What would be the best way to run a motor off a constant 3.0V by bringing 6V (four AA batteries) down to 3.0V?

Thread Starter

DSMJR!

Joined Jan 14, 2020
5
I need 3.0V to run a motor; it has to be constant so the motor will run at 5 rpm. I looked into a voltage regulator but I can't find one that brings it down to 3V only 3.3V. So I tried two 1N4001 diodes with a 3.3V regulator to bring it down to very close to 3.0V, but for some reason the voltage was fluctuating between 2.8V and 3.1V; so that won't work because the voltage fluctuation will change the rpm of the motor. I also tried a voltage divider circuit with the 3.3V regulator because I was desperate, and like I thought the motor stalled. Do any of you have any ideas, or is there something I overlooked?
 

Ylli

Joined Nov 13, 2015
892
If you really need the motor to maintain 5 RPM, you will need a full fledged speed controller. Otherwise with a constant voltage, the RPM will change significantly with load.
 

pmd34

Joined Feb 22, 2014
503
You could actually pulse width modulate (switch off and on fast) your 6V from the battery with something as simple as a NE555 timer to power your motor, this will be most efficient, or you could use an LM317 adjustable regulator but you are wasting 50% of your power.
 

Alec_t

Joined Sep 17, 2013
10,902
What is the load that the motor is driving and requires 5rpm? That may influence the best solution for your project.
 

Thread Starter

DSMJR!

Joined Jan 14, 2020
5
What is the load that the motor is driving and requires 5rpm? That may influence the best solution for your project.
You could actually pulse width modulate (switch off and on fast) your 6V from the battery with something as simple as a NE555 timer to power your motor, this will be most efficient, or you could use an LM317 adjustable regulator but you are wasting 50% of your power.
There really isn't any serious load it just has to turn a plastic part. And since it is being powered from batteries I would like it to be as efficient as possible.
 

Thread Starter

DSMJR!

Joined Jan 14, 2020
5
You could actually pulse width modulate (switch off and on fast) your 6V from the battery with something as simple as a NE555 timer to power your motor, this will be most efficient, or you could use an LM317 adjustable regulator but you are wasting 50% of your power.
I've used PWM with the arduino, but I've never done it with the 555; how would that work?
 

pmd34

Joined Feb 22, 2014
503
This sort of thing would do it:
Though im more in favour of using N-Channel mosfets for such things. 555 timers are very common for producing simple pulses, there are also other smaller chips available such as the MIC1555
But make sure you dont apply the full "raw" 6V to the motor for any long period of time as it will take a lot of current and is likely to overheat and burn out the motor.
 

Thread Starter

DSMJR!

Joined Jan 14, 2020
5
This sort of thing would do it:
Though im more in favour of using N-Channel mosfets for such things. 555 timers are very common for producing simple pulses, there are also other smaller chips available such as the MIC1555
But make sure you dont apply the full "raw" 6V to the motor for any long period of time as it will take a lot of current and is likely to overheat and burn out the motor.
So the motor is running fairly high RPM if you have the gearing involved, as suggested, I would use a 555 and don't bother reducing the voltage, just control rpm.
http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm
Overvolage is not a problem, it is high load current that matters, just don't over-speed it.
Max.
VERY interesting I will try this. Thanks a lot guys.
 
Last edited:

Ylli

Joined Nov 13, 2015
892
Many years ago, I was working with an engineer that was designing a speed control for a DC motor to move a medical imaging patient table. This was a fairly large motor, perhaps 4 inches diameter, 10 inches long. When hooked up to the speed controller it could be varied in speed from many hundreds of RPM to less than 10 RPM. What amazed me was that when set at the slowest speed, it continued to produce maximum torque. Normally if you try to control the speed of a motor by simply reducing the terminal voltage, the torque drops dramatically. Not with his design.

This design was a full PID implementation, but I discovered that the biggest feature that allowed the motor to produce such torque at low speeds was that the circuit compensated for armature resistance. Implimenting a circuit to do this is fairly simple as a linear regulator, somewhat more complicated as a PWM circuit. If you really do need to accurately control the speed under varying loads, I can point you to some web pages.
 

shortbus

Joined Sep 30, 2009
7,448
I was working with an engineer that was designing a speed control for a DC motor to move a medical imaging patient table. This was a fairly large motor, perhaps 4 inches diameter, 10 inches long. When hooked up to the speed controller it could be varied in speed from many hundreds of RPM to less than 10 RPM. What amazed me was that when set at the slowest speed, it continued to produce maximum torque. Normally if you try to control the speed of a motor by simply reducing the terminal voltage, the torque drops dramatically.
That sounds more like an industrial servo motor and it's drive.
 
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