Voltage Regulator Selection help for motor

Discussion in 'The Projects Forum' started by rasosina, Oct 6, 2015.

  1. rasosina

    Thread Starter Member

    Jun 30, 2010
    Hi All,

    I'm working on an electronic project that needs to run a DC motor at a constant speed (only start stop operation needed from motor). I have found a motor (Namiki 22CL-3501PG) which suits my torque requirements. My power source will be 2 AA rechargeable Batteries (ENERGIZER NH15-2300) which i'm planning on connecting in series to get 2.4V input voltage. I just need to find an appropriate voltage regulator to supply the motor with 12V and I was wondering what's the best way to go about doing this design?

    1. Would I need to find a regulator that can supply 12V with an enable signal and control the enable with a micro controller to turn on/off the motor?
    - if this is the case, in the motor specs it says stall current is 1.8A, would the regulator need to be able to supply all of that current at 12V? I have not been successful in finding any boost DC/DC supplies that can supply 1.8A @12V with a 2.4V input.
    2. Would I need to run this motor via PWM?
    - if so then what's the best way to generate the PWM at 12V? I'm using a PIC micro controller with 3.3V input voltage.
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Are you expecting that all of the power to run the motor comes from two AA batteries? The motor requires 1.8A*12V = 21.6W. Any step-up-converter is no better than about 80% efficient, so you need ~30W from your batteries. Two AA cells will supply 30W for about 2seconds...

    You need one of these:

    Last edited: Oct 6, 2015
  3. MaxHeadRoom


    Jul 18, 2013
    Were this me I would be looking at a RC 3pack size LiPo for 12v also the advantage of rechargeable as well as the current capacity.
  4. rasosina

    Thread Starter Member

    Jun 30, 2010
    thanks for your input guys, but i found my solution. turns out my regulator doesn't need to supply all of the 1.8A stall current. 500mA would be more than enough for my load. So i'll just have to find a converter that can supply 500mA @12V with 2.4V input voltage.

    would work to 0.5A * 12V = 6W load power
    6W / 2.4V = 2.5A current from battery. If my load runs for 15-20 seconds continuously I think it should be ok.

  5. InspectorGadget

    Active Member

    Nov 5, 2010
    You're going to have significant losses at 2.5A out of the batteries and inefficiency with such a great step-up ratio. Best to use higher starting voltage and make your step-up more modest.

    What is your application? What are you doing with this? Design of an electronic system is more subtle than arbitrarily selecting a starting point and an ending point and then saying, "OK, I've got to do anything necessary to get from A to B." Sometimes it's best to look at the whole problem and consider alternatives that make things easier for you. Or maybe the losses are acceptable and the primary-compatible rechargeable batteries have other advantages. In any event it helps to know what you're doing.
    SgtWookie likes this.
  6. SgtWookie


    Jul 17, 2007
    You first mention that the motor meets your torque requirements, and later you say that you think that you'll need less than 1/3 of the stall current continuously. Good luck with your expectations of meeting your torque requirement, as you will need it - along with more current.
  7. rasosina

    Thread Starter Member

    Jun 30, 2010
    Hi All,

    Thanks for everyone's input. To clarify, the motor has stall torque of 1.6Nm @1.8A and continuous torque of 0.5Nm @0.5A. The continuous torque rating was meeting my requirements. I shouldn't have been looking at stall current.

    The application is automating opening and closing of my blinds. The the system is pretty basic:

    PV module
    -> MPPT charger
    -> Batteries (i'm thinking 4.8V rechargeable LiPo as MaxHeadRoom suggested)
    -> 3.3V switch mode buck DC/DC -> PIC micro controller, sensors, LEDs and other components
    -> 12V switch mode boost DC/DC -> DC motor

    The motor would take about 5 seconds to fully open or close the blinds, so it's ok if losses are high as there's a PV module that will recharge the battery throughout the day.

    Basic operation is: remote control sends open/close signal to IR sensor, the uC will then operate the motor in forward or reverse mode. There will be limit switches at top and bottom that would signal back to the uC to stop.

    All suggestions/comments/criticisms welcome

    Last edited: Oct 8, 2015