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I have a solar panel charging a lipo battery, that is the default/normal state.

When battery is charged, I want to cut the solar panel from the battery. Using my Arduino, I can send a high signal, and that should disconnect the panel.enter image description here

What can I use for the switch? Will a transistor work? The way I understand transistors, they work in reverse, if input is 1, then output/load is active. But I do not want to waste power keeping the switch closed most of the time.

So I came up with this idea, is there any problem with this one:

enter image description here

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  • \$\begingroup\$ The title should be 'Low input to close switch'! \$\endgroup\$ – rosewater Jul 4 '20 at 16:00
  • \$\begingroup\$ In your left drawing there is no power to the Arduino, so it can't sense the battery voltage or do anything to a switch. In the right diagram the battery and solar cell are in series, which I don't think you want. \$\endgroup\$ – Elliot Alderson Jul 4 '20 at 17:42
  • \$\begingroup\$ I omitted the battery sense logic from the diagram and arduino power circuit so we don't get distracted by them. Those things are already working properly. And the battery and solar cell are not in series, the positive of panel is feeding into positive terminal of battery \$\endgroup\$ – rosewater Jul 4 '20 at 18:35
  • \$\begingroup\$ @rosewater, why have you not corrected the title? \$\endgroup\$ – jsotola Jul 5 '20 at 1:10
  • \$\begingroup\$ @jsotoia thanks for the reminder. I just fixed the title! \$\endgroup\$ – rosewater Jul 5 '20 at 11:46
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There exist two complementary types of transistors. E.g. for MOSFETs, these are called P-channel or N-channel. You could use a P-channel type for your task. Inserted in the positive voltage path, you can switch the cell off by applying low voltage (0V) to the gate. You would also need a resistor to pull the gate to positive voltage when the MOSFET is not switched off. And you need to make sure that the Arduino does not get too high voltage at its pin.

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