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 ?

 

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

 

c5 is 25v 1000uf

i was trying smooth the noise from the motor with one in parallel.

 

R6 /7 are a waste of time,,lower R5 to less than 470 ohms...

Better with a 1uF cap polyester type..

 

1uf ? would that be enough during the inrush current when the motor starts ?

 

1uf ? would that be enough during the inrush current when the motor starts ?

If the noise from the motor is your concern, increase the frequency of the PWM signal by reducing the value of C1. That will solve your problem.

 

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.

 

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.

 

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

 

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.