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very simple transfer switch

Discussion in 'General Electronics Discussion' started by kerpap, Jan 20, 2014.

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  1. kerpap


    Jan 20, 2014
    I am trying to make a very small simple transfer switch.
    what I have is a solar cell and a battery pack. I would like to kick over to the battery pack when the solar cell is not producing enough power.

    I am guessing some sort of transistor will do the trick.

    can anyone point me in the right direction?

    thanks! :)
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    A pair of diodes will do the trick.

    Connect the battery to the load via a diode. Then connect the solar panel to the load via another diode.

    The source able to maintain the highest voltage will supply power to the load.

    You might want to use schottky diodes to minimise the voltage drop across them.
  3. kerpap


    Jan 20, 2014
    one thing that may make this tricky is that the solar cell and battery pack are at different voltages.
    the device runs on a range from 5 - 12v and the solar cell is 5v 14a the battery pack is 12V
    so the battery pack will always win.

    perhaps a relay may be in order.

    I need the loss of power from the solar cell to be what switches over to the battery.

    I may need to make a 5V 14a battery pack for it.
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