Supply a DC motor with a SMPS power supply

Question

I want to supply power to a motor from a SMPS power supply. But the problem is SMPS supply have a feedback loop and a fail-back mechanism, so on the startup motor shows a near zero resistance [according to the electrical model of the DC motor ].

I don't have privileges to open up the SMPS unit and bypass that mechanism. So I need to find a walk around on this. Any idea guys?

I know motor soft starter unit will work, but I don't have that luxury to afford a one. Any other quick and dirty trick to make this work?

Answer 1

You can try something like this

^{simulate this circuit – Schematic created using CircuitLab}

Set the limit resistor high enough to keep the SMPS from current limiting, and the RC for enough delay to let the motor get up some speed. The relatively slow rise of the gate voltage will allow further motor acceleration during turn-on, but make sure the FET is beefy enough to a) do a good job of shorting the limit resistor, and b) soak up the power dissipated during turn-on.

Answer 2

For anyone wanting to play with the values here is a working schematic (using @WhatRoughBeast and @Brian-Drummond responses) that you can run the simulation (DC Time domain) with:

^{simulate this circuit – Schematic created using CircuitLab}

You'll notice at 4v the power MOSFET is triggered