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DIY smooth transition from 12V solar to 12V mains at night

Discussion in 'General Electronics Discussion' started by wingnut, Sep 9, 2020.

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  1. wingnut


    Aug 9, 2012
    Hi all

    I have set up a system which smoothly transitions from solar in the day to using mains at night. It uses the 12V from a car battery to power a 12V TV. This battery is charged by a PV panel. At night, as the voltage of the battery drops, the TV is powered by its mains transformed and rectified wall wart which supplies 12V. Both the battery leads and the wall wart leads go to the 12V jack which powers the TV. To stop this 12V mains supply charging the battery I put a blocking diode on the positive lead near the battery.

    My theory is this, that in the day when the battery voltage is high, the battery (charged by the sun) will power the TV, but when this drops at night to below the 12.2V, the mains takes up the strain smoothly transitioning to mains power. It seems to work because the wall wart goes cold during the day (showing it is not using mains power) and warms up at night as it draws mains power. I only have off the grid solar power.

    A person does not know what they do not know so I would like to ask you experts who know much more than me if this setup all sounds fine and dandy. I did blow one satellite decoder using this system for a few months, but maybe that was just time and chance and not due to the transition from solar to mains.

    Thank you all

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Usually one uses 2 diodes, one for the battery, the other for the wall wart, to prevent current from flowing either from wall wart to batterr (you have this one) and to prevent current from flowing from battery to wall wart (this one is missing).
  3. wingnut


    Aug 9, 2012
    Thank you very much Harald. That sounds like a good idea, and I will add another blocking diode. I don't know why I assumed the wall wart would have its own diode.
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