Optimized battery life

Discussion in 'The Projects Forum' started by capg163, Nov 18, 2010.

  1. capg163

    Thread Starter New Member

    Nov 18, 2010
    I am working on a prototype where I need to operate a very small DC motor at 1.5 volts. The motor pulls 0.15mA. I need the motor to run on rechargeable batteries (AA size) and optimze the circuit for maximum battery life.

    1) What would be the best rechargeable battery for this purpose. I found a Li-Ion 3.7V 2600 mAh battery, but the voltage is to high.

    2) For this type of application, is it best to run the batteries in parallel or series.

    3) How do I regulate the voltage to exactly 1.5 volts.

    4) It the motor is run constantly, what would be the maximum battery life?

    I am really a novice at electronics (as you may be able to tell from the questions I am asking). Any help would be greatly appreciated.

  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    Do you have a datasheet for the motor? What will it be turning?
  3. wayneh


    Sep 9, 2010
    My rechargeable NiMH AA batteries are something like 2500mAh. The voltage will fall from ~1.4 to ~0.9 when it needs recharging. (It's not good to run them down farther.)

    Just guessing, but I'd bet this would work great for your motor, although it would slow down. If you really need accurate 1.5v (constant speed) everything changes.
  4. iONic

    AAC Fanatic!

    Nov 16, 2007
    It all depends on what your appliction needs. Is weight a factor, is size and shape a factor?
    Lthium batt's are probably the lightest for their size. If speed consistency is a factor than any unregulated supply, even the 1.2V NiMH battery will give you much variation. If a higher voltage source is regulated to a constant 1.5V you will gain consistant speed but loose some current to the regulating circuitry. You would need a very very low dropout voltage regulator with dropout voltages in the uA. Not sure they are out there.
  5. bertus


    Apr 5, 2008
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Does the motor need to run at a well regulated RPM, hence the 1.5V, or is it a single battery motor that just needs to spin?

    Will the motor be running continually? Is 150mA the current the motor draws with no load or loaded with a fan/belt/gear/etc?

    What is your desired run time between battery changes?

    Reason I ask is a buck converter would be the best way to get 1.5V from 4V at pretty high efficiency, but the simpler designs aren't extremely regulated, causing variations in voltage, which changes motor RPM.