Turn sig gen into motor speed control

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Tubetec

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Just wondering if anyone would explain how I could use my arbitrary sig gen to power a small brushed dc motor of approx 100ma current draw ,is it simply a matter of providing a dc waveform  and varying the duty cycle or is it the voltage I need to vary  to modulate the speed ? I think I saw something about using two channels of a sig gen to power a motor,but im not sure and I dont want to blow the output stage on my gen up , any help greatly appriciated.
 

Tubetec

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I did find one circuit that placed an op amp before an Lm 317 and allowed a pwm signal to control the motor ,would this be a better way to go ?
 

abbey road d enfer

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Both DC (voltage) control and PWM are valid ways of controlling a motor's speed. PWM supposedly has a slight advantage at starting at low voltage.
A signal generator does not help since the cyclic ratio is fixed (50% for half-wave, 100% full-wave).
The main difference between DC-control and PWM is efficiency/power dissipation.
The main issue with low-speed DC motors is stability since the motor is always on the verge of stalling. That's why they need to have a tacho-based servo-control.
 

cyrano

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I've seen audio phools use an audio power amplifier after the generator to run Lenco motors. These need about 20 watts of audio power, IIRC.

But that's an AC synchronous motor. You just need a little range. Say from 45 to 55 Hz if you're in a 50 Hz mains zone.

The argument is that analog is -obviously- much better than PWM. :D
 

abbey road d enfer

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cyrano said:
I've seen audio phools use an audio power amplifier after the generator to run Lenco motors.
There are still many Hammond players that use a LF generator and dedicated power amp to act as a varispeed.
Hammond motors are also AC synchronous.
 

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