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I have 12V peristaltic pump and need to control its flow (lowering down more specifically)

Two options I came across:

  1. POT in series

  2. Voltage divider

Is there any shortcomings in above schemes?

What is best way to reduce flow without involving controller i.e using analog circuitry?

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  • \$\begingroup\$ Reduced torque (easier to stall, poorer speed stability) is a shortcoming of both, which can be improved by using PWM control. \$\endgroup\$ – jippie Feb 27 '16 at 7:08
  • \$\begingroup\$ Can you please suggest any ref circuit? Thanks \$\endgroup\$ – Electroholic Feb 27 '16 at 7:20
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    \$\begingroup\$ Personally I wouldn't bother designing it for a one off job and just check eBay for a cheap PWM module that does the job at the required specs. \$\endgroup\$ – jippie Feb 27 '16 at 7:23
  • \$\begingroup\$ I want to make it without controller. Is there any option to do so? \$\endgroup\$ – Electroholic Feb 27 '16 at 8:49
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    \$\begingroup\$ Leave alone the electrical section to its original and do your mod on the fluid flow rate by installing a proportional valve. \$\endgroup\$ – soosai steven Feb 27 '16 at 9:20
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The pot or voltage divider circuits don't work well because as the motor comes under load the current demand will increase and the voltage will drop. If you try it under load you will probably hear the motor speed rise and fall as the peristaltic rollers engage and disengage.

Here are two ideas:

  1. Run the pump from a 6 V battery.
  2. Drop the voltage using diodes.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Using diodes to drop voltage.

Diodes have a much more constant voltage drop at varying currents. The circuit of Figure 1 shows a means of getting a range of near-constant voltages very easily. Allow 0.7 to 0.9 V voltage drop per diode. You haven't given us a motor rating so I've assumed it's small and that the voltage drop is 0.7 per diode.

Note that if you test with a multimeter the last two diodes on my schematic they would show 9.2 V as there is no current passing through them and, therefore, no voltage drop.

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