Raspberry Pi Stack Exchange is a question and answer site for users and developers of hardware and software for Raspberry Pi. It only takes a minute to sign up.
Sign up to join this community
I am thinking about modding some sort of system where it would be necessary to connect a MOLEX (Internal PSU connection) to a Micro-USB 5V (VCC) connection.
Now, since I'm not fully aware of the steps, is it necessary to set up a NPN BJT transistor connection to run it through? Could I instead just connect the 5V molex connection straight to the 5V Micro-USB connection in-line, or will that fry the Pi?
You can connect directly.
You'd use a transistor only if the current used by the Pi was greater than the current supplied by the device that the Molex cable is connected to, or if you were using a different supply voltage. In either case, you would need a different supply as well as the 5v supply.
In other words: if whatever is attached to the Molex end provides at least 1 amp at 5 volts, you should be able to run a Pi. If it provides 2.5 amps at 5 volts, you will be able to run a Pi 2 with all USB ports.
The official power requirements can be found here: https://www.raspberrypi.org/help/faqs/#powerReqs
