I've got a rudamentary range extender system set up using two raspberry pi 3s and an Ethernet cable. One of the pi's is in a hallway with a clear signal from the original WiFi network, and the Ethernet cable runs along the wall to the living room where the signal was weak to the second pi which is broadcasting a new WiFi network. Now here's where the question starts - I've got both boards running off of one power cable, as I have wires running from the 5v and ground gpio pins taped along the Ethernet cable and connected to the 5v and ground of the other pi (yes I know this isn't ideal, it's a calculated risk). Problem is, while this worked just fine in close range tests, it appears enough current is being lost through the longer power line for the second pi to not receive enough (red light is on when the network is not being used, but as soon as there starts to be a bit of a load the light goes off). I've thought of a couple solutions but want to make sure I'm not frying my Pi.
1 - as the pi 3 has two 5v pins, could I run a second power line to increase current carrying capacity? The question here would be does using the second 5v pin result in a 10v connection or would it just double the wire connecting the two 5v rails? If it just doubles the wire would I also have to use a second ground wire?
2 - what about the 3.3v pins? I know the 3.3v rail is also used to power things like the LAN, so if I ran the 3.3 to 3.3 would that just bridge the two 3.3v rails resulting in more power to the networking (as you recall the red light goes off when the WiFi is being used intensively) or would that result in an effective 8.3 volts and fry the board? If it would work, as with option 1, would I need a second ground wire?
3 (probably the most dangerous) - this one screams nope at me but is worth mentioning - I've got two power adapters that are both insufficient to power the Pi. If I connected one to each in addition to the gpio powerline, would bridging the two 5v result in sufficient power or just overload the Pi's?