DC Motor Slow Start

Discussion in 'The Projects Forum' started by czars, May 11, 2013.

  1. czars

    Thread Starter New Member

    Jul 9, 2009
    7
    0
    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?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    Does the switching supply not have current limiting?
     
  3. cork_ie

    Member

    Oct 8, 2011
    348
    58
    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
     
  4. czars

    Thread Starter New Member

    Jul 9, 2009
    7
    0
    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.
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,789
    945
    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.

    [​IMG]
     
    aws505 likes this.
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,789
    945
    An even simpler arrangement that avoids any momentary disconnect through the switch.

    [​IMG]
     
  7. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    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.
     
  8. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
  9. Shagas

    Active Member

    May 13, 2013
    802
    74
    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.
     
  10. edwardholmes91

    Member

    Feb 25, 2013
    183
    18
    I'm a little confused with the switch, is it just a standard SPST? I've never seen that symbol before.
     
  11. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    I've never seen that symbol either, but I'm taking it as a SPDT slide switch, in this case wired to be a SPST.
     
  12. Shagas

    Active Member

    May 13, 2013
    802
    74
    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
     
Loading...