Hi there -

I'm currently using this circuit to power a motor - and it's working pretty well.

The only issue, though, is that there is not much of a slope between "off" and "on" - the motor essentially won't run at a particularly "slow" speed.

Since I'm new to this, I'm curious if this is something that can be changed in the circuitry or something particular to these types of motors.

Thanks.

 

Is there presently any load on the motor?
Max.

 

No.

 

Did you try the simple 555 circuit?
http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm
Or $3.00 on ebay.
Max.

 

I'm curious if this is something that can be changed in the circuitry or something particular to these types of motors.

As the duty cycle is reduced, so is the average drive torque. The motor can't run if that torque is less than the frictional torque. Frictional torque varies widely from one motor to another and is likely to increase with decreasing motor cost.

 

Yes - the strange thing about the 555 circuit is that it seems to give a wider range of motor operation - but the sacrifice is that there isn't a strong "off" - the motor keeps humming, even when it is no longer rotating. Maybe this all ties into what Alec_t is saying - though I don't understand all the direct implications there: I'm just an amateur. Is there another circuit that covers all of these bases?

 

Whatever circuit you use to create the PWM you are likely to experience the same 'it suddenly stops', due to the type of motor.

 

Yes - the strange thing about the 555 circuit is that it seems to give a wider range of motor operation - but the sacrifice is that there isn't a strong "off" - the motor keeps humming, even when it is no longer rotating.

You could use a pot type with a rear OFF switch to create a defined OFF.
Max.

 

If you are trying to run a motor really slow, like less than 100 RPM, PWM will not do that. You need a gear motor + PWM so that the actual motor is running much faster.

Bob

 

You might look at post," How to start a motor gradually ", pratto, under Chat. Similar motor problem.

 

If not requiring the highest rpm of the motor, it is usually more economical to go with a smaller motor and gearbox reduction.
This would solve your problem.
Max.

 

What type of motor is it ? (Permanent magnet, shunt or series. ) This could have a bearing on the problem.

Les.

 

In order to get very low speeds out of that sort of motor, you'd have to add an encoder to it to get positive feedback regarding its current speed. Take a look at this thread, there's a rather nice circuit there by @Bernard that more or less complies with what you want.

​