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I have a 3d printer in my car powered by a bluetti eb3a. The bluetti is charged by the 12v outlet in my car while driving. I have a 24v solar panel i want to mount to the roof of the car. My bluetti has only one dc 7909 input. So got a a Y splitter to combine power from the car and panel. But when plug it into the car outlet that turns off when i turn off the car, the solar panel turns on the stereo. Thats not the case with the outlets that are always on. I am worried that i will danage the car electrical system from a 24v solar panel flowing electricity back into the car?
Connecting them in parallel means the solar panel's 24V output gets mixed with the car's 12V systems. It's not uncommon for car systems to run a little high like 14-16V to charge the battery but 24V is definitely quite on the high side. That might make the lead acid battery explode and will probably damage other systems as well.
This might be fixable with diodes but I feel like that's probably still not ideal to try to mix 12V with 24V on the same circuit. I would put a switch and have it be like a toggle kind of deal. Or maybe some connector that toggles a switch on insertion similar to headphone jacks that disables the speakers when plugged in.
Good thing i asked the experts. Any i deas for a way to switch to solar power when i turn off the car? Like some form of diy relay switch
A relay switch could work. You would put the car 12V and ground across the coil connections, the 12V on the NO connection, the panel on the NC connection, and the power pack on the C connection. Make sure you get a 12VDC relay.
Are you going to have the panel installed permanently on your car?
Definitely don't connect a 24V source directly to your cars 12V system. There's a good chance of frying something important. A fuse would not protect from overvoltage so don't rely on those to protect components.