I am trying to build a DIY one-way peristaltic pump with a 12V 100W DC motor (possible candidate : https://www.ebay.com/itm/DC-12V-100W-13000-15000rpm-775-motor-High-speed-Large-torque-DC-motor/352550303190)

which will be controlled by something like this PWM controller (10-50V, rated for 40A continuous & 60A max current) (https://www.ebay.com/itm/DC-10-55V-12V-24V-48V-30A-PWM-DC-Motor-Speed-Driver-Controller-Soft-Start-Switch/322616619257)

and will be powered by an SMPS supply such as this 12V 20A supply (https://www.ebay.com/itm/AC-to-DC-240-Watt-12-24-Volt-20-10-Amp-LED-Driver-Switching-SMPS-Power-Supply/183703093948)

So my question is:

  1. Will this setup work?
  2. Is either of the PWM controller or SMPS supply overkill or underwhelming?
  3. If this setup works, is it because of the PWM?

I ask because I've heard that DC motors draw 5~10 times their normal running current when they start up, so such setups involving SMPS power supplies may regard the initial current spike as a problem and may fail to 'turn on' properly, but a PWM helps with that problem.

But my understanding is that a PWM turns the flow of electricity on/off really fast so as to modulate the total electricity passed through but the current load (amps) stays untouched, so I'm not really sure what happens here.


1 Answer 1


This PWM appears to be a good choice as it has an unspecified SOFT START.

This means the duty cycle must start from 0 to the pot set value for some reasonable preset time such as >0.1 second by design assumptions for small motor start time.

Motors have an inductive where current rises with dI/dt = V/L so if dt starts at 0 then the soft start PWM ought to eliminate the or reduce the 10x start surge significantly. Normally the start surge is due to the full voltage integrated to reach V+/Rs the coil resistance. But with a "soft-start" or ramped PWM duty cycle to set level by Pot, the average voltage starts low and the pump starts slow. I would expect this soft period to be at least 100ms but preferably >1s with only 10% of the starting current to avoid full power start of 10x rated current.

If the Soft-start was done right for motors, with this 100W/12V = 8.2A motor a 15A PWM soft-start could work but I see it has a 30A rating which will run cooler.

  • \$\begingroup\$ Nice mustache Tony \$\endgroup\$
    – Huisman
    Commented Dec 16, 2019 at 8:40
  • \$\begingroup\$ Thank you! I have learned today :) There seems to be relatively few (cheap) controllers which claim to have the soft start function. Assuming that it is not a basic feature for such cheap $10 controllers, you're saying that the setup might not work if I used a similar controller but without the soft start function, right? \$\endgroup\$
    – Bottlejean
    Commented Dec 16, 2019 at 17:03

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