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Battery Charger with auto shut-off feature

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by hardcore misery, Jul 7, 2007.

  1. hardcore misery

    hardcore misery New Member

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    Is it possible to make a battery charger that turns off automatically when the battery installed(for example, a cellphone battery) is already full-charged by the battery charger? or install a timer(which can be setup by the user, whether to set the timer at 3hrs or anytime you desired based on the estimated time the battery will be in full-charged)and shuts-off the battery charger?

    it would be impractical to interface the batter charger on a Visual Basic program, so is there any way to do this?
     
  2. Leftyretro

    Leftyretro New Member

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    Most 'automatic' battery chargers utilize a end of charge voltage set-point to stop the main charge and/or switch to a trickle or maintaining charge.

    Certainly a timer, mechanical or electronic, is a simple addition to make but without the voltage derived end of charge function it would still be possible to overcharge and damage batteries due to underestimating the state of charge of the battery when charging starts.

    I'm sure there exists somewhere battery chargers with serial or other communications ports for computer communications, however standalone chargers are the most common.

    Lefty
     
  3. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    You can interface the battery charger to the PC's Visual Basic program, using the PC's parallel port.

    The port can drive a serial ADC, say 10 or 12 bit, the VB prog can read the battery state and then switch a relay
    via the port to disconnect the charger from the battery at a predetermined voltage.
     
  4. dave

    Dave New Member

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  5. hardcore misery

    hardcore misery New Member

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    yes, but it would be impractical to use a PC just for timing a battery charger... i hope that there are other ways to do that...
     
  6. mcs51mc

    mcs51mc New Member

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    Some do... :)

    Please keep in mind that every type (chemistry) of battery needs other "end of charge" detection and other charging way!
     

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  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Hi,
    I read you OP as though you were asking if there was a way with VB?

    it would be impractical to interface the batter charger on a Visual Basic program, so is there any way to do this?[/I]

    You could use a simple PIC, that has a 10bit ADC and say an internal osc.
    Write a program to monitor the Vbty state and switch OFF a relay.

    You could also use a OPA comparator to monitor the Vbty and switch OFF the
    charge to the battery.

    A timer is not the best way to go, as you dont know how long you will have set the timer for, the battery may not be fully discharged??
     
  8. hardcore misery

    hardcore misery New Member

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    your idea is very interesting:) however, i even don't have any knowledge in basic programming with PIC's

    i have two ideas for this b.charger.

    1. Put a timer circuit for switching off the battery charger (condition: this is good for those who knows the estimated time for charging up a battery)

    2. Put an auto-shut off circuit that detects the battery whether it is fully charged.

    if i we were only thought with basic programming for PIC's
     
  9. Gayan Soyza

    Gayan Soyza Active Member

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    You still did not mention what battery you are going to charge.

    Timer method is good if you know the EXACT TIME that it reaches to its fully charged condition from a dead battery. Otherwise it will be overcharged.

    This can be done with a simple comparator IC to detect whether it is exceeding its calculated value.But personally I don't like this method.

    once you trickle charge your batteries no more problem occured.
     
  10. hardcore misery

    hardcore misery New Member

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    oops! i forgot to mention that... it is for a cellphone battery...

    just thinking of this..

    cellphone charger -> "auto-shut off circuit" -> cellphone

    so is there any chance for this?

    thinking also for added features:

    the charger shuts off then triggers an alarming sound or flashlights
     
    Last edited: Jul 9, 2007
  11. hardcore misery

    hardcore misery New Member

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    help me please..
     
  12. mneary

    mneary New Member

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    You scared us away when you said 'cellphone'. The present state of cellphone batteries is lithium, which requires more than casual knowledge of the battery to prevent over/undercharging and fire. Some batteries have built in microprocessors that you need to communicate with.

    I don't think this is a beginner project.
     
  13. hardcore misery

    hardcore misery New Member

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    so there are no ways to do this project with stand-alone circuits? so the only way is the PC-interfacing thing?
     
