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Charging batteries

Discussion in 'Electronic Equipment' started by Alan, Oct 3, 2005.

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  1. Alan

    Alan Guest

    Hi all, I have got a few different battery types that all need charging.

    There are different voltages ranging from 3.5 up to 9 volts, they are used
    to drive small electric ride on toys and similar usage.

    They are all sealed dry batteries.

    My question is this, do I need to buy a special multi voltage , variable
    amperage charger OR can I use a Walwart type power supply that allows me to
    lower and raise the voltage from 12 all the way down to 3 volts.... but the
    amps remain the same.

    I understand about trickle charging batteries as I worked as a mechanic for
    a few years but my knowledge is limited.

    Lastly is there a fundamental difference between trickle charging and
    Walwart style charging?

    I am just worried that I will roast all the batteries and end up having to
    buy them all again.

    Regards Alan

    PS I would like a set up using crocodile clips rather than a plug in affair,
    as all the batteries are different shapes.
     
  2. Robert Baer

    Robert Baer Guest

    "Dry" batteries is a term normally used for the origonal carbon-zinc
    batteries, and are *NOT* rechargeable.
    And alkaline batteries are also *NOT* rechargeable (except for the
    Renewal(TM) type).
    I do not think that crocodile clips will fit.....
     
  3. mike

    mike Guest

    Need to know a LOT more about the batteries.
    If they're nicad or nimh, you can probably get away with charging at
    C/10. Use a high voltage supply in series with an appropriate light
    bulb. Select the light bulb for approximately what you need.
    Won't be perfect, but works.
    mike

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  4. Robert Baer

    Robert Baer Guest

    NOT a good idea: 1) too much voltage can cause over-charging and
    might cause damage, and 2) light bulbs have a fairly low resistance,
    which could result in too much current.
    The open-circuit voltage of the supply used for charging should be
    set to the highest voltage that the particular cell chemistry supports:
    NiCd runs from 1.20V to 1.35V; Li-ion runs from 4.1V to 4.2V; NiMh is
    about 1.2V.
    Either pick a resistor for C/10 rate based on "discharged" cell
    voltage near 80 percent of charged rating, or make a "constant current"
    limiter with a JFET and resistor.
    BEST, is to use a charger made for the cells; they are made to
    optimize charging time and protectionof the cells.
     
  5. mike

    mike Guest

    What you say is partially correct. You can certainly choose a voltage
    and light bulb that overcharges the batteries. The objective is NOT to
    do that.
    A light bulb makes a perfectly good positive TC resistor and a current
    source that is rather invariant over a reasonable voltage range,
    depending on the source voltage and bulb selection. If you select the
    voltage and light bulb correctly, it works just fine. It's plenty good
    for battery charging at approximately C/10 for nicads and NiMH.
    I am partial to #382 bulbs because they're small. YOu get 35ma give or
    take charging current. Parallel as many as you need.

    DO NOT GUESS. MEASURE THE CHARGE CURRENT.

    If you have wildly varying charge current requiremets, you can put the
    bulbs inside the device and the external voltage source.
    mike


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    Wanted, Serial cable for Dell Axim X5 PDA.
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    FS 500MHz Tek DSOscilloscope TDS540 Make Offer
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