Where to place a smoothing cap

Thread Starter

anishkgt

Joined Mar 21, 2017
396
HI All,

The circuit mentioned here is a pwm motor speed controller using a NE555 ic. Where would it be ideal to place a smoothing cap for the motor, before the NTC or after it ?
Capture.PNG
 

ericgibbs

Joined Jan 29, 2010
9,538
hi anish,
Wouldn't fitting a smoothing capacitor across the motor defeat the purpose of using PWM .??
What is the value of C5.?
R5 value of 10K is too high, I would use a 470R or 1K.
E
 

Thread Starter

anishkgt

Joined Mar 21, 2017
396
does the motor used determine at what frequency it should run ? I would not be running the motor very slowly as the application for the motor is to run circular saw.
 

KeithWalker

Joined Jul 10, 2017
660
does the motor used determine at what frequency it should run ? I would not be running the motor very slowly as the application for the motor is to run circular saw.
The construction of the motor determines the amount of noise it will make and at what frequency it will make the most noise. The noise is caused by the vibrations of any loose windings plus the vibration of the armature, especially if it has low mass, as in small inexpensive motors. 2 KHz or higher is usually the best frequency for quieting the vibrations.
 

Thread Starter

anishkgt

Joined Mar 21, 2017
396
Sorry about my silly questions, just a beginner with electronics. Learning as I do things.

So I was thinking a cap as low as 0.01uf, would that be ok ? The motor used here is a 775 dc motor. Runs on 12v at 5.7A max
 

KeithWalker

Joined Jul 10, 2017
660
Sorry about my silly questions, just a beginner with electronics. Learning as I do things.

So I was thinking a cap as low as 0.01uf, would that be ok ? The motor used here is a 775 dc motor. Runs on 12v at 5.7A max
I have not done any calculations to find out what frequency your circuit is running at or what frequency it will be with a 0.01uF capacitor. I suggest that you try it and see what happens. It will not cause any damage.
 
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