Battery charger cutoff device

Discussion in 'The Projects Forum' started by beaver07, Jun 19, 2013.

  1. beaver07

    Thread Starter New Member

    May 11, 2011
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    I’m a novice, so please bear with my ignorance. I want to build a device that will sense when a rechargeable battery is fully charged and then stop charging it. The charger that I have is the common type small 110 volt transformer which plugs directly to the device to be charged. I have several items in need of such a device , and the batteries range in output voltages from 1.5 to 19 VDC.

    Many years ago I built (but not designed) some electronic stuff using tubes, but, although I understand resistors and capacitors, I am not knowledgeable with regard to solid state circuitry.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Your better off buying a dedicated charger for the rechargeable battery type, as there are several types of rechargeable batteries.
     
  3. #12

    Expert

    Nov 30, 2010
    16,266
    6,777
    Let me push a bit harder on that. There are several recent types of batteries that are VERY picky about their charging methods. You can't do a universal charger any more. You are going to have to decide whether to limit the types of batteries you wish to maintain and/or build several different charger designs, many of them based on an integrated chip that was designed for THAT battery type.
     
  4. beaver07

    Thread Starter New Member

    May 11, 2011
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    Maybe I misstated my question. I don't need to build a charger, I only need something that goes between the charger and the device being charged. I'm hoping that that "something" will sense when the battery is fully charged and then stop the charge.
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Yes that is exactly what chargers do, stop when its full
     
  6. beaver07

    Thread Starter New Member

    May 11, 2011
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    I am a little confused. Let me explain why. I have an electric shaver for example whose user manual says that if the charger is allowed to continue after the LED begins to blink, the battery life will be shortened. This admonition also appears in a toy RC helicopter's manual. Please explain.
     
  7. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    What kind of charger are you using ????
    Personal I would buy a better charger and use that..
     
  8. Shagas

    Active Member

    May 13, 2013
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    What this probably means is that the recharger is not intelligent , in the sense that It doesnt cut-off the supply to the battery when it senses that it's full .
    It's about cost reduction.
    I'm guessing you are using a cheap shaver and a toy Rc helicopter speaks for itself.
     
  9. Shagas

    Active Member

    May 13, 2013
    802
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    It's not that simple.
    The charger has to be digitally programmable and has to be 'told' what battery is being connected and how many cells they consist of .
    You can make a charger that charges a specific say 'Nimh 2 cells' but that's not going to be easy either if you are a novice .


    Get a good universal charger for any type of chemisty and cell count . You can get decent ones for pretty cheap 30-70 bucks if i'm not mistaken .
    Check out hobbyking dot com . They sell everything for Rc models and you will find chargers there
     
    Last edited: Jun 19, 2013
  10. Shagas

    Active Member

    May 13, 2013
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    I think that you can't do it as simply as that
     
  11. beaver07

    Thread Starter New Member

    May 11, 2011
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    Is there some way to make something that detects a balance such as when the charging current equals the battery's fully charged state? Could such a thing then discontinue the charging?
     
  12. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,036
    Yes, but the devil is in your "battery's fully charged state". That determination depends on different criteria for every battery, it's chemistry (lead vs. ni-cad vs LiIon, etc.), its capacity, even its temperature. So unless you have a smart human to match a charger to the right battery, you need a complex smart charger that can run experiments on the attached battery to attempt to determine how to best charge that battery. That's not so easy.
     
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