  14. mneary

    mneary New Member

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    There may be a way, but it'll require more documentation than you've provided. A lot more. You've only finally mentioned 'cellphone' after three days.
     
  15. Gayan Soyza

    Gayan Soyza Active Member

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    Here is one similar to simple NIMH charger.It designed for Li-ION.

    See the attachments.But I cannot give a full guarantee with the charger,but it is quiet good done with familiar components.

    If you have NIMH charger you can alter it to a LI-ION charger.

    Here is the main link
    http://www.shdesigns.org/lionchg.html
     

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  16. hardcore misery

    hardcore misery New Member

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    Thanks for all the response! i think i forgot to say something... all i need is a circuit with a switching feature(on/off) but the charger will be any cellphone charger which is already built.

    my friend recommended me to use a comparator that switches off the charger if it detects the cellphone battery if its already full-charged.( but i don't have any circuit yet) this project is tentative. we need to think of other projects which is
    also great... but i will pursue this project, if my group decided on this...
     
  17. mneary

    mneary New Member

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    The requirements keep coming, one at a time, every few days.....

    I gather you want mains shutoff when the battery is charged.

    To shut off the mains, you can detect the current consumed by the charger. When it falls below a set threshold, you can cut off the mains (presumably to avoid wasting the standby current?)
     
  18. hardcore misery

    hardcore misery New Member

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    sorry for that sir:(

    i'll be back soon, if my group wants to pursue with this project... so how can we do your idea sir?
     
  19. mcs51mc

    mcs51mc New Member

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    1) Read some theory about charging principles (Cypress app note for example)
    2) Monitor battery current and voltage during some charge cycles
    3) Analyse that data using your brain(s)
    4) Translate your idea(s) into an electronic drawning
    5) Submit it to this forum

    Then, and only then advice will follow... ... :):):)
     
  20. hardcore misery

    hardcore misery New Member

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    folks...

    Our group decided to use voltage comparators, one of my friend advised me to use an LM2901 quad comparator... but my problem is i can't understand how will i work on this component...

    based from this site: http://home.cogeco.ca/~rpaisley4/Comparators.html

    where can i put the 3V to 4V supply of the charger to the comparator? how can the comparator measure the voltage of a charging battery to know when to shut-off?
    can someone explain to me the basic concept for this comparator? or any can
    give some sample circuits?

    Requirements:

    >Supply Voltage for the cellphone battery is 3.7V
    >the Load Current of the supply must be 1A or greater to accommodate 3 or more cellphones to charge.

    here is the features of LM2901, let me know if it fits the requirements of the battery charger...

    Features
    • Single or Dual Supply Operation
    • Wide Range of Supply Voltage
    LM2901,LM339/LM339A,LM239/LM239A: 2 ~ 36V
    (or ±1 ~ ±18V)
    LM3302: 2 ~ 28V (or ±1 ~ ±14V)
    • Low Supply Current Drain 800μA Typ.
    • Open Collector Outputs for Wired and Connectors
    • Low Input Bias Current 25nA Typ.
    • Low Input Offset Current ±2.3nA Typ.
    • Low Input Offset Voltage ±1.4mV Typ.
    • Input Common Mode Voltage Range Includes Ground.
    • Low Output Saturation Voltage
    • Output Compatible With TTL, DTL and MOS Logic
     
  21. mneary

    mneary New Member

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    I didn't think you could find another major change to throw at us, but suddenly you've decided to charge three or more batteries (phones?) at a time. I don't think that anyone could have guessed that.

    Now you're charging cellphones instead of standalone batteries? That's good, actually, because cellphones usually have a complete battery charger, well matched to their own battery. (The "charger" for cellphones is usually just a semi-regulated supply at around 120% to 150% of the battery voltage.)

    But if you do it this way, you only need a simple power source. My cellphone (with a 3.7V 900mAH battery) uses a 4.8V 0.9A power supply. The power source doesn't need to be switched off; the phone knows and does everything.

    One amp for three or more phones? My phone uses a 0.9A supply.
     

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