DC Motor Slow Start

Thread Starter

czars

Joined Jul 9, 2009
7
I want to run a small DC motor (6v @0.5A) from a 1 amp switching supply. However the motor starting current is too great for the supply. Does anyone know of an easy circuit that I can use to limit the motor starting current so that it will start and run on the switching supply?
 

cork_ie

Joined Oct 8, 2011
428
PWM may help - depends on the motor and what load is attched to it.

a Large capacitor in parallel with the switching supply would also help, it is worth a try
 

Thread Starter

czars

Joined Jul 9, 2009
7
The supply seems to have fold-back current limiting. The supply cycles (voltage goes up and down) at about a 2 second rate when the motor is attached.

I'd like to come up with some kind of voltage ramp up circuit that could limit the current that the motor would receive.

Putting a large capacitor across the regulator output concerns me because a large capacitor generally has a low ESR and may still cause the supply to shut down.
 

Kermit2

Joined Feb 5, 2010
4,162
You could try a high wattage low value resistor in a soft start circuit.

several 1 or 2 Ohm, 1 Watt resistors in series, or a single 5 or 6 Ohm, 5 watt resistor should work. The values are subject to change depending on how the motor reacts to them.

 

John P

Joined Oct 14, 2008
1,821
How about an electronic current-limiting circuit? Depending on how much voltage drop you can tolerate, you might get by without an op amp, though if you only have 5V to play with, maybe a circuit with an amplifier would be best.
 

Shagas

Joined May 13, 2013
804
SlowStartStop.gif

That's a really easy way to make a slow start for a motor.
(I hope the attachment shows up)


Bascially you use a transistor to drive the motor . The base is biased by a potential divider made by a resistor and a capacitor. When you power it up , the base will be at 0volts because the capacitor is empty , it starts charging up through the resistor and base voltage starts climbing and your motor gets a soft start .
If you are looking at the picture , it doesn't have to be a darlington imo.
 

Shagas

Joined May 13, 2013
804
If you are talking about the picture that I linked..

I have no idea , I think that it's just some push switch . I don't think it's important anyway
 
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