NiMH battery charger HELP!

Discussion in 'The Projects Forum' started by wheetnee, Oct 3, 2009.

  1. wheetnee

    Thread Starter New Member

    Oct 1, 2009
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    ---close-----
    will keep up work later
    thanks guys
     
    Last edited: Oct 6, 2009
  2. HarveyH42

    Active Member

    Jul 22, 2007
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    A good start would be a data sheet for the batteries, the manufacturer will usually provide pretty detailed information on how best to charge their batteries. Chargers are pretty cheap these days, so haven't thought about building one in a while, don't see much reason to. There are several chips available to handle most of the work, that I've read about in past threads (use Search), might be what you need, or the data sheets might give you some ideas from what the do, and how the work. Might try Google for 'PIC Smart Charger', although an AVR micro would probably be a better choice. :)
     
  3. wheetnee

    Thread Starter New Member

    Oct 1, 2009
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    well its a electrical engineering school project and our task is to build a charger with wires/resistors/op amps/ transistors/ capacitors...
    and the data sheet for our battery doesnt give much information on how to charge it :S
    oh what kind of chips?
    thanks for your suggestions btw!
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    For NI-MH, if you plan to "quick charge" them, you need reliable temp sensing for the cells and a way to terminate when the temp rise rate gets faster. NI-MH fast chargers are not easy to build, voltage sensing is not reliable IMHO although some may be using it. The significant change in voltage occurs well after the battery is being overcharged. The temp rises continuously during charging but rises faster at the full charge point. You have to detect the change in slope of the temp/time curve to detect full charge.

    I recommend you go to the battery manufacturer's web site as they may have application info available.
     
  5. tibbles

    Active Member

    Jun 27, 2008
    249
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    hi all
    ive just built one of these not computer controlled though, i will try an find the schematic, a very simple circuit o here it http://www.talkingelectronics.com/te_interactive_index.html hows that for service.
    will try and get back on the computer interface,i must admit i dont like using the ports for non standard applications.
     
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    If this has to be a computer controlled fast charger, IMHO it is not a 2-3 week project. Maybe EE students are smarter now than they were when I was in school....:D

    I don't remember knowing any graduating seniors who could have pulled it off.:p

    You need to research battery makers info on cell characteristics. Also, search the web for charger circuits and application info.
     
  7. wheetnee

    Thread Starter New Member

    Oct 1, 2009
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    the project was actaully assigned 2 weeks ago but me and my group kinda procrastatinated with the research and were totally confused so we only have around 2-3 weeks left to hand it in! :(
    this was our datasheet: http://data.energizer.com/PDFs/nh12-850.pdf

    also, our Teacher Assistant said as the battery is charging, the resistance of it changes, so its hard to regulate the amount of current flowing through the battery. Efficiency is one of the areas we are marked on, So I'm not sure how to make it work ,I guess we need to build some sort of current regulator?

    for the charging 1/2/3/4 batteries, my group was considering if we took one battery out or switched one off, how would the circuit be affected? would the current flowing in the batteries have to change?

    should I add resistors between each battery?

    oh and our group plans to charge the batteries in about 6 hours? (3 hours seems to hard, we calculated we needed 1.2 Amps flowing in the batteries and thats way too much from our supply)

    thanks for all the replies so far...

    any other suggestions?
     
  8. tibbles

    Active Member

    Jun 27, 2008
    249
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    as you can see the batteries will be charged in series,i am having disscussions on another forum regarding charge rate, the designer has chosen to stipulate that the batteries are fully discharged when put on charge, this presumably dispenses with any sophisicated monitoring circuit.

    you can probably use the computer to do the timing and prograr
     
  9. tibbles

    Active Member

    Jun 27, 2008
    249
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  10. wheetnee

    Thread Starter New Member

    Oct 1, 2009
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    --------------------------
     
    Last edited: Oct 5, 2009
  11. tibbles

    Active Member

    Jun 27, 2008
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  12. tibbles

    Active Member

    Jun 27, 2008
    249
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  13. Bernard

    AAC Fanatic!

    Aug 7, 2008
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  14. tibbles

    Active Member

    Jun 27, 2008
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  15. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Google: Pansonic Ni MH Handbook
     
  16. wheetnee

    Thread Starter New Member

    Oct 1, 2009
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    if i were to draw a schematic on just the batteries alone,,, would it look like this?

    [​IMG]

    i just want an idea on how to connect the batteries in the battery charger before connecting to the rest of the circuit. series or in parallel? with resistors or capacitors in between?i also have to implement DAQ in it too, where does that go? are they any ideas bout the battery connection? i'm really new to building stuff like this so im kinda confused! thanks guys for all your great help tho! i really appreciate it as i have to meet my group tomorrow and i wanna show i had some progress haha
     
  17. tibbles

    Active Member

    Jun 27, 2008
    249
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    whatnee, i have posted several circuits you clearly havent looked at these! they answer most of your questions.
    to get down to basics,go on maplins website, you need an AA four battery holder and a pp3 clip --yes they are connected in series
    so if you remove a battery there will be no circuit as in christmas tree bulbs.
     
  18. tibbles

    Active Member

    Jun 27, 2008
    249
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    a possible plan b for computer monitering your charger if all else fails.
    there are plenty of pc based oscilloscopes around many with free trials which i believe use a simple input to your sound card.
    you could quite easily convert your temperature/voltage/current values to a frequency and monitor them on the oscilloscope.
    well it was just a thought.
     
  19. tibbles

    Active Member

    Jun 27, 2008
    249
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    ps
    check your power supply- 12 volt should be ok .check polarity, check its DC and capable of supplying at least 2 amps, sometimes stated as
    2000 ma, as there will be losses in your circuit,
     
  20. tibbles

    Active Member

    Jun 27, 2008
    249
    3
    perhaps someone could help me with this one, i made my own charger because i couldnt find one that charged 8 cells, but i was a bit puzzled by the voltage needed- say 4 cells in series =around 5 volts. presumably the charger needs to be set at something higher than that.
    im wondering how sophisticated these chargers need to be, i have a couple of b&d drills which have been charging quite happily for the last 6 years ,with nothing more than a 7 volt dc power supply straight to the cells.
    regards
    d
     
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