SparkFun Forums

[MKR]

Pretty much a newb here. I'm a sculptor looking to set up an efficient independent circuit. I've got a 20RPM 6-12V DC gear motor from Sparkfun.

The specs are:
Stall Current: 1 Amp
No Load Current: .08 Amps
Insulation Resistance: 20 MOhms
Stall Torque 375 oz-in

It needs to power a 17" pulley driven steel ferris wheel for about 8 hours a day before recharge. I'd like to control the speed with a potentiometer.

I'm looking at running 4 x 3.7 v 1000mA lithium ion rechargeable batteries in a series to bring up the voltage. I think I need a 12v regulator in the mix. I think I need to control the amperage with more than a pot switch, though. Should I have a fuse or power diode in there? I've never taken a class or workshop in electrical engineering although, I'd like to in the future. I'm just working off tutorials and info pages. I'm having trouble finding model circuits schematics that don't over simplify or over complicate what I'm trying to do. The only thing I know for sure is Power = Voltage x Current and Resistance = V/C I'm not sure how to apply that to the relationship between the battery and the Motor and how to limit the waste. Can anyone help me figure out how to figure this out? Thanks in advance.

[skimask]

PWM DC motor speed control

[mcdowra]

To be a bit more specific and expand on skimask answer. You could connect the positive supply to one lead on the motor. Then use a logic level N channel mosfet to connect the ground to the other lead of the motor. I believe sparkfun sells one that would be appropriate.

You have your power supply ground connected to the source pin of the mosfet. You have your motor lead (that goes to ground) connected to the drain pin on the mosfet and you connect your pwm pin to the gate of the mosfet. When the gate sees voltage it will connect the source and drain completing the circuit. You alter the duty cycle of the pwm and the motor speeds up and slows down

[jremington]

+1 for PWM suggestion above. For that motor, you can use a single transistor (plus appropriate base resistor and a "inductive kick" protection diode across the motor terminals) as the motor driver. Then you will need something like an Arduino, or a 555 timer-based circuit to generate the PWM signal.

Here is an example of the latter: http://www.discovercircuits.com/DJ-Circ ... lepwm2.htm

[Ross Robotics]

I'm looking at running 4 x 3.7 v 1000mA lithium ion rechargeable batteries in a series to bring up the voltage

If you are running a 12V motor at 1A, then this will only last an hour. I would advise looking into a more heavy battery. If you are new to LiPos, I would advise against running them in series. They can be very dangerous. Just get a 4 cell LiPo and be done with it.

Is this the motor your looking at, https://www.sparkfun.com/products/12511? If so you may need a regulator, there's no datasheet stating what the maximum voltage is. That regulator needs to be able handle 2A just to be on the safe side. You may need another regulator if you need to power supporting components.

Search Google for running a 12V DC motor with PWM control. You will likely find a schematic.

[anthonyM]

I've search Google for "running a 12V DC motor with PWM control" and this is one of the results I need:

Thanks for your help.
Regards.