L298 heating problem.

Discussion in 'The Projects Forum' started by temuri, Aug 26, 2013.

  1. temuri

    Thread Starter New Member

    Aug 25, 2013
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    Hi everyone,
    i am making a line follower + ball potter and got stuck in the initial phase.
    I need a little help with l298. Below i have posted the schematic i followed. The problem is when both enable pins are given high logic the IC heats up excessively even with a heat sink. Moreover, the motors only run when i lift the car from behind and at the floor they just give jerk, i have to push it from behind to make it go forward.
    I tested it directly on the battery, it works fine so i confirmed that my car is not over weighted.
    Battery = 2.5A, 12V.
    Motors = RS 545.
     
  2. tshuck

    Well-Known Member

    Oct 18, 2012
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    See the datasheet-the table in figure 6, page 6, in particular...

    Edit: you are probably also overloading your battery. See the stall current listed here
     
    Last edited: Aug 26, 2013
  3. CVMichael

    Senior Member

    Aug 3, 2007
    416
    17
    If you connect the motors directly to the battery, does it work? (does it move forward without pushing it?)

    Are you using motors with gears, or are the wheels connected directly to the motor shaft? (yes, this is a trick question)
     
  4. temuri

    Thread Starter New Member

    Aug 25, 2013
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    the stall current is 2A.
     
  5. tshuck

    Well-Known Member

    Oct 18, 2012
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    Per motor...are you only using one!?
     
  6. temuri

    Thread Starter New Member

    Aug 25, 2013
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    Yes the motors work perfectly fine when i connect them directly to battery.
    I connected them directly with wheels.
     
  7. temuri

    Thread Starter New Member

    Aug 25, 2013
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    per motor. i am using 2 motors.

    they both run fine when connected directly to the battry.
     
    Last edited: Aug 26, 2013
  8. tshuck

    Well-Known Member

    Oct 18, 2012
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    So your total stall current exceeds what you've said your battery can supply...
     
  9. temuri

    Thread Starter New Member

    Aug 25, 2013
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    so i have to use a 4A battery?
     
  10. temuri

    Thread Starter New Member

    Aug 25, 2013
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    A friend suggested me to use a transistor between the motor supply and o/p pins so it would reduce the current load on IC but i dont know how to do it and what transistor family would suit the requirement?
     
  11. tshuck

    Well-Known Member

    Oct 18, 2012
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    You have to use a battery that is capable of supplying the rated stall current for your motors.

    I'm curious, where are you getting your battery data, because it is not generally given as you have?

    So your friend is suggesting a driver for your driver?:confused:
     
  12. temuri

    Thread Starter New Member

    Aug 25, 2013
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  13. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Besides sizing the battery to handle the stall current, you might use one L298 for each motor. The two channels on the IC can be paralleled to increase max current to 4 amps. This gives a nice safety margin.

    See page 7, Figure 7:
    View attachment L298.pdf
     
    Last edited: Aug 26, 2013
  14. CVMichael

    Senior Member

    Aug 3, 2007
    416
    17
    I attached a schematic on how I connected the L298N to a microcontroller.

    You can see it in action here: http://www.youtube.com/watch?v=L3Dpe1v6G-w

    The EN_A and EN_B goes to a PWM signal to the micro, where I select the speed of the motors.

    For direction, for example if I want to turn on motor 2, then I set IN3 to high to go forward (depending on how you connect the wires on the motor), and I turn OFF IN3, and enable IN4 to go in reverse.

    You just have to remember NEVER to set IN3 AND IN4 high at the same time. So make sure you set IN3 low first and then set IN4 to high, and vice versa.

    I think this is what is happening in your case, that explains why the motor does not get a lot of power, because you are setting both inputs on high, but it should be only one at any time.
     
  15. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    You need more motor gearing, that will shift the run speed much higher in the motor powerband where it is more efficient and will draw much less current.
     
  16. temuri

    Thread Starter New Member

    Aug 25, 2013
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    i will try it.
     
  17. temuri

    Thread Starter New Member

    Aug 25, 2013
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    i fixed the inputs, that is I3 is high and I4 is low and vice versa for the other bridge so that the car will go only forward and i can steer it through pwm. But like i stated it doesnt moves forward on the ground i have to push it from behind.
     
  18. CVMichael

    Senior Member

    Aug 3, 2007
    416
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    Maybe you should post a picture with the motor and wheels?
     
  19. tshuck

    Well-Known Member

    Oct 18, 2012
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    Torque is dependent on current. Considering you aren't supplying the proper stall current, it's no surprise you aren't getting the stall torque...
     
  20. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The correct gearing will fix that fine, he just ignored my suggestion in post #15. :)
     
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