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Solar Panel Voltage Increase?

  1. Aug 19, 2016 #1

    I Have built a 50w solar panel that gives an output of ~ 9.2v @ 5-6 amps during a good day. This is not enough to charge a 12v battery. To get around this, I am trying to use a DC-DC boost converter (specifications are below) and it is set to give an output voltage of 13.5v. The only problem I have is that the output voltage drops out after 10 seconds if the output voltage is set beyond 12.5v. Input voltage becomes the same as output voltage thereafter.

    Here are the specifications of the Dc-Dc boost converter:

    Size:(LxWxH) 70 x 39 x 32 mm
    Wide Input Voltage Range: DC 6 ~ 35V
    Output Voltage: DC 1 ~ 35V
    Conversion Efficiency: 90%
    Maximum Output Current : 5A
    Maximum Input Current : 7A
    Operating Frequency : 120KHz

    What a
    m I doing wrong?

  2. jcsd
  3. Aug 19, 2016 #2


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    Staff: Mentor

    Welcome to the PF.

    That's a pretty small input-output voltage differential for a simple boost DC-DC converter. You might need to use a SEPIC topology converter instead. Which boost converter chip are you using and with what component values?
  4. Aug 19, 2016 #3


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    Staff: Mentor

    Or, wait. You are using a canned commercial DC-DC converter module? Can you link to the datasheet?
  5. Aug 19, 2016 #4
    Thanks for the response.

    I am using this dc-dc boost converter: link.

    I do not really care much about the output amp value. Only the output voltage has to be at least 13.5 for the boost converter to charge the battery. Unfortunately it doesn't last long and it will return to the open circuit voltage of the solar panel after 10-15 seconds. The booster also makes some ticking noises before the voltage drops to solar panel voltage.
  6. Aug 20, 2016 #5


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    Science Advisor

    Your description of shutting down is almost always due to overload, current or thermal overload in this case. That particular model seems to be discontinued. Check this site to see if another model will fill your needs. Link. And pay attention to the warning about its usage!
  7. Aug 20, 2016 #6


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    Gold Member

  8. Aug 20, 2016 #7


    Staff: Mentor

    What is the voltage of the 12V battery before connecting it to the solar panel?
  9. Aug 20, 2016 #8

    jim hardy

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    Science Advisor
    Gold Member

    As TomG and anorlunda have hinted it might be a problem of application.

    What controls output current to the battery ? How much do you measure going to the battery ? Did you notice this caution in the directions at link you posted ?

  10. Aug 21, 2016 #9

    jim hardy

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    Science Advisor
    Gold Member

    Without some numbers we can only guess what is wrong.
    Hook it up again and take some measurements.

    1. What is voltage from solar panel just before the stepup converter shuts down?
    2. What is current into the battery at that time ?

    Can you try this experiment - rewire your panels in series not parallel so they make 18 volts instead of 9 ?
    Then connect them straight to battery without the converter and see how much current flows when sun is bright. Don't leave them connected very long lest you overcharge the battery.
    That gives us a data point on solar panel's current capability.

    Then insert your converter between the solar panel and battery and let it step 18 volts down to 13.5
    In bright sun it should operate as step down and in weak sun it should act as step up,
    and if i have read that datasheet correctly it'll auto-select whichever it needs.
    With a little bit of luck the inherent current limiting nature of your solar panel will cure the trouble.
    If not you might have to employ a current limiter.

    old jim
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