connecting negative power supply

Discussion in 'General Electronics Chat' started by Aladdin83, Aug 19, 2008.

  1. Aladdin83

    Thread Starter New Member

    Jul 20, 2008
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    Hi all, I have two 12V batteries connected in series, to get 12V I can connect my load to directly to one of the batteriesto get a -12V I connect my load in reverse ** how can I get +12V and -12V from those batteries that are connected in series to use on a dual supply OPAMP IC, the IC has a -V and +V pins but it doesnt have a gnd pin
     
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    The connection between the batteries is the 0V point with +12V and -12V (with respect to 0V) either side.
     
  3. Aladdin83

    Thread Starter New Member

    Jul 20, 2008
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    thank you, I get the idea, but since the IC has no gnd pin, what would be the reference for the +/-12V in the IC? or should I just connect the positive end of the batteries to the +V pin and negative end to the -V pin and it would work?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    1) Connect the + terminal of one battery to the +V terminal of the opamp.
    2) Connect the - terminal of that same battery to the + terminal of the 2nd battery.
    3) Connect the - terminal of the 2nd battery to the -V terminal of the opamp.
    4) The two +/- connected battery terminals are your ground reference for other portions of the circuit.
     
  5. Aladdin83

    Thread Starter New Member

    Jul 20, 2008
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    thanks for the reply, so from now on, the mid point between the two batteries would be the ground for everything else I add.. what if I add a load that needs 24V to batteries, would that effect the circuit?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    It may or may not. It depends upon what you're adding. Right now, your question is far too broad in scope to give a decent answer.
     
  7. Aladdin83

    Thread Starter New Member

    Jul 20, 2008
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    ok, my project is to control a cart that has two dc motors on the back and two free wheels in the front, by a microcontroller.....I have the two batteries connected to motor drivers and the motor drivers connected to the motors of course, so I am using the 24V potential difference to control the drivers and I want to use the same batteries for my control system... would it effect the control system when the motors go to full speed and draws too much current from the batteries?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    You normally wouldn't want to "slam" full power to DC motors; that would be a waste of power. It would also make it more likely to lose control of it entirely, as the wheels may slip due to unequal traction. Plan on slowly increasing the average current flow to the motors by gradually increasing the PWM duty cycle. Rapid changes are not likely to work in your favor; it will also tend to waste a good deal of power in the batteries due to their internal resistance.

    [eta]
    DC motors generate back-EMF as their speed increases. The back-EMF is what limits their current draw for a given speed at a given load. As their load increases, their speed drops, the back-EMF drops, and current draw increases until equilibrium is reached, or the load increases to the point where the motor is stalled. A stalled motor will draw maximum current. If the situation is not handled correctly, the motor may overheat and burn up.
     
    Last edited: Aug 19, 2008
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