charger as power supply

Discussion in 'General Electronics Chat' started by fourls, Dec 28, 2012.

  1. fourls

    Thread Starter New Member

    Dec 28, 2012

    I am looking to find a battery charger combo where the battery charger not only charges the battery but also can be used directly as the power source to power me product. I am currently using a 9.6v nimh battery and would like to stay with that voltage if I can. Any help or suggestions of where I might find this would be greatly appreciated. thanks.
  2. KrisBlueNZ


    Oct 17, 2012
    You will need a separate output.

    You can't connect your load across the battery, unless its current drain is very low, because the load current would interfere with the charger's ability to monitor the current going into the battery, and you can't really power your load from a circuit that's designed to charge a battery, because a charger is not a simple voltage regulator.

    You need a power supply and a battery charger, either as separate modules or as a combined unit. Ideally this would include automatic changeover to the battery when the power fails.
  3. crutschow


    Mar 14, 2008
    If you Google "battery management IC" you will get many hits from companies such as Linear Technology, Maxim, and TI that make many different types of such devices. One of those will likely do what you want by monitoring the load current and controlling the battery charge current at the same time.
  4. ScottWang


    Aug 23, 2012
    You should separate to two output as KrisBlueNZ said.
    You can use LM317 to build your power source and charger.
    One LM317 for the voltage power source, and another LM317 can provide the current limit, the current of Battery is unknow, so assuming that the current is 2A, so the charge current is I = 2A/4=500mA, you just set the current limit on 500mA for the LM317, you will need about 4 hrs to completed the charge.
    You can find the current limit formula on the below page of the datasheet.

    LM317 datasheet, page 5 for the adjustable power, page 9 for the ccurrent limit:

    You also can search on google as : lm317 circuit, lm317 schematic, it will easy to bring you to get the info you want.
  5. fourls

    Thread Starter New Member

    Dec 28, 2012
    I don't need the charger to power the motor in my product and charge the battery at the same time. It would be fine if the motor ran on battery power if the battery is plugged in, or ran on the power of the charger with the battery sitting on the shelf somewhere and charging took place at a time when the product was not in use. I am currently using a 9.6v battery pack like is used in a r/c car.
  6. #12


    Nov 30, 2010
    You're still asking for a 2 purpose device. One of them deals with the picky charging requirements of the NiMh battery and the other deals with the current the motor wants. Very different animals.
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Are you talking about the small rectangular type that are rated at about 150 MA-hr?

    I use a constant-voltage charger to charge mine, that could drive two outputs if the current drain is not too high.

    What is the current load?
  8. MKCheruvu


    Nov 20, 2012
    A constant Voltage/current Power supply may suit your requirnment. where in upto a load current the supply acts as a constant Volatge source .When the Load current reaches to a pre-set current value, Supply goes into a constant current mode.
  9. takao21203

    Distinguished Member

    Apr 28, 2012
    There are some charger with USB outlet.

    Besides that, I have never seen or heard of this, to use a battery charger for power supply. Except a 12V charger, which often does not have a controller.
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    NiMH is not that critical, if this supply is to be connected all the time then just use a voltage regulated supply and it will float charge the battery and also provide any current as needed to operate the device. It's done in a lot of commercial products.