# PWM frequency for speed control of DC motor...

T

#### they call me frenchy!

Jan 1, 1970
0
Howdy,

I have an application where I am designing a simple speed controller
for a 12VDC brush motor (pump). The motor draws approx 6 amps
continuous when running, depending on the load. I have the electronic
schematic all nailed down for driving the pump, but I need to set the
optimum PWM frequency for the motor that I am using. Can anyone refer
me to a nice text that discusses optimum PWM frequency choice for
optimum efficiency, etc. I assume that it is dependent on the motor
inductance, etc and I would like to research this matter fully. I've
found a few texts that touch on the topic, but none that delve into
it.

Any suggestions would be appreciated.
Thank you,
frenchy

P

#### Phil Allison

Jan 1, 1970
0

I have an application where I am designing a simple speed controller
for a 12VDC brush motor (pump). The motor draws approx 6 amps
continuous when running, depending on the load. I have the electronic
schematic all nailed down for driving the pump, but I need to set the
optimum PWM frequency for the motor that I am using. Can anyone refer
me to a nice text that discusses optimum PWM frequency choice for
optimum efficiency, etc. I assume that it is dependent on the motor
inductance, etc and I would like to research this matter fully. I've
found a few texts that touch on the topic, but none that delve into
it.

** The PWM frequency that provides the most overall efficiency is the LOWEST
one that results in relatively smooth current flow in the motor - ie no
more than 10 % ripple at the PWM switching frequency.

High ripple percentages means the rms value of the motor current starts to
exceed the average value - the aim is to have them both the same. The rms
value is what generates waste heat ( I squared R losses) while the average
current value is proportional to motor torque & does the work.

As permanent magnet DC motors vary so much, this frequency can only be found
for sure with the motor on test with PWM drive and a scope monitoring the
current in the motor circuit.

Having said that, the frequency will likely be around 1 to 5 kHz .

........ Phil

C

#### colin

Jan 1, 1970
0
they call me frenchy! said:
Howdy,

I have an application where I am designing a simple speed controller
for a 12VDC brush motor (pump). The motor draws approx 6 amps
continuous when running, depending on the load. I have the electronic
schematic all nailed down for driving the pump, but I need to set the
optimum PWM frequency for the motor that I am using. Can anyone refer
me to a nice text that discusses optimum PWM frequency choice for
optimum efficiency, etc. I assume that it is dependent on the motor
inductance, etc and I would like to research this matter fully. I've
found a few texts that touch on the topic, but none that delve into
it.

IMO adjust upwards until its no longer audible.

too high and you get switching losses,
too low and the current has a large AC component and it sings,
at some point the motor inductance will smooth out the current just enough.

Colin =^.^=

P

#### Phil Allison

Jan 1, 1970
0
"colin the fucking quarter wit "

IMO adjust upwards until its no longer audible.

** Even manic baboons have far more insightful opinions.

too high and you get switching losses,
too low and the current has a large AC component and it sings,

** So fucking whaaaaaaaat ????????????

The OP is after ** energy efficiency **

- you PIC poking CUNTHEAD !!

at some point the motor inductance will smooth out the current just
enough.

** For what exactly ?

Roller skates ?

........ Phil

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