 2011)

EVfun said:


> Generally around 15 kHz because it keeps the motor quiet. Low frequencies can allow motors to whine or growl. At low speeds (less than 15% throttle or over heating) the Curtis C series controllers switch at 1500 Hz and that creates an annoying whine in a number of motors (the ADC 9 inch is classic for this.)


Thank you, EVfun. That was a quick feedback. - So, the Curtis C series switches at about 1500 Hz across the entire current range of their controller. Is that correct? - I mean they don't use different frequencies at different load or speed levels. (?) - However, at the lower speeds (or over heating) they may make annoying noise because of that switching speed. - 

It is also very helpful that you say "around 15 KHz," because that means other controllers that you know of have been built (with success) using that kind of frequency. That is most important. - 

Thank you greatly. - That information may be buried in some other posts, but it would take me hours to find it. 

Good on you !
Gary B.


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## Gary B (Jun 2, 2011)

Hello again EVfun. - I just found this item (below) that relates to what we spoke of earlier. - It indicates that my "assumption" about what you said was not correct. - It appears that "some" Curtis controllers DO change the PWM frequency across the load and speed range. - (as follows)



An ESC (ElectronicSpeedControl) should sense the current overload and safely shutdown requiring some sort of reset after locked-rotor condition has been removed. Otherwise, U BURN up controllers and/or motor. Curtis controllers do this by dropping to a lower PWM freq which makes it easier to sense the amps and shutdown quickly enough before the MOSFETs liberate the smoke







EVMAN source.


Still, the 15 KHz information is invaluable.


Thanks.
Gary B


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## EVfun (Mar 14, 2010)

The Curtis 1221C and 1231C controllers do use a different frequency at different loads. Below 15% duty cycle they switch at 1500 Hz and above 15% duty cycle they switch at 15 kHz. The low frequency at low duty cycles help them regulate current at low speeds. The older B series Curtis controllers (15 kHz all the time) could be a bit jumpy right from a stop in a light car and with a low impedance motor they could prematurely fail from high peak currents. The ADC 9 inch motor and a driver how took off in second gear all the time could kill a Curtis 1221B controller. 

The Zilla controller switches at 15.7 kHz and has its own system of cycle dithering to help regulate current at low speeds. It allows for a smoother takeoff but without the motor whine that can come from low frequency. It makes a subtle white noise hiss at very low power.


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## Gary B (Jun 2, 2011)

Got it, EVfun ! - The clarification itself is informative and useful.
Thank you.
Assumptions in this EV world can be dangerous and expensive.

Good on you.
Gary B


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## dougingraham (Jul 26, 2011)

Gary B said:


> Couldn't find this in other threads by searching.
> With the experience I've seen on this site, I'm sure someone has checked this out. - What frequencies are "normally" (?) used in these motor controllers for the PWM? (Curtis, et. al.) - My dumb guess is that it's greater than 2 Hz and less than 500 KHz. But that leaves a lot of room. -
> 
> Thanks for the help.
> Gary B.


The Soliton 1 has two selections, 8khz and 14khz I believe. You can hear the 8khz but almost nobody can hear the 14khz. The reason to use the 8khz is the switching efficiency is better.

From a practical standpoint you could run fine down to something under 1khz but most people would quickly get annoyed listening to the whine. The inductance of the motor is plenty large enough for even fairly low frequencies. I would choose some frequency nobody could hear in the upper teens if I was designing a controller. There is little advantage to switching faster than this and the disadvantage is the increase in switching losses. I suppose you could use smaller input caps if you switched faster. Now for a charger or DC/DC converter there are advantages to switching at higher frequencies. You can use smaller inductors and capacitors and get increased efficiencies in other areas which can offset the lower efficiency in the power switches.


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## Gary B (Jun 2, 2011)

Thank you, Doug. - - - I have had zero experience running controllers (other than my little electric scooter). - I never hear a peep from that, so the idea of the operating frequency for PWM never crossed my mind as being an audible problem. Where are the "microphones and speakers"? - Where does it cross the electronic/physical interface? - Is it sympathetic microphonics in the controller case or in the motor, do you believe. ? - (Now going off main subject.)


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## piotrsko (Dec 9, 2007)

the term is i believe called magnetostriction. all metals in a field will deflect somewhat in proportion to their permeability. this deflection will cause noise that varies as a result of the size of the field and material ensconced within.


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## dougingraham (Jul 26, 2011)

Gary B said:


> Thank you, Doug. - - - I have had zero experience running controllers (other than my little electric scooter). - I never hear a peep from that, so the idea of the operating frequency for PWM never crossed my mind as being an audible problem. Where are the "microphones and speakers"? - Where does it cross the electronic/physical interface? - Is it sympathetic microphonics in the controller case or in the motor, do you believe. ? - (Now going off main subject.)


The windings in the motor will make noise when you hit them with current at audio frequencies. Some of the RC electronic speed controls will play a little tune on the motor windings when the controller wakes up so you know it is awake.


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## Gary B (Jun 2, 2011)

You are kidding me ! ! ! -
You made my day !
Thanks.


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