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Rechargeable batteries

  1. Jun 25, 2009 #1
    are there batteries that recharge while they are in use? basically, the context is that i need a battery to be powering a control system all the time, but this battery will obviously drain. i wanted a solar recharger so there is no maintenance, but now i'm not even sure if this type of system exists.

    the control system only draws 150mA of current and can have 9 - 12 VDC input.

    any advice?
  2. jcsd
  3. Jun 25, 2009 #2
    If the solar panel can supply 300 mA for example, then divert 150 mA to the control circuit, and the other 150 mA to recharge the battery
  4. Jun 25, 2009 #3
    You can not drain and charge a battery at the same time. Thats like using a electrical machine as a motor and a generator at the same time. Like waht suggestion you can manage the power between both of the components but you can't have your load in the same circuit as your charging circuit.
  5. Jun 25, 2009 #4
    There is no problem in charging and using rechargeable batteries at the same time. As long as the solar charger does not damage the batteries when they are not in use, the batteries can be recharging while the batteries are being used. If the solar cells cannot supply enough current to supply the cuurent drain when the batteries are in use, the actual current drain will be reduced by the current from the solar cells.
    I can drive my car with the headlights on and the air conditioner running, while the alternator is recharging my battery.
  6. Jun 25, 2009 #5


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    Staff Emeritus
    Science Advisor
    Gold Member

    The typical solution (for DC applications, at least), is to define four voltages:

    (1) the minimum voltage your load needs to operate
    (2) the battery voltage when at a full state-of-charge
    (3) the battery voltage when nearly empty
    (4) the voltage supplied by the charger circuit

    Make sure that (2) and (3) are greater than or equal to (1). Also, make sure that (4) is greater than (2); in other words, make sure that charger is capable of trickle charging the battery when it's full.

    For example: Car electronics need 12V to operate. Car batteries provide 13.4V or so when full. The alternator, which charges the battery, generally produces about 14V.

    - Warren
  7. Jun 25, 2009 #6


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    Staff: Mentor

    I don't think this is true. If the charger and battery are in parallel, the battery will supply energy to the circuit if its voltage is higher than the charger and pull energy from the circuit if its voltage is lower. That's what happens when you jump start a car.
  8. Jun 25, 2009 #7
    Yes, but you are not charging and discharging the battery at the same time in that situation. The battery is in one state or another, charging or discharging. Current either flows into the battery, or out of the battery, not both.
  9. Jun 26, 2009 #8


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    Gold Member

    Exactly, not both at the same time. Current flow is the key here.
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