HELP; solving noise on power rail

Discussion in 'The Projects Forum' started by helijoc, Nov 16, 2013.

  1. helijoc

    Thread Starter New Member

    Nov 16, 2013
    10
    2
    My project consists of a MC33926 Motor Driver Carrier, Arduino Pro Mini, motor, and video monitor.

    The Arduino sends PWM to the controller to drive a small 1 amp brushed motor. The video monitor watches the process.

    I have a 12 volt battery powering everything, the monitor takes 12v, the arduino receives 12v and regulates it to 5v which is shared with the motor controller logic. I am using a 7805 to drop the voltage to the motor side of the controller for the motor power.

    My problem is the monitor is getting horizontal lines and I have tracked it down to the 12 v power line. I have put caps on the motor, twisted the wires, etc. Nothing was working until I disconnected the 7805 from the 12v battery and used a second battery sharing the same ground. All the noise went away, so now to find a solution that allows me to use only one battery.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Most likely a ground loop caused by the motor current flowing along the power supply wiring going to the input of the regulator or into the Arduino board. Try returning the wiring feeding the motor board (both positive and negative sides) all the way to the (single) battery terminals rather than connecting it to the Arduino board.
     
  3. helijoc

    Thread Starter New Member

    Nov 16, 2013
    10
    2
    The arduino communicates with the controller, the controller powers the motor. The motor wires connect to the controller. The 7805 is connected to the battery, it supplies 5 volts to the controller which pass it on to the motor based on the PWM from the arduino.
    The 5 volt wiring that feeds the motor board, the one connected to the arduino is for the logic not motor power.
     
  4. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    I agree it sounds very much like some ground loop/power distribution problem
    @helijoc! Can you show some pictures and the schematic for your setup.
     
  5. helijoc

    Thread Starter New Member

    Nov 16, 2013
    10
    2
    I don't have a schematic like we are used to looking at since I am basically connecting pre made circuit boards together, how about a block diagram?
     
  6. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    Here's an approach I used with success on 12 VDC Busses. First pick a fair size torroid 1.50- 1.75 in. diameter. Wind one heavy(14 awg) Formvar or Haptz magnet wire cw(clockwise) up one half of the torroid (feed path) and then a second wire up the opposite half ccw (counter-clockwise) of the torroid (return path) Now the current paths are diametrically opposed to one another. The torroid itself will be a choke for high frequency harmonic currents. Coat asbly. w/ conformal coating or varnish to mechanically secure the winds.

    Cheers, DPW [Everything has limitations...and I hate limitations.]
     
  7. helijoc

    Thread Starter New Member

    Nov 16, 2013
    10
    2
    This sounds interesting, I will keep it in my "toolbox". I am wondering if I need to be so extreme with this project. Size is somewhat of a limitation, I am trying to keep it in as small of a package as possible. the total current on the whole system when the motor is running is 1.3 amps. The motor is capable of 1 amp stalled but typically only pulls 4-500 mah.

    [​IMG]


    [​IMG]
     
  8. helijoc

    Thread Starter New Member

    Nov 16, 2013
    10
    2
    I was wondering if a buck converter or DC-DC converter would simulate the "second battery" and provide the isolation.
     
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