I need to control a 12 volt 5amp device from one of the pins on a Arduino BT.
Since the board has a max out of 5 volts I need some type of affordable relay.
Not necessarily, you could use a logic-level power mosfet instead:
- source terminal to Arduino ground and the -ve side of your 12v supply
- gate terminal to the Arduino pin through a 100 ohm resistor
- drain terminal to the -ve side of your 12v load
- +ve side of your 12v load to +12v
If the load is very inductive (e.g. motor or solenoid), add a 5A diode in parallel with the load (anode to mosfet drain, cathode to +12v).