H-Bridge to control dc motor

Discussion in 'Embedded Systems and Microcontrollers' started by skusku, Feb 24, 2013.

  1. skusku

    Thread Starter Active Member

    Aug 9, 2009
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    Hi guys. Hope this is the correct place for thread.
    I want to control a dc motor by using an Arduino.

    What I don't know is whether the H-bridge will be able to handle the current? I'm taking a 12V cordless ryobi drill apart and that motor needs to be controlled. At this moment im thinking of using a L293D H-Bridge IC.

    The other thing that bothers me is the 12v battery pack that comes with the drill controls the motor just fine, but using a 7.2ah 12V battery just makes it do nothing. Is the 7.2ah too much?
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    The capacity of the battery is not you main concern for the h-bridge design. The important number to find out is the current rating on the motor that you are trying to drive and make sure the h-bridge can handle that. I believe the L293 can only handle 1 amp. A higher capacity battery should just run the system longer.
     
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    The particular motor current rating you want is the stall current which can be much higher than the running current.
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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  5. skusku

    Thread Starter Active Member

    Aug 9, 2009
    63
    1
    Thanks but the problem is there are no ratings on the motors. I will check the part numbers to see if I can maybe find something.

    Just to clear confusion, So the battery output current will not blow the H-Bridge IC, but if the dc motor pulls too much current then the IC might lose the magic smoke?
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The H-Bridge can work with the battery Voltage, but may release magic smoke when the current surge is over 2A frequently. I've seen L298N Drivers get warm when driving a pair of 500mA@6V Hobby motors.

    The good news is that you are under 15V, so there may be an IC with everything you need built.

    What we need is the peak (stalled) current rating of the motor, and current drawn by the motor when spinning free. I'm guessing the voltages will be between 12 and 13.8 or so.
     
  7. skusku

    Thread Starter Active Member

    Aug 9, 2009
    63
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    So basically it means that if the power supply or battery is rated at lets say 5amps, it will only put current out for what is needed by load? Is that correct?
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Yes.

    A car battery is rated for several hundred amps or more. It doesn't "push" that current until a low enough resistance (starter motor) is connected. Example, the dashboard lights which use very little current.


    Look up Ohm's law. The supply needs to be capable of providing the needed current for a desirable amount of time.

    That's why so many different batteries are available. Some don't use very much current at all, such as a watch, and have a small button cell. Items with motors in them tend to draw a lot of current, and use larger batteries so the batteries aren't dead after one use.
     
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