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Battery suggestion for handheld unit?

Discussion in 'Electronic Basics' started by Joseph, Feb 27, 2007.

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  1. Joseph

    Joseph Guest

    I'm making a handheld unit and the enclosure that was dictated to me does
    not have a battery compartment door on it...so I have to use internal
    rechargables. my. The unit will get used 1hr/day, 5V @120mA, so my initial
    thoughts are to use 2 or 3 AA in series. The product life needs to be 5
    years without having to open the unit and replace totally dead batteries.

    Anyone know if the Sanyo NiMH Eneloops (low self discharge) will last 5
    years with proper care? How about the idea of just trickle-charging (C/10)
    the batteries overnight? A 13 hour timeout is still recomended for safety
    reasons - is there an easier way to do the timer than a separate processor?

    Li-ion are $$. Are they so 'good' you recommend them?

    Are pre-made battery charger OEM circuit-boards available? Somethng powered
    from a cheap wall-wart.

    thanks in advance
     
  2. The 5 year issue is going to be a problem. I like NiMHs (perform well and
    cost-effective) but I don't think you can count on 5 years. Li-ions are
    often rated at a maximum life of 3-4 years, even if not used (unless stored
    at a low temperature).
     
  3. Eric R Snow

    Eric R Snow Guest

    I've been looking at Li Ion batteries recently as NiMH replacements.
    Different sellers rate their lifetimes different. Their self discharge
    is considerably less than NiMH chemistry. Especially after the
    batteries are a couple years old. Li Ion can also be charged no matter
    how discharged they are (or are not), NiMH batteries cannot. Li Ion
    also have a higher capacity by weight and volume. There several
    companies making and selling charging ICs for cheap. Note that some
    batteries do not come with over discharge protection. However, ICs are
    available cheaply to remedy this also. After all the research I've
    done NiMH batteries lose in the final analysis. Over the lifetime of
    the battery they are more expensive to use.
    ERS
     
  4. Rich Grise

    Rich Grise Guest

    Find an old-style "cordless" phone, and hack into it to see how they
    do it. :) I've had one where the battery lasted about 5 years, but it
    was on trickle charge all of the time I wasn't using it. It used a 3-cell
    (about the size of AA cells) NiCd pack.

    Good Luck!
    Rich
     
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