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Discussion in 'Misc Electronics' started by Dr. Slick, Oct 10, 2004.

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  1. Dr. Slick

    Dr. Slick Guest

    Good Evening,

    I'm building a 12 volt recharging system with
    a 12 volt, 0.375A (12"x12") solar cell, and this charge

    The battery is a 12 volt NiMH, 3AH.

    I would also like to be able to use a hank-cranked
    dynamo charger, and also a way to recharge the battery
    using regular 120 AC mains. The dynamo that i wish to
    use comes from a very cheap survival radio, that uses
    3.6 volt NiMH, but i think there are Zener diodes that
    limit the voltage coming from the generator to 7-8
    volts, so i think i can remove these to get more
    voltage (closer to 13-14 volts?).

    I believe i could just use a regular 13.8 volt
    DC power supply, and have a 3-way switch to go from
    the solar cell, to the dynamo, or to the AC power
    supply, directly to the charge controller above.

    I other words, the charge controller (made for
    photovoltaics) would be used for any of the three
    sources of DC power.

    Does this sound like a good idea? Or should
    i get a separate charger for the DC power supply?

    Is there a cheap, simple LED circuit that can
    indicate the charging function and the state of the

    Thanks for your help,

  2. CWatters

    CWatters Guest

    Best check that charge controller is designed to work with NiMH cells. They
    behave differently to Lead Acid cells.
    Might work but I suspect you may have to turn the dynamo 3 or 4 times faster
    (12/3.6 = 3.333 times). This might not be possible without changing the
    gearing? At that voltage/rpm the dynamo may not be very efficient.
    You need to find out more info. Ask the makers if it's possible to power the
    charge controller fro a DC source and what input voltage range is required
    to charge 10 NiMH cells.
  3. James Meyer

    James Meyer Guest

    You don't need a charge controller for the solar cell source. Its
    output is 1/10th of the battery's capacity and that amount of charge current
    will be fine with no controller in the system.

    You don't need a charge controller with the dynamo either.

    If you use a "normal" commercial battery charger for the 120 volt AC
    source, you won't need a seperate controller either.

    A simple voltmeter will give you all the information you need to
    determine the health of the battery.

  4. CWatters

    CWatters Guest

    The 1/10th overcharge rate is usually ok (in that the battery won't over
    heat or explode) but it might shorten the life of the battery if used long
    term. Manufacturers recommend a lower rate if you are planning to leave the
    battery on float for very long periods.
    eg cells that exhibit a higher than normal "on charge" voltage are less
    healthy.... or did you mean you can use a volt meter as a charge state
    indicator? That's only possible if you calibrate it carefully :)
  5. Joerg

    Joerg Guest

    Hi Dr. Slick,
    Look into real alternators for motorcycles or cars. These are usually
    much better quality and longer lasting. And cheap. Better bearings, too.

    Regards, Joerg
  6. Tom Seim

    Tom Seim Guest

    The charger you are going to use is not designed for a NiMH (they dont
    say, but I am sure it is a lead-acid type). Refer to a NiMH manual
    before you go ahead with this. Otherwise be aware that the battey
    might catch fire.
  7. James Meyer

    James Meyer Guest

    Solar cells will only provide current when the sun's shining. That
    reduces the total current available over the long term to a value that should be
    safe. Not to mention that most solar cell manufacturers rate their cells for a
    perfectly clear day on top of Mt. Everest during a solar flare. :cool:
    I meant that if one weren't going to automate the process or attempt to
    provide legally binding measurements, that a quick look at the voltmeter would
    provide all the information one should need to determine the condition of the
    battery. Of course the voltage would be different depending on the load and the
    temperature and whether the current was going into or out of the battery.

  8. m II

    m II Guest

    and when the planet is closest to the sun

  9. Dr. Slick

    Dr. Slick Guest

    You may be right, as the batteries they sell seem to be lead

    I was also looking at this charge controller:

    It seems a bit simple, but it may be good enough
    for what we need. It says it can take NiMH too.

  10. too.

    An alternator for an automobile, and probably a motorcycle also, are way
    too much for a charger that needs only a half amp. Cars use a hundred
    times that current.

    I've used a hard disk spindle motor to drive some LEDs. Try it
    It depends on the motor, obviously it has to have permanent magnets.
  11. Joerg

    Joerg Guest

    Hi Watson A.Name,
    The one I saw in a friend's scooter was just the size of a fist. After
    all, you need some mass and size if you want to operate it with a hand.
    Either the other hand needs to grab it or it would have to be mounted on
    something. There should also be suitable versions for riding lawn mowers
    and stuff like that.
    I have to try that. Wish I had kept the last HD that had croaked.

    Regards, Joerg
  12. Tom Seim

    Tom Seim Guest

    To safely charge NiMH you must sense & terminate charging on either:
    1. dV/dt drop
    2. dT/dt drop
    This circuit doesn't seem to do either. Check out:,C1,C1003,C1037,C1078,C1088,P7601,D5235

  13. Dave VanHorn

    Dave VanHorn Guest

    Newer NIMH's, like the C type cells from Sanyo, can take long term
    overcharge without problems. Check your data sheets.
  14. Dr. Slick

    Dr. Slick Guest

    Do you have to worry about Low Voltage disconnect with
    NiMH? With lead-acid, you obviously do...

  15. Dr. Slick

    Dr. Slick Guest

    This will power two 40-60 watt lights, with a
    motion detector attached.

    Are lead-acid batteries really the way to go?
    Some charge regulators don't have a low voltage disconnect
    circuits, so the battery can be drained if you aren't
    careful. If i'm not mistaken, NiMH don't have this
    problem, right?

  16. Tom Seim

    Tom Seim Guest

    Well, I did that. From Sanyo's manual

    "Also, to obtain a long service life from the Twicell, over-charging
    must be avoided as much as possible."

    This assertion that over-charging is ok comes up time and again. Yeah,
    it's ok if you don't care about battery life.

  17. Ken Smith

    Ken Smith Guest

    IIRC the Silver Chloride (or something like that) battery loved being
    discharged. You had to discharge it for storage. You could charge it up,
    use it for a day and then run it flat. Discharged it would last for

    The down sides were: Charged it went bad in a month and they cost a *LOT*
    to replace. The only Silver Chloride batteries still in use that I know
    of are the ones for testing blasting caps.
  18. Dr. Slick

    Dr. Slick Guest

    NiCD cells DO like to be drained completely flat.

    Otherwise you get the old memory effect if you
    try to recharge them when they are only partially
    discharged, and the cells will then not hold a full

  19. The scooter size still takes too much power to operate by hand. And the
    smaller engines on lawn mowers that I've seen use the coil for the
    ignition to generate power for the lights, etc. This is a part of the
    flywheel, and can't be removed and used as a unit.
  20. N. Thornton

    N. Thornton Guest

    Yup. Youll need more speed for more V though.
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