9V battery charger

Discussion in 'The Projects Forum' started by emilj726, Jan 10, 2013.

  1. emilj726

    Thread Starter Active Member

    Oct 1, 2010
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    Can anybody offer any insight on how the following circuit works?
    I am trying to design a battery charger circuit I think this would be a good start.
     
    Last edited: Jan 10, 2013
  2. wayneh

    Expert

    Sep 9, 2010
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    The op-amp (which should be replaced with a comparator) watches the battery voltage and turns off charging (and turns on the red LED) when the voltage exceeds the setpoint. That's not the greatest strategy for every battery chemistry. What type of battery are you charging?

    What is IC2?
     
  3. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    CD4011 quad nand gate.
    The battery is a POWEREX TRUE 9.6V, NiMH 230 mAh.
     
  4. emilj726

    Thread Starter Active Member

    Oct 1, 2010
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    What supply voltage should I use? 9V?
    230mAh battery is 230ma for charge current ok?
    The charge current depends on R10 correct?
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    It would perhaps be more simple using a LM317 as constant current source. And a timer switch. I am not sure if your battery can tolerate fast charging. And I could not find any info about it. If the charge-current is 1/10th the ampHr rating of the cell. You should be safe as a rule of thumb. At this charging current your battery should be fully charged after 12 to 14 hours (dependent on drain state). Letting it charge longer may damage the battery. The best thing would probably be use a dedicated charger IC. They would probably cost you less then building the schematic you showed us.
     
  6. emilj726

    Thread Starter Active Member

    Oct 1, 2010
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    Yeah using the LM317 would be easier but I had all of the components except Q1(I will use something else for that) in my junk box so I started building it.
    Any suggestions for Q1?

    Plus I have never designed anything with CD4011 so I figured this would be a great chance for that.
     
  7. emilj726

    Thread Starter Active Member

    Oct 1, 2010
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    So when output of the comparator is high IC2B is acting as a one shot, hence Q2 is now biased via R12 and R13 turning on Q2.
    R11 is now connected to ground hence monitoring the voltage across the battery? Am understanding that correctly?

    What is the purpose of R8?

    If anyone can verify this It would be greatly appriciated.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    Charging NiMH by voltage control is not a good strategy, since the voltage peaks and begins to drop during overcharge. The better commercial NiMH chargers use ∆V, I believe, meaning they watch the slope of the voltage versus time. When that becomes low or negative, charging is stopped.
     
  9. emilj726

    Thread Starter Active Member

    Oct 1, 2010
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    So, maybe I can use this circuit as a monitoring voltage type circuit rather than a charging circuit?
     
  10. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    I guess I do need to go with a LM317 type of circuit.
    Can anyone post a circuit I can start with?
     
  11. bertus

    Administrator

    Apr 5, 2008
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  12. emilj726

    Thread Starter Active Member

    Oct 1, 2010
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    Interesting!
     
  13. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If you don't want to kill your battery by improper charging, I'd suggest building a circuit out of a charge controller IC that monitors ΔV and ΔT.

    The Maxim DS2711 would give you the features you want at the same time as simplifying your circuit. See Figure 3 on page 6 of the PDF Datasheet just linked. The DS2711 can work with NiMH or NiCD batteries. If you plan on charging LiIon batteries, you will need a much more advanced charge controller and protection circuitry.

    Optimum charging monitors both voltage and temperature. The most common is "Delta V", when the voltage over time reverses slope. To add faster response, "Delta T" is also added, which detects when the temperature starts to rise rapidly over a given time, indicating full charge.

    If you use only ΔV, if a cell is weak, it will be killed if the charger waits for the slope to to go negative, while a ΔT circuit will charge the battery to maximum capacity without overheating it.

    Batteries should NOT get too hot to hold you finger on for 5 seconds during a charge cycle if you expect to get the maximum lifetime from them. Some warming always present, due to the inefficiency of battery chemistry being emitted as heat.

    --ETA: The above, less the charge control IC, is mentioned in the PDF linked a few posts up.
     
    Last edited: Jan 11, 2013
  14. sohag513

    New Member

    Jun 26, 2012
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