I'm using 24V 25W 100RPM DC geared motor for boom barrier gate application.So I added an overload protection for that circuit but whenever the motor starts the inrush current is produced and it triggers the overload protection circuit.How will I reduce the inrush current? Some say about soft-start but that doesn't fit for my application.

  • \$\begingroup\$ You may need that inrush current to overcome the mechanical inertia... \$\endgroup\$ – Solar Mike Jan 30 at 5:25

24V 25W 100RPM DC geared motor That is about 1 amp of current but does not include startup current or 'jammed motor' current. Startup is at least 3 to 5 amps for a 10th of a second. A 1 ohm 10 watt wirewound resistor can choke back the high start current, as the voltage drop across the resistor is 1 volt per amp of current the motor draws, but this simple trick is limited to a 2 ohm resistor at 20 watts.

With a 1 ohm resistor a startup current of 3 amps creates a 3 volt drop to the motor, so for a 10th of a second the motor 'sees' only 21 volts. With a 2 ohm resistor the drop is 6 volts, so now the motor has 18 volts at startup. You cannot increase the resistor any more as the motor has to have enough torque to get in motion to move the load. If it bogs down at 2 ohms then 1 ohm is your limit.

As for a jammed motor only a fuse can stop damage to the motor or power source. Since the motor pulls at least 3 amps to start, a 5 amp MDL (slow-blow) fuse in series with the 24 volt line should work well. All of these parts including an inline fuse holder can be bought at many supply stores. No need to buy expensive electronic current limiters. This simple setup does not justify the cost.

NOTE: it triggers the overload protection circuit. There is the assumption that the power supply has enough current to start and run this motor. If the power supply is not rated for 3 to 5 amps at 24 volts then a more robust power supply maybe the answer, still possibly using the resistor.


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