i want to create a switch that will turn on/off the power to my OBD Port on my car when i turn engine on/off. reason being i have an OBD wifi dondle plugged in all the time. problem is the OBD Port has a constant 12v power so will always stay on.so the wifi dongle will drain he battery plus its not a good idea to leave it on as someone else could connect to it.
i am going to de solder the 12v pin inside the wifi dongle and put a switch in between . i was thinking on using a transistor. so when i turn engine on 12v from the cigarette lighter goes to the base of the transistor. that in turn will complete the circuit of the 12v into the wifi dongle.
i have bread boarded the following. 12v from car cigarette lighter goes to a 5v regulator. then 5v to 2.2k resistor to base pin of a MJD122G transistor collector pin is connected to OBD PORTS 12V then Emitter pin connects to the 12v inside the wifi dongle. This all works fine and turns the wifi on/off as expected. problem is if i run more than 500MA the transistor gets very hot. maybe all it needs is a little heat sink ?
i then thought why not use a small solid state relay like the 12v G3MB-202P DC-AC i could simply just connect 12v from cigarette lighter to the input of the relay. would this solid state relay get hot too ? im not sure what route to take with this.
so which one would be best to use ssr or transistor ? my transistor design is smaller which is a plus and i do light building my own things