Help with solar switch

Discussion in 'General Electronics Chat' started by AlanF, Mar 18, 2017.

  1. AlanF

    AlanF

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    Hi, I am currently building a tracking system for a solar thermal panel. I had planned to use a small PV cell to switch a 12v relay to operate the motor system to track the sun. The cell produces about 5v max and it seemed to switch a relay ok on initial testing but I am having doubts- will it just burn out the coil constantly being on the edge? Is there a better way of tripping the drive once the cell hits full power and cutting as it moves into shade- any help appreciated (very basic level please).
     
    AlanF, Mar 18, 2017
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  2. AlanF

    KMoffett

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    KMoffett, Mar 19, 2017
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  3. AlanF

    AlanF

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    Thanks for trying but that is still way beyond me I am afraid. My latest thinking is to use a mosfet(whatever that is exactly) as an alternative to a relay to switch the motor on/off.
    I may need to enlist help locally as this is quickly moving beyond my very basic knowledge.
     
    AlanF, Mar 20, 2017
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  4. AlanF

    KMoffett

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    KMoffett, Mar 20, 2017
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  5. AlanF

    AlanF

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    Thanks again, but I dont want a whole control just something to use with the PV cell I already have. I have all the rest worked out. I just need a device to trigger the 12v motor supply when the PV hits 3-4v and cut off when it drops below that. Is that not some sort of transistor used as a switch?
     
    AlanF, Mar 20, 2017
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  6. AlanF

    AnalogKid

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    Partially energizing a relay coil will not harm it in any way (assuming it is rated for continuous operation). However, at lower coil currents the contacts might just barely make contact, or "chatter". Better to use the gain of a transistor to reduce the area between off and on, or a comparator to determine a true decision point.

    ak
     
    AnalogKid, Mar 20, 2017
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  7. AlanF

    AlanF

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    Great, thanks for that- feel like I am getting somewhere. I might try with a relay and see how it goes.
    Is this what I really need though?
    https://www.coolcomponents.co.uk/en/dev-boards/other/mosfet-power-control-kit.html
     
    AlanF, Mar 21, 2017
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  8. AlanF

    AnalogKid

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    Or something like that, depending on the load your control system is driving. That board reduces the number of things to be soldered, but some soldering is in your future.

    ak
     
    AnalogKid, Mar 21, 2017
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  9. AlanF

    AlanF

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    Thanks again, it is great that you give your time to help others. Soldering is not a problem but I would rather wire it all up with auto spade connectors if possible.
    I could always just use the transistor device to activate the original relay coil- job done(hopefully). Is there something-simple- that could be put into the circuit to keep the drive running for a few seconds each time the PV trips? That would move it enough to follow the sun but allow a break between activations.
     
    AlanF, Mar 21, 2017
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  10. AlanF

    AnalogKid

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    You can. That will work as an alternative to a true tracking circuit with hysteresis to prevent hunting. But something will have to reset the system to the morning position, a task that is a natural consequence of a differential tracker.

    ak
     
    AnalogKid, Mar 21, 2017
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  11. AlanF

    AlanF

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    I have a day/night sensor which trips a second relay to reverse the motor current and drive it back to East. Limit stops at 90degrees East and West ,also an overheat thermostat if the water pump fails. Its just getting the West drive to follow the sun that was giving me a problem. It is all driven from an old car battery which will have 3 PV cells connected in series to keep it topped up -hopefully.
    Anyway thanks for your help I am just off for another test run :)
     
    AlanF, Mar 21, 2017
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  12. AlanF

    AlanF

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    Test went well. I think my problem was I needed a "smaller" relay. Using a 5A one from an old Kia Picanto and its working a treat. Switches at about 70% sunon PV, moves and cuts out. I can always try a transistor but I think I will be ok. Thanks to everyone who helps here, you are stars!
     
    AlanF, Mar 22, 2017
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