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Electronics => Electronics => Topic started by: jsmoker on February 23, 2009, 02:08:14 PM

Title: Simple DC motor controller
Post by: jsmoker on February 23, 2009, 02:08:14 PM

I'm trying drive a small DC motor (I want it to be adjustable but max it out at 1amp which happens around 2.2V) and I found this circuit online.

http://www.elecfree.com/electronic/simple-miniature-motor-controller-by-lm317/

This was perfect for what I wanted to do....unfortunately it didn't work.  Why is that?  I tried two different motors i.e. a one inch long motor with the same diameter as a nickel and and a motor from a phone vibrator.  I used a power supply and set it to 24 volts.  For the big motor, it did nothing.  The power supply showed it was pulling 40mA, and I think that's all from the LM317.  The small one did a little better.  When I turned the pot to 10k I got about a 0.2V drop, but that's it.  I tried putting a small power resistor in line,  I large regular resistor inline, and ditto for parallel (didn't think it would help but I just did it for good measure).  Why doesn't it work?

I tried a transistor earlier but when I set it to 0.5 Amps it started to drift right away and at an exponential rate to max out the power supply (I melted a hole in my breadboard.)

I might have to resort to a PWM circuit using a 555 oscillator, but its so much more intensive to make rather than the LM317, a pot, a resistor, and a capacitor.

Thanks for any help.

Title: Re: Simple DC motor controller
Post by: SmAsH on February 23, 2009, 02:43:30 PM

is that what the motor is rated for?

Title: Re: Simple DC motor controller
Post by: jsmoker on February 23, 2009, 03:42:04 PM

I don't know, it's a reused motor with no markings.  I ran it at 0.5 Amps at like 2.2 Volts for a long time and it didn't get hot.  I've never taken it above 1.5 Amps.

Title: Re: Simple DC motor controller
Post by: Admin on March 01, 2009, 07:53:44 AM

Is this for something that needs to be 'production quality' or just a cheap hack to get something done fast?

For a quick hack . . . I know you own a microcontroller - hook up a potentiometer to the ADC, and have it output a proportional PWM to a NPN MOSFET.

As for getting that circuit to work . . . multimeter every node on that circuit. I'm sure you'll notice something unusual. Does the LM317 get warm? Do you have a second LM317 assuming maybe the current one is broken?

Since you are using a voltage regulator, you are basically burning away quite a lot of power. You also don't care about having perfect voltage. As such, you could simply use a resistor and a potentiometer to create your variable voltage without the regulator.

FYI, for the 555 timer method, it will take the exact same number of components:
http://www.kpsec.freeuk.com/555timer.htm
(http://www.kpsec.freeuk.com/images/555ast.gif)