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Solar panel controller

Discussion in 'General Electronics Discussion' started by bigone5500, Apr 9, 2014.

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  1. bigone5500

    bigone5500

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    I want to build a controller for a couple solar panels I have. They are 10w and produce ~20v each in full sun. I want to use this to charge a 12v sealed lead acid battery. I would like it to charge to a set voltage and shut off. This controller may also be used on small lawnmower batteries too which I assume are basically the same. I have tried a few basic schematics but they did not work as I had anticipated.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Google for MPPT Solar Charger. It may be cheaper to buy one, but that won't allow you to change voltage.
     
  3. bigone5500

    bigone5500

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    Apr 9, 2014
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    That's a 10A controller, suitable for a 120W panel. You may be able to find a cheaper option for (say) 5A. But in any case it is reasonably cheap.
     
  5. bigone5500

    bigone5500

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    Thanks.
     
  6. bigone5500

    bigone5500

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    I bought a solar controller today from harbor freight that can handle 100w or 7A.

    My question now is that when I connect the two panels together in parallel, I will need a blocking diode. How do I calculate what size diode I need. These two panels produce .6A current each at 20vdc and have 10w output in full sunlight.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    If the panels are oriented in the same direction and will not be shaded, you will not need any diodes.

    If you really want to use some diodes, I would recommend 30V 1A schottky diodes. They will waste the minimum amount of power.
     
  8. bigone5500

    bigone5500

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    Ok. I will try them out without a diode. I thought you had to have one to keep them from bleeding into each other. Thanks.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    As long as they are similar (i.e. same make and model) panels in the same plane (and facing the same -- not opposite -- direction) and you do not expect one to be in shade when the other is not, they will not leak charge into each other.

    Is there a link to the charger you bought?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, that may not be an MPPT charge controller, but it should still do the job.

    I'm a little concerned that the instructions tell you to disconnect the solar panels if the green light comes on though...
     
  11. bigone5500

    bigone5500

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    It was dirt cheap so if it doesn't do the job I'm not out much. I will just spend a little more next time.

    About the instructions, I think it may mean that if the unit is over charging the batteries then disconnect it...I hope...
     
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