Hi. I'm trying to do a project that involves switching an external device that has its own power source. The device runs on 5V and 3A. Which relay should I use?
AC or DC , resistive or inductive load ?
As mentioned look at relay specifications for the answers - the cheap hobby Chinese modules give little information , so start looking at RS components or similar .
The relay will connect and disconnect the power between a charger and a cellphone.
ProjectBegins: The relay will connect and disconnect the power between a charger and a cellphone.
Then use a Mosfet, much simpler and cheaper. With DC currents it's not worth to use a relay.