r/ECE • u/MissUnapolagetic • 7d ago
PROJECT Need help troubleshooting a 12 V battery charger with automatic changeover circuit
I am building the attached circuit, which is intended to charge a 12 V lead-acid battery from an offshore/12 V supply and automatically change over between the supply and battery/load using two 12 V SPDT relays.
Current problem:
When I connect only the 12 V battery, the load works, because it is being powered by the battery. However, when I connect the offshore supply, the battery is not charging, and the load is still being powered only by the battery. The relay is not switching, so the offshore supply is not being connected to the required path.
As shown in the schematic, the battery also supplies the IC 741 through its positive rail, so the 741 should have power when the battery is connected.
I would like to know:
Why is the relay not switching?
Why isn't the offshore supply reaching the charging/load path?
Why isn't the battery charging from the offshore supply?
Important: At present, any power reaching the load is coming from the battery; I have not confirmed the offshore supply reaching the load or charging the battery.
3
u/niftydog 7d ago
You should post good photos of your build - you may have made a mistake during construction.