PWM solar charger

Discussion in 'The Projects Forum' started by raymond86, Jun 19, 2010.

  1. raymond86

    Thread Starter New Member

    Jun 19, 2010
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    i need help in designing pwm solar lead acid battery charger. I have designed the charger circuit and when i simulated it, it worked and when i constructed it, it failed to charge the 12V battery.the pwm signal will be geberated by a PIC 16F877A microcontroller. I have uploaded the circuit please help me rectify the problem.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    It looks to me like your polarized capacitors are shown connected backwards in your schematic.

    hgmjr
     
  3. russpatterson

    Member

    Feb 1, 2010
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    16
    Interesting design. Are you using a standard solar panel that outputs 18-22V? What's L1, the inductor, for? Are you doing a buck converter? I don't think you need to do that unless you want to add the MPPT type stuff to your circuit.

    I have a schematic, work in progress, on my blog you can check out that does a battery charger and a motor controller. No MPPT yet for just battery charging but effectively works that way when running the motor.

    http://backyardsolar.blogspot.com/
     
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  4. SgtWookie

    Expert

    Jul 17, 2007
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    I don't know why you are using an LM350 regulator, as that is throwing away a good bit of power by generating heat.

    Like hgmjr says, your caps are upside-down.

    The MOSFET is installed backwards. The body diode will conduct continuously, and the MOSFET will get hot.

    The method of discharging the gate will result in slow turn-off times and a hot MOSFET.

    D1 is inadequate for the current, and it is not a fast recovery type.

    C1 is far too small.

    The PIC16F877 is obsolete. You will pay considerably more for that uC than it's more modern replacement, the PIC16F887.
     
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  5. retched

    AAC Fanatic!

    Dec 5, 2009
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    I agree with the sarge.

    A re-design is in you best interests.

    I would start with the PIC. Get yourself a nice cheap and powerful 16F887 then go from there.
     
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  6. SgtWookie

    Expert

    Jul 17, 2007
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    Have a look at the attached article; a MPPT charge controller that doesn't require a multiplier.

    You might consider implementing the math in the uC. Remember though, using math operators in C (or other language) on a PIC will bloat your code really quickly.
     
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  7. raymond86

    Thread Starter New Member

    Jun 19, 2010
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    thanks for your assistance i am using a buck converter in this case
     
  8. retched

    AAC Fanatic!

    Dec 5, 2009
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    I may be lost in the mix, help me out.

    You are trying to charge a battery (lead acid 12v type) using a solar panel or array.

    You are bucking the voltage?

    What is the output of the solar system?

    The way I am envisioning it, the PIC could be measuring the voltage of the battery between pwm high pulses to get the battery charge level.

    The PWM signal sent from the pic triggers a mosfet that lets the solar power get to the battery.

    As long as the charge time for the caps are faster than the PWM level, and the voltage of the cap output doesn't exceed the mosfet ratings, all should be good.

    Now, The voltage from the panel(s) should be set to the fast charge, then trickle charge levels. You could use resistors and or linear regulators for this process, but the whole point, to me, is to NOT waste the power from the solar panels.

    If theres heat there is waste.

    Are you using the battery while charging it?
     
  9. retched

    AAC Fanatic!

    Dec 5, 2009
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    Doing some research, you may want to think of using this:
    http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1037,C1078,C1089,P89360

    This is a very impressive IC. It handles the charging, safety, and all that good stuff.

    From the description from the linear website:
     
  10. SgtWookie

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    Jul 17, 2007
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  11. retched

    AAC Fanatic!

    Dec 5, 2009
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    Good read. I am impressed by the design.
     
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