Increase Pump Volume with DC Motor Speed Control | Beginner's Guide

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Discussion Overview

The discussion revolves around controlling the speed of a DC motor to adjust the volume of liquid pumped by a system. Participants explore various methods for achieving this control, including voltage adjustments and alternative techniques, while addressing concerns about motor reliability and safety.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant expresses concern about running a 12V motor at lower voltages, questioning why it may burn out and whether it can be safely run at higher voltages.
  • Another participant shares their experience of successfully operating a 12V DC motor at voltages ranging from 7V to 14V, suggesting that studying the motor's datasheet is important.
  • Several participants propose using a pulse width modulation (PWM) controller as a more effective method for controlling motor speed rather than simply lowering the voltage.
  • One participant suggests using diodes to drop the voltage, noting that this method can provide a consistent voltage drop regardless of current and loading.
  • A participant inquires about the type of motor used in the pump, indicating that a permanent magnet DC (PMDC) motor would be preferable for PWM control.
  • A cautionary note is raised regarding the safety of using DC motors with volatile liquids, highlighting the risk of arcing and the need for proper ventilation.

Areas of Agreement / Disagreement

Participants generally agree that using a PWM controller is a better approach for controlling motor speed, but there is no consensus on the best method for voltage adjustment or the implications of running the motor at different voltages. Concerns about safety and motor type also remain unresolved.

Contextual Notes

Participants do not provide specific details about the motor's electrical characteristics or the exact nature of the liquid being pumped, which may affect the discussion's conclusions.

Who May Find This Useful

Individuals interested in DIY projects involving DC motors, liquid pumping systems, and those seeking to understand motor control techniques may find this discussion beneficial.

jjackson927
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Hi everyone,

I'm new here and I'm electrically stupid. I am working on a mock up of a system designed to pump a variable amount of liquid. I was looking the OEM manual for a small 12v pump and it said that the motor may burn out if run at a voltage lower than 12v.

I understand that the way to change DC motor speed is to vary the voltage. So my idea was to run the motor inline with a resistor to give it 6v and to then be able to switch it to 12v to increase the volume pumped.

So I guess my question is why would the motor burn out if run at low voltage? Can I run it at 12v and up it to 24v (it doesn't say anything about running it at high voltage)? Am I completely off base?

I realize my extreme limitations in this area, I'm just trying to put together a small scale mock up as proof of concept. Any help in this area would be greatly appreciated.

Thanks,
Joe
 
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welcome to PF!
no you are not completely off base.
i had used a 12VDC motor and we could up the speed from 7V to 14V.(60rpm tp 110rpm)
study the datasheet of the motor in hand and find out its electrical characteristics.
all in all its fun trying reliability.
 
Better to use a pulse width speed controller maybe.
 
Or drop the voltage with diodes which produce a fairly contstant voltage drop irrespective of current and loading of the motor.
 
Pumblechook said:
Better to use a pulse width speed controller maybe.

Yes, you do not slow down a DC motor by providing it a lower voltage -- the torque falls off too fast with voltage for that. Instead, you pulse-width-modulate the 12V power source to slow the motor down. So you would chop the 12V power at a few hundred Hz, for example to slow the motor down and still maintain a good torque.
 
Wow thanks, I'll look into that and post back with what i find.
 
What kind of motor is it that runs the pump? Series wound or PMDC? I hope you have a PMDC motor and a 12v PWM controller is definitely the way to go.
 
Hi,

A quick note of caution as you don’t mention if your liquid is volatile or not, DC motors have a horrible tendency to arc across the contacts internally so if you are trying to pump petrol or something, please proceed with extreme caution in a very well ventilated space, if you don’t your proof of concept may well be up for a darwin award.

Utwig
 

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