Charge a battery in-circuit

Discussion in 'The Projects Forum' started by aterhune1984, Mar 1, 2011.

  1. aterhune1984

    Thread Starter New Member

    Nov 24, 2010
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    I am a bit confused I suppose on how to charge a re-chargable 3.6v battery in circuit... Basically I will be putting the battery in a device that runs off of 3.6V I will not be removing the battery in order to charge it, it will stay in the device... I am confused as to how to charge the battery without powering or damaging the device the battery is running at the same time... if that makes any sense??? Likely I will be using a AC to DC wall charger to power the recharging circuit.

    Thanks
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    Need much more info! Is this a device that can be powered either way, but normally does NOT charge the battery, and now you want to modify it so that the battery charges while plugged in?
     
  3. aterhune1984

    Thread Starter New Member

    Nov 24, 2010
    25
    0
    This device will be solely battery powered with 3.6V battery. Plugging this device into the AC DC adapter will charge the battery but will not power the device itself while it is charged in, After unplugging the charger the device will function as normal.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,792
    948
    [​IMG]

    This will be the kind of charger terminal you will need. The wiring will be slightly different in your case however.

    When the plug is NOT in the socket, a contact will be closed and allow the battery to power the device.

    When the plug is inserted it will open that contact and connect the battery to the charger instead.

    Do you understand the description?
     
  5. aterhune1984

    Thread Starter New Member

    Nov 24, 2010
    25
    0
    That part makes sense however I do not know how to charge a rechargable battery, it may seem trivial but I am lost for now. do you connect negative to positive, and positive to negative to charge it, etc, is there a good tutorial out there on how to charge a rechargable battery?
     
  6. wayneh

    Expert

    Sep 9, 2010
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    A brief search will find you more than ever dreamed of. Most charging strategies work to reduce charging current as the state-of-charge of the battery approaches 100%. High current to quickly get most of the power back into the battery, followed by a lower current to avoid heating and overcharging, and finally a trickle to keep the battery fresh and take it to 100% charge without going over. A key goal is to NOT overcharge, as this causes irreversible damage to the battery. The simplest strategy that takes care of these concerns is charging under a constant, regulated voltage, perhaps with a current limiter to protect the charger when a charging a near-dead battery. Current starts high and falls to almost nothing as the battery is held at the target voltage.
     
  7. ddurgin

    New Member

    Mar 2, 2011
    4
    1
    3.6V sounds like a Lithium-ion. If so, you'll need a 4.2V regulated source current limited to about 600mA for most cells. Wire (+) to (+). Li batteries are only sold with built in protection circuits. Voltage will rise from ~3.6V to 4.2V while in current limit mode, then the current will taper off durring constant voltage time. The battery is charged when current drops to ~100mA. Terminate charge there, do not trickle charge if Lithium-ion. Good Luck.
    Hope this help!

    DD
     
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