12V Motor Soft Start Circuit Ideas

Discussion in 'The Projects Forum' started by TurboDan, Jun 3, 2009.

  1. TurboDan

    Thread Starter New Member

    Jun 3, 2009

    This is my first post!

    I am looking to design a soft start motor control for the radiator fan setup that i have in my car. I'm looking at using an IRF1010E MOSFET and maybe a RC timing circuit hooked up to the gate to do the actual fade on. Fading out is not important, as I am looking to simply reduce the load on the charging system during start up. Also, the precise fade time is not important, as long as it is about 5 to 10 seconds.

    The fan currently is hooked up to the ground, and receives +12V from a relay. If an n-channel FET is used, I think it would be alright to hook this circuit up to the ground of the radiator fan motor, so that when the fan receives 12v, the mosfet would slowly allow more ground. The fan motor currently uses about 10 amps continuously, with a 30A transient upon startup. I'm basically looking for comments on how to go about this, or if my idea looks good, let me know. Im not against using some sort of timing chip in the design, I was just thinking the the RC circuit may be a little more robust in weather extremes? Thanks in advance!


    AAC Fanatic!

    Jul 1, 2008
    Is it really worth the effort? I mean DC brush motors are not like an AC Induction motor. They don't have a large start current.
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    You can use a mosfet between the ground wire of the fan and battery ground, then put a capacitor on the gate of the mosfet and a resistor to give a soft turn on. You shoulkd probably put another (higher calue) resistor on the gate of the mosfet too to discharge the cap when the fan is off.