USB to charge Nickel Metal Hydride battery pack

Discussion in 'The Projects Forum' started by alyeomans, Jun 18, 2016.

  1. alyeomans

    Thread Starter Member

    Sep 13, 2010
    29
    2
    Hi All

    I am looking to implement a method for charging 3 nickel metal hydride batteries from USB. The charging power will be triggered from an FT232RL chip once the usb connection is enumerated.

    So focusing on USB 2 with a maximum charge current of 500mA. Battery pack includes 3 cells in series with a nominal voltage of 3.6V and maximum charge voltage of about 4.6V ish. Previously to charge NMH I have used a constant current source and monitored the battery voltage for the voltage drop.

    Should I use the USB 5V through a 10R resistor to the battery? Or any other recommended methods?

    Alyeomans
     
  2. hp1729

    Well-Known Member

    Nov 23, 2015
    1,948
    219
    I recommend charging at a lower current for a longer period.
     
  3. alyeomans

    Thread Starter Member

    Sep 13, 2010
    29
    2
    Thanks hp1729 Pack capacity is 4500mah so I'd like to keep is as high as possible as this makes the negative delta voltage easier to detect.

    I'll post the circuit shortly.

    A
     
  4. alyeomans

    Thread Starter Member

    Sep 13, 2010
    29
    2
    See attached schematic (currently work in progress). I maybe mistaken however is the USB 5V and a resistor mainly acting like a current source?

    [​IMG]
     
  5. hp1729

    Well-Known Member

    Nov 23, 2015
    1,948
    219
    Charge rate is always 100 mA? Are you going to overcharge the battery at that rate? Ah! You monitor the voltage and shut off charging when complete? Good! Recharge when the battery drops below a certain amount.
     
Loading...