Motor control schematic critique appreciated.

Discussion in 'General Electronics Chat' started by Tobias, Sep 2, 2010.

  1. Tobias

    Thread Starter Active Member

    May 19, 2008
    158
    0
    Attached is a schematic for a board that I use to control four motors. I deleted have the circuitry to make it easier to read. The MOSFET spec sheet is attached too.

    I have two motors with the specs below operating on 24v. I have an input signal that is a PWM (75hz). This signal controls the speed of the motors. Each motor has an 18 tooth sprocket. I need to keep the two motors 'timed' between each other. Meaning I need to see equal amount of time between a left motor sprocket tooth to a right motor sprocket tooth and then right to left. I have the timing part sorted out pretty good.

    I want some input as to if I am going to motor control side correct. Once in a while I notice that a motor will start to turn slower than normal. So far I have just replaced the diode and MOSFET to fix the problem. I just am not too sure what is really happening or why. Once in a while a MOSFET will avalanche, short out and the motor will run all the time. I am betting the ES2D isn't an adequate piece. Any input is appreciated.



    Model Number N6835 Category 24V, Class F, Needle Bearings On Driveshaft Speed (rpm) 62 Rated Torque (lb-in) 79 Rated Voltage 24V Amps (24V model) 9.2 Amps (130V model) N/A Peak Torque (lb-in) 177 Motor HP 1/4 Gear Ratio 40 Radial Load (lbs) 120 Length XH (inch) 9.87 Weight (lbs) 9.9 Product Type 33A5FEPM-5N Accessory Shaft YES Connection Diagram 07410101
     
  2. gootee

    Senior Member

    Apr 24, 2007
    447
    50
    Do you have an oscilloscope? If so, have you looked at the gate voltage waveforms? And the output waveforms?

    You could be turning the MOSFETS on or off too slowly, sometimes, causing them to spend too much time in a not-fully-on state, with higher resistance and thus more heat generation. You generally want to bang the gates hard and fast. Do the MOSFETS ever get hot?

    Or, you could be getting ringing or even oscillation. Should there be a resistor in series with each gate? Or maybe a snubber network is needed somewhere?
     
  3. RmACK

    Active Member

    Nov 23, 2007
    54
    0
    +1 to gootee's advise. What are IC1a and IC2a?
     
  4. Tobias

    Thread Starter Active Member

    May 19, 2008
    158
    0
    IC1A and IC2A are the MOSFET drivers. Data sheet is attached. It will be this evening when I can get a scope hooked up to it and I will get a screen shot
    Toby
     
  5. gootee

    Senior Member

    Apr 24, 2007
    447
    50
    The gate voltage waveform alone should tell at least half the story. The output waveform will be extremely useful, too, especially if the gate looks OK.
     
  6. RmACK

    Active Member

    Nov 23, 2007
    54
    0
    Oh yes, the FAN3122, I recall seeing those last year -they were about the most low impedance driver I could find but were out of stock so used a TI part. I'm looking forward to seeing that gate drive since you're not using any gate resistance.
     
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