On my boat I'd like to have a 12V cigarette lighter socket that is powered on when the house battery voltage is above 12.8V. I'd like this socket to be switched off when the house battery voltage has dropped under 12V and only to be powered on again when 12.8V is reached, for example when the solar panel has charged the battery sufficiently again. A bit like the Victron Orion-Tr Smart DC-DC converter would do (in DC-DC converter mode, not charging, see 4.2 at: https://www.victronenergy.com/upload/documents/Orion-Tr_Smart_DC-DC_Charger_-_Non-Isolated/34439-Orion-Tr_Smart_DC-DC_Charger-pdf-en.pdf ).
Not being an electronics engineer by trade I have tried to put a circuit together using a Schmitt Trigger and adjusted the resistors to achieve the above specified cut on/off thresholds. In simulation-world it seems to work, but would it do so too in the real world?
Any pro advice to make this dream a reality?
July 22, 2023
The first thing that jumps at me is that you should put a diode (commonly called a "flywheel diode") across the relay coil to prevent voltage spikes when the relay is de-energized. I think it would also be wise to give the op-amp some sort of feedback, say a zener diode to set a definite voltage when the op-amp is turned on, or even a high ohm resistor output to inverting input. When I made a living at this op-amps were known to sometimes lock up when there was no feedback
July 25, 2023
